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The coastal oceans can be highly variable, especially near ocean fronts. The Ushant Front is the dominant oceanographic feature in the Iroise Sea (NE Atlantic) during summer, separating warm stratified offshore waters from cool vertically-mixed nearshore waters. Mesozooplankton community structure was investigated over an annual cycle to examine relationships with oceanographic conditions. DNA metabarcoding of COI and 18S genes was used in communities from six sites along two cross-shelf transects. Taxonomic assignments of 380 and 296 OTUs (COI and 18S, respectively) identified 21 classes across 13 phyla. Meroplankton relative abundances peaked in spring and summer, particularly for polychaete and decapod larvae, respectively, corresponding to the reproductive periods of these taxa. Meroplankton was most affected by season, while holoplankton varied most by shelf position. Copepods with a mixed feeding strategy were associated with the most offshore sites, especially in the presence of the front, while filter-feeding or carnivorous copepods were associated with nearshore sites. In sum, mesozooplankton communities in well-mixed coastal waters were distinct from those found in the Ushant Front (high thermal stratification and chlorophyll-a). Furthermore, the benthic compartment, through its partial life cycle in the water column, contributed to high heterogeneity in planktonic communities over short temporal and spatial scales.

The coastal oceans can be highly variable, especially near ocean fronts. The Ushant Front is the dominant oceanographic feature in the Iroise Sea (NE Atlantic) during summer, separating warm stratified offshore waters from cool vertically-mixed nearshore waters. Mesozooplankton community structure was investigated over an annual cycle to examine relationships with oceanographic conditions. DNA metabarcoding of COI and 18S genes was used in communities from six sites along two cross-shelf transects. Taxonomic assignments of 380 and 296 OTUs (COI and 18S, respectively) identified 21 classes across 13 phyla. Meroplankton relative abundances peaked in spring and summer, particularly for polychaete and decapod larvae, respectively, corresponding to the reproductive periods of these taxa. Meroplankton was most affected by season, while holoplankton varied most by shelf position. Copepods with a mixed feeding strategy were associated with the most offshore sites, especially in the presence of the front, while filter-feeding or carnivorous copepods were associated with nearshore sites. In sum, mesozooplankton communities in well-mixed coastal waters were distinct from those found in the Ushant Front (high thermal stratification and chlorophyll-a). Furthermore, the benthic compartment, through its partial life cycle in the water column, contributed to high heterogeneity in planktonic communities over short temporal and spatial scales.

Sea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10~km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite Synthetic Aperture Radar, satellite and airborne multi‐angle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple angle from airplane. This second paper focuses on the retrieval of the current gradient magnitude and scale, using roughness observations at different scales, from airplane and from satellite. Two main results are obtained: (i) Trajectories of selected drifters show that the front is only 50~m wide and unambiguously exhibits convergence and cyclonic vorticity up to 100~f (with f the Coriolis frequency). This far exceeds previously documented values for submesoscale deep ocean fronts. (ii) Correct estimation of such extreme current gradients using surface roughness hinges on instruments with sufficiently high spatial resolution. Lower resolution roughness sensors can still detect the front, as demonstrated from observations and a simplified model, but cannot properly estimate the current gradient magnitude and the frontal width. Those results provide guidelines for monitoring intense current gradients from space using sea surface roughness. PLAIN LANGUAGE SUMMARY Ocean surface currents are not uniform horizontally, but involve structures of many different sizes. After focusing on large scale currents (about 1000~km) and eddies (about 100~km), attention is nowadays turning towards fine scale (about 1~km) fronts and

