ALBERT

Description: 〈b〉The CMEMS GlobColour 〈i〉Chlorophyll-a〈/i〉 Product Based on Satellite Observation〈/b〉〈br〉 Philippe Garnesson, Antoine Mangin, Odile Fanton d'Andon, Julien Demaria, and Marine Bretagnon〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-155,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉This work concerns the chlorophyll products based on Satellite Observation and disseminated in the frame of the Copernicus Marine Environmental Monitoring Service (CMEMS).〈/p〉 〈p〉 This work highlights the main advantages provided by the Copernicus Globcolour processor which is used to serve the CMEMS with a long time series from 1997 to present with level 3 & 4 products at Global level (4 km of spatial resolution) and for the Atlantic level 4 product (1 km).〈/p〉 〈p〉 It discusses the different ways to merge data coming from different sensors and it is shown that the GlobColour processor approach provide a better flexibility. At present, it is the only one CMEMS processor able to ingest the OLCI-S3A in the merged product (OLCI-S3A data are ingested in the operational CMEMS products since the April 2018 release).〈/p〉 〈p〉 Behind the merging, the flagging strategy to go from level 2 provided by spatial agencies to the level 3 CMEMS products is also discussed. A better spatial coverage is demonstrated, including the coastal area which is of particular interest for many users involved in the EU Water Framework and Marine Strategy Framework Directive.〈/p〉

Description: 〈b〉The land–sea coastal border: a quantitative definition by considering the wind and wave conditions in a wave-dominated, micro-tidal environment〈/b〉〈br〉 Agustín Sánchez-Arcilla, Jue Lin-Ye, Manuel García-León, Vicente Gràcia, and Elena Pallarès〈br〉 Ocean Sci., 15, 113-126, https://doi.org/10.5194/os-15-113-2019, 2019〈br〉 A quantitative definition for the coastal border isotropy of met-ocean processes is proposed. Wind velocity and significant wave height anisotropies are examined along four transects at the north-western Mediterranean coast. Both decrease offshore, determining a coastal fringe of width of 2–4 km. The joint probability structure reflects a decoupling near the coast and a stronger dependence in the bay-like part, where the wave field is being more actively generated by the overlaying wind.

Description: 〈b〉Could the two anticyclonic eddies during winter 2003/2004 be reproduced and predicted in the northern South China Sea?〈/b〉〈br〉 Dazhi Xu, Wei Zhuang, and Youfang Yan〈br〉 Ocean Sci., 15, 97-111, https://doi.org/10.5194/os-15-97-2019, 2019〈br〉 The reproductivity and predictability of mesoscale eddies in the northern South China Sea are investigated with a focus on two anticyclonic eddies based on an assimilated system. The results show that generation, evolution, and propagation paths of these two eddies can be well reproduced and forecasted when the observed amplitude 〉8 cm. However, when their amplitudes are

Description: 〈b〉Frontogenesis of the Angola–Benguela Frontal Zone〈/b〉〈br〉 Shunya Koseki, Hervé Giordani, and Katerina Goubanova〈br〉 Ocean Sci., 15, 83-96, https://doi.org/10.5194/os-15-83-2019, 2019〈br〉 With an ocean frontogenetic function, the frontogenesis of the Angola–Benguela Frontal Zone (ABFZ) is investigated. On an annual-mean timescale, the meridional confluence of Angola and Benguela currents and tilting effect due to the upwelling are the main sources to generate the ABFZ. The annual cycle of the ABFZ is also mainly driven by these two effects.

Description: 〈b〉Measuring rates of present-day relative sea-level rise in low-elevation coastal zones: a critical evaluation〈/b〉〈br〉 Molly E. Keogh and Torbjörn E. Törnqvist〈br〉 Ocean Sci., 15, 61-73, https://doi.org/10.5194/os-15-61-2019, 2019〈br〉 Relative sea-level rise is traditionally measured with tide gauges, but we question the reliability of tide-gauge data in low-elevation coastal zones. Benchmark data show that tide gauges typically do not record subsidence in the shallow subsurface and thus underestimate rates of relative sea-level rise. We present an alternative method of measuring relative sea-level rise and conclude that low-elevation coastal zones may be at higher risk of flooding than previously assumed.

Description: 〈b〉Eddy-induced Track Reversal and Upper Ocean Physical-Biogeochemical Response of Tropical Cyclone Madi in the Bay of Bengal〈/b〉〈br〉 Riyanka Roy Chowdhury, S. Prasanna Kumar, and Arun Chakraborty〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-133,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 Highlights: Documented role of oceanic cyclonic eddies in modifying track and life cycle of cyclone by way of abrupt track reversal and rapid decay. Cyclone-induced increase in the chlorophyll a biomass ranged from 5 to 7 fold, while the net primary productivity from 2.5 to 8 fold. A 3.7 fold increase in cyclone-induced CO〈sub〉2〈/sub〉 out-gassing indicative of the altering regional CO〈sub〉2〈/sub〉 balance in the BoB, which is a weak sink.

Description: 〈b〉Numerical issues of the Total Exchange Flow (TEF) analysis framework for quantifying estuarine circulation〈/b〉〈br〉 Marvin Lorenz, Knut Klingbeil, Parker MacCready, and Hans Burchard〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-147,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Estuaries are areas where riverine and oceanic waters meet and mix. The exchange flow of an estuary describes the water properties of the inflowing and outflowing water. These can be described by simple bulk values for volume fluxes and salinities. This work focuses on the numerics of one computational method for these values, the Total Exchange Flow. We show that only the so called dividing salinity method is able to reliably calculate the correct values, even for complex situations.

Description: 〈b〉Discovering sounds in Patagonia: characterizing sei whale (〈i〉Balaenoptera borealis〈/i〉) downsweeps in the south-eastern Pacific Ocean〈/b〉〈br〉 Sonia Español-Jiménez, Paulina A. Bahamonde, Gustavo Chiang, and Verena Häussermann〈br〉 Ocean Sci., 15, 75-82, https://doi.org/10.5194/os-15-75-2019, 2019〈br〉 Sei whales are one of the least known baleen whales. We found them in southern Chile, on the Patagonian coast. We set up hydrophones in the Penas Gulf in 2016 and 2017 to investigate how this Patagonian sei whale might be communicating. We could identify sei whale downs-weep calls (a type of vocalization that starts at a high frequency and ends at a lower). We found that sei whales in the Penas Gulf perform calls distinctly differently from the sounds previously described.

Description: 〈b〉Impact of wave physics on ocean–wave coupling in CMEMS-IBI Part B: Validation study〈/b〉〈br〉 Romain Rainaud, Lotfi Aouf, Alice Dalphinet, Marcos Garcia Sotillo, Enrique Alvarez-Fanjul, Guillaume Reffray, Bruno Levier, Stéphane Law-Chune, Pablo Lorente, and Cristina Toledano〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-167,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This work highlights the relevance of coupling wave model with ocean model in order to improve key surface ocean parameters and in general to better describe the ocean circulation at small and large scale. The results focus on the Iberian Biscay and Ireland ocean region with fine grid resolution of 2.5 km for the ocean model. The main conclusion is the improvement of wave physics induces a better ocean mixing at the upper layer and a positive impact for sea surface height in storm events.

Description: 〈b〉Factors controlling pCO〈sub〉2〈/sub〉 variability in the eastern Gulf of Cádiz (SW Iberian Península)〈/b〉〈br〉 Dolores Jiménez-López, Ana Sierra, Teodora Ortega, Soledad Garrido, Nerea Hernández-Puyuelo, Ricardo Sánchez-Leal, and Jesús Forja〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2019-6,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 The present study describes the surface distribution of the partial pressure of CO〈sub〉2〈/sub〉 in the continental shelf of the eastern Gulf of Cádiz. For this, eight oceanographic cruises were carried out between March 2014 and February 2016. This distribution presents a linear dependence with the temperature and it decreases with distance from the coast. The Gulf of Cádiz acts as a sink of CO〈sub〉2〈/sub〉 with a mean value for the study period of −0.18 ± 20 1.32 mmol m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉.

Description: 〈b〉The impact of sea-level rise on tidal characteristics around Australia〈/b〉〈br〉 Alexander Harker, J. A. Mattias Green, Michael Schindelegger, and Sophie-Berenice Wilmes〈br〉 Ocean Sci., 15, 147-159, https://doi.org/10.5194/os-15-147-2019, 2019〈br〉 We used a computer model to help predict how changing sea levels around Australia will affect the ebb and flow of the tide. We found that sea-level rise and coastal flooding affect where energy from the tide is dissipated and how the tide flows around the coastline. We found that we must consider how sea-level rise will affect tides across the rest of the world, as that will have an impact on Australia too. This sort of investigation can help direct coastal management and protection efforts.

Description: 〈b〉Mediterranean ocean colour Level 3 operational multi-sensor processing〈/b〉〈br〉 Gianluca Volpe, Simone Colella, Vittorio E. Brando, Vega Forneris, Flavio La Padula, Annalisa Di Cicco, Michela Sammartino, Marco Bracaglia, Florinda Artuso, and Rosalia Santoleri〈br〉 Ocean Sci., 15, 127-146, https://doi.org/10.5194/os-15-127-2019, 2019〈br〉 This work fully describes all the technical steps that are currently put in place in the context of the European Copernicus Marine Environment and Monitoring Service to make ocean colour data freely available to the general public. These data are useful for mapping phytoplankton dynamics on a daily and basin scale. The multi-sensor output compares well to data collected during dedicated field cruises, proving that the operational product can be successfully used for environmental monitoring.

Description: 〈b〉Water exchange between the Sea of Azov and the Black Sea through the Kerch Strait〈/b〉〈br〉 Ivan Zavialov and Alexander Osadchiev〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2019-2,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This study is focused on water exchange between the Sea of Azov and the Black Sea. The Sea of Azov is a small and freshened sea that receives a large freshwater discharge and, therefore, can be regarded as a large river estuary connected by narrow Kerch Strait with the Black Sea. In this work we show that water transport through the Kerch Strait is governed by wind forcing and do not show dependence on river discharge rate to the Sea of Azov on intra-annual time scale.

Description: 〈b〉The impact of a new high-resolution ocean model on the Met Office North-West European Shelf forecasting system〈/b〉〈br〉 Marina Tonani, Peter Sykes, Robert R. King, Niall McConnell, Anne-Christine Pequignet, Enda O'Dea, Jennifer A. Graham, Jeff Polton, and John Siddorn〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2019-4,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 A new high resolution ocean model at 1.5 km has replaced the 7 km system for delivering short term forecasts of the North-West European shelf Seas. The products, temperature, salinity, currents, sea surface height, are available on the Copernicus Marine Service catalogue. This study is focus on the high resolution impact on the quality of the products delivered to the users. Results show that the high resolution model is better resolving the variability of the physical variables.

Description: 〈b〉Validation metrics for ice edge position forecasts〈/b〉〈br〉 Arne Melsom, Cyril Palerme, and Malte Müller〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-149,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 Retreating sea ice in the Arctic Ocean gives rise to increased naval traffic with shorter navigation distances. Hence, information about the position of the sea ice edge is crucial for safe navigation. In the present study we explore methods for examining the quality of sea ice edge forecasts. We conclude that the forecast quality can be monitored with results from a set of four quantities. We also recommend the use of maps which display discrepancies in the positions of the sea ice edge.

Description: 〈b〉Simulating the spread of disinfection by-products and anthropogenic bromoform emissions from ballast water discharge in Southeast Asia〈/b〉〈br〉 Josefine Maas, Susann Tegtmeier, Birgit Quack, Arne Biastoch, Jonathan V. Durgadoo, Siren Rühs, Stephan Gollasch, and Matej David〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-151,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 In a large-scale analysis, the spread of disinfection by-products from oxidative ballast water treatment is investigated, with focus on Southeast Asia where major ports are located. Especially halogenated compounds such as bromoform (CHBr〈sub〉3〈/sub〉) are produced in the ballast water and once emitted into the environment can participate in ozone depletion. Anthropogenic bromoform is rapidly emitted to the atmosphere and can locally double around large ports. A large-scale impact cannot be found.

Description: 〈b〉Isoneutral control of effective diapycnal mixing in numerical ocean models with neutral rotated diffusion tensors〈/b〉〈br〉 Antoine Hochet, Rémi Tailleux, David Ferreira, and Till Kuhlbrodt〈br〉 Ocean Sci., 15, 21-32, https://doi.org/10.5194/os-15-21-2019, 2019〈br〉 〈p〉It is well known that there is an infinite number of ways of constructing a globally defined density variable for the ocean, with each possible density variable having, a priori, its own distinct diapycnal diffusivity. Because no globally defined density variable can be exactly neutral, numerical ocean models tend to use rotated diffusion tensors mixing separately in the directions parallel and perpendicular to the local neutral vector at rates defined by the isoneutral and dianeutral mixing coefficients respectively. To constrain these mixing coefficients from observations, one widely used tool is inverse methods based on Walin-type water mass analyses. Such methods, however, can only constrain the diapycnal diffusivity of the globally defined density variable 〈span〉〈i〉γ〈/i〉〈/span〉 – such as 〈span〉〈i〉σ〈/i〉〈sub〉2〈/sub〉〈/span〉 – that underlies the inverse method. To use such a method to constrain the dianeutral mixing coefficient therefore requires understanding the relations between the different diapycnal diffusivities. However, this is complicated by the fact that the effective diapycnal diffusivity experienced by 〈span〉〈i〉γ〈/i〉〈/span〉 is necessarily partly controlled by isoneutral diffusion owing to the unavoidable misalignment between iso-〈span〉〈i〉γ〈/i〉〈/span〉 surfaces and the neutral directions. Here, this effect is quantified by evaluating the effective diapycnal diffusion coefficient pertaining to five widely used density variables: 〈span〉〈i〉γ〈/i〉〈sup〉〈i〉n〈/i〉〈/sup〉〈/span〉 of 〈span〉〈a href="https://www.ocean-sci.net/#bib1.bibx10"〉Jackett and McDougall〈/a〉 (〈a href="https://www.ocean-sci.net/#bib1.bibx10"〉1997〈/a〉)〈/span〉; the Lorenz reference state density 〈span〉〈i〉ρ〈/i〉〈sub〉ref〈/sub〉〈/span〉 of 〈span〉〈a href="https://www.ocean-sci.net/#bib1.bibx30"〉Saenz et al.〈/a〉 (〈a href="https://www.ocean-sci.net/#bib1.bibx30"〉2015〈/a〉)〈/span〉; and three potential density variables 〈span〉〈i〉σ〈/i〉〈sub〉0〈/sub〉〈/span〉, 〈span〉〈i〉σ〈/i〉〈sub〉2〈/sub〉〈/span〉 and 〈span〉〈i〉σ〈/i〉〈sub〉4〈/sub〉〈/span〉. Computations are based on the World Ocean Circulation Experiment climatology, assuming either a uniform value for the isoneutral mixing coefficient or spatially varying values inferred from an inverse calculation. Isopycnal mixing contributions to the effective diapycnal mixing yield values consistently larger than 〈span〉10〈sup〉−3〈/sup〉〈/span〉 〈span〉m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉〈/span〉 in the deep ocean for all density variables, with 〈span〉〈i〉γ〈/i〉〈sup〉〈i〉n〈/i〉〈/sup〉〈/span〉 suffering the least from the isoneutral control of effective diapycnal mixing and 〈span〉〈i〉σ〈/i〉〈sub〉0〈/sub〉〈/span〉 suffering the most. These high values are due to spatially localised large values of non-neutrality, mostly in the deep Southern Ocean. Removing only 5 % of these high values on each density surface reduces the effective diapycnal diffusivities to less than 〈span〉10〈sup〉−4〈/sup〉〈/span〉 〈span〉m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉〈/span〉. The main implication of this work is to highlight the conceptual and practical difficulties of relating the diapycnal mixing diffusivities inferred from global budgets or inverse methods relying on Walin-like water mass analyses to locally defined dianeutral diffusivities. Doing so requires the ability to separate the relative contribution of isoneutral mixing from the effective diapycnal mixing. Because it corresponds to a special case of Walin-type water mass analysis, the determination of spurious diapycnal mixing based on monitoring the evolution of the Lorenz reference state may also be affected by the above issues when using a realistic nonlinear equation of state. The present results thus suggest that part of previously published spurious diapycnal mixing estimates could be due to isoneutral mixing contamination.〈/p〉

Description: 〈b〉Remote sensing of upwelling off Australia's north-east coast〈/b〉〈br〉 Mochamad Furqon Azis Ismail, Joachim Ribbe, Johannes Karstensen, and Vincent Rossi〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-142,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Cross-shelf processes drive the exchange of water between the continental shelf and western boundary currents, leading to the import and export of heat, freshwater, sediments, nutrients, plankton, fish larvae, and other properties. Upwelling is an important process which modulates those exchanges. It regulates primary productivity, which in turn promotes higher trophic levels and fisheries. In this paper, we investigate upwelling events in the East Australian Current (EAC) intensification zone off Southeast Queensland through the analysis of remotely-sensed Chlorophyll-a (Chl-a) and Sea Surface Temperature (SST) as well as wind and ocean reanalysis products. A particular focus is on identifying the likely mechanisms that drive upwelling events during the austral autumn to winter which are evident from cold SST and enhanced Chl-a concentrations. Four complementary Upwelling Indices (UIs) are derived. Chl-a (UI〈sub〉Chla〈/sub〉) and SST (UI〈sub〉SST〈/sub〉) based indices characterize the oceanic response to upwelling, while indices based on wind (UI〈sub〉w〈/sub〉) and current (UI〈sub〉c〈/sub〉) data capture the forcing of upwelling. The spatial and temporal variability of all UIs is examined over the continental shelf. It reveals distinct seasonal patterns. For the northern region, UIs identify the well-known Southeast Fraser Island Upwelling System. It prevails during the austral spring to early summer and is driven by current- and upwelling favourable wind. In contrast, upwelling is enhanced over the southern shelf during austral autumn to winter. About 70 % of all UI〈sub〉SST〈/sub〉 and UI〈sub〉Chla〈/sub〉 identified upwelling events occur during this period. A case study is presented that provides observational evidence for the existence of a shelf-break upwelling. Simultaneous downwelling favourable wind stress and upwelling favourable current-driven bottom stress establish a flow convergence in the bottom boundary layer (BBL). These convergent BBL flows force upwelling of cold and nutrient-rich slope waters as evident from negative SST anomaly and enhanced Chl-a in austral autumn to winter. It is evident from these results that the shelf region is characterised by two distinct seasonally reoccurring upwelling regimes.〈/p〉

Description: 〈b〉Regional circulation patterns of Mediterranean Outflow Water near the Iberian and African continental slopes〈/b〉〈br〉 Álvaro de Pascual-Collar, Marcos García-Sotillo, Bruno Levier, Roland Aznar, Pablo Lorente, Arancha Amo, and Enrique Fanjul〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-143,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 The Mediterranean Outflow Water (MOW) is a dense water mass originated in the Gibraltar Straight. The CMEMS IBI ocean reanalysis is used to provide a detailed view of the circulation and mixing processes of MOW near the Iberian and African Continental slopes. This work emphasizes the relevance of the complex bathymetric features defining the circulation and variability processes of MOW in this region.

Description: 〈b〉Impacts of Three Gorges Dam's operation on spatial-temporal patterns of tide-river dynamics in the Yangtze River estuary, China〈/b〉〈br〉 Huayang Cai, Xianyi Zhang, Leicheng Guo, Min Zhang, Feng Liu, and Qingshu Yang〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-138,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 In this study we assessed the impacts of the world’s largest dam, Three Gorges Dam (TGD), on tide-river dynamics and concluded that the strongest impacts occurred during autumn and winter owing to the TGD's operation. The results obtained will, hopefully, enhance our understanding of the impacts of large-scale human interventions on estuarine hydrodynamics and guide effective and sustainable water management in the Yangtze River estuary and other estuaries with substantial freshwater discharge.

Description: 〈b〉DUACS DT-2018: 25 years of reprocessed sea level altimeter products〈/b〉〈br〉 Guillaume Taburet, Antonio Sanchez-Roman, Maxime Ballarotta, Marie-Isabelle Pujol, Jean-François Legeais, Florent Fournier, Yannice Faugere, and Gerald Dibarboure〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-150,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This paper deals with sea level altimeter products. These geophysical data are distributed as along-track and gridded data through Copernicus program CMEMS and C3S. We present here in detail a new reprocessing of the data (DT2018) from 1993 to 2017. The main changes and their impacts since last version (DT2014) are carefully discussed. This comparison is made using independent dataset. DT2018 sea level products are improved at global and regional scale and especially in coastal areas.

Description: 〈b〉The ECMWF operational ensemble reanalysis-analysis system for ocean and sea-ice: a description of the system and assessment〈/b〉〈br〉 Hao Zuo, Magdalena Alonso Balmaseda, Steffen Tietsche, Kristian Mogensen, and Michael Mayer〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-154,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Ocean and sea-ice reanalysis is valuable data with broad applications. This manuscript is a reference document for the ECMWF ocean and sea-ice ensemble analysis system OCEAN5, and historical reanalysis ORAS5. Description of the system and assessment of ORAS5 in the sense of several key ECVs have been documented here. This data set is particularly important for users with interest on studying, e.g., Climate Change Indicators, ocean state/environment monitoring, NWP initialization and validation.

Description: 〈b〉Wave–current interactions in a wind-jet region〈/b〉〈br〉 Laura Ràfols, Manel Grifoll, and Manuel Espino〈br〉 Ocean Sci., 15, 1-20, https://doi.org/10.5194/os-15-1-2019, 2019〈br〉 This study investigates the effects of the wave–current interactions in a region where episodes of strong cross-shelf wind occur. To do so, a coupled system between two numerical models has been implemented. The results do not show substantial differences in the water current patterns, but a clear effect on the water column stratification has been found. Additionally, stronger impact is observed for the wave period rather than the wave height.

Description: 〈b〉Marine Ecosystem forecasts: skill performance of the CMEMS Mediterranean Sea model system〈/b〉〈br〉 Stefano Salon, Gianpiero Cossarini, Giorgio Bolzon, Laura Feudale, Paolo Lazzari, Anna Teruzzi, Cosimo Solidoro, and Alessandro Crise〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-145,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 The quality of the upgraded version of the CMEMS biogeochemical operational system of the Mediterranean Sea (MedBFM) is assessed in terms of consistency and forecast skill, following a mixed validation protocol that exploits different reference data from satellite, oceanographic databases, Biogeochemical Argo floats, literature. We demonstrate that the GODAE metrics paradigm can be efficiently applied to validate an operational model system for biogeochemical and ecosystem forecasts. The accuracy of the CMEMS biogeochemical products for Mediterranean Sea can be achieved from basin-wide and seasonal scale to mesoscale and weekly scale, and its level depends on the specific variable and the availability of reference data. In particular, the use of the Biogeochemical Argo floats data allows for a relevant enhancement of the validation framework of operational biogeochemical models, providing new skill metrics for key biogeochemical processes and dynamics (e.g. deep chlorophyll maximum depth), which can be easily implemented to routinely monitor the quality of the products and highlight any possible anomaly.

Description: 〈b〉Assessment of ocean analysis and forecast from an atmosphere-ocean coupled data assimilation operational system〈/b〉〈br〉 Catherine Guiavarc'h, Christopher Harris, Daniel J. Lea, Jonah Roberts-Jones, Andrew Ryan, and Isabella Ascione〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-170,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Coupled atmosphere-ocean modelling systems allow changes in the ocean to directly and immediately feed back on the atmosphere and enable improved weather prediction and ocean forecasts. This is particularly true if the coupled feedbacks are also considered in the way real-time observations of the atmospheric and oceanic states are used to obtain the initial conditions for the forecasts. Here we demonstrate promising performance from such a coupled system when used for ocean prediction.

Description: 〈b〉Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116〈/b〉〈br〉 Pingyang Li, Jens Mühle, Stephen A. Montzka, David E. Oram, Benjamin R. Miller, Ray F. Weiss, Paul J. Fraser, and Toste Tanhua〈br〉 Ocean Sci., 15, 33-60, https://doi.org/10.5194/os-15-33-2019, 2019〈br〉 Use of CFCs as oceanic transient tracers is difficult for recently ventilated water masses as their atmospheric mole fractions have been decreasing. To explore novel tracers, we synthesized consistent annual mean atmospheric histories of HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 (CF4) and PFC-116 in both hemispheres and reconstructed their solubility functions in water and seawater. This work is also potentially useful for tracer studies in a range of natural waters.

Description: 〈b〉Using Canonical Correlation Analysis to produce dynamically-based highly-efficient statistical observation operators〈/b〉〈br〉 Eric Jansen, Sam Pimentel, Wang-Hung Tse, Dimitra Denaxa, Gerasimos Korres, Isabelle Mirouze, and Andrea Storto〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-166,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 The assimilation of satellite SST data into ocean models is complex. The temperature of the thin uppermost layer that is measured by satellites may differ from the much thicker upper layer used in numerical models, leading to biased results. This paper shows how canonical correlation analysis can be used to generate observation operators from existing datasets of model states and corresponding observation values. This type of operator can correct for near-surface effects when assimilating SST.

Description: 〈b〉The CORA 5.2 dataset: global in-situ Temperature and Salinity measurements dataset. Data description and validation〈/b〉〈br〉 Tanguy Szekely, Jérôme Gourrion, Sylvie Pouliquen, and Gilles Reverdin〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-144,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉We present the Copernicus in-situ ocean dataset of temperature and salinity (version V5.2). The ocean subsurface sampling varied widely from 1950 to 2017, as a result of changes in the instrument technology and development of in-situ observational networks (in particular, tropical moorings, ARGO program). The global ocean temperature data coverage on an annual basis grows thus from 10 % in 1950 (30 % for the North Atlantic basin) to 25 % in 2000 (60 % for the North Atlantic basin) and reaches a plateau exceeding 80 % (95 % for the North Atlantic Ocean) after the deployment of the ARGO program. The average depth reached by the profiles also increases from 1950 to 2017. The validation framework is presented, and an objective analysis-based method is developed to assess the quality of the dataset validation process. Analyses of the ocean variability are calculated without taking into account the data quality flags (raw dataset OA), with the near real time quality flags (NRT dataset OA) and with the delayed time mode quality flags (CORA dataset OA). The comparison of the objective analysis variability shows that the near real time dataset managed to detect and to flag most of the large measurement errors, reducing the analysis error bar compared to the raw dataset error bar. It also shows that the ocean variability of the delayed time mode validated dataset is almost exempt from the random error induced variability.〈/p〉

Description: 〈b〉Characteristics of Water Masses in the Atlantic Ocean based on GLODAPv2 data〈/b〉〈br〉 Mian Liu and Toste Tanhua〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-139,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉The characteristics of the main water masses in the Atlantic Ocean are investigated and defined as Source Water Types (SWTs) from their formation area by six key properties based on the GLODAPv2 observational data. These include both conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) variables. For this we divided the Atlantic Ocean into four vertical layers by distinct potential densities in the shallow and intermediate water column, and additionally by concentration of silicate in the deep waters. The SWTs in the upper/central water layer originates from subduction during winter and are defined as central waters, formed in four distinct areas; East North Atlantic Central water (ENACW), West North Atlantic Central Water (WNACW), East South Atlantic Central Water (ESACW) and West South Atlantic Central Water (WSACW). Below the upper/central layer the intermediate layer consist of three main SWTs; Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Overflow Water (MOW). The North Atlantic Deep Water (NADW) is the dominating SWT in the deep and overflow layer, and is divided into upper and lower NADW based on the different origins and properties. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). Antarctic Bottom Water (AABW) is the only natural SWT in the bottom layer and this SWT is redefined as North East Atlantic Bottom Water (NEABW) in the north of equator due to the change of key properties, especial silicate. Similar with NADW, two additional SWTS, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea in order to understand the origin of AABW. The definition of water masses in biogeochemical space is useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples.〈/p〉

Description: 〈b〉A CMEMS forecasting system for the marine ecosystem of IBI European waters〈/b〉〈br〉 Elodie Gutknecht, Guillaume Reffray, Alexandre Mignot, Tomasz Dabrowski, and Marcos G. Sottilo〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-161,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 As part of the Copernicus Marine Environment Monitoring Service, an operational ocean forecasting system monitors the ocean dynamics and marine ecosystems of the European waters. This paper assesses the performances of the key biogeochemical variables (oxygen, nutrients, chl-a, primary production), using a 7-year retrospective simulation (2010–2016). The simulation can be used to better understand the current state, the changes and the health of European marine ecosystems.

Description: 〈b〉Skill assessment of global, regional and coastal circulation forecast models: evaluating the benefits of dynamical downscaling in IBI surface waters〈/b〉〈br〉 Pablo Lorente, Marcos García-Sotillo, Arancha Amo-Baladrón, Roland Aznar, Bruno Levier, José Carlos Sánchez-Garrido, Simone Sammartino, Álvaro De Pascual, Guillaume Reffray, Cristina Toledano, and Enrique Álvarez-Fanjul〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-168,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface, ranging from global to local scales in a two-phase strategy. Firstly, a comparison of CMEMS-GLOBAL and the nested CMEMS-IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI and the nested SAMPA high-resolution coastal forecast system in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2-day quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the potential added value of coastal models with respect to coarser parent regional systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the Western Alboran Sea to put in a broader perspective the context of the onset, development and end of such flow reversal episodes.〈/p〉

Description: 〈b〉Distribution of Water Masses in the Atlantic Ocean based on GLODAPv2〈/b〉〈br〉 Mian Liu and Toste Tanhua〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-140,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30 °N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66 °N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.〈/p〉

Description: 〈b〉Characterizing ERA-interim and ERA5 surface wind biases using ASCAT〈/b〉〈br〉 Maria Belmonte Rivas and Ad Stoffelen〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-160,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This paper describes the differences between ocean surface winds provided by ERA reanalyses and satellite scatterometer observations. This work is motivated by the widespread use of reanalysis winds for ocean forcing in marine forecasting centers, and the application of scatterometer observations as a means to characterize reanalysis wind errors, which we conjecture are related to deficiencies in the physics of the underlying assimilating model.

Description: 〈b〉Assimilation of SST data in the POSEIDON system using the SOSSTA statistical-dynamical observation operator〈/b〉〈br〉 Gerasimos Korres, Dimitra Denaxa, Eric Jansen, Isabelle Mirouze, Sam Pimentel, Wang-Hung Tse, and Andrea Storto〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-158,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 A statistical-dynamical observation operator (SOSSTA) for satellite SST data assimilation able to account for SST diurnal variability, is formulated and implemented into the POSEIDON forecasting system (Aegean Sea). Model experiments where daytime SST retrievals from the SEVIRI infrared radiometer are introduced into the data assimilation procedure through the application of the observation operator, showed an improvement of the POSEIDON modelling system performance.

Description: 〈b〉An ensemble probabilisitic approach to reconstruct the biogeochemical state of the North Atlantic Ocean using ocean colour images〈/b〉〈br〉 Florent Garnier, Pierre Brasseur, Jean-Michel Brankart, Yeray Santana-Falcon, and Emmanuel Cosme〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-153,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉In this paper, we investigate the potential of using a probabilistic modelling approach in the prospect of ocean colour data assimilation. The main objective of the study is to assess the benefits of using error covariances based on an explicit simulation of model uncertainties. The relevance of this approach is evaluated by considering 3D observational updates of the ensemble (one update at one time step) performed every 5 days (over one year) using the statistics of a North Atlantic coupled NEMO/PISCES stochastic ensemble simulation involving 60 members, as previously described in Garnier et al, 2016. 〈/p〉 〈p〉 In this experiment, SeaWIFS ocean colour data are used to update the ensemble with a low rank ensemble Kalman Filter analysis scheme. The non-Gaussian behaviour of the model variables is taken into account using anamorphic transformations. Comparisons between the updated ensemble and the MERIS satellite observations shows that the integration of high resolution SeaWIFS data significantly improves the representation and the ensemble statistics of chlorophyll concentrations. We also show that these improvements consistently cascade in the water column chlorophyll distributions and on non-observed variables closely linked with the primary production. 〈/p〉 〈p〉In addition, we present first results illustrating the potential of our approach for biogeochemical forecasts. The objective is to examine the model response to data assimilation in the perspective of future operational applications. For this purpose, we perform a 60 member simulation initiated from updated biogeochemical states. This forecast simulation shows that ocean colour data assimilation would be skillful considering integration cycles of the order of a day. Finally, the intend of this article is to point out the feasibility of operational biogeochemical data assimilation in the near future.〈/p〉

Description: 〈b〉Relations of physical and biogenic reworking of sandy sediments in the southeastern North Sea〈/b〉〈br〉 Knut Krämer, Soeren Ahmerkamp, Ulrike Schückel, Moritz Holtappels, and Christian Winter〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-152,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 The sandy seafloor in shelf seas is constantly overturned by waves and currents but also by a large number of animals searching for shelter and food. By taking a close look at the seafloor surface with the help of a laser scanner, this study evaluates their contribution to the overall reworking of sediment: It makes up as much as 14 % of the physically driven reworking. The activity of the organisms varies with the seasons and between different locations and can be estimated from physical values.

Description: 〈b〉The Arctic Front and its variability in the Norwegian Sea〈/b〉〈br〉 Roshin P. Raj, Sourav Chatterjee, Laurent Bertino, Antonio Turiel, and Marcos Portebella〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-159,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 In this study we investigated the variability of the Arctic Front (AF), an important biologically productive region in the Norwegian Sea, using a suite of satellite data, atmospheric reanalysis and a regional coupled ocean-sea ice data assimilation system. We show evidences of the two-way interaction between the atmosphere and the ocean at the AF. The North Atlantic Oscillation is found to influence the strength of the AF and may have a profound influence on the region’s biological productivity.

Description: 〈b〉Evaluation of Arctic Ocean surface salinities from SMOS and two CMEMS reanalyses against in-situ data sets〈/b〉〈br〉 Jiping Xie, Roshin P. Raj, Laurent Bertino, Annette Samuelsen, and Tsuyoshi Wakamatsu〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-163,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 1 comment)〈br〉 Focused on the Arctic sea surface salinity (SSS), two gridded SMOS products, two CMEMS reanalyzed products, and two climatologies (PHC and WOA) are evaluated by intercomparison and against in-situ data during the years of 2011–2013. The quantitative SSS evaluation also sheds light on the uncertainty analyzing of the different products, which also give useful information needed for the assimilation of the SMOS SSS products into ocean forecast/reanalysis systems at next.

Description: 〈b〉Copernicus (CMEMS) operational model intercomparison in the western Mediterranean Sea: Insights from an eddy tracker〈/b〉〈br〉 Evan Mason, Simon Ruiz, Romain Bourdalle-Badie, Guillaume Reffray, Marcos Garcia-Sotillo, and Ananda Pascual〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-169,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Rapid evolution of operational ocean models is driven by advances in numerics and sophisticated data assimilation schemes, computational power, and storage capacity. The Copernicus Marine Service (CMEMS) is a major provider of operational products that are made available through an online catalogue. The service includes global and regional forecasts in near-real-time and reanalysis modes. Here we apply an eddy tracker to daily SSH fields from three such reanalysis products from the CMEMS catalogue, with the objective to evaluate their performance in terms of their eddy properties and three-dimensional composite structures over the period 2013 through 2016. The products are (i) the Global Analysis Forecast, (ii) the Mediterranean Analysis Forecast, and (iii) the Iberia-Biscay-Ireland Analysis Forecast. The common domain between these reanalyses is the western Mediterranean Sea (WMED) between the Strait of Gibraltar and Sardinia. This is a complex region with strong density gradients, especially in the Alboran Sea in the west where Atlantic and Mediterranean waters compete. Surface eddy property maps over the WMED of eddy radii, amplitudes and nonlinearity are consistent between the models, as well as with gridded altimetric data that serve as a reference. Mean 3D eddy composites are shown only for three subregions in the Alboran Sea. These are mostly consistent between the models, with minor differences being attributed to details of the respective model configurations. This information can be informative for the ongoing development of these CMEMS operational modeling systems.

Description: 〈b〉On the resolutions of ocean altimetry maps〈/b〉〈br〉 Maxime Ballarotta, Clément Ubelmann, Marie-Isabelle Pujol, Guillaume Taburet, Florent Fournier, Jean-François Legeais, Yannice Faugere, Antoine Delepoulle, Dudley Chelton, Gérald Dibarboure, and Nicolas Picot〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-156,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This study investigates the resolving capabilities of the DUACS gridded products delivered through the CMEMS catalogue. Our method is based on the spectral coherence. While altimeter along-track resolves scales in the order of few tens of kilometers, we found that the merging of these along-track data into continuous maps in time and space leads to effective resolution ranging from ~ 800 km wavelength at the Equator to 100 km wavelength at high latitude.

Description: 〈b〉Evaluating the impact of atmospheric forcing resolution and air-sea coupling on near-coastal regional ocean prediction〈/b〉〈br〉 Huw W. Lewis, John Siddorn, Juan Manuel Castillo Sanchez, Jon Petch, John M. Edwards, and Tim Smyth〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-162,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Oceans are modified at the surface by winds and by exchange of heat with the atmosphere. The effect of changing information about the atmosphere that is available to drive an ocean model of north-west Europe, which can simulate small-scale details of the ocean state, is tested. We show that simulated temperatures agree better with observations located near the coast around south-west UK when using data from a high resolution atmosphere model, and when atmosphere and ocean feedbacks are included.

Description: 〈b〉The global distribution of the M1 ocean tide〈/b〉〈br〉 Philip L. Woodworth〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-146,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 This is the first investigation of the worldwide distribution of the degree-3 M1 ocean tide using over 800 tide gauge records and a global tide model. M1 is confirmed to have a geographical variation in the Atlantic and other basins consistent with the suggestion of Platzman and Cartwright that M1 is generated through the spatial and temporal overlap of M1 in the tidal potential and one (or at least a small number) of diurnal ocean normal modes.

Description: 〈b〉Technical note: On the importance of a three-dimensional approach for modelling the transport of neustic microplastics〈/b〉〈br〉 Isabel Jalón-Rojas, Xiao-Hua Wang, and Erick Fredj〈br〉 Ocean Sci. Discuss., https//doi.org/10.5194/os-2018-136,2019〈br〉 〈b〉Manuscript under review for OS〈/b〉 (discussion: open, 0 comments)〈br〉 Simplified 2DH numerical models are typically used for simulating the transport of floating microplastics. This paper demonstrates the impact of vertical mixing on the horizontal transport and fate of microplastics in a bay, and therefore the importance of a 3D approach for an accurate modelling of microplastics transport. These results have important implications for the assessment and prediction of pollution hot spots in coastal systems, as well as for planning effective clean-up programs.

Description: Atmospheric forcing applied as ocean model boundary conditions can have a critical impact on the quality of ocean forecasts. This paper assesses the sensitivity of an eddy-resolving (1.5 km resolution) regional ocean model of the North-West European shelf (NWS) to atmospheric forcing resolution and air-sea coupling. The analysis is focused on a month-long simulation experiment for July 2014 and evaluation of simulated sea surface temperature (SST) in a shallow near-coastal region to the south-west of the UK (Celtic Sea and western English Channel). Observations above and below the sea surface at the L4 ocean buoy from the Western Channel Observatory are used to evaluate ocean and atmosphere model data. The impacts of differences in the atmospheric forcing are illustrated by comparing results from an ocean model run in forcing mode using operational global-scale numerical weather prediction (NWP) data with a run forced by a convective scale regional atmosphere model. The value of dynamically representing feedbacks between the atmosphere and ocean state is assessed through use of these model components within a fully coupled ocean-wave-atmosphere system. Simulated SST show considerable sensitivity to atmospheric forcing and to the impact of model coupling in near-coastal areas. A warm ocean bias relative to in-situ observations in the simulation forced by global-scale NWP (0.7 K mean difference, warmer relative to all observations in the model domain) is shown to be reduced (to 0.4 K) through use of the 1.5 km resolution atmosphere forcing. When simulated in coupled mode, this bias is further reduced by 0.2 K. Results demonstrate much greater variability of both surface energy balance terms and near-surface winds in the higher resolution atmosphere model data, as might be expected. Assessment of the surface energy balance and wind forcing over the ocean is challenging due to a scarcity of observations. It can however be demonstrated that the wind speed over the ocean simulated by the high resolution atmosphere agreed with the limited number of observations less well than the global-scale NWP data. Further partially-coupled experiments are discussed to better understand why the degraded wind forcing does not detrimentally impact on SST results.

Description: The DUACS system produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, geophysics and biology communities. These maps are constructed from optimal interpolation of altimeter observations and are provided on a global 1/4° × 1/4° (longitude × latitude) and daily grid resolution framework (1/8° × 1/8° longitude × latitude grid for the regional products) through the Copernicus Marine Environment Monitoring Service (CMEMS). Yet, the dynamical content of these maps is not ensured to have a full 1/4° spatial and 1-day resolution, due to the filtering properties of the optimal interpolation. In the present study, we estimate the effective spatial and temporal resolutions of the newly reprocessed delayed-time DUACS maps (aka, DUACS-DT2018). Our approach is based on the spectral coherence between maps and independent datasets (along-track and tide gauge observations), which represents the correlation between two sea level signals as a function of wavelength. We found that the spatial resolution of the DUACS-DT2018 global maps based on sampling by three altimeters simultaneously ranges from ~ 100 km-wavelength at high latitude to ~ 800 km-wavelength in the Equatorial band and the mean temporal resolution is ~ 28 days period. The mean effective spatial resolution at mid-latitude is estimated to ~ 200 km. The mean effective spatial resolution is ~ 120 km for the regional Mediterranean Sea product and ~ 140 km for the regional Black Sea product. An inter-comparison with former DUACS reprocessing systems (aka, DUACS-DT2010 and DUACS-DT2014) highlights the progress of the system over the past 8 years, in particular a gain of resolution in highly turbulent regions. The same diagnostic applied to maps constructed with two altimeters and maps with three altimeters confirms a modest increase of resolving capabilities and accuracies in the DUACS maps with the number of missions.

Description: For more than twenty years, the multi-satellite DUACS system has been providing Near Real Time (NRT) and Delayed Time (DT) altimetric products. These data are ranging from along-track to multi-mission maps of Sea Level Anomaly (SLA) and Absolute Dynamic Topography (ADT). A reprocessing of 25 years of data, namely: DUACS DT2018, has been carried out and is available through the Copernicus Marine Environment Monitoring Service (CMEMS) and Copernicus Climate Change Service (C3S) since April 2018. Several changes have been implemented in the DT2018 processing in order to improve the quality of the products. New altimeter standards and geophysical corrections has been used, refined data selection has been implemented and Optimal Interpolation (OI) parameters have been reviewed for global and regional map generation. Through this paper, an extensive assessment has been carried out. The error budget associated to the DT2018 products at global and regional scales has been refined and the improvements compared with the previous version quantified (DT2014; Pujol et al., 2016). The DT2018 errors at mesoscales are reduced by nearly 3 to 4 % for global and regional products compared to the DT2014. This reduction is much more important in coastal areas (reduction is up to 10 %) where it is directly linked to the altimeter geophysical corrections used in the DT2018 processing. Conclusions are very similar concerning geostrophic currents, where error is reduced by 5 % and up to 10 % in coastal areas.

Description: This work concerns the chlorophyll products based on Satellite Observation and disseminated in the frame of the Copernicus Marine Environmental Monitoring Service (CMEMS). This work highlights the main advantages provided by the Copernicus Globcolour processor which is used to serve the CMEMS with a long time series from 1997 to present with level 3 & 4 products at Global level (4 km of spatial resolution) and for the Atlantic level 4 product (1 km). It discusses the different ways to merge data coming from different sensors and it is shown that the GlobColour processor approach provide a better flexibility. At present, it is the only one CMEMS processor able to ingest the OLCI-S3A in the merged product (OLCI-S3A data are ingested in the operational CMEMS products since the April 2018 release). Behind the merging, the flagging strategy to go from level 2 provided by spatial agencies to the level 3 CMEMS products is also discussed. A better spatial coverage is demonstrated, including the coastal area which is of particular interest for many users involved in the EU Water Framework and Marine Strategy Framework Directive.

Description: The Mediterranean Outflow Water (MOW) is a dense water mass originated in the Gibraltar Straight. After exiting the Gulf of Cadiz, the MOW forms a reservoir region west of the Iberian continental slopes with a buoyant depth of approximately 1000 m depth. This region is a key role as the main centre where the MOW is mixed and distributed into the North Atlantic. The seafloor in this area is characterised by the presence of a complex bathymetry with three abyssal plains separated by mountain chains. Despite of this topographic features does not reach the surface, they influence ocean flows at intermediate and deep ocean layers conditioning the distribution and circulation of MOW. The CMEMS IBI ocean reanalysis is used to provide a detailed view of the circulation and mixing processes of MOW near the Iberian and African Continental slopes. This work emphasizes the relevance of the complex bathymetric features defining the circulation processes of MOW in this region. The high resolution of the IBI reanalysis allows to make a description of the meso-scale features forced by the topography. The temperature, salinity, velocity, transport, and vorticity fields are analysed to understand the circulation patterns of MOW. The high-resolution circulation patterns found reveals that Horseshoe Basin and the continental slope near Cape Ghir are key areas controlling the mixing processes of MOW with the surrounding waters mases, mainly North Atlantic Central Water (NACW), and Antarctic Intermediate Water (AAIW). The water masses variability is also analysed by means of composite analysis, results indicate the existence of a variability of the MOW tongue which retracts and expands westwards in opposition to the movement of the underlying North Atlantic Deep Water.

Description: The worldwide distribution of the small degree-3 M1 ocean tide is investigated using a quasi-global data set of over 800 tide gauge records and a global tide model. M1 is confirmed to have a geographical variation in the Atlantic consistent with the suggestion of Platzman and Cartwright that M1 is generated in the ocean as a consequence of the spatial and temporal overlap of M1 in the tidal potential and one (or at least a small number) of diurnal ocean normal modes. As a consequence, it is particularly strong around the UK and on North Sea coasts. This analysis shows that their suggestion is also consistent to a great extent with the observed small amplitudes in the Pacific and Indian Oceans. However, there are differences at the regional and local level which require much further study via more sophisticated ocean tidal modelling. By contrast, the M1' tide is shown to have a geographical distribution consistent with expectations from other degree-2 diurnal tides, apart from locations such as around the UK where tidal interactions introduce complications. As far as we know, this is the first time that these small tidal constituents have been mapped on a global basis and, in particular, the first time that the ocean response to the degree-3 component of the tidal potential has been investigated globally.

Description: This paper analyses the differences between ERA-Interim and ERA5 surface winds fields relative to ASCAT ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress equivalent winds (U10S), and air-sea relative motion using ocean current velocities. In terms of instantaneous RMS wind speed agreement, ERA5 winds show a 20 % improvement relative to ERA interim, and a performance similar to that of currently operational ECMWF forecasts. ERA5 also performs better than ERA-interim in terms of mean and transient wind errors, wind divergence and wind stress curl biases. Yet, both ERA products show systematic errors in the partition of the wind kinetic energy into zonal and meridional, mean and transient components. ERA winds are characterized by excessive mean zonal winds (westerlies) with defective mean poleward flows at mid-latitudes, and defective mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic at mid and high latitudes, with implications for Ekman upwelling estimates, and lack detail in the representation of SST gradient effects (along the equatorial cold tongues and WBC jets) and mesoscale convective airflows (along the ITCZ and the warm flanks for the WBC jets). It is conjectured that large-scale mean wind biases in ERA are related to their lack of high frequency (transient wind) variability, which should be promoting residual meridional circulations in the Ferrell and Hadley cells.

Description: In spite of their long-standing availability, the optimal assimilation of sea surface temperature (SST) observations retrieved from infrared and microwave space-borne sensors is still challenging in oceanographic forecast systems. One prominent problem stems from the fact that ocean general circulation models do not resolve the diurnal variability of SST data as measured by satellites. In order to improve SST data assimilation schemes and enhance the exploitation of swath SST data, an observation operator capable of representing the SST diurnal cycle is introduced and called SOSSTA. Firstly, a one-dimensional turbulence model is used to produce a data set of upper ocean temperature profiles with corresponding skin and subskin SSTs. A canonical correlation analysis is then used to extract the maximally correlated modes of variability between temperatures at depth and skin/subskin SST, conditioned to atmospheric state (insolation and wind speed). These canonical correlations form the novel observation operator, which is implemented in the POSEIDON model forecasting system (Aegean Sea) to test the assimilation of daytime SST retrievals from the SEVIRI infrared radiometer. Comparison of misfits (off-line assessment) suggests that the new operator outperforms the mere use of the first model level to calculate SST innovations. Real-world data assimilation experiments indicate that the use of the SOSSTA operator is beneficial to the skill scores and in particular improves the sea surface height analysis and forecast skill scores, whose improvement is maintained throughout a one year long experiment.

Description: In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface, ranging from global to local scales in a two-phase strategy. Firstly, a comparison of CMEMS-GLOBAL and the nested CMEMS-IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI and the nested SAMPA high-resolution coastal forecast system in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2-day quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the potential added value of coastal models with respect to coarser parent regional systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the Western Alboran Sea to put in a broader perspective the context of the onset, development and end of such flow reversal episodes.

Description: As part of the Copernicus Marine Environment Monitoring Service (CMEMS), an operational ocean forecasting system was developed to monitor the ocean dynamics and marine ecosystems of the European waters; and more specifically on the IBI (Iberia-Biscay-Ireland) area. The CMEMS IBI physical-biogeochemical coupled system covers the North-East Atlantic Ocean from the Canary Islands to Iceland, including the North Sea and the Western Mediterranean, with a NEMO-PISCES 1/36° model application. Since its operational launch in April 2018, this CMEMS IBI system has provided a weekly short-term (7-days) forecast of the ocean dynamics and key biogeochemical variables of the marine ecosystem. The main goal of this paper is to assess the performances of the IBI biogeochemical system, using a 7-year retrospective simulation that spans from 2010 to 2016. The model results are validated with available satellite and in situ observations from the International Council for the Exploration of the Sea (ICES), the European Marine Observation and Data Network (EMODnet) and the Biogeochemical-Argo float network. The simulation successfully reproduces the spatial distribution and seasonal cycles of oxygen, nutrients, chlorophyll-a, and net primary production. This simulation can be a useful tool to better understand the current state and changes in the marine biogeochemistry of European waters. It can also provide key variables for developing indicators to monitor the health of European marine ecosystems. These indicators may be of interest to scientists, policy makers, environmental agencies and the general public.

Description: The quality of the upgraded version of the CMEMS biogeochemical operational system of the Mediterranean Sea (MedBFM) is assessed in terms of consistency and forecast skill, following a mixed validation protocol that exploits different reference data from satellite, oceanographic databases, Biogeochemical Argo floats, literature. We demonstrate that the GODAE metrics paradigm can be efficiently applied to validate an operational model system for biogeochemical and ecosystem forecasts. The accuracy of the CMEMS biogeochemical products for Mediterranean Sea can be achieved from basin-wide and seasonal scale to mesoscale and weekly scale, and its level depends on the specific variable and the availability of reference data. In particular, the use of the Biogeochemical Argo floats data allows for a relevant enhancement of the validation framework of operational biogeochemical models, providing new skill metrics for key biogeochemical processes and dynamics (e.g. deep chlorophyll maximum depth), which can be easily implemented to routinely monitor the quality of the products and highlight any possible anomaly.

Description: The development of coupled atmosphere-ocean prediction systems with utility on the short-range Numerical Weather Prediction (NWP) and ocean forecasting timescales has accelerated over the last decade. This builds on a body of evidence showing the benefit, particularly for weather forecasting, of more correctly representing the feedbacks between surface ocean and atmosphere. It prepares the way for more unified prediction systems with the capability of providing consistent surface meteorology, wave and surface ocean products to users for whom this is important. Here we describe a coupled ocean-atmosphere system, with weakly coupled data assimilation, which was operationalised at the Met Office as part of the Copernicus Marine Environment Service (CMEMS). We compare the ocean performance to that of an equivalent ocean-only system run at the Met Office, and other CMEMS products. Sea surface temperatures in particular are shown to verify better than in the ocean-only systems, although other aspects including temperature profiles and surface currents are slightly degraded. We then discuss the plans to improve the current system in future as part of the development of a coupled NWP system at the Met Office.

Description: We present the Copernicus in-situ ocean dataset of temperature and salinity (version V5.2). The ocean subsurface sampling varied widely from 1950 to 2017, as a result of changes in the instrument technology and development of in-situ observational networks (in particular, tropical moorings, ARGO program). The global ocean temperature data coverage on an annual basis grows thus from 10 % in 1950 (30 % for the North Atlantic basin) to 25 % in 2000 (60 % for the North Atlantic basin) and reaches a plateau exceeding 80 % (95 % for the North Atlantic Ocean) after the deployment of the ARGO program. The average depth reached by the profiles also increases from 1950 to 2017. The validation framework is presented, and an objective analysis-based method is developed to assess the quality of the dataset validation process. Analyses of the ocean variability are calculated without taking into account the data quality flags (raw dataset OA), with the near real time quality flags (NRT dataset OA) and with the delayed time mode quality flags (CORA dataset OA). The comparison of the objective analysis variability shows that the near real time dataset managed to detect and to flag most of the large measurement errors, reducing the analysis error bar compared to the raw dataset error bar. It also shows that the ocean variability of the delayed time mode validated dataset is almost exempt from the random error induced variability.

Description: Although the stratification of the upper Arctic Ocean is mostly salinity-driven, the sea surface salinity (SSS) is still poorly known in the Arctic, due to its strong variability and the sparseness of in-situ observations. Recently, two gridded SSS products have been derived from the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, independently developed by the Barcelona Expert Centre (BEC) in Spain and the Ocean Salinity Expertise Center (CECOS) of the Centre Aval de Traitemenent des Donnees SMOS (CATDS) in France, respectively. In parallel, there are two reanalysis products providing the Arctic SSS in the framework of the Copernicus Marine Environment Monitoring Services (CMEMS), one global, and another regional product. While the regional Arctic TOPAZ4 system assimilates a large set of sea-ice and ocean observations with an Ensemble Kalman Filter, the global reanalysis combines in-situ and satellite data using a multivariate ensemble optimal interpolation method. In this study, focused on the Arctic Ocean, these four salinity products, together with the climatology both World Ocean Atlas (WOA) of 2013 and Polar science center Hydrographic Climatology (PHC), are evaluated against in-situ datasets during 2011–2013. For the validation the in-situ observations are divided in two; those that have been assimilated and those that have not. The deviations of SSS between the different products and against the in-situ observations show largest disagreements below the sea-ice and in the marginal ice zone (MIZ), especially during the summer months. In the Beaufort Sea, the summer SSS from the BEC product has the smallest – saline – bias (~0.6 psu) with the smallest root mean squared difference (RSMD) of 2.6 psu. This suggests a potential value of assimilating of this product into the forthcoming Arctic reanalyses. Keywords: Arctic Ocean; sea surface salinity; SMOS; reanalysis; absolute deviation;

Description: The paper documents seasonality, interannual to decadal variability and trends in temperature, salinity and density over a transect in the shallow northern Adriatic Sea (Mediterranean Sea) between 1979 and 2017. Amplitude of seasonality decreases with depth, and is much larger in temperature and density than in salinity. Interannual to decadal variability in temperature and salinity are differently correlated in surface and bottom layers, indicating different mechanisms which govern their variability. Trends in temperature are large (up to 6 °C over 100 years), significant through the area and not sensitive to the sampling interval and time series length. In contrast, trends in salinity are largely weak and insignificant and depend on the time series length. The warming of the area is stronger during spring and summer. Such large temperature trends and their spatial variability indicate substantial changes in the thermohaline circulation in this area known as a dense water formation site, with a potential to affect biogeochemical and ecological properties of the whole Adriatic Sea.

Description: Here we present a technique that utilises a segmented flow coil equilibrator coupled to a Proton Transfer Reaction-Mass Spectrometer to measure a broad range of dissolved organic gases. Due to its unique design composed of a segmented flow and a headspace-water separator, the equilibrator is highly efficient for gas exchange and has a fast response time (under 1 min). The system allows for both discrete and continuous measurements of volatile organic compounds in seawater due to its ease of changing sample intake and low sample water flow (100 cm3 min-1). The equilibrator setup is both relatively inexpensive and compact. Hence it can be easily reproduced and installed on a variety of oceanic platforms, particularly where space is limited. As a result of its smooth and unreactive surfaces, the segmented flow coil equilibrator is expected to be less sensitive to biofouling and easier to clean than membrane-based equilibration systems. The equilibrator fully equilibrates for gases that are similarly soluble or more soluble than toluene. The method has been successfully deployed in the Canadian Arctic. Here, some example data of underway surface water and Niskin bottle measurements in the sea ice zone are presented to illustrate the efficacy of this measurement system.

Description: The Iberian Biscay Ireland (IBI) wave system has the challenge to improve wave forecast and the coupling with ocean circulation model dedicated to western european coast. The momentum and heat fluxes at the sea surface are strongly controlled by the waves and there is a need of using accurate sea state from wave model. This work describes the more recent version of the IBI wave system and highlight the performance of system in comparison with satellite altimeters and buoys wave data. The validation process has been performed for 1-year run of the wave model MFWAM with boundary conditions provided by the global wave system. The results show on the one hand a slightly improvement on significant wave height and peak period, and on the other hand a better surface stress for high wind conditions. This latter is a consequence of using a tail wave spectrum shaped as the Philipps wave spectrum for high frequency waves.

Description: Oceanic emissions of the climate relevant trace gases carbonyl sulfide (OCS) and carbon disulfide (CS2) are a major source to their atmospheric budget. Their current and future emission estimates are still uncertain due to incomplete process understanding and, therefore, inexact quantification across different biogeochemical regimes. Here we present the first concurrent measurements of both gases together with related fractions of the dissolved organic matter (DOM) pool, i.e. solid-phase extractable dissolved organic sulfur (DOSSPE), chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM) from the Eastern Tropical South Pacific (ETSP). These observations are used to estimate in-situ production rates and identify their drivers. We find different limiting factors of marine photoproduction: while OCS production is limited by the humic-like DOM fraction that can act as a photosensitizer, high CS2 production coincides with high DOSSPE concentration. The lack of correlation between OCS production and DOSSPE may be explained by the active cycling of sulfur between OCS and dissolved inorganic sulfide via OCS photoproduction and hydrolysis. In addition, the only existing parameterization for OCS dark production is validated and updated with new rates from the ETSP and the Indian Ocean. Our results will help to predict oceanic concentrations and emissions of both gases on regional and, potentially, global scales.

Description: The Atlantic Meridional Overturning Circulation (AMOC) impacts ocean and atmosphere temperatures on a wide range of temporal and spatial scales. Here we use observational data sets to validate model-based inferences on the usefulness of thermodynamics theory in reconstructing AMOC variability at low-frequency, and further build on this reconstruction to provide prediction of the near-future (2019–2022) North Atlantic state. An easily-observed surface quantity – the rate of warm to cold transformation of water masses at high latitudes – is found to lead the observed AMOC at 45° N by 5–6 years and to drive its 1993–2010 decline and its ongoing recovery, with suggestive prediction of extreme intensities for the early 2020's. We further demonstrate that AMOC variability drove a bi-decadal warming-to-cooling reversal in the subpolar North Atlantic before triggering a recent return to warming conditions that should prevail at least until 2021. Overall, this mechanistic approach of AMOC variability and its impact on ocean temperature brings new keys for understanding and predicting climatic conditions in the North Atlantic and beyond.

Description: Very near surface ocean currents are dominated by wind and wave forcing and have large impacts on the transport of buoyant materials in the ocean, but have proved difficult to measure with many modern instrumentations. Here, observations of ocean currents at two depths within the first meter of the surface are made utilizing trajectory data from both drogued and undrogued CARTHE drifters, which have draft depths of 60 cm and 5 cm, respectively. Trajectory data of dense, co-located drogued and undrogued drifters, were collected during the LAgrangian Submesoscale ExpeRiment (LASER) that took place from January to March of 2016 in the Northern Gulf of Mexico. Examination of the drifter velocities reveals that the surface currents become strongly wind- and wave-driven during periods of high wind, with the pre-existing regional circulation having a smaller, but non-negligible, influence on the total surface velocity. During these high wind events, we deconstruct the full surface current velocities captured by each drifter type into their wind- and wave-driven components after subtracting an estimate for the regional circulation which pre-exists each wind event. In order to capture the regional circulation in the absence of strong wind and wave forcing, a Lagrangian variational method is used to create hourly velocity fields for both drifter types separately, during the hours preceding each high wind event. Synoptic wind and wave output data from the Unified Wave INterface–Coupled Model (UWIN–CM), a fully coupled atmosphere, wave and ocean circulation model, are used for analysis. The wind-driven component of the surface current exhibits a rotation to the right with depth between the two surface layers measured. We find that the averaged wind-driven surface current from 0–5 cm (0–60 cm) travels at ~ 3.4–6.0 % (~ 2.3–4.1 %) of the wind speed, and is deflected ~ 5°–55° (~ 30–85°) to the right of the wind, reaching higher deflection angles at higher wind speeds. Results provide new insight to the vertical shear present in wind-driven surface currents under high winds, which have vital implications for any surface transport problem.

Description: Observation operators (OOs) are a central component of any data assimilation system. As they project the state variables of a numerical model into the space of the observations, they also provide an ideal opportunity to correct for effects that are not or not sufficiently described by the model. In such cases a dynamical OO, an OO that interfaces to a secondary and more specialised model, often provides the best results. However, given the large number of observations to be assimilated in a typical atmospheric or oceanographic model, the computational resources needed for using a fully dynamical OO mean that this option is usually not feasible. This paper presents a method, based on canonical correlation analysis (CCA), that can be used to generate highly-efficient statistical OOs that are based on a dynamical model. These OOs can provide an approximation to the dynamical model at a fraction of the computational cost. One possible application of such an OO is the modelling of the diurnal cycle of sea surface temperature (SST) in ocean general circulation models (OGCMs). Satellites that measure SST measure the temperature of the thin uppermost layer of the ocean. This layer is strongly affected by the atmospheric conditions and its temperature can differ significantly from the water below. This causes a discrepancy between the SST measurements and the upper layer of the OGCM, which typically has a thickness of around 1 m. The CCA OO method is used to parametrise the diurnal cycle of SST. The CCA OO is based on an input dataset from the General Ocean Turbulence Model (GOTM), a high-resolution water column model that has been specifically tuned for this purpose. The parameterisations of the CCA OO are found to be in good agreement with the results from GOTM, showing the potential of this method for use in data assimilation systems.

Description: In this paper, we investigate the potential of using a probabilistic modelling approach in the prospect of ocean colour data assimilation. The main objective of the study is to assess the benefits of using error covariances based on an explicit simulation of model uncertainties. The relevance of this approach is evaluated by considering 3D observational updates of the ensemble (one update at one time step) performed every 5 days (over one year) using the statistics of a North Atlantic coupled NEMO/PISCES stochastic ensemble simulation involving 60 members, as previously described in Garnier et al, 2016. In this experiment, SeaWIFS ocean colour data are used to update the ensemble with a low rank ensemble Kalman Filter analysis scheme. The non-Gaussian behaviour of the model variables is taken into account using anamorphic transformations. Comparisons between the updated ensemble and the MERIS satellite observations shows that the integration of high resolution SeaWIFS data significantly improves the representation and the ensemble statistics of chlorophyll concentrations. We also show that these improvements consistently cascade in the water column chlorophyll distributions and on non-observed variables closely linked with the primary production. In addition, we present first results illustrating the potential of our approach for biogeochemical forecasts. The objective is to examine the model response to data assimilation in the perspective of future operational applications. For this purpose, we perform a 60 member simulation initiated from updated biogeochemical states. This forecast simulation shows that ocean colour data assimilation would be skillful considering integration cycles of the order of a day. Finally, the intend of this article is to point out the feasibility of operational biogeochemical data assimilation in the near future.

Description: Understanding and estimating the distribution and transport of microplastics in marine environments has been recognized as a major global research issue. Most of the existing research on transport modelling has focused on low-dense particles floating in surface waters, using a 2D Lagrangian approach and ignoring the vertical displacement of particles. In this work, we evaluate to what extent the vertical movement of particles within surface waters by mixing processes may affect the horizontal transport and fate of microplastics. The aim is to determinate whether a 2D approach is sufficient for the accurate modelling of neustic-microplastics transport or a 3D approach is necessary. For this purpose, we compare visually and statistically the microplastics transport patterns of three simulations in a coastal system: one using a 2D approach; and two using a 3D approach with weak and strong vertical turbulence, respectively. The 2D simulation roughly reproduced the transport and accumulation patterns, but accurate results required a 3D approach. This was particularly important for strong vertical turbulence and regions characterized by strong vertical current shear. Moreover, a 2D approach can lead to errors in the results even with negligible turbulence due to simplifications in the velocity field. A 3D modelling approach is therefore key to an accurate estimation and prediction of microplastics distribution in coastal systems, and consequently for planning mitigation and cleaning programs.

Description: The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30 °N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66 °N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.

Description: The North-West European shelf ocean forecasting system has been providing oceanographic products for the European continental shelf seas for more than fifteen years. In that time several different configurations have been implemented, updating the model and the data assimilation components. The latest configuration to be put in operations, an eddy resolving model at 1.5 km (AMM15), replaces the 7 km model (AMM7) that has been used for a number of years. This has improved the ability to resolve the mesoscale variability in this area. An overview of this new system and its initial validation is provided in this paper, highlighting the differences with the previous version. Validation of the model is based on the results of two years (2016–2017) trial experiments run with the low and high resolution systems in their operational configuration. The 1.5 km system has been validated against observations and the low resolution system, trying to understand the impact of the high resolution on the quality of the products delivered to the users. Although the number of observations is a limiting factor, especially for the assessment of model variables like currents and salinity, the new system has been proven to be an improvement in resolving fine scale structures and variability and provides more accurate information on the major physical variables, like temperature, salinity and horizontal currents. AMM15 improvements are evident from the validation against high-resolution observations, available in some selected areas of the model domain. However, validation at the basin scale and using daily means penalised the high-resolution system and does not reflect its superior performance. This increment in resolution also improves the capabilities to provide marine information closer to the coast even if the coastal processes are not fully resolved by the model.

Description: For more than a century, estuarine exchange flow has been quantified by means of the Knudsen relations which connect bulk quantities such as inflow and outflow volume fluxes and salinities. These relations are closely linked to estuarine mixing. The recently developed Total Exchange flow (TEF) which uses salinity coordinates to calculate these bulk quantities allows an exact formulation of the Knudsen relations in realistic cases. There are however numerical issues, since the original method does not converge to the TEF bulk values for an increasing number of salinity classes. In the present study, this problem is investigated and the method of dividing salinities, described by MacCready et al. (2018), is mathematically introduced. A challenging yet compact analytical scenario for a well-mixed estuarine exchange flow is investigated for both methods, showing the proper convergence of the dividing salinity method. Furthermore, the dividing salinity method is applied to model results of the Baltic Sea to demonstrate the analysis of realistic exchange flows and exchange flows with more than two layers.

Description: The life cycle of the tropical cyclone Madi in the southwestern Bay of Bengal (BoB) during 6th to 12th December 2013 was studied using a suite of ocean and atmospheric data. Madi formed as a depression on 6th December and intensified into a very severe cyclonic storm by 8th December. What was distinct about Madi was its (1) swift weakening from very severe cyclone to a severe cyclone while moving towards north on 9th, (2) abrupt track reversal close to 180-degree in a southwestward direction on 10th, and (3) rapid decay in the open ocean by 12th December while still moving southwestward. Using both in situ and remote sensing data, we show that oceanic cyclonic eddies played a leading role in the ensuing series of events that followed its genesis. The sudden weakening of the cyclone before its track reversal was facilitated by the oceanic cyclonic (cold-core) eddy, which reduced the ocean heat content and cooled the upper ocean through upward eddy-pumping of subsurface waters. When Madi moved over cyclonic eddy-core, its further northward movement was arrested. Subsequently, the prevailing northeasterly winds assisted the slow moving system to change its track to a southwesterly path. While travelling towards southwestward direction, the system rapidly decayed when it passed over the regions of cyclonic eddies located near the western boundary of the BoB. Though Madi was a category-2 cyclone, it had a profound impact on the physical and biogeochemical state of the upper ocean. Cyclone-induced enhancement in the chlorophyll a ranged from 5 to 7-fold, while increase in the net primary productivity ranged from 2.5 to 8-fold. Similarly, the CO2 out-gassing into the atmosphere showed a 3.7-fold increase compared to the pre-cyclone values. Our study points to the crucial role oceanic eddies play in the life cycle of cyclone in the BoB. Eddies being ubiquitous and tropical cyclones occur twice a year in the BoB, there is an urgent need to incorporate them in the models for the better prediction of the cyclone track and intensity.

Description: Global circulation of intermediate water masses has been extensively studied; however, its regional and local circulation along continental margins and variability and implications on sea floor morphologies are still not well known. In this study the intermediate water mass variability in the Gulf of Cádiz and adjacent areas has been analysed and its implications discussed. Remarkable seasonal variations of the Antarctic Intermediate Water (AAIW) and the Subarctic Intermediate Water (SAIW) are determined. During autumn a greater presence of the AAIW seems to be related to a reduction in the presence of SAIW and Eastern North Atlantic Central Water (ENACW). This interaction also affects the Mediterranean Outflow Water (MOW), which is pushed by the AAIW toward the upper continental slope. In the rest of the seasons, the SAIW is the predominant water mass reducing the presence of the AAIW. This seasonal variability for the predominance of these intermediate water masses is explained by a novel model based on the concatenation of several wind-driven processes acting during the different seasons. Our finding is important for a better understanding of regional intermediate water mass variability with implications in the Atlantic Meridional Overturning Circulation (AMOC) but further research is needed in order to decode their changes during the geological past and their role, especially related to the AAIW, in controlling both the morphology and the sedimentation along the continental slopes.

Description: Spatiotemporal variations of the partial pressure of CO2 (pCO2) were studied during 8 oceanographic cruises conducted between March 2014 and February 2016 in surface waters of the eastern shelf of the Gulf of Cádiz (SW Iberian Península) between the Guadalquivir River and Cape Trafalgar. pCO2 presented a range of variation between 320.6 and 513.6 µatm, with highest values during summer and autumn and lowest during spring and winter, showing a linear dependence between pCO2 and temperature. The distributions of pCO2 were not homogeneous. Spatially, there was a general decrease from coastal to off-shore stations associated with continental inputs and presented an increase in the zones deeper than 400 m due to the influence of the eastward branch of the Azores Current. On the other side, the study area acted as source of CO2 to the atmosphere during summer and autumn and as a sink in spring and winter, with a mean value for the study period of −0.18 ± 1.32 mmol m−2 d−1. In the Guadalquivir and Sancti Petri sections, the CO2 fluxes decreased towards offshore, whereas in the Trafalgar section increased due to the presence of an upwelling. These results highlighted the Gulf of Cádiz as a CO2 sink, with a capture capacity of 14.9 Gg year−1.

Description: The Persian Gulf Water and Red Sea Water are salty and dense waters recirculating at subsurface in the Gulf of Oman and the Gulf of Aden respectively, under the influence of mesoscale eddies which dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that the Persian Gulf Water is driven by mesoscale eddies in the form of filaments and submesoscale structures. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their impact on the spread of Persian Gulf Water and Red Sea Water. We use a three-dimensional hydrostatic model with submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration is an idealized version of the Gulf of Oman and Aden: a zonal row of mesoscale vortices interacting with north and south topographic slopes. Intense submesoscale vortices are generated in the simulations along the continental slopes due to two different mechanisms. The first mechanism is due to frictional generation of vorticity in the bottom boundary layer, which detaches from the topography, forms an unstable vorticity filament, and undergoes horizontal shear instability that leads to the formation of submesoscale coherent vortices. The second mechanism is inviscid and implies arrested topographic Rossby waves breaking and forming submesoscale coherent vortices where a mesoscale anticyclone interacts with the topographic slope. Submesoscale vortices subsequently drift away, merge and form larger vortices. They can also pair with opposite signed vortices and travel across the domain. They can weaken or disappear via several mechanisms, in particular fusion into the larger eddies or erosion on the topography. Particle patches are advected and sheared by vortices and are entrained into filaments. Their size first grows as the square root of time, a signature of the merging processes, then it increases linearly with time, corresponding to their ballistic advection by submesoscale eddies. On the contrary, witout intense submesoscale eddies, particles are mainly advected by mesoscale eddies; this implies a weaker dispersion of particles than in the previous case. This shows the important role of submesoscale eddies in spreading Persian Gulf Water and Red Sea Water.

Description: We investigate the long-term variability of extreme high sea levels (ESL) in the southern German Bight and associated large-scale forcing mechanisms in the climate system using simulations covering the last 1000 years. To this end, global MPI-ESM simulations from the PMIP3 past1000 project are dynamically scaled-down with a regionally coupled climate system model focusing on the North Sea. We find that the statistics of simulated ESL compare well with observations from the tide gauge record at Cuxhaven but show large variations on interannual to centennial timescales. ESL arise independent of preferred systematic oscillations and are to a large extent decoupled from variations of the background sea level (BSL). Large scale circulation regimes associated with periods of high ESL are regionally consistent and similar to those associated with elevated BSL, but the location of the respective centers of action of the governing sea level pressure (SLP) dipole differs. While BSL variations correlate well with the wintertime North Atlantic Oscillation (NAO), ESL variations are rather associated with a dipole between northeastern Scandinavia and the Gulf of Biscay, leading to a stronger local north-westerly wind component in the North Sea. Potential links with solar or volcanic forcing are masked due to the high ESL variability. The high internal variability stresses the irreducible uncertainties related to traditional extreme value estimates based on shorter subsets which fail to account for long-term variations. Existing estimates of future changes in ESL may be dominated by natural variability rather than climate change signals, thus requiring larger ensemble simulations to assess future flood risks.

Description: The upwelling system off the southern Caribbean coast is probably the main nutrients source that support the biological productivity in this oligotrophic sea. The Subtropical Water Mass (SUW) that forms the subsurface salinity maximum in the Caribbean is the main source of upwelled waters in this system. Salinity and temperature vs. depth profiles from 4 oceanographic cruises in the western sector of the Caribbean upwelling system, showed that the salinity of upwelled SUW waters is ~ 0.2 g kg−1 lower than the SUW salinity in the central Caribbean and have a slight seasonal variation that agree with with the rainy/dry seasons in the region. Besides, the depth of these SUW waters in the continental slope (~ 100 m) is ~ 50 m shallower than the SUW depth in the rest of the Caribbean sea. The origin of these modified SUW waters was analyzed using the Mercator numerical model, which reproduces the main vertical characteristics of the subsurface salinity maximum. Modeled data showed that SUW waters upwelled off La Guajira peninsula come from the western Caribbean and arrive to the system transported by an intense Caribbean Coastal Undercurrent (CaCU, mean speed ~ 0.4 m s−1). The lower salinity observed in the upwelled SUW waters may be the result of intense vertical mixing processes with diluted surface waters in the Panama-Colombia gyro that could occur when the CaCU flows below this region before reaching the upwelling zones. The mixing processes in the SUW by double diffusion and mechanical turbulence driven by vertical shear of horizontal currents, were analyzed using the Turner angle and the Thorpe scale, respectively. Double diffusion by salt fingers was found between the SUW and the Central North Atlantic Waters (NACW) with diffusivity values ~ 10−5 m2 s−1. But the mechanical diffusivity was two orders of magnitude higher (10−3 m2 s−1.) than the double diffusivities in the entire water column, generating salt fluxes from the SUW towards surface and towards depth over 2 g kg−1 m d−1. Beyond modifying the salt content in coastal SUW waters, these mixing processes may also alter the nutrient content of upwelling waters, with effects still unknown to the upwelling ecosystem.

Description: We present a 3D unstructured-grid hydrodynamic model for the northwestern Gulf of Mexico that utilizes a high-resolution grid for the main estuarine systems along the Texas-Louisiana coast. This model, based on the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) with hybrid horizontal and vertical grids, is driven by the observed river discharge, reanalysis atmospheric forcing, and open boundary conditions from the global models. The model reproduces well the temporal and spatial variation of observed water level, salinity, temperature, and current velocity both in Galveston Bay and on the shelf. We apply the validated model to examine the remote influence from large rivers, specifically the Mississippi and Atchafalaya rivers, on the salinity regime along the Texas coast. Numerical experiments reveal that the Mississippi-Atchafalaya discharge could significantly decrease the salinity on the inner shelf along the Texas coast and its influence highly depends on the wind field and the resulting shelf current. Winter wind tends to constrain the Mississippi-Atchafalaya water against the shore, forming a narrow lower-salinity band all the way to the southwestern Texas coast. Under summer wind, the influence of the discharge on salinity is limited to the upper Texas coast while extended offshore. The decrease in salinity at the mouth of Galveston Bay due to the Mississippi-Atchafalaya discharge leads to a decrease in horizontal density gradient, a weakened estuarine circulation inside the bay, a decrease in the salt flux, and a smaller estuarine-ocean exchange. We highlight the flexibility of the model that simulates not only estuarine dynamics and shelf-wide transport but also the interaction between them.

Description: The phenomenon of wave set-up may substantially contribute to the formation of devastating coastal flooding in certain coastal areas. We study the appearance and properties of empirical probability distributions of the occurrence of different set-up heights in about 80 km long section of coastline near Tallinn in the Gulf of Finland, the eastern Baltic Sea. The study area is often attacked by high waves propagating from various directions and the approach angle of waves varies largely along the shore. The distribution in question is approximated by an exponential distribution with a quadratic polynomial as the exponent. Even though different segments of the study area host substantially different wave regimes, the leading term of this polynomial is usually small (between −0.005 and 0.005) and varies insignificantly along the study area. Consequently, the distribution of wave set-up heights substantially deviates from a Rayleigh or Weibull distribution (that usually reflect the distribution of different wave heights). In about 3/4 of occasions it is fairly well approximated by a standard exponential distribution. In about 25 % of coastal segments it matches a Wald (inverse Gaussian) distribution. This property signals that very high extreme set-up events may in some locations occur substantially more frequently than it could be expected from the probability of occurrence of severe seas.

Description: Marine science and engineering commonly require reliable information about seafloor depth (bathymetry), e.g. for studies of ocean circulation, bottom habitats, fishing resources, sediment transport, geohazards and site selection for platforms and cables. Baltic Sea bathymetric properties are analysed here using the using the newly released Digital Bathymetric Model (DBM) by the European Marine Observation and Data Network (EMODnet). The analyses include hypsometry, volume, descriptive depth statistics, and km-scale seafloor ruggedness, i.e. terrain heterogeneity, for the Baltic Sea as a whole as well as for 17 sub-basins defined by the Baltic Marine Environment Protection Commission (HELCOM). We compare the new EMODnet DBM with IOWTOPO, the previously most widely used DBM of the Baltic Sea which has served as the primary gridded bathymetric resource in physical and environmental studies for nearly two decades. The area of deep water exchange between the Bothnian Sea and the Northern Baltic Proper across the Åland Sea is specifically analysed in terms of depths and locations of critical bathymetric sills. The EMODnet DBM provides a bathymetric sill depth of 88 m at the northern side of the Åland Sea and 60 m at the southern side, differing from previously identified sill depths of 100 and 70 m respectively. High-resolution multibeam bathymetry acquired from this deep water exchange path, where vigorous bottom currents interacted with the seafloor, allows us to assess what we are missing in presently available DBMs in terms of physical characterisation and our ability to then interpret seafloor processes and highlights the need for continued work towards complete high-resolution mapping of the Baltic Sea seafloor.

Description: Sound scattering layers SSLs distribution and their relationship to pelagic habitat characteristics is a first step to understand their role in ecosystem dynamics and their interactions with other pelagic components such as small pelagic fish. In this study two areas of the Senegalese shelf have been characterized during upwelling season corresponding to a cold inshore area and a deeper and warmer stratified offshore area that was sharply separated by a strong thermal boundary. Marine pelagic organisms usually aggregates and occurs as SSLs on echosounder. Mean SSL thickness and SSL vertical depth increase with continental shelf depth; thickest and deepest SSLs were observed in the offshore part of the continental shelf. SSLs preferendum was reported for stratified water conditions rather than fresh upwelled water. The SSLs spatiotemporal variability was mostly explained by bottom depth which influence depth, thickness, and biomass of the SSLs. Diel period and water physico-chemical characteristics had also an effect on SSL depth and SSL thickness but not on SSL biomass. Despite chlorophyll-a has statistically no effect on SSLs structure, we report that the chlorophyll-a peak was always located above or in the middle of the SSLs, often matching with the peak of SSLs biomass. Such observations indicate trophic relationships, highlighting SSLs being mainly composed of phytoplanktivorous organisms. Acoustic mapping technique of mixed layer depth is not always efficient in east border upwelling system. Lastly, over the Senegalese continental shelf the level of dissolved oxygen was not found limitative (no hypoxia) for SSLs marine pelagic organisms during upwelling event.

Description: We processed daily ocean-color satellite observations to construct a monthly climatology of phytoplankton pigment concentrations in the Senegalo-Mauritanian region. Thanks to the difficulty of the problem, we proposed a new method. It primarily consists in associating, in well-identified clusters, similar pixels in terms of ocean-color parameters and in situ pigment concentrations taken from a global ocean database. The association is carried using a new Self Organized Map (2S-SOM). Its major advantage is to allow taking into account the specificity of the optical properties of the water by adding specific weights to the different ocean color parameters and the in situ measurements. In the retrieval phase, the pigment concentration of a pixel is estimated by taking the pigment concentration values associated with the 2S-SOM cluster presenting the ocean-color satellite spectral measurements, which are the closest to those of the pixel under study according to some distance. The method was validated by using a cross-validation procedure. We focused our study on the fucoxanthin concentration, which is related to the abundance of diatoms. We showed that the fucoxanthin starts to develop in December, presents its maximum intensity in March when the upwelling intensity is maximum, extends up to the coast of Guinea in April and begins to decrease in May. The results are in agreement with previous observations and recent in situ measurements. The method is very general and can be applied in every oceanic region.

Description: Previous studies have indicated that most of the net sinking associated with the downward branch of the Atlantic Meridional Overturning Circulation (AMOC) must occur near the subpolar North Atlantic boundaries. In this work we have used monthly mean fields of a high-resolution ocean model (0.1 deg at the equator) to quantify this sinking. To this end we have calculated the Eulerian net vertical transport (WΣ) from the modelled vertical velocities, its seasonal variability and its spatial distribution under repeated climatological atmospheric forcing conditions. Based on this simulation, we find that for the whole subpolar North Atlantic WΣ peaks at about −14 Sv at a depth of 1139 m, matching both the mean depth and the magnitude of the meridional transport of the AMOC at 45° N. It displays a seasonal variability of around 10 Sv. Three sinking regimes are identified according to the characteristics of the accumulated W with respect to the distance to the coast: one within the first 110 km and onto the bathymetric slope at around the peak of the boundary current speed (regime I), the second between 110 km and 290 km covering the remainder of the shelf where mesoscale eddies exchange properties (momentum, heat, mass) between the interior and the boundary (regime II), and the third sinking regime at larger distances from the coast where WΣ is mostly driven by the ocean's interior eddies (regime III). Regimes I and II accumulate ∼ 90 % of the total sinking and display smaller seasonal changes and spatial variability than regime III. We find that such a distinction in regimes is also useful to describe the characteristics of WΣ in marginal seas located far from the overflow areas, although the regime boundaries can shift a few tens of km inshore or offshore depending on the bathymetric slope and shelf width of each marginal sea. The largest contributions to the sinking come from the Labrador Sea, the Newfoundland region and the overflow regions. The magnitude, the seasonal variability and the depth at which WΣ peaks vary for each region, thus revealing a complex picture of sinking in the subpolar North Atlantic.

Description: This paper revisits Stommel's vision for a global glider network and the Argo design specification. A concept of floats with wings, so-called slow underwater gliders, is explored. An analysis of the energy/power consumption shows that, by operating gliders with half the vehicle volume at half the speed compared to present gliders, the energy requirements for long duration missions can be met with available battery capacities. Simulation experiments of slow gliders are conducted using the horizontal current fields from an eddy-permitting ocean reanalysis product. By employing a semi-Lagrangian, streamwise navigation whereby the glider steers at right angles to ocean currents, we show that the concept is feasible. The simulated glider tracks demonstrate the potential for efficient coverage of key oceanographic features and variability.

Description: The Galápagos Archipelago and Marine Reserve lies 1000 km off the coast of Ecuador and is among the world's most iconic wildlife refuges. However, plastic litter is now found even in this remote and iconic island archipelago. Prior to this study, the sources of this plastic litter on Galápagos coastlines were unidentified. Local sources are widely expected to be small, given the limited population and environmentally-conscious tourism industry. Here, we show that remote coastal sources of plastic pollution are also fairly localized and limited to South and Central American coastlines, in particular Northern Peru and Southern Ecuador. Using virtual floating plastic particles transported in high-resolution ocean surface currents, we analysed the backward-in-time and forward-in-time pathways and connectivity between the Galápagos region and the coastlines around the East Pacific Ocean. We also analysed how incorporation of wave-driven currents (Stokes drift) affects these pathways and connectivity. We found that only virtual particles that enter the ocean from Peru, Ecuador and (when waves are not taken into account) Colombia can reach the Galápagos. It takes these particles a few months to travel from their coastal sources on the American continent to the Galápagos region. The connectivity does not seem to vary substantially between El Niño and La Niña years. Identifying these sources and the timing and patterns of the transport can be useful for identifying integrated management opportunities to reduce plastic pollution from reaching the Galápagos Archipelago.

Description: In order to simulate submesoscale turbulent patterns and processes (STPPs) and to analyse their properties and dynamics, the Regional Ocean Modeling System (ROMS) is applied to a subregion of the Baltic Sea around the island of Bornholm. The modeled STPPs provide an aid for the interpretation of observations that were taken during the Expedition Clockwork Ocean in the same region in June 2016. To create a realistic mesoscale and submesoscale environment, ROMS with 500-m horizontal resolution is one-way nested into an existing operational model. The comparison of the results with satellite images shows good agreement. STPPs with horizontal scales

Description: Low-frequency sea level variability can be a critical factor for several wave energy converter (WEC) systems, for instance linear systems with at a limited stroke length. Consequently, when investigating suitable areas for deployment of those WEC systems, sea level variability should be taken into account. In order to facilitate wave energy developers in finding the most suitable areas for wave energy park installations, this paper describes a study that gives them an additional tool by exploring the annual and monthly variability of the sea level in the Baltic Sea and adjacent seawaters, with focus on the Swedish Exclusive Economic Zone. Over 10 years of reanalysis data from the Copernicus project have been used to conduct this investigation. The results are presented by means of maps showing the maximum range and the standard deviation of the sea level with a horizontal spatial resolution of about 1 km. A case study illustrates how the results can be used by the WEC developers to limit the energy absorption loss of their devices due to sea level variation. Depending on the WEC technology one wants to examine, the results lead to different conclusions. For the Uppsala point absorber L12 and the sea state considered in the case study, the most suitable sites where to deploy WEC parks are found in the Gotland Basins and in the Bothnian Sea, where the energy loss due to mean level variations is negligible.

Description: Subglacial discharge has significant impacts on water circulation, material transport, and biological productivity in proglacial fjords of Greenland. To help clarify the fjord water properties and the effect of subglacial discharge, we investigated the water mass structures of Bowdoin Fjord in northwestern Greenland based on summer hydrographic observations, including turbidity, in 2014 and 2016. We estimated the fraction of subglacial discharge from the observational data and interpreted the observed differences in subglacial discharge behavior between two summer seasons with the numerical model results. At a depth of 60–80 m, temperature profiles were distinctively different in 2014 and 2016, and a larger fraction of submarine meltwater was detected in 2014. At a depth of 15–40 m, where the most turbid water was observed, the maximum subglacial discharge fractions near the ice front were estimated to be ~ 6 % in 2014 and ~ 4 % in 2016. The higher discharge fraction in 2014 was due to the stronger stratification, as suggested by numerical experiments performed with different initial stratifications. Turbidity near the surface was higher in 2016 than in 2014, suggesting a stronger influence of turbid subglacial discharge. The higher turbidity in 2016 could primarily be attributed to a greater amount of subglacial discharge, as inferred from the numerical experiments forced by different amounts of discharge. This study indicates that ambient fjord stratification difference is an important factor controlling the vertical distribution of subglacial discharge, together with its amount.

Description: The flow (flux) of climate critical gases, such as carbon dioxide (CO2), between the ocean and the atmosphere is a fundamental component of our climate and the biogeochemical development of the oceans. Therefore, the accurate calculation of these air-sea gas fluxes is critical if we are to monitor the health of our oceans and changes to our climate. FluxEngine is an open source software toolbox that allows users to easily perform calculations of air-sea gas fluxes from model, in-situ and Earth observation data. The original development and verification of the toolbox was described in a previous publication and the toolbox is already being used by scientists across multiple disciplines. The toolbox has now been considerably updated to allow its use as a Python library, to enable simplified installation, verification of its installation, to enable the handling of multiple sparingly soluble gases and greatly expanded functionality for supporting in situ dataset analyses. This new functionality for supporting in situ analyses includes user defined grids, time periods and projections, the ability to re-analyse in situ CO2 data to a common temperature dataset and the ability to easily calculate gas fluxes using in situ data from drifting buoys, fixed moorings and research cruises. Here we describe these new capabilities and then demonstrate their application through illustrative case studies. The first case study demonstrates the workflow for accurately calculating CO2 fluxes using in situ data from four research cruises from the Surface Ocean CO2 Atlas (SOCAT) database. The second case study shows that reanalysing an eight month time series of pCO2 data collected from a fixed station in the Baltic Sea can remove errors equal to 35 % of the net air-sea gas flux. The third case study demonstrates that biological surfactants could supress individual nitrous oxide sea-air gas fluxes by up to 13 %. The final case study illustrates how a dissipation-based gas transfer parameterisation can be implemented and used. The updated version of the toolbox (version 3) and all documentation is now freely available.

Description: This work examines the accuracy and validity of two variants of Radon transform and two variants of the Two-Dimensional Fast Fourier Transform (2D FFT) that have been previously used for estimating the propagation speed of Sea Surface Height Anomalies (SSHA) derived from satellite borne altimeters. The examination employs numerically simulated SSHA signals made up of 20 or 50 modes where one, randomly selected, mode has a larger amplitude than the uniform amplitude of the other modes. Since the dominant input mode is ab-initio known, we can clearly define "success" in detecting its phase/propagation speed. We show that all previously employed variants fail to detect the phase speed of the dominant input mode even when its amplitude is 5 times larger than all other modes and that they successfully detect the phase speed of the dominant input mode only when its amplitude is 10 times (or more) larger than the other modes. This requirement is an unrealistic limitation on oceanic SSHA observations. In addition, three of the variant methods “detect” a dominant mode even when all modes have the exact same amplitude. The accuracy with which the four algorithms identify a dominant input mode decreases with the increase in the number of modes in the signal. Our findings cast a doubt on the reliability of phase speed estimates of SSHA observations and the reported “too fast” phase speed of baroclinic Rossby waves in the ocean.

Description: We assess the role of ocean feedbacks in the simulation of the present climate and on the downscaled climate change signal in the Mediterranean Sea with the regionally coupled model REMO-OASIS-MPIOM (ROM). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea. In our setup the Atlantic and Black Sea circulations are simulated explicitly. Simulations forced by ERA-Interim show a good representation of the present Mediterranean climate. Our analysis of the RCP8.5 scenario driven by MPI-ESM shows that the Mediterranean waters will be warmer and saltier across most of the basin by the end of the century. In the upper ocean layer temperature is projected to have a mean increase of 2.73 °C, while the mean salinity increases by 0.17 psu, presenting a decreasing trend in the Western Mediterranean, opposite to the rest of the basin. The warming initially takes place at the surface and propagates gradually to the deeper layers.

Description: Diatoms account for 40 % of marine primary production and are considered to be key players in the biological carbon pump. Ocean acidification (OA) is expected to affect diatoms primarily by changing the availability of CO2 as a substrate for photosynthesis or through altered ecological interactions within the marine food web. Yet, there is little consensus how entire diatom communities will respond to increasing CO2. To address this question, we synthesized the literature from over a decade of OA-experiments with natural diatom communities to uncover: 1) if and how bulk diatom communities respond to elevated CO2; 2) if shifts within the diatom communities could be expected and how they are expressed with respect to taxonomic affiliation and size structure. We found that diatom communities responded to high CO2 in ~60 % of the experiments and in this case more often positively (56 %) than negatively (32 %; 12 % did not report the direction of change). Shifts among different diatom species were observed in 65 % of the experiments. Our synthesis supports the hypothesis that high CO2 particularly favors larger species as 12 out of 13 experiments which investigated cell size found a shift towards larger species. Unraveling winners and losers with respect to taxonomic affiliation was difficult due to a limited database, but there is evidence that the genus Pseudo-nitzschia could be among the losers. We conclude that OA-induced changes in diatom competitiveness and assemblage structure must be classified as a “risk for ecosystem services” due to the pivotal role diatoms play in trophic transfer and biogeochemical cycles.

Description: While Earth system models project a reduction, or even a shut-down, of deep convection in the North Atlantic Ocean in response to anthropogenic forcing, deep convection returned to the Irminger Sea in 2008 and occurred several times since then to reach exceptional depths 〉 1,500 m in 2015 and 2016. In this context, we used Argo data to show that deep convection persisted in the Irminger Sea during two additional years in 2017 and 2018 with maximum convection depth 〉 1,300 m. In this article, we investigate the respective roles of air-sea flux and preconditioning of the water column to explain this exceptional 4-year persistence of deep convection; we quantified them in terms of buoyancy and analyzed both the heat and freshwater components. Contrary to the very negative air-sea buoyancy flux that was observed during winter 2015, the buoyancy fluxes over the Irminger Sea during winters 2016, 2017 and 2018 were close to climatological average. We estimated the preconditioning of the water column as the buoyancy that needs to be removed (B) from the end of summer water column to homogenize the water column down to a given depth. B was lower for winters 2016–2018 than for the mean 2008–2015, including a vanishing stratification from 600 m down to ~1,300 m. It means that less air-sea buoyancy loss was necessary to reach a given convection depth than in the mean and once convection reached 600 m little additional buoyancy loss was needed to homogenize the water column down to 1,300 m. We showed that the decrease in B was due to the combined effects of a cooling of the intermediate water (200–800 m) and a decrease in salinity in the 1,200–1,400 m layer. This favorable preconditioning permitted the very deep convection observed in 2016–2018 despite the atmospheric forcing was close to the climatological average.

Description: The coastal Gulf of Mexico (GOM) and Coastal Sea off Korea (CSK) both suffer from human-induced eutrophication. We used a N-mass balance model in two different regions with different nitrogen input sources to estimate organic carbon fluxes and predict future carbon fluxes under different model scenarios. The coastal GOM receives nitrogen predominantly from the Mississippi and Atchafalaya Rivers and atmospheric nitrogen deposition (AN-D) is only a minor component in this region. However, in the CSK, groundwater and atmospheric nitrogen deposition are more important controlling factors. Our model includes the fluxes of nitrogen to the ocean from the atmosphere, groundwater, and rivers, based on observational and literature data, and identifies three zones (brown, green and blue waters) in the coastal GOM and CSK with different productivity and carbon fluxes. Based on our model results, the potential primary production rate in the inner (brown water) zone are more than 2 (GOM) and 1.5 gC m−2 day−1 (CSK). In the middle (green water) zone, potential production is between 0.1 to 2 (GOM) and 0.3 to 1.5 gC m−2 day−1 (CSK). In the offshore (blue water) zone, productivity is less than 0.1 (GOM) and 0.3 (CSK) gC m−2 day−1. Through our model scenario results, overall oxygen demand in the GOM would increase approximately 21 % if we fail to reduce riverine N input, likely increasing considerably the area affected by hypoxia. Comparing the results from the U.S. with those from Korea shows the importance of considering both riverine and atmospheric inputs of nitrogen. This has direct implications for investigating how changes in energy technologies can lead to changes in the production of various atmospheric contaminants that affect air quality, climate and the health of local populations.

Description: The predictability of the sea surface height expression of baroclinic tides is examined with 96 hr forecasts produced by the AMSEAS operational forecast model during 2013–2014. The phase-locked tide, both barotropic and baroclinic, is identified by harmonic analysis of the 2 year record and found to agree well with observations from tide gauges and satellite altimetry within the Caribbean Sea. The non-phase-locked baroclinic tide, which is created by the time-variable mesoscale stratification and currents, may be identified from residual sea level anomaly (SLA) near the tidal frequencies. The predictability of the non-phase-locked tide is assessed by measuring the difference between a forecast – centered at T+36 hr, T+60 hr, or T+84 hr – and the model's later verifying analysis for the same time. Within the Caribbean Sea, where a baroclinic tidal sea level range of ±5 cm is typical, the forecast error for the non-phase-locked tidal SLA is correlated with the forecast error for the sub-tidal (mesoscale) SLA. Root-mean-square values of the former range from 0.5 cm to 2 cm, while the latter ranges from 1 cm to 6 cm, for a typical 84 hr forecast. The spatial and temporal variability of the forecast error is related to the dynamical origins of the non-phase-locked tide and is briefly surveyed within the model.

Description: During 2017 Austral winter, an open ocean polynya appeared in the Lazarev Sea, centered over Maud Rise. The vertical structure of the water column presented temporal and spatial variability with a weak stratification during the period of observations from January 2015 to January 2019. While over the Northern Maud Rise area, a highly stratified layer was identified between 80–180 m depth. This layer works as a thermal barrier where the energy from summer months is stored, preventing the warm sub-surface waters from mixing with the shallow waters. So far, a complete description of the polynya formation and maintenance processes is still lacking. To characterize the internal structure of the ocean during the 2017 Maud Rise polynya event we use in situ observations and ocean model reanalysis data. The obtained results revealed that the incidence of thermobaric convection, diapycnal and isopycnal mixing processes over the Maud Rise drives the exchange of energy in the water column. We highlight three relevant factors that contribute to the energy flux for the open-ocean polynya preconditioning: level of instability, pycnocline fluctuation, and bathymetric influence. Another remarkable feature is the warmer summer surface layer over the Maud Rise, which transfers heat to intermediate layers accumulating energy for almost four months. Energy storage at the thermal barrier is evaluated based on heat flux calculations to quantify the exchange of energy between the different water layers. These processes together operate as an ocean preconditioning to the formation and maintenance of an open-ocean polynya event.

Description: The Pacific-Indian Ocean associated mode (PIOAM) is the product of the tropical air-sea interaction at the cross-basin scale and the main mode of ocean variation in the tropics. Evaluating the capability of current climate models to simulate the PIOAM and finding the possible factors that affect the simulation results are beneficial to obtain more accurate future climate change prediction. Based on 55-yr the Hadley Centre Global Sea Ice and Sea Surface Temperature (HadISST) reanalysis and the output data from twenty-one Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) models, the PIOAM in these CMIP5 models is assessed. It is found that the explained variance of PIOAM in almost all twenty-one CMIP5 models are underestimated. Although all models reproduce the spatial pattern of the positive sea surface temperature anomaly in the eastern equatorial Pacific well, only one-third of these models successfully simulate the ENSO mode with the east-west inverse phase in the Pacific Ocean. