Research papers

The current filters are: Starting year = 2018, Ending year = 2019
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Bourassa M.A., Meissner T., Cerovecki I., Chang P.S., Dong X., De Chiara G., Donlon C., Dukhovskoy D.S., Elya J., Fore A., Fewings M.R., Foster R.C., Guille S.T., Haus B.K., Hristova-Veleva S., Holbach H.M., Jelenak Z., Knaff J.A., Kranz S.A., Manaster A., Mazloff M., Mears C., Mouche A., Portabella M., Reul N., Ricciardulli L., Rodríguez E., Sampson C., Solis D., Stoffelen A., Stukel M.R., Stiles B., Weissman D., Wentz F. (2019)
Frontiers in Marine Science, 6, 443 DOI: https://doi.org/10.3389/fmars.2019.00443. (BibTeX: bourassa.etal.2019)
Abstract: See
Strengths and weakness of remotely sensed winds are discussed, along with the current capabilities for remotely sensing winds and stress. Future missions are briefly mentioned. The observational needs for a wide range of wind and stress applications are provided. These needs strongly support a short list of desired capabilities of future missions and constellations.
Keywords: satellite, wind, stress, ocean, requirements
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Cabré A., Pelegrí J.L., Vallès-Casanova I. (2019)
Journal of Geophysical Research: Oceans, 124, 7, 4820-4837. DOI: 10.1029/2019JC015160. (BibTeX: cabre.etal.2019)
Abstract: See
Here we explore the water transfer between the subtropical and tropical gyres of the South Atlantic Ocean to better understand its unique equatorward heat delivery. A Lagrangian technique is applied to the reanalysis product GLORYS2V4 in order to trace back the western boundary flow in the tropical (North Brazil Undercurrent, NBUC) and subtropical (Brazil Current) gyres. Most of the northward NBUC core transport (14.9 Sv at 8°S) arrives from the eastern boundary subtropical current (Benguela Current) via the zonal South Equatorial Current. This subtropical‐tropical transfer represents the core of the returning limb of the Atlantic meridional overturning circulation and accounts for most of the observed increase in heat and salt‐volume transports (0.18 PW and 0.19 Sv from 30°S to 8°S, respectively) across the South Atlantic. The NBUC also includes Antarctic Intermediate Water below 400 m (7.4 Sv at 8°S) coming from the interior subtropical gyre, as well as water from the current\'s surface and peripheral components coming from the tropical gyre (13.3 Sv at 8°S). The Brazil Current (9.9 Sv at 29°S) is mostly composed of subtropical water originating in the upper 800mwest of the eastern boundary current at 30°S (8.5 Sv), with a minor contribution of surface tropical water that transfers to the subtropics (1.4 Sv).
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Carnicer O., De La Fuente P., Canepa A., Keith I., Rebolledo-Monsalve E., Diogène J., Fernández-Tejedor M. (2019)
Frontiers in Marine Science, 6, 235 DOI: 10.3389/fmars.2019.00235. (BibTeX: carnicer.etal.2019)
Abstract: See
It is likely that harmful algal blooms have increased in frequency, intensity, and geographic distribution in the last decades in response to anthropogenic activities. The Galápagos Islands are renowned for their exceptional biological diversity; however, marine dinoflagellate communities have not been represented in biodiversity assessments. Therefore, this study aims to provide key information about dinoflagellate diversity and abundances, with special attention to harmful species, during a weak La Niña event in the Galápagos Marine Reserve (GMR). The study was performed during March–April 2017 and four transects were conducted at four Islands (Santa Cruz, Santa Fé, Seymour, and Pinzón) representing the southern region of the GMR. Water net samples were collected at 2, 5, and 10 nautical miles (nm) from the coast, at a total of 48 sampling sites. The presence of toxic species, and their cell abundance was estimated in seven transects at 0, 15, and 30 m of depth. A total of 152 taxa belonging to 7 orders, 22 families, and 38 genera were registered. The number of taxa found is almost three times higher than the maximum observed in previous studies. Dinoflagellate species richness among stations ranged between 53 and 23 taxa and was higher in northern sites. From the applied cluster analysis, five dinoflagellate assemblages were identified as a discrete community structure, one was found only in Santa Fé Island, which is probably related to the presence of the Equatorial Undercurrent (EUC). Regarding cell abundance estimations, low abundances were registered throughout the sampling sites and no blooms were detected. Higher abundances were registered in the northern transects coinciding with one of the most productive areas of the archipelago, situated north of Santa Cruz. Among the identified taxa, 19 of them were potentially toxic, including epiphytic species, allowing the possibility of blooms in benthic areas. This study presents the first record of several dinoflagellate species in the area (both nontoxic and harmful species) and thus, emphasizing the need for the implementation of phytoplankton monitoring programs by the government to prevent potential ecological, sanitary and economic impacts in the GMR.
Keywords: harmful algal blooms, dinoflagellate assemblages, richness, spatial variability, CCA, Generalized Additive Models, environmental parameters
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Castellanos P., Olmedo E., Pelegrí J.L., Turiel A., Campos E.J.D. (2019)
Remote Sensing, 11(7), 802, 1-17. DOI: 10.3390/rs11070802. (BibTeX: castellanos.etal.2019)
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Three of the world’s most energetic regions are in the tropical and South Atlantic: the North Brazil Current Retroflection, the Brazil-Malvinas Confluence, and the Agulhas Current Retroflection. All three regions display offshore diversions of major boundary currents, which define the intensity of the returning limb of the Atlantic meridional overturning circulation. In this work, we use a sea-surface salinity (SSS) satellite product, combined with a high-resolution numerical model and in situ measurements, in order to explore the seasonal variation of the surface currents and transports in these three regions. The analysis of the model output shows that the SSS patterns reflect the surface velocity structure, with the largest horizontal SSS gradients coinciding with those areas of highest velocity and the most predominant velocity vector being 90º anticlockwise (clockwise) from the horizontal SSS gradient in the northern (southern) hemisphere. This information is then applied to the SSS satellite product to obtain maps of water velocity and salt transports, leading to a quantitative tool to estimate both water and salt transports in key regions of the world ocean.
Keywords: sea surface salinity; SMOS; retroflections; surface velocity; water transport; salt transport
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Corcione V., Grieco G., Portabella M., Nunziata F., Migliaccio M. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 6, 3331-3340. DOI: 10.1109/TGRS.2018.2883364. (BibTeX: corcione.etal.2019)
Abstract: See
In this paper, the synthetic aperture radar (SAR) azimuth cutoff method is thoroughly revised and a new and general implementation is proposed. The key roles of the pixel spacing, the size of the image box, and the texture of the SAR scene are analyzed and optimized in terms of azimuth cutoff estimation. The reliability of the azimuth cutoff estimation is analyzed by measuring the distance between the measured and fitted autocorrelation functions. This analysis shows that it is of paramount importance to ilter unfeasible/unreliable azimuth cutoff values. To identify those values in an objective way, a criterion that is based on the \"Chi-squared\" test performed over a large data set of Sentinel-1 SAR imagery is defined and proven to be effective. The new robust implementation of the azimuth cutoff estimation at about 1-km grid spacing is then used to produce averaged azimuth cutoff at about 10-km grid spacing. The performance of the new estimation procedure, analyzed using a azimuth cutoff-to-wind-speed forward model, is shown to provide improved wind speed retrievals, with a root-mean-square error of 1.8–2 m/s when verified against independent numerical weather prediction model output and scatterometer winds.
Keywords: Cutoff frequency, sea surface, spectral analysis, synthetic aperture radar.
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Grieco G., Stoffelen A., Portabella M., Belmonte M., Lin W., Fabra F. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 5, 2990-3000. DOI: 10.1109/TGRS.2018.2879059. (BibTeX: grieco.etal.2019)
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A quality control scheme for TechDemoSat 1 (TDS-1) and Cyclone Global Navigation Satellite System (GNSS) delay-Doppler maps (DDMs) is presented and the results of its application to a data set of more than 700 000 DDMs are discussed. This scheme is proven to be effective for such purpose and its output indices can be successfully used as quality indicators of the DDM. This paper shows that most of the TDS-1 DDMs are affected by some distortions that are attributable to an insufficiently accurate estimation of the specular point location. The errors, moreover, can severely alter the symmetry of the isodelay lines with respect to the iso-Doppler lines leading to an asymmetry in the arrival time of the waveforms. Furthermore, these errors may affect the convolution of the GNSS reflected signal with the Woodward ambiguity function, leading to an unwanted redistribution of the incoming echo energy among the DDM bins. Such distortions may, in turn, affect the accuracy of the wind field retrieval using either the stare processing approach or the more consolidated methods of inverting a Geophysical Model Function based on the DDM peak and/or leading edge slope.
Keywords: Accuracy, error, quality control (QC), reflected Global Navigation Satellite System (GNSS-R), stare processing, wind.
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Grieco G., Stoffelen A., Portabella M. (2019)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 1-11. DOI: 10.1109/JSTARS.2019.2938327. (BibTeX: grieco.etal.2019a)
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Global navigation satellite system reflectometry (GNSS-R)-derived winds from the cyclone GNSS (CYGNSS) satellite constellation are expected to significantly improve weather forecasts in the tropical region. Delay–Doppler maps (DDMs) acquired by the TechDemosat-1 (TDS-1) GNSS-R satellite mission suffer from distortions that are highly correlated to on-board specular point estimation inaccuracies. Such distortions may affect wind retrievals, especially when multilook approaches aiming at exploiting the ambiguity-free area of the DDM are applied. This article demonstrates: that CYGNSS DDMs are also affected by such distortions; the rationale ofDDMshape asymmetries induced by specular point location inaccuracies; and a simple strategy for reducing such induced distortions.Two different datasets have been used, consisting of both regular and raw intermediate frequency CYGNSS measurements. The results show that, similar to TDS-1, the CYGNSS DDM distortions are correlated to specular point location inaccuracies. Furthermore, such inaccuracies are significantly reduced if more accurate specular point related parameters are used to recompress the raw GNSS-R echo, highlighting some sampling issues that are common to both TDS-1 and CYGNSS missions. These results suggest that multilook wind retrieval approaches aiming at exploiting also the peripheral parts of theDDM may be seriously compromised by such distortions. The latter may be substantially reduced by oversampling the outcomingDDMand by a posteriori choosing the proper DDM subsample. For future upcoming GNSS-R missions, it is strongly recommended to store the raw data for eventual reprocessing in case of miscalibration or processing issues such as those shown in this article.
Keywords: Delay–Doppler map (DDM) distortions, global navigation satellite system (GNSS), reflectometry.
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Guallar C., Flos J. (2019)
Progress in Oceanography, 176 (BibTeX: guallar.flos.2019)
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The link between phytoplankton primary production (PPP) and chromophoric dissolved organic matter (CDOM) has been demonstrated indirectly in the laboratory, but not directly in the sea. Here, for the first time, we report a strong link between PPP and CDOM in a study carried out in coastal marine waters around Barcelona (NW Mediterranean) in contrasting seasons. We measured relevant correlations between a254 CDOM concentration and both PPP (r=0.89, p < 0.001, n=16; r=0.76, p < 0.01, n=10; and r=0.68, p < 0.001, n=26; for summer, winter–spring and both seasons together, respectively) and the specific production rate at optimal light intensity (Pm B; r=0.77, p < 0.001, n=16; r=0.86, p < 0.01, n=10; and r=0.85, p < 0.001, n=26; for the same seasons). Based on our findings, we design a model that predicts PPP very well, using a254 CDOM, water temperature and photosynthetically active radiation (PAR) (R2=0.84, p < 0.001, n=26). Relationships between CDOM concentration parameters (measured at wavelengths of 280, 300, 340, 355, 375, 412 and 460 nm) and variables associated to CDOM processes (chlorophyll-a, bacterial abundance, turbidity related to sediment resuspension and PAR) were also evaluated. Bacterial abundance is significantly correlated with CDOM concentration measured at higher wavelengths when all samples are considered (e.g., r=0.82, p < 0.001, n=26, for a355 CDOM). However, in seasonal data analysis, the correlations decrease slightly (summer season: e.g., r=0.79, p < 0.001, n=16, for a355 CDOM) or become non-significant (winter– spring season: e.g., r=-0.02, p=0.95, n=10, for a355 CDOM). Sunlight photobleaching and sediment resuspension processes significantly influence CDOM dynamics in the summer (for a300 CDOM: r=-0.72, p < 0.001, n=16; and r=0.67, p < 0.01, n=16, respectively).
Keywords: Phytoplankton primary production Carbon uptake CDOM production Bacteria Photodegradation Sediment resuspension
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Gupta M., Gabarro C., Turiel A., Portabella M., Martinez J. (2019)
Journal of Glaciology, 65, (251), 481-493. DOI: 10.1017/jog.2019.26. (BibTeX: gupta.etal.2019a)
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Arctic sea ice is going through a dramatic change in its extent and volume at an unprecedented rate. Sea-ice thickness (SIT) is a controlling geophysical variable that needs to be understood with greater accuracy. For the first time, a SIT-retrieval method that exclusively uses only airborne SIT data for training the empirical algorithm to retrieve SIT from Soil Moisture Ocean Salinity (SMOS) brightness temperature (TB) at different polarization is presented. A large amount of airborne SIT data has been used from various field campaigns in the Arctic conducted by different countries during 2011–15. The algorithm attempts to circumvent the issue related to discrimination between TB signatures of thin SIT versus low sea-ice concentration. The computed SIT has a rms error of 0.10 m, which seems reasonably good (as compared to the existing algorithms) for analysis at the used 25 km grid. This new SIT retrieval product is designed for direct operational application in ice prediction/climate models.
Keywords: Remote sensing; Sea ice; Laser altimetry; Electromagnetic induction; Ice thickness measurements
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Hackert E.C., Kovach R.M., Busalacchi A.J., Ballabrera-Poy J. (2019)
Journal of Geophysical Research: Oceans, 124, 7, 4546-4556. DOI: http://dx.doi.org/10.1029/2019JC015130. (BibTeX: hackert.etal.2019)
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This study demonstrates the positive impact of including gridded Aquarius and Soil Moisture, Active/Passive (SMAP) sea surface salinity (SSS) into initialization of intermediate complexity coupled model forecasts for the tropical Indo‐Pacific. An experiment that assimilates conventional ocean observations serves as the control. In a separate experiment, Aquarius and SMAP satellite SSS are additionally assimilated into the coupled model initialization. Analysis of the initialization differences with the control indicates that SSS assimilation causes a freshening and shallowing of the mixed layer depth near the equator and enhanced Kelvin wave amplitude. For each month from September 2011 to September 2017, 12‐month‐coupled ENSO forecasts are initialized from both the control and satellite SSS assimilation experiments. The experiment assimilating Aquarius and SMAP SSS significantly outperforms the control relative to observed NINO3.4 sea surface temperature anomalies. This work highlights the potential importance of inclusion of satellite SSS for improving the initialization of operational ENSO coupled forecasts.
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Hernández-Guerra A., Talley L.D., Pelegrí J.L., Vélez-Belchí P., Baringer M.O., Macdonald A.M., McDonagh E.L. (2019)
Progress in Oceanography, 176 DOI: 10.1016/j.pocean.2019.102136. (BibTeX: hernandezguerra.etal.2019)
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Mass transports for the thermocline, intermediate, deep and abyssal layers in the Atlantic Ocean, at 30°S and for 2003 and 2011, have been estimated using data from GO-SHIP hydrographic transoceanic sections and applying three inverse models with different constraints. The uppermost layers comprise South Atlantic Central Water (SACW) and Antarctic Intermediate Water (AAIW), with a net northward transport in the range of 12.1–14.7 Sv in 2003 and 11.7–17.7 Sv in 2011, which can be considered as the northward returning limb of the Meridional Overturning Circulation (MOC). The western boundary Brazil Current transports twice as much SACW in 2003 (−20.2 ± 0.7 Sv) than in 2011 (−9.7 ± 0.7 Sv). A poleward current consisting of AAIW and Upper Circumpolar Deep Water (UCDW) flows beneath the Brazil Current. The eastern boundary Benguela Current, characterized by a high mesoscale eddy activity, transports 15.6 ± 0.9 Sv in 2003 and 11.2 ± 0.8 Sv in 2011, east of the Walvis Ridge. In the ocean interior, the northward flow is mainly located east of the Mid Atlantic Ridge (MAR) where Agulhas Rings (ARs), observed in both 2003 and 2011, transport warm and salty water from the Indian to the Atlantic Ocean. For the deep layers, the southward transport of North Atlantic Deep Water (NADW) occurs as the Deep Western Boundary Current and also in the eastern basin. The western and eastern basins transport similar amounts of NADW to the south during both years, although the eastern pathway changes substantially between both years. The total NADW transport, which is also considered the MOC, is in the range 16.3–24.5 Sv in 2003 and 17.1–29.6 Sv in 2011, hence with no significant change.
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Lavergne T., Sorensen A.M., Kern S., Tonboe R., Notz D., Aaboe S., Bell L., Dybkjaer G., Eastwood S., Gabarró C., Heygster G., Killie M.A., Kreiner M.B., Lavelle J., Saldo R., Sandven S., Pedersen LT. (2019)
The Cryosphere, 13, 49-78. DOI: 10.5194/tc-13-49-2019. (BibTeX: lavergne.etal.2019a)
Abstract: See
We introduce the OSI-450, the SICCI-25km and the SICCI-50km climate data records of gridded global seaice concentration. These three records are derived from passive microwave satellite data and offer three distinct advantages compared to existing records: first, all three records provide quantitative information on uncertainty and possibly applied filtering at every grid point and every time step. Second, they are based on dynamic tie points, which capture the time evolution of surface characteristics of the ice cover and accommodate potential calibration differences between satellite missions. Third, they are produced in the context of sustained services offering committed extension, documentation, traceability, and user support. The three records differ in the underlying satellite data (SMMR & SSM/I & SSMIS or AMSR-E & AMSR2), in the imaging frequency channels (37 GHz and either 6 or 19 GHz), in their horizontal resolution (25 or 50 km), and in the time period they cover. We introduce the underlying algorithms and provide an evaluation. We find that all three records compare well with independent estimates of sea-ice concentration both in regions with very high sea-ice concentration and in regions with very low sea-ice concentration. We hence trust that these records will prove helpful for a better understanding of the evolution of the Earth’s sea-ice cover.
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Lin W., Portabella M., Foti G., Stoffelen A., Gommenginger C., He Y. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 2, 655-666. DOI: 10.1109/TGRS.2018.2859191. (BibTeX: lin.etal.2019b)
Abstract: See
This paper presents a comprehensive procedure to improve the wind geophysical model function (GMF) for the Global Navigation Satellite System Reflectometry (GNSS-R) instrument onboard the TechDemoSat-1 satellite. The observable used to define the GMF is extracted from the measured delay- Doppler maps (DDMs) by correcting for the nongeophysical effects within the measurements. Besides the instrument and the geometric effects as provided in the bistatic radar equation, a calibration term that accounts for the uncalibrated receiver antenna gain and the unknown transmitter antenna gain is proposed to optimize the calculation of GNSS-R observables. Such calibration term is presented as a function of observing elevation and azimuth angles and is shown to remarkably reduce the measurement uncertainties. First, an empirical wind-only GMF is developed using the collocated Advanced Scatterometer (ASCAT) winds and European Centre for Medium-Range Weather Forecasts (ECMWF) model wind output. This empirical GMF agrees well with the model output. Then, the sensitivity of the observable to waves is analyzed using the collocated ECMWF wave parameters. The results show that it is difficult to include mean square slope (MSS) in the development of an empirical GMF, since the difference between ECMWF MSS and the MSS sensed by GNSS-R varies with incidence angle and wind speed. However, it is relevant to take significant wave height (Hs) in account, particularly for low wind conditions. Consequently, a wind/Hs approach is proposed for improved wind retrievals.
Keywords: Advanced Scatterometer (ASCAT); Calibration; Global Navigation Satellite System Reflectometry (GNSS-R); Wave; Winds
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Lin W., Dong X., Portabella M., Lang S., He Y., Yun R., Wang Z., Xu X., Zhu D., Liu J. (2019)
IEEE Transactions on Geoscience and Remote Sensing, 57, 2, 627-639. DOI: 10.1109/TGRS.2018.2858852. (BibTeX: lin.etal.2019c)
Abstract: See
The China-France Oceanography Satellite (CFOSAT) to be launched in October 2018 will carry two innovative payloads, i.e., the surface wave investigation and monitoring instrument and the rotating fan-beam scatterometer [CFOSAT scatterometer (CFOSCAT)]. Both instruments, operated in Ku-band microwave frequency, are dedicated to the measurement of sea surface wave spectra and wind vectors, respectively. This paper provides an overview of the system definition and characteristics of the CFOSCAT instrument. A prelaunch analysis is carried out to estimate the scatterometer backscatter and wind quality based on the developed CFOSCAT simulator prototype. The overall simulation includes two parts: first, a forward model is developed to simulate the ocean backscatter signals, accounting for both instrument and geophysical noise. Second, a wind inversion processor is used to retrieve wind vectors from the outputs of the forward model. The benefits and challenges of the novel observing geometries are addressed in terms of the CFOSCAT wind retrieval. The simulations show that the backscatter accuracy and the retrieved wind quality of CFOSCAT are quite promising and meet the CFOSAT mission requirements.
Keywords: Backscatter; Inversion; Measurement errors; Remote sensing; Rotating fan-beam scatterometer; Simulation; Wind.
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Orué-Echevarría D., Pelegrí J.L., Alonso-González I.J., Benítez-Barrios V.M., De La Fuente P., Emelianov M., Gasser M., Herrero C., Isern-Fontanet J., Peña-Izquierdo J., Ramírez-Garrido S., Rosell-Fieschi M., Salvador J., Saraceno M., Valla D., Vidal M. (2019)
Data in Brief, 22, 185–194. DOI: 10.1016/j.dib.2018.12.004. (BibTeX: orueechevarria.etal.2019b)
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This oceanographic dataset was gathered during the TIC-MOC cruise, which was designed to characterize the dynamics of the Brazil-Malvinas Confluence. The cruise was carried on board the R/V Hespérides ,with departure from Ushuaia and arrival to Salvador de Bahía. A total of 66 conductivity-temperature-depth (CTD) stations were completed between 8 and 22 March 2015, offshore from the continental platform and within 45°S-35°S and 61°W-50°W. At each station, water samples were collected, which were used to calibrate the CTD salinity-oxygen sensors and to determine inorganic nutrient concentrations, and the horizontal current was measured. Along its track, the vessel recorded surface temperature and salinity, as well as the horizontal flow down to about 700 m. Lastly, eight position-transmitting drifters were launched and two profiling
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Orué-Echevarría D., Pelegrí J.L., Machín F., Hernández-Guerra A., Emelianov M. (2019)
Journal of Geophysical Research: Oceans, 124, 1, 527-554. DOI: 10.1029/2018JC014733. (BibTeX: orueechevarria.etal.2019d)
Abstract: See
The Brazil‐Malvinas Confluence arises from the frontal encountering of the subtropical Brazil Current and subantarctic Malvinas Current. It displays a complex regional circulation that is accompanied by mesoscale features and thermohaline intrusions. Here we combine altimetry and cruise data to describe the circulation pattern in the upper 2,000 m at two spatial scales encircling the frontal system. The major regional features appear south of the confluence latitude at 39–40°S: (a) a relatively weak Malvinas Current near 41°S, 56°W (28.3 ± 1.4 Sv), followed by its cyclonic retroflection; (b) an intense subtropical anticyclone (59.3 ± 10.7 Sv) that replaces the Brazil Current overshoot; and (c) a very intense subantarctic inflow (78.9 ± 13.7 Sv) near 53°W that is maintained through both an upstream (near 42°S) earlier diversion of the Malvinas Current and the cyclonic recirculation of the flow exiting east along the confluence. North of the confluence, the Brazil Current provides a net input of 30.8 ± 12.0 Sv (29.1 ± 8.3 Sv along the slope). The southern inflow splits nearly equal between barotropic and baroclinic contributions while the entire northern flow is essentially baroclinic. These northern and southern inputs add to an eastward along‐front transport of 109.7 ± 15.1 Sv, with significant contribution of highly oxygenated, relatively fresh Subantarctic Mode and Antarctic Intermediate Waters (58.7 ± 5.6 Sv). The regional circulation experiences substantial temporal variability, with southern waters flowing into the Brazil‐Malvinas Confluence through along‐slope and interior pathways and partly recirculating within the subtropical South Atlantic gyre.
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Piles M., Ballabrera-Poy J., Muñoz-Sabater J. (2019)
Remote Sensing, 11, 95 DOI: 10.3390/rs11010095. (BibTeX: piles.etal.2019a)
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Soil moisture observations are expected to play an important role in monitoring global climate trends. However, measuring soil moisture is challenging because of its high spatial and temporal variability. Point-scale in-situ measurements are scarce and, excluding model-based estimates, remote sensing remains the only practical way to observe soil moisture at a global scale. The ESA-led Soil Moisture and Ocean Salinity (SMOS) mission, launched in 2009, measures the Earth’s surface natural emissivity at L-band and provides highly accurate soil moisture information with a 3-day revisiting time. Using the first six full annual cycles of SMOS measurements (June 2010–June 2016), this study investigates the temporal variability of global surface soil moisture. The soil moisture time series are decomposed into a linear trend, interannual, seasonal, and high-frequency residual (i.e., subseasonal) components. The relative distribution of soil moisture variance among its temporal components is first illustrated at selected target sites representative of terrestrial biomes with distinct vegetation type and seasonality. A comparison with GLDAS-Noah and ERA5 modeled soil moisture at these sites shows general agreement in terms of temporal phase except in areas with limited temporal coverage in winter season due to snow. A comparison with ground-based estimates at one of the sites shows good agreement of both temporal phase and absolute magnitude. A global asseSMent of the dominant features and spatial distribution of soil moisture variability is then provided. Results show that, despite still being a relatively short data set, SMOS data provides coherent and reliable variability patterns at both seasonal and interannual scales. Subseasonal components are characterized as white noise. The observed linear trends, based upon one strong El Niño event in 2016, are consistent with the known El Niño Southern Oscillation (ENSO) teleconnections. This work provides new insight into recent changes in surface soil moisture and can help further our understanding of the terrestrial branch of the water cycle and of global patterns of climate anomalies. Also, it is an important support to multi-decadal soil moisture observational data records, hydrological studies and land data assimilation projects using remotely sensed observations.
Keywords: SMOS; Soil moisture; Climatology; Trends; Signal decomposition
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Romera-Castillo C., Álvarez M., Pelegrí J.L., Hansell D.A., Álvarez-Salgado X.A. (2019)
Global Biogeochemical Cycles, 33, 9, 1162-1173. DOI: 10.1029/2018GB006162. (BibTeX: romeracastillo.etal.2019)
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Most dissolved organic carbon (DOC) sequestered in the deep ocean has residence times of decades to thousands of years, with clear implications for climate regulation, though some net removal is typically observed with increasing water mass age. Here, a high‐quality‐high‐resolution data set has allowed us to identify net additions of recalcitrant DOC in specific water masses of the deep South Atlantic. Overall, the South Atlantic is a net source of recalcitrant DOC, adding 0.027 ± 0.019 Pg C/year, while the North Atlantic is a net sink that removes 0.298 ± 0.141 Pg C/year. We find that the balance of addition/removal of recalcitrant DOC depends not only on the origin but also on the temperature, age, and depth of the water masses that circulate and mix in the Atlantic Ocean. Future changes in the water mass composition and circulation patterns due to climate change would eventually affect that balance, altering the carbon cycle.
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Salat J., Pascual J., Flexas M., Chin T.M., Vazquez-Cuervo J. (2019)
Ocean Dynamics, 69, 1067–1084. DOI: 0.1007/s10236-019-01285-z. (BibTeX: salat.etal.2019)
Abstract: See
Marine and atmospheric parameters, including temperature observations from surface to 80 m (at 6 depths) are measured sinceSeptember 1973 on a higher-than-weekly frequency, at a coastal station 4 km offshore L’Estartit (Costa Brava; NWMediterranean). This constitutes the longest available uninterrupted oceanographic time series in the Mediterranean Sea. Thepresent contribution focuses on observed climatic trends in temperature (°C/year) of air (AT; 0.05), sea surface (SST; 0.03), sea at80 m depth (S80T; 0.02) and sea level (SL; 3.1 mm/year) as well as comparison with trends estimated from coincident high-resolution satellite data. The trending evolution is not uniform across seasons, being significantly higher in spring for both ATandSST, while in autumn for S80T. Other climatological results are a stratification increase (0.02 °C/year in summer temperaturedifference between 20 m (S20T) and S80T), trends in summer conditions at sea (when S20T > 18 °C), estimated as 0.5 and0.9 days/year for the starting day and period respectively, and a decreasing trend of nearly 2 days/year in the period of conditionsfavourable for marine evaporation (when AT < SST). This last trend may be related to the observed decrease of coastalprecipitation in spring. The long-term consistency in the in situ SST measurements presents an opportunity to validate themulti-decadal trends. The good agreement for 2013–2018 (RMS 0.5–0.6, bias−0.1 to−0.2; trends of 0.09 °C/year in situ vs.0.06 to 0.08 °C/year from satellite) allows considering this observational site as ground truth for satellite observations and amonitoring site for climate change
Keywords: Oceanographic time series.Climate trends.Satellite ground truth.Stratification.Seasonality.Mediterranean Sea
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Torres G., Carnicer O., Canepa A., De La Fuente P., Recalde S., Narea R., Pinto E., Borbor-Córdova M.J. (2019)
Frontiers in Marine Science, 6, 145 DOI: 10.3389/fmars.2019.00145. (BibTeX: torres.etal.2019)
Abstract: See
Among marine phytoplankton, dinoflagellates are a key component in marine ecosystems as primary producers. Some species synthesize toxins, associated with human seafood poisoning, and mortality in marine organisms. Thus, there is a large necessity to understand the role of environmental variables in dinoflagellates spatialtemporal patterns in response to future climate scenarios. In that sense, a monthly four-year (2013–2017) monitoring was taken to evaluate dinoflagellates abundances and physical-chemical parameters in the water column at different depths. Sampling sites were established at 10 miles in four locations within the Ecuadorian coast. A total of 102 taxa were identified, corresponding to 8 orders, 22 families, and 31 genera. Eight potentially harmful genera were registered but no massive blooms were detected. The most frequent dinoflagellates were Gymnodinium sp. and Gyrodinium sp. Environmental variables showed different mixing layer thickness and a conspicuous and deepening thermocline/oxycline/halocline and nutricline depending on annual and seasonal oceanographic fluctuations. This study confirms that seasonal and spatial distribution of the environmental variables are linked to the main current systems on the Eastern Tropical Pacific, thus the warm Panama current lead to a less dinoflagellates abundance in the north of Ecuador (Esmeraldas), while the Equatorial Upwelling and the cold nutrient-rich Humboldt Current influence dinoflagellates abundance at the central (Manta, La Libertad) and South of Ecuador (Puerto Bolivar), respectively. Interannual variability of dinoflagellates abundance is associated with ENSO and upwelling conditions. Climate change scenarios predict an increase in water surface temperature and extreme events frequency in tropical areas, so it is crucial to involve policy-makers and stakeholders in the implementation of future laws involving long-term monitoring and sanitary programs, not covered at present.
Keywords: dinoflagellates, HABs, ENSO, tropical Eastern Pacific, nutrients, upwelling, humboldt current
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Viúdez A. (2019)
Journal of Fluid Mechanics, 859, R1 DOI: 10.1017/jfm.2018.892. (BibTeX: viudez.2019a)
Abstract: See
Exact solutions for multipolar azimuthal-mode vortices in two-dimensional Euler flows are presented. Flow solutions with non-vanishing far-field velocity are provided for any set of azimuthal wavenumbers m and arbitrary number n of vorticity shells. For azimuthal wavenumbers mD0 and mD1, the far-field velocity is a rigid motion and unsteady flow solutions with vanishing far-field velocity are obtained by means of a time-dependent change of reference frame. Addition of these first two modes, in the case of n = 1, results in a particular Chaplygin–Lamb (C–L) dipole, with continuous and vanishing vorticity at the vortex boundary. Numerical simulations suggest that this particular C–L dipole is stable.
Keywords: Vortex dynamics; Vortex flows
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Viúdez A. (2019)
Journal of Fluid Mechanics, 868, R1, 1-13. DOI: 10.1017/jfm.2019.234. (BibTeX: viudez.2019b)
Abstract: See
An exact solution of a baroclinic three-dimensional vortex dipole in geophysical flows with constant background rotation and constant background stratification is provided under the quasi-geostrophic (QG) approximation. The motion of the dipole is unsteady but the potential vorticity contours move rigidly. The vortex comprises three potential vorticity anomaly modes, with a radial dependence given by the spherical Bessel functions and with azimuthal and polar dependences given by the spherical harmonics. The first mode, or spherical mode, accounts for the horizontal asymmetry of the vortex dipole and curvature of the dipole’s horizontal trajectory. The second mode, or dipolar mode, accounts for the speed of displacement of the vortex dipole. A third mode, or vertical tilting mode, accounts for the dipole’s vertical asymmetry. The QG vertical velocity field has two contributions: the first one is octupolar and depends entirely on the dipolar mode, and the second one is dipolar and depends on the nonlinear interaction between dipolar and vertical tilting modes.
Keywords: baroclinic flows, quasi-geostrophic flows, vortex dynamics
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Viúdez A. (2019)
Journal of Fluid Mechanics, 878, R5, 1-11. DOI: 10.1017/jfm.2019.730. (BibTeX: viudez.2019c)
Abstract: See
An exact solution of a stable vortex tripole in two-dimensional (2-D) Euler flows is provided. The stable tripole is composed of an inner elliptical vortex and two small-amplitude lateral vortices. The non-vanishing vorticity field of this tripole, referred to as here as an embedded tripole because of the closeness of its vortices, is given in elliptical coordinates .; / by the even radial and angular order-0 Mathieu functions Je0./ce0./ truncated at the external branch of the vorticity isoline passing through the two critical points closest to the vortex centre. This tripole mode has a rigid vorticity field which rotates with constant angular velocity equal to 0Je0.1/ce0.0/=2, where 1 is the first zero of Je0 0./ and 0 is a constant modal amplitude. It is argued that embedded 2-D tripoles may be conceptually regarded as the superposition of two asymmetric Chaplygin–Lamb dipoles, separated a distance equal to 2R, as long as their individual trajectory curvature radius R is much shorter than their dipole extent radius.
Keywords: vortex dynamics, vortex instability, vortex interactions
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Zamanillo M., Ortega-Retuerta E., Nunes S., Estrada M., Sala M.M., Royer S.-J., López-Sandoval D.C., Emelianov M., Vaqué D., Marrasé C., Simó R. (2019)
Science of The Total Environment, 691, 736-748. DOI: 10.1016/j.scitotenv.2019.06.524. (BibTeX: zamanillo.etal.2019f)
Abstract: See
Transparent exopolymer particles (TEP) are an abundant class of suspended organic particles, mainly formed by polysaccharides, which play important roles in biogeochemical and ecological processes in the ocean. In this study we investigated horizontal and vertical TEP distributions (within the euphotic layer, including the upper surface) and their short-term variability along with a suite of environmental and biological variables in four distinct regions of the Southern Ocean. TEP concentrations in the surface (4 m) averaged 102.3 ± 40.4 μg XG eq. L−1 and typically decreased with depth. Chlorophyll a (Chl a) concentration was a better predictor of TEP variability across the horizontal (R2 = 0.66, p < 0.001) and vertical (R2 = 0.74, p < 0.001) scales than prokaryotic heterotrophic abundance and production. Incubation experiments further confirmed the main role of phytoplankton as TEP producers. The highest surface TEP concentrations were found north of the South Orkney Islands (144.4 ± 21.7 μg XG eq. L−1), where the phytoplankton was dominated by cryptophytes and haptophytes; however, the highest TEP:Chl a ratios were found south of these islands (153.4 ± 29.8 μg XG eq (μg Chl a)−1, compared to a mean of 79.3 ± 54.9 μg XG eq (μg Chl a)−1 in the whole cruise, in association with haptophyte dominance, proximity of sea ice and high exposure to solar radiation. TEP were generally enriched in the upper surface (10 cm) respect to 4 m, despite a lack of biomass enrichment, suggesting either upward transport by positive buoyancy or bubble scavenging, or higher production at the upper surface by light stress or aggregation. TEP concentrations did not present any significant cyclic diel pattern. Altogether, our results suggest that photobiological stress, sea ice melt and turbulence add to phytoplankton productivity in driving TEP distribution across the Antarctic Peninsula area and Atlantic sector of the Southern Ocean.
Keywords: Transparent exopolymer particles; Phytoplankton; Prokaryotes; Solar radiation dose; Southern Ocean
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Aulicino G., Cotroneo Y., Ansorge I., van der Berg M., Cesarano C., Belmonte M., Olmedo E. (2018)
Earth System Science Data, 10, 1227–1236. DOI: 10.5194/essd-10-1227-2018. (BibTeX: aulicino.etal.2018)
Abstract: See
We present here sea surface salinity (SSS) and temperature (SST) data collected on board the S.A. Agulhas-I and S.A. Agulhas-II research vessels, in the framework of the South African National Antarctic Programme (SANAP). Onboard Sea-Bird thermosalinographs were regularly calibrated and continuously monitored in-between cruises, and no appreciable sensor drift emerged. Water samples were taken on a daily basis and later analyzed with a Portasal salinometer; some CTD measurements collected along the cruises were used to validate the data. No systematic differences appeared after a rigorous quality control on continuous data. Results show that salinity measurement error was a few hundredths of a unit on the practical salinity scale. Quality control included several steps, among which an automatic detection of unreliable values through selected threshold criteria and an attribution of quality flags based on multiple criteria, i.e., analysis of information included in the cruise reports, detection of insufficient flow and/or presence of air bubbles and ice crystals in the seawater pipe, visual inspection of individual campaigns, and ex post check of sea ice maps for confirming ice field locations. This data processing led us to discard about 36% of acquired observations, while reliable data showed an excellent agreement with several independent SSS products. Nevertheless, a sea ice flag has been included for identifying valid data which could have been affected by scattered sea ice contamination. In our opinion, this dataset, available through an unrestricted repository at https://doi.org/10.7289/V56M3545, contributes to improving the knowledge of surface water features in one of the most important regions for global climate. The dataset will be highly valuable for studies focusing on climate variability in the Atlantic sector of the Southern Ocean, especially across the Antarctic Circumpolar Current and its fronts. Furthermore, we expect that the collected SSS data will represent a valuable tool for the calibration and validation of recent satellite observations provided by SMOS and Aquarius missions.
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Belmonte M., Otosaka I., Stoffelen A., Verhoef A. (2018)
The Cryosphere, 12, 2941–2953. DOI: 10.5194/tc-12-2941-2018. (BibTeX: belmonte.etal.2018)
Abstract: See
This paper presents the first long-term climate datarecord of sea ice extents and backscatter derived from inter-calibrated satellite scatterometer missions (ERS, QuikSCATand ASCAT) extending from 1992 to the present date (Ver-hoef et al., 2018). This record provides a valuable indepen-dent account of the evolution of Arctic and Antarctic seaice extents, one that is in excellent agreement with the pas-sive microwave records during the fall and winter months butshows higher sensitivity to lower concentration and meltingsea ice during the spring and summer months. The scatterom-eter record also provides a depiction of sea ice backscat-ter at C- and Ku-bands, allowing the separation of seasonaland perennial sea ice in the Arctic and further differentia-tion between second-year (SY) and older multiyear (MY) iceclasses, revealing the emergence of SY ice as the dominantperennial ice type after the historical sea ice loss in 2007 andbearing new evidence on the loss of multiyear ice in the Arc-tic over the last 25 years. The relative good agreement be-tween the backscatter-based sea ice (FY, SY and older MY)classes and the ice thickness record from Cryosat suggests itsapplicability as a reliable proxy in the historical reconstruc-tion of sea ice thickness in the Arctic
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Cardellach E., Wickert J., Baggen R., Benito J., Camps A., Catarino N., Chapron B., Dielacher A., Fabra F., Flato G., Fragner H., Gabarró C., Gommenginger C., Haas C., Healy S., Hernández-Pajares M., Hoeg P., Jäggi A., Kainulainen J., Khan S.A., Lemke N.M.K., Li W., Nghiem S.V., Pierdicca N., Portabella M., Rautiainen K., Rius A., Sasgen I., Semmling M., Shum C.K., Soulat F., Steiner A.K., Tailhades S., Thomas M., Vilaseca R., Zuffada C. (2018)
IEEE Access, 6, 13980 - 14018. DOI: 10.1109/ACCESS.2018.2814072. (BibTeX: cardellach.etal.2018)
Abstract: See
The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA\'s Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a ``dynamic mapper\'\' of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035,covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.
Keywords: Polar science, GNSS, reflectometry, GNSS-R, sea ice, altimetry, polarimetry, radio-occultation, Low Earth Orbiter.
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Catalá T.S., Martínez-Pérez A.M., Nieto-Cid M., Álvarez M., Otero J., Emelianov M., Reche I., Arístegui J., Álvarez-Salgado X.A. (2018)
Progress in Oceanography, 165, 35-51. DOI: 10.1016/j.pocean.2018.05.002. (BibTeX: catala.etal.2018)
Abstract: See
Chromophoric dissolved organic matter (CDOM) in the open Mediterranean Sea (MedSea) is barely documented, remaining the basin–wide patterns in intermediate and deep waters still enigmatic. Here, full–depth distributions of CDOM absorption coefficients and spectral slopes recorded during the HOTMIX 2014 cruise are presented and their respective environmental drivers resolved. General Additive Models (GAMs) in surface waters and Optimum MultiParameter (OMP) water mass analysis in deep waters were applied. In the surface, apparent oxygen utilisation (AOU), a proxy to cumulative net community respiration, explained most of the variability of dissolved organic carbon (DOC) and the absorption coefficient at 254 nm (a254), whereas the absorption coefficient at 325 nm (a325), and the spectral slopes were mostly explained by potential temperature, a proxy to stratification and solar radiation, indicating that both water column stability and photobleaching may drive the variability of the UV–A absorbing CDOM components. In deep waters, the effect of water mass mixing and basin–scale mineralization were discerned from local mineralization processes. Water mass mixing and basin– scale mineralization contributed more substantially to explain the variability of DOC, a254 and a325 (82–91%) than the variability of the spectral slopes (35–64%). Local mineralization processes indicate that DOC and CDOM play a more relevant role in the carbon cycle in the Eastern (EastMed) than in the Western (WestMed) Mediterranean: whereas DOC contributed to 66 ± 10% of the oxygen demand in the EastMed, it represented only 24 ± 4% in the WestMed. Independently of basins and layers, a254 revealed as an excellent proxy to the concentration of DOC in the MedSea. Also, the unexpected inverse relationship of a325 with AOU indicates that the consumption of the UV–A absorbing CDOM fraction prevails over their production.
Keywords: Dissolved organic carbon Chromophoric dissolved organic matter Water masses Biogeochemistry Mediterranean Sea
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García-Olivares A., Solé J., Osychenko O. (2018)
Energy Conversion and Management, 158, 266-285. DOI: 10.1016/j.enconman.2017.12.053. (BibTeX: garciaolivares.etal.2018)
Abstract: See
A 100% renewable economy would give a lasting solution to the challenges raised by climate change, energy security, sustainability, and pollution. The conversion of the present transport system appears to be one of the most difficult aspects of such renewable transition. This study reviews the technologies and systems that are being proposed or proven as alternative to fossil-fuel based transportation, and their prospects for their entry into the post-carbon era, from both technological and energetic viewpoints. The energetic cost of the transition from the current transportation system into global 100% renewable transportation is estimated, as well as the electrical energy required for the operation of the new renewable transportation sector. A 100% renewable transport providing the same service as global transport in 2014 would demand about 18% less energy. The main reduction is expected in road transport (69%), but the shipping and air sectors would notably increase their consumptions: 163% and 149%, respectively. The analysis concludes that a 100% renewable transportation is feasible, but not necessarily compatible with indefinite increase of resources consumption. The major material and energy limitations and obstacles of each transport sector for this transition are shown.
Keywords: 100% renewable system Transportation Transition cost Embedded energy
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Hoareau N., Turiel A., Portabella M., Ballabrera-Poy J., Vogelzang J. (2018)
IEEE Transactions on Geoscience and Remote Sensing, 56, 9, 5525-5536. DOI: doi.org/10.1109/TGRS.2018.2819240. (BibTeX: hoareau.etal.2018a)
Abstract: See
The Soil Moisture and Ocean Salinity (SMOS) and Aquarius satellite missions have produced the first sea-surface salinity (SSS) maps from space. The quality of the retrieved SSS must be assessed, in terms of its validation against sparse ground truth, but also in terms of its ability to detect and characterize geophysical processes, such as mesoscale features. Such characterization is sometimes elusive due to the presence of noise and processing artifacts that continue to affect stateof- the-art remote sensing SSS maps. A new method, based on singularity analysis, is proposed to contribute to the assessment of the geophysical characteristics of such maps. Singularity analysis can be used to directly assess the spatial consistency of the SSS fields and to improve the estimation of the wavenumber spectra slope through a new method, the singularity power spectra (SPS). To demonstrate the SPS performance and utility, we applied SPS to different gridded SSS maps, such as SMOS and Aquarius high-level products, the output of a numerical simulation, in situ reanalysis, and climatology, as well as to other sea-surface temperature products for reference. The singularity analysis and SPS methods reveal that both the SMOS level 4 and the Aquarius combined active passive products are both able to describe the geometry of the existing geophysical structures and provide consistent spectral slopes. This paper demonstrates that beyond the remaining sources of uncertainty in remote sensing SSS products, valuable dynamical information on the ocean state can be extracted from these SSS products.
Keywords: Aquarius, geophysical consistence, remote sensing, sea-surface salinity (SSS), singularity analysis, singularity power spectra (SPS), Soil Moisture and Ocean Salinity (SMOS).
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Hoareau N., Portabella M., Lin W., Ballabrera-Poy J., Turiel A. (2018)
IEEE Transactions on Geoscience and Remote Sensing, 56, 9, 5160-5168. DOI: doi.org/10.1109/TGRS.2018.2810442. (BibTeX: hoareau.etal.2018c)
Abstract: See
The triple collocation (TC) technique allows the simultaneous calibration of three independent, collocated data sources, while providing an estimate of their accuracy. In this paper, the TC is adapted to validate different salinity data products along the tropical band. The representativeness error (the true variance resolved by the relatively high-resolution systems but not by the relatively low-resolution system) is accounted for in the validation process. A method based on the intercalibration capabilities of TC is used to estimate the representativeness error for each triplet, which is found to impact between 15% and 50% the error estimation of the different products. The method also sorts the different products in terms of their resolving spatiotemporal scales. Six salinity products (sorted from smaller to larger scales) used were: the in situ data from the Global Tropical Moored Buoy Array (TAO), the GLORYS2V3 ocean reanalysis output provided by Copernicus, the satellite-derived Aquarius Level 3 version 4 (AV4) and Soil Moisture and Ocean Salinity (SMOS) objectively analyzed (SOA) maps, and the climatology maps provided by the World Ocean Atlas (WOA). This calibration study is limited to the year 2013, a year when all the products were available. This validation approach aims to assess the quality of the different salinity products at the satellite-resolved spatiotemporal scales. The results show that, at the AV4 resolved scales, the Aquarius product has an error of 0.17, and outperforms TAO, GLORYS2V3, and the SOA maps. However, at the SOA resolved scales (which are coarser than those of the Aquarius product because of the large OA correlation radii used), the SMOS product has an error of 0.20, slightly lower than that of GLORYS2V3, Aquarius, and TAO. The WOA products show the highest errors. Higher order calibration may lead to a more accurate assessment of the quality of the climatological products.
Keywords: Error analysis; Remote sensing; Sea measurements
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Llanillo P.J., Pelegrí J.L., Talley L.D., Peña-Izquierdo J., Cordero R.R. (2018)
Journal of Geophysical Research: Oceans, 123, 3, 1722-1744. DOI: 10.1002/2017JC013509. (BibTeX: llanillo.etal.2018)
Abstract: See
Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP-OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical equatorial pathway, and (3) derive a refined annual-mean oxygen budget for the ESP-OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical-equatorial advection, with more than one-third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ’s core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen-rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical-equatorial pathway. Considering the entire OMZ, net oxygen supply (3.8460.42 mmol kg21 yr21) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical-equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical-equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One-quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%).
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Martínez J., González-Gambau V., Turiel A. (2018)
IEEE Geoscience and Remote Sensing Letters, 15, 7, 1060-1064. DOI: 10.1109/LGRS.2018.2818285. (BibTeX: martinez.etal.2018b)
Abstract: See
Since the beginning of the soil moisture and ocean salinity mission, the pervading presence of radio frequency interferences (RFI) has been one of the most problematic issues. The effect of an RFI is not just a hot spot but also six tails along the three main axes, and the general presence of ripples which degrade the quality of L1 brightness temperature snapshots. The standard mitigation technique is to apply an apodization (Blackman), but such a low-pass filter leaves traces of the tails and spreads the signal of the main lobes. New RFI mitigation techniques, such as nodal sampling, are very effective in reducing the impact of tails and ripples, but in some cases they lead to the spread of the RFI main lobe, with a significant loss of data on the affected area. In this letter, we propose a new technique to reduce their spread by an adaptive thresholding on a bandpass filtered version of the snapshot, with a significant recovery of data
Keywords: Imaging; Interferometry; Remote sensing; Radio frequency interferences (RFI); Signal processing; Soil moisture and ocean salinity (SMOS).
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Martínez-Pérez A.M., Catalá T.S., Nieto-Cid M., Otero J., Álvarez M., Emelianov M., Reche I., Álvarez-Salgado X.A., Arístegui J. (2018)
Progress in Oceanography, 170, 93-106. DOI: 10.1016/j.pocean.2018.10.019. (BibTeX: martinezperez.etal.2018)
Abstract: See
Fluorescent dissolved organic matter (FDOM) in the Mediterranean Sea was analysed by excitation–emission matrix (EEM) spectroscopy and parallel factor (PARAFAC) analysis during the cruise HOTMIX 2014. A 4–component model, including 3 humic–like and 1 protein–like compounds, was obtained. To decipher the environmental factors that dictate the distributions of these components, we run generalized additive models (GAMs) in the epipelagic layer and an optimum multiparametric (OMP) water masses analysis in the meso– and bathypelagic layers. In the epipelagic layer, apparent oxygen utilization (AOU) and temperature presented the most significant effects on the variability of the marine humic-like peak M fluorescence, suggesting that its distribution was controlled by the net community respiration of organic matter and photobleaching. On the contrary, the variability of the soil humic-like peak E and the protein–like peak T fluorescence was explained mainly by the prokaryotic heterotrophic abundance, which decreased eastwards. In the meso– and bathypelagic layers, water mass mixing and basin–scale mineralization processes explained>72% and 63% of the humic–like and protein–like fluorescence variability, respectively. When analysing the two basins separately, the OMP model offered a better explanation of the distribution of fluorescence in the eastern Mediterranean Sea, as expected from the reduced biological activity in this ultra–oligotrophic basin. Furthermore, while western Mediterranean deep waters display the usual trend in the global ocean (increase of humic–like fluorescence and decrease of protein–like fluorescence with higher AOU values), the eastern Mediterranean deep waters presented an opposite trend. Different initial fluorescence intensities of the water masses that mix in the eastern basin, with Adriatic and Aegean origins, seem to be behind this contrasting pattern. The analysis of the transect–scale mineralization processes corroborate this hypothesis, suggesting a production of humic–like and a consumption of protein–like fluorescence in parallel with water mass ageing. Remarkably, the transect–scale variability of the chromophoric dissolved organic matter (CDOM) absorbing at the excitation wavelength of the humic–like peak M indicates an unexpected loss with increasing AOU, which suggests that the consumption of the non–- fluorescent fraction of CDOM absorbing at that wavelength exceeded the production of the fluorescent fraction observed here.
Keywords: Dissolved organic matter Fluorescence spectroscopy PARAFAC Water mass analysis Mediterranean Sea
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Olivar M.P., Contreras T., Hulley P.A., Emelianov M., López-Pérez C., Tuset V., Castellón A. (2018)
Progress in Oceanography, 160, 83-100. DOI: 10.1016/j.pocean.2017.12.005. (BibTeX: olivar.etal.2018)
Abstract: See
The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1m2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Fortyseven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species (Diaphus cf. vanhoeffeni and Vinciguerria nimbaria), the transforming stages displayed vertical migration into the upper 100m at night, in a manner similar to their adult stages.
Keywords: Early life-history Ontogenetic vertical migration Mesopelagic fishes Lanternfishes Lightfishes Hatchetfishes
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Olmedo E., Taupier-Letage I., Turiel A., Alvera-Azcárate A. (2018)
Remote Sensing, 10, 485, 1-24. DOI: 10.3390/rs10030485. (BibTeX: olmedo.etal.2018)
Abstract: See
A new methodology using a combination of debiased non-Bayesian retrieval, DINEOF (Data Interpolating Empirical Orthogonal Functions) and multifractal fusion has been used to obtain Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) fields over the North Atlantic Ocean and the Mediterranean Sea. The debiased non-Bayesian retrieval mitigates the systematic errors produced by the contamination of the land over the sea. In addition, this retrieval improves the coverage by means of multiyear statistical filtering criteria. This methodology allows obtaining SMOS SSS fields in the Mediterranean Sea. However, the resulting SSS suffers from a seasonal (and other time-dependent) bias. This time-dependent bias has been characterized by means of specific Empirical Orthogonal Functions (EOFs). Finally, high resolution Sea Surface Temperature (OSTIA SST) maps have been used for improving the spatial and temporal resolution of the SMOS SSS maps. The presented methodology practically reduces the error of the SMOS SSS in the Mediterranean Sea by half. As a result, the SSS dynamics described by the new SMOS maps in the Algerian Basin and the Balearic Front agrees with the one described by in situ SSS, and the mesoscale structures described by SMOS in the Alboran Sea and in the Gulf of Lion coincide with the ones described by the high resolution remotely-sensed SST images (AVHRR).
Keywords: sea surface salinity; remote sensing; mediterranean sea; smos; alboran sea; data processing; quality assessment
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Olmedo E., Gabarró C., González-Gambau V., Martínez J., Ballabrera-Poy J., Turiel A., Portabella M., Fournier S., Lee T. (2018)
Remote Sensing, 10, 11, 1772. DOI: 10.3390/rs10111772. (BibTeX: olmedo.etal.2018a)
Abstract: See
This paper aims to present and assess the quality of seven years (2011–2017) of 25 km nine-day Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) objectively analyzed maps in the Arctic and sub-Arctic oceans (50ºN–90ºN). The SMOS SSS maps presented in this work are an improved version of the preliminary three-year dataset generated and freely distributed by the Barcelona Expert Center. In this new version, a time-dependent bias correction has been applied to mitigate the seasonal bias that affected the previous SSS maps. An extensive database of in situ data (Argo floats and thermosalinograph measurements) has been used for assessing the accuracy of this product. The standard deviation of the difference between the new SMOS SSS maps and Argo SSS ranges from 0.25 and 0.35. The major features of the inter-annual SSS variations observed by the thermosalinographs are also captured by the SMOS SSS maps. However, the validation in some regions of the Arctic Ocean has not been feasible because of the lack of in situ data. In those regions, qualitative comparisons with SSS provided by models and the remotely sensed SSS provided by Aquarius and SMAP have been performed. Despite the differences between SMOS and SMAP, both datasets show consistent SSS variations with respect to the model and the river discharge in situ data, but present a larger dynamic range than that of the model. This result suggests that, in those regions, the use of the remotely sensed SSS may help to improve the models.
Keywords: sea surface salinity; remote sensing; Arctic ocean; SMOS; Arctic rivers; data processing; quality assessment
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Perissi I., Falsini S., Bardi U., Natalini D., Green M., Jones A., Solé J. (2018)
Sustainability, 10, 11, Article number 4225. DOI: 10.3390/su10114225. (BibTeX: perissi.etal.2018)
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The Paris Agreement, ratified in 2015, pledged to reduce greenhouse gas emissions within a Global Carbon Budget that limits the global temperature increase to less than 2º C. With the Roadmap 2050 mitigation measures, the European Union has a target to reduce emissions by 80% of their 1990 value by 2050 but without giving an estimation or a maximum ceiling for the total amount of cumulative greenhouse gases emissions over that period. Thus, the impact of the EU regulations on global warming remains unestimated. The aim and the novelty of this study are to develop a set of potential European emissions trajectories, within the Global Carbon Budget and at the same time satisfying the Roadmap 2050 goals. The result of the study highlights the urgency to reinforce mitigation measures for Europe as soon as possible because any delay in policy implementation risks the Roadmap 2050 mitigation package being insufficient to achieve the objectives of the Paris treaty.
Keywords: carbon budget; greenhouse gases; decarbonization; climate change
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Ramírez-Pérez M., Twardowski M., Trees C., Piera J., McKee D. (2018)
Journal of Geophysical Research: Oceans, 123, 720-737. DOI: http://dx.doi.org/10.1002/2017JC013453. (BibTeX: ramirezperez.etal.2018)
Abstract: See
A deconvolution approach is presented to use spectral light absorption and attenuation data to estimate the concentration of the major nonwater compounds in complex shelf sea waters. The inversion procedure requires knowledge of local material-specific inherent optical properties (SIOPs) which are determined from natural samples using a bio-optical model that differentiates between Case I and Case II waters and uses least squares linear regression analysis to provide optimal SIOP values. A synthetic data set is used to demonstrate that the approach is fundamentally consistent and to test the sensitivity to injection of controlled levels of artificial noise into the input data. Self-consistency of the approach is further demonstrated by application to field data collected in the Ligurian Sea, with chlorophyll (Chl), the nonbiogenic component of total suspended solids (TSSnd), and colored dissolved organic material (CDOM) retrieved with RMSE of 0.61 mg m -3, 0.35 g m -3, and 0.02 m -1, respectively. The utility of the approach is finally demonstrated by application to depth profiles of in situ absorption and attenuation data resulting in profiles of optically significant constituents with associated error bar estimates. The advantages of this procedure lie in the simple input requirements, the avoidance of error amplification, full exploitation of the available spectral information from both absorption and attenuation channels, and the reasonably successful retrieval of constituent concentrations in an optically complex shelf sea.
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Romera-Castillo C., Pinto M., Langer T.M., Álvarez-Salgado X.A., Herndl G.J. (2018)
Nature Communications, 9, 1430 DOI: 10.1038/s41467-018-03798-5. (BibTeX: romeracastillo.etal.2018)
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Approximately 5.25 trillion plastic pieces are floating at the sea surface. The impact of plastic pollution on the lowest trophic levels of the food web, however, remains unknown. Here we show that plastics release dissolved organic carbon (DOC) into the ambient seawater stimulating the activity of heterotrophic microbes. Our estimates indicate that globally up to 23,600 metric tons of DOC are leaching from marine plastics annually. About 60% of it is available to microbial utilization in less than 5 days. If exposed to solar radiation, however, this DOC becomes less labile. Thus, plastic pollution of marine surface waters likely alters the composition and activity of the base of the marine food webs. It is predicted that plastic waste entering the ocean will increase by a factor of ten within the next decade, resulting in an increase in plastic-derived DOC that might have unaccounted consequences for marine microbes and for the ocean system.
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Sabatés A., Salat J., Tilves U., Raya V., E. Purcell J., Pascual M., Gili J.M., Fuentes V.L. (2018)
Journal of Marine Systems, 187, 52-61. DOI: 10.1016/j.jmarsys.2018.06.013. (BibTeX: sabates.etal.2018b)
Abstract: See
This study investigates the possible pathways for Pelagia noctiluca intrusions over the shelf to understand the interactions between jellyfish and fish larvae. To assess how the presence of P. noctiluca may influence populations of Engraulis encrasicolus and Trachurus trachurus, we analyzed the effect of environmental conditions on the abundance and spatial distribution of P. noctiluca, medusae and ephyrae, and early life stages of these two fish species along the Catalan coast. The highest concentrations of P. noctiluca were found offshore, all along the Northern Current path. Their occurrence over the shelf was associated with intrusions of open sea waters that contoured anticyclonic eddies generated by the oscillatory behaviour of the current. Anchovy larvae were found widely over the shelf, but were especially abundant in the north and in waters influenced by the Ebro river. Spatial patterns of anchovy larvae were defined better by physical environmental factors than by the presence of P. noctiluca, whose distribution clearly was determined by the circulation. The differences in environmental conditions controlling the populations of P. noctiluca and E. encrasicolus larvae prevent their general coexistence over the shelf and prey-predator interactions remained limited to the areas affected by offshore intrusions. It is remarkable that the occurrence of T. trachurus larvae and juveniles was limited to locations over the shelf where jellyfish were observed and never offshore. This suggests that the association between fish and jellyfish occur once jellyfish have been advected from offshore towards the shelf, favouring the survival of larvae and juveniles of T. trachurus.
Keywords: Medusa; Engraulis encrasicolus; Trachurus trachurus; Shelf-slope front; Eddies; NW Mediterranean
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Santis W., Aimola L., Campos E.J.D., Castellanos P. (2018)
Dynamics of Atmospheres and Oceans, 81, 30-41. DOI: 10.1016/j.dynatmoce.2017.11.004. (BibTeX: santis.etal.2018)
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The interdecadal variability of the atmospheric and oceanic meridional overturning circulation is studied, using a coupled model with two narrow meridional barriers representing the land and a flat bottomed Aquaplanet. Empirical orthogonal function (EOF) analysis are usedin the atmospheric and oceanic meridional overturning cells, revealing the atmospheric interdecadal variability is dominated by an annular mode, in both hemispheres, whichintroduces in the ocean a set of patterns of variability. The most energetic EOFs in the oceanare the barotropic responses from the annular mode. The interaction between the heat anomalies, due to the barotropic response, and the thermohaline circulation of each basinleads to a resonance mechanism that feeds back to the atmospheric forcing, modulatingthe annular mode spectrum. Besides the barotropic response, the annular mode introduces anomalies of salinity and temperature in the subtropical Atlantic that affects its upper buoy-ancy. These anomalies are incorporated within the ocean circulation and advected until theareas of deep sinking in the northern Atlantic, impacting on its overturning circulation as well
Keywords: AMOC Annular mode Idealized experiments
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Santis W., Aímola L., Castellanos P., Campos E.J.D. (2018)
International Journal of Climatology, 38, S1, e985-e997. DOI: 10.1002/joc.5424. (BibTeX: santis.etal.2018d)
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The role that the Indonesian Throughflow plays on climate is investigated in an alternative scenario, expected during glacial ages. The equatorwards shift of the Southern Hemisphere westerlies found in glacial ages acts to decrease the Agulhas Leakage (AL) and the thermohaline circulation (THC) in the Atlantic. Recent results suggest that these changes are followed by an increased THC in the Pacific, through an inter-basin seesaw mechanism. The enhanced circulation in the Pacific demands thermocline water to cross the equator towards northern latitudes, which shifts the water source of the throughflow from the low-salinity North Pacific to the relative saltier South Pacific. It is shown that in this equilibrium, the salinity anomalies of the throughflow impact the inter-basin seesaw towards the restoration of the modern climate, enhancing the North Atlantic Deep Water (NADW) formation and decreasing the THC in the Pacific. These results are consistent with paleo-observations and provide new insights to interpreting the climate changes in glacial periods.
Keywords: Indonesian Throughflow; inter-basin seesaw effect; meridional overturning circulation; idealized experiments
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von Schuckmann K., Le Traon P.Y., Smith N., Pascual A., Brasseur P., Fennel K., Djavidnia S., Aaboe S., Alvarez-Fanjul E., Autret E., Axell L., Aznar R., Benincasa M., Bentamy A., Boberg F., Bourdallé-Badie R., Buongiorno-Nardelli B., Brando V.E., Bricaud C., Breivik L.A., Brewin R.J.W., Capet A., Ceschin A., Ciliberti S., Cossarini G., de Alfonso M., de Pascual-Collar A., de Kloe J., Deshayes J., Desportes C., Drévillon M., Drillet Y., Droghei R., Dubois C., Embury O., Etienne H., Fratianni C., García-Lafuente J., García-Sotillo M., Garric G., Gasparin F., Gerin R., Good S., Gourrion J., Grégoire M., Greiner E., Guinehut S., Gutknecht E., Hernandez F., Hernandez O., Hoyer J., Jackson L., Jandt S., Josey S., Juza M., Kennedy J., Kokkini Z., Korres G., Kouts M., Lagemaa P., Lavergne T., le Cann B., Legeais J.F., Lemieux-Dudon B., Levier B., Lien V., Maljutenko I., Manzano F., Marcos M., Marinova V., Masina S., Mauri E., Mayer M., Melet A., Mélin F., Meyssignac B., Monier M., Müller M., Mulet S., Naranjo C., Notarstefano G., Paulmier A., Pérez-Gomez B., Pérez-Gonzalez I., Peneva E., Perruche C., Peterson K.A., Pinardi N., Pisano A., Pardo S., Poulain P.M., Raj R.P., Raudsepp U., Ravdas M., Reid R., Rio M.H., Salon S., Samuelsen A., Sammartino M., Sammartino S., Britt-Sando A., Santoleri R., Sathyendranath S., She J., Simoncelli S., Solidoro C., Stoffelen A., Storto A., Szerkely T., Tamm S., Tietsche S., Tinker J., Tintore J., Trindade A., van Zanten D., Vandenbulcke L., Verhoef A., Verbrugge N., Viktorsson L., von Schuckmann K., Wakelin S.L., Zacharioudaki A., Zuo H. (2018)
Journal of Operational Oceanography, 11, sup1, S1-S142. DOI: 10.1080/1755876X.2018.1489208. (BibTeX: vonschuckmann.etal.2018a)
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Solé J., García-Olivares A., Turiel A., Ballabrera-Poy J. (2018)
Renewable Energy, 116, 258-271. DOI: 10.1016/j.renene.2017.09.035. (BibTeX: sole.etal.2018)
Abstract: See
We use the concept of Energy Return On energy Invested (EROI) to calculate the amount of the available net energy that can be reasonably expected from World oil liquids during the next decades (till 2040). Our results indicate a decline in the available oil liquids net energy from 2015 to 2040. Such net energy evaluation is used as a starting point to discuss the feasibility of a Renewable Transition (RT). To evaluate the maximum rate of Renewable Energy Sources (RES) development for the RT, we assume that, by 2040, the RES will achieve a power of 11 TW (1012 Watt). In this case, by 2040, between 10 and 20% of net energy from liquid hydrocarbons will be required. Taking into account the oil liquids net energy decay, we calculate the minimum annual rate of RES deployment to compensate it in different scenarios. Our study shows that if we aim at keeping an increase of 3% of net energy per annum, an 8% annual rate of RES deployment is required. Such results point out the urgent necessity of a determined policy at different levels (regional, national and international) favoring the RT implementation in the next decades
Keywords: EROI Energy transition Renewable energy Fossil fuels Oil liquids Net energy URR (Ultimate Recoverable Resources)
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Sturm U., Schade S., Ceccaroni L., Gold M., Kyba C.C.M., Claramunt B., Haklay M., Kasperowski D., Albert A., Piera J., Brier J., Kullenberg C., Luna S. (2018)
RIO Research Ideas and Outcomes, 4 DOI: 10.3897/rio.4.e23394. (BibTeX: sturm.etal.2018a)
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Apps for mobile devices and web-based platforms are increasingly used in citizen science projects. While extensive research has been done in multiple areas of studies, from Human-Computer Interaction to public engagement in science, we are not aware of a collection of recommendations specific for citizen science that provides support and advice for planning, design and data management of mobile apps and platforms that will assist learning from best practice and successful implementations. In two workshops, citizen science practitioners with experience in mobile application and web-platform development and implementation came together to analyse, discuss and define recommendations for the initiators of technology based citizen science projects. Many of the recommendations produced during the two workshops are applicable to citizen science project that do not use mobile devices to collect data. Therefore, we propose to closely connect the results presented here with ECSA’s Ten Principles of Citizen Science.
Keywords: Citizen science; Digital technologies; Design; Reuse; Interoperability; Sustainability
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Viúdez A. (2018)
Journal of Geophysical Research: Oceans, 123, 5, 3705-3722. DOI: 10.1029/2017JC013735. (BibTeX: viudez.2018a)
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Two fundamental modes of vertical velocity (w) in mesoscale subsurface eddies are described using the quasigeostrophic (QG) approximation and nonhydrostatic numerical modeling. The first mode of w (the spheroidal mode) arises when a spheroidal upright subsurface eddy acquires horizontal eccentricity and becomes an ellipsoid, still upright, vertically symmetric vortex. In this case, the vertical displacement of isopycnals vanishes at the middepth z50. Conservation of potential vorticity anomaly (PVA) on elliptical concave/convex isopycnals entails a three-dimensional octupolar pattern of w which also vanishes at z50. The second mode of w (the tilted mode) arises when the eddy remains spheroidal but its vertical axis tilts relative to the vertical direction. In this case, the displacement of isopycnals is largest at the middepth z50 and has a dipolar distribution. The associated w is largest at the middepth and develops also a dipolar pattern. In both spheroidal and tilted modes, the vertical velocity pattern may be inferred from the fast advection of PVA conserving fluid particles on slower translating concave/convex or tilted isopycnals. This implies that the vertical velocity of both modes is approximately QG and may be correctly inferred from the QG omega equation as long as the Rossby number remains small. Under more general circumstances, the vortex is both spheroidal and tilted. In this case, both spheroidal and tilted modes coexist but remain, to a large extent, uncoupled, rotating with different and, at least at a first order of approximation, constant phase speeds.