Sea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10~km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite Synthetic Aperture Radar, satellite and airborne multi‐angle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple angle from airplane. This second paper focuses on the retrieval of the current gradient magnitude and scale, using roughness observations at different scales, from airplane and from satellite. Two main results are obtained: (i) Trajectories of selected drifters show that the front is only 50~m wide and unambiguously exhibits convergence and cyclonic vorticity up to 100~f (with f the Coriolis frequency). This far exceeds previously documented values for submesoscale deep ocean fronts. (ii) Correct estimation of such extreme current gradients using surface roughness hinges on instruments with sufficiently high spatial resolution. Lower resolution roughness sensors can still detect the front, as demonstrated from observations and a simplified model, but cannot properly estimate the current gradient magnitude and the frontal width. Those results provide guidelines for monitoring intense current gradients from space using sea surface roughness. PLAIN LANGUAGE SUMMARY Ocean surface currents are not uniform horizontally, but involve structures of many different sizes. After focusing on large scale currents (about 1000~km) and eddies (about 100~km), attention is nowadays turning towards fine scale (about 1~km) fronts and

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(8), (2019): 5999-6014, doi: 10.1029/2019JC015034., Oceanic fronts are dynamically active regions of the global ocean that support upwelling and downwelling with significant implications for phytoplankton production and export. However (on time scales urn:x-wiley:jgrc:media:jgrc23568:jgrc23568-math-0001 the inertial time scale), the vertical velocity is 103–104 times weaker than the horizontal velocity and is difficult to observe directly. Using intensive field observations in conjunction with a process study ocean model, we examine vertical motion and its effect on phytoplankton fluxes at multiple spatial horizontal scales in an oligotrophic region in the Western Mediterranean Sea. The mesoscale ageostrophic vertical velocity (∼10 m/day) inferred from our observations shapes the large‐scale phytoplankton distribution but does not explain the narrow (1–10 km wide) features of high chlorophyll content extending 40–60 m downward from the deep chlorophyll maximum. Using modeling, we show that downwelling submesoscale features concentrate 80% of the downward vertical flux of phytoplankton within just 15% of the horizontal area. These submesoscale spatial structures serve as conduits between the surface mixed layer and pycnocline and can contribute to exporting carbon from the sunlit surface layers to the ocean interior., The AlborEx experiment was conducted in the framework of PERSEUS EU‐funded project (Grant 287600) and was led by the Spanish National Research Council (CSIC) and involved other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy); and Woods Hole Oceanographic Institution (WHOI, ONR Grant N00014‐16‐1‐3130). Glider operations were partially funded by JERICO FP7 project. Part of this work has been carried out as part of the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. CMEMS is implemented by Mercator Ocean in the framework of a delegation agreement with the European Union. S. R. and A. P. acknowledge support from WHOI Subcontract A101339. Data available from authors: Ship CTDs, glider and VM‐ADCP data files are available in the SOCIB data catalog (https://doi.org/10.25704/z5y2-qpye); model data are available at IMEDEA data catalog https://ide.imedea.uib-csic.es/thredds/catalog/data/projects/alborex/catalog.html. We thank all the crew and participants on board R/V SOCIB for their collaboration and Marc Torner and the SOCIB glider Facility for their efficient cooperation. We also thank B. Mourre for numerical data from the Western Mediterranean Operational Model to initialize the Process Study Ocean Model. Figures were created using the cmocean colormaps package (Thyng et al., 2016).

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(8), (2019): 5999-6014, doi: 10.1029/2019JC015034., Oceanic fronts are dynamically active regions of the global ocean that support upwelling and downwelling with significant implications for phytoplankton production and export. However (on time scales urn:x-wiley:jgrc:media:jgrc23568:jgrc23568-math-0001 the inertial time scale), the vertical velocity is 103–104 times weaker than the horizontal velocity and is difficult to observe directly. Using intensive field observations in conjunction with a process study ocean model, we examine vertical motion and its effect on phytoplankton fluxes at multiple spatial horizontal scales in an oligotrophic region in the Western Mediterranean Sea. The mesoscale ageostrophic vertical velocity (∼10 m/day) inferred from our observations shapes the large‐scale phytoplankton distribution but does not explain the narrow (1–10 km wide) features of high chlorophyll content extending 40–60 m downward from the deep chlorophyll maximum. Using modeling, we show that downwelling submesoscale features concentrate 80% of the downward vertical flux of phytoplankton within just 15% of the horizontal area. These submesoscale spatial structures serve as conduits between the surface mixed layer and pycnocline and can contribute to exporting carbon from the sunlit surface layers to the ocean interior., The AlborEx experiment was conducted in the framework of PERSEUS EU‐funded project (Grant 287600) and was led by the Spanish National Research Council (CSIC) and involved other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy); and Woods Hole Oceanographic Institution (WHOI, ONR Grant N00014‐16‐1‐3130). Glider operations were partially funded by JERICO FP7 project. Part of this work has been carried out as part of the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. CMEMS is implemented by Mercator Ocean in the framework of a delegation agreement with the European Union. S. R. and A. P. acknowledge support from WHOI Subcontract A101339. Data available from authors: Ship CTDs, glider and VM‐ADCP data files are available in the SOCIB data catalog (https://doi.org/10.25704/z5y2-qpye); model data are available at IMEDEA data catalog https://ide.imedea.uib-csic.es/thredds/catalog/data/projects/alborex/catalog.html. We thank all the crew and participants on board R/V SOCIB for their collaboration and Marc Torner and the SOCIB glider Facility for their efficient cooperation. We also thank B. Mourre for numerical data from the Western Mediterranean Operational Model to initialize the Process Study Ocean Model. Figures were created using the cmocean colormaps package (Thyng et al., 2016).

Sea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10~km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite Synthetic Aperture Radar, satellite and airborne multi‐angle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple angle from airplane. This second paper focuses on the retrieval of the current gradient magnitude and scale, using roughness observations at different scales, from airplane and from satellite. Two main results are obtained: (i) Trajectories of selected drifters show that the front is only 50~m wide and unambiguously exhibits convergence and cyclonic vorticity up to 100~f (with f the Coriolis frequency). This far exceeds previously documented values for submesoscale deep ocean fronts. (ii) Correct estimation of such extreme current gradients using surface roughness hinges on instruments with sufficiently high spatial resolution. Lower resolution roughness sensors can still detect the front, as demonstrated from observations and a simplified model, but cannot properly estimate the current gradient magnitude and the frontal width. Those results provide guidelines for monitoring intense current gradients from space using sea surface roughness. PLAIN LANGUAGE SUMMARY Ocean surface currents are not uniform horizontally, but involve structures of many different sizes. After focusing on large scale currents (about 1000~km) and eddies (about 100~km), attention is nowadays turning towards fine scale (about 1~km) fronts and

Sea surface roughness is affected by surface current gradients, which provides a means of monitoring from satellite sharp oceanic fronts. This paper is the second report of an experiment designed to compare observations of sea surface roughness and surface currents at an unprecedented accuracy, owing to the conjunction of numerous deployed drifters and roughness instruments. About 200 drifters sampled a thin 10~km elongated submesoscale front, also monitored by a high density of roughness instruments: satellite Synthetic Aperture Radar, satellite and airborne multi‐angle sunglint radiometers. The first paper focused on the retrieval of the current gradient direction (convergence and cyclonic vorticity) at the front, using roughness observations at multiple angle from airplane. This second paper focuses on the retrieval of the current gradient magnitude and scale, using roughness observations at different scales, from airplane and from satellite. Two main results are obtained: (i) Trajectories of selected drifters show that the front is only 50~m wide and unambiguously exhibits convergence and cyclonic vorticity up to 100~f (with f the Coriolis frequency). This far exceeds previously documented values for submesoscale deep ocean fronts. (ii) Correct estimation of such extreme current gradients using surface roughness hinges on instruments with sufficiently high spatial resolution. Lower resolution roughness sensors can still detect the front, as demonstrated from observations and a simplified model, but cannot properly estimate the current gradient magnitude and the frontal width. Those results provide guidelines for monitoring intense current gradients from space using sea surface roughness. PLAIN LANGUAGE SUMMARY Ocean surface currents are not uniform horizontally, but involve structures of many different sizes. After focusing on large scale currents (about 1000~km) and eddies (about 100~km), attention is nowadays turning towards fine scale (about 1~km) fronts and

© The Authors, 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Pascual, A., Ruiz, S., Olita, A., Troupin, C., Claret, M., Casas, B., Mourre, B., Poulain, P. M., Tovar-Sanchez, A., Capet, A., Mason, E., Allen, J. T., Mahadevan, A., & Tintore, J. A multiplatform experiment to unravel meso- and submesoscale processes in an intense front (AlborEx). Frontiers in Marine Science, 4(39), (2017), doi:10.3389/fmars.2017.00039., The challenges associated with meso- and submesoscale variability (between 1 and 100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data and numerical simulations to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1 m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior., The AlborEx experiment was conducted in the framework of PERSEUS EU-funded project (Grant agreement no: 287600). The experiment was led by the Spanish National Research Council (CSIC) institution with strong involvement and cooperation from other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy), McGill University (Canada); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy) and Woods Hole Oceanographic Institution (WHOI, USA). Glider operations were partially funded by JERICO FP7 project. AP acknowledges support from the Spanish National Research Program (E-MOTION/CTM2012-31014 and PRE-SWOT/CTM2016-78607-P). SR and AP are also supported by the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. EM is supported by a post-doctoral grant from the Conselleria d'Educació, Cultura i Universitats del Govern de les Illes Balears (Mallorca, Spain) and the European Social Fund. AC is a FNRS researcher under the FNRS BENTHOX project (Convention T.1009.15). The altimeter products were produced by Ssalto/Duacs and distributed by CMEMS. The profiling floats and some drifters were contributed by the Argo-Italy program. The authors are in debt with A. Massanet, F. Margirier, M. Palmer, C. Castilla, P. Balaguer and for their efficient work and implication during the AlborEx cruise. We also thank M. Menna, G. Notarstefano and A. Bussani for their help with the drifter and float data processing and the production of some figures. This article was initiated during a research visit of the first two authors to Woods Hole Oceanographic Institution.

© The Authors, 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Pascual, A., Ruiz, S., Olita, A., Troupin, C., Claret, M., Casas, B., Mourre, B., Poulain, P. M., Tovar-Sanchez, A., Capet, A., Mason, E., Allen, J. T., Mahadevan, A., & Tintore, J. A multiplatform experiment to unravel meso- and submesoscale processes in an intense front (AlborEx). Frontiers in Marine Science, 4(39), (2017), doi:10.3389/fmars.2017.00039., The challenges associated with meso- and submesoscale variability (between 1 and 100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data and numerical simulations to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1 m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior., The AlborEx experiment was conducted in the framework of PERSEUS EU-funded project (Grant agreement no: 287600). The experiment was led by the Spanish National Research Council (CSIC) institution with strong involvement and cooperation from other national and international partners: Balearic Islands Coastal Observing and Forecasting System (SOCIB, Spain); Consiglio Nazionale delle Ricerche (CNR, Italy), McGill University (Canada); Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italy) and Woods Hole Oceanographic Institution (WHOI, USA). Glider operations were partially funded by JERICO FP7 project. AP acknowledges support from the Spanish National Research Program (E-MOTION/CTM2012-31014 and PRE-SWOT/CTM2016-78607-P). SR and AP are also supported by the Copernicus Marine Environment Monitoring Service (CMEMS) MedSUB project. EM is supported by a post-doctoral grant from the Conselleria d'Educació, Cultura i Universitats del Govern de les Illes Balears (Mallorca, Spain) and the European Social Fund. AC is a FNRS researcher under the FNRS BENTHOX project (Convention T.1009.15). The altimeter products were produced by Ssalto/Duacs and distributed by CMEMS. The profiling floats and some drifters were contributed by the Argo-Italy program. The authors are in debt with A. Massanet, F. Margirier, M. Palmer, C. Castilla, P. Balaguer and for their efficient work and implication during the AlborEx cruise. We also thank M. Menna, G. Notarstefano and A. Bussani for their help with the drifter and float data processing and the production of some figures. This article was initiated during a research visit of the first two authors to Woods Hole Oceanographic Institution.

Oceanic fronts are dynamically active regions of the global ocean that support upwelling and downwelling with significant implications for phytoplankton production and export. However (on time scales (Formula presented.) the inertial time scale), the vertical velocity is 10–10 times weaker than the horizontal velocity and is difficult to observe directly. Using intensive field observations in conjunction with a process study ocean model, we examine vertical motion and its effect on phytoplankton fluxes at multiple spatial horizontal scales in an oligotrophic region in the Western Mediterranean Sea. The mesoscale ageostrophic vertical velocity (∼10 m/day) inferred from our observations shapes the large-scale phytoplankton distribution but does not explain the narrow (1–10 km wide) features of high chlorophyll content extending 40–60 m downward from the deep chlorophyll maximum. Using modeling, we show that downwelling submesoscale features concentrate 80% of the downward vertical flux of phytoplankton within just 15% of the horizontal area. These submesoscale spatial structures serve as conduits between the surface mixed layer and pycnocline and can contribute to exporting carbon from the sunlit surface layers to the ocean interior.

Small-scale ocean flows have increasingly ageostrophic dynamics that are important for the ocean energy budget and biogeochemical cycles. Numerical models indicate that the ageostrophic flow and vertical velocities associated with frontogenesis are a dominant mechanism of surface to interior ocean material transport. The increasingly unbalanced flow may also provide a pathway to downscale energy from the mesoscale to microscale.In situ observations of these flows are challenging due to the characteristics of the flow, such as small spatial scales and short lifetimes of hours to days. To observe the physical properties, generation, and evolution of these features, a new experimental method was developed at UCLA that incorporates simultaneous sampling by remote sensing and in situ instruments onboard satellites, aircraft, and vessels.On April 14, 2011, a small-scale frontal feature confined to the upper 10 m of the water column was measured near Catalina Island, California. The front had a maximum horizontal temperature gradient of 0.0031℃ m-1 and slope of 0.0146. To our knowledge, this is the first time such high resolution and comprehensive in situ observations have been made of submesoscale features.

Small-scale ocean flows have increasingly ageostrophic dynamics that are important for the ocean energy budget and biogeochemical cycles. Numerical models indicate that the ageostrophic flow and vertical velocities associated with frontogenesis are a dominant mechanism of surface to interior ocean material transport. The increasingly unbalanced flow may also provide a pathway to downscale energy from the mesoscale to microscale.In situ observations of these flows are challenging due to the characteristics of the flow, such as small spatial scales and short lifetimes of hours to days. To observe the physical properties, generation, and evolution of these features, a new experimental method was developed at UCLA that incorporates simultaneous sampling by remote sensing and in situ instruments onboard satellites, aircraft, and vessels.On April 14, 2011, a small-scale frontal feature confined to the upper 10 m of the water column was measured near Catalina Island, California. The front had a maximum horizontal temperature gradient of 0.0031℃ m-1 and slope of 0.0146. To our knowledge, this is the first time such high resolution and comprehensive in situ observations have been made of submesoscale features.

Postcard of the Ocean Front, Promenade and Beach in Venice, California from a color photograph. The image depicts a crowd of people walking next to the Plunge. Several sunbathers can be seen on the beach in the distance. The Plunge has many arched windows and several banners of the American flag. "A-57856" and "C.T. Photochrom" -- printed on back.; Handwritten manuscript on back. Postmarked from Venice, California in August 1918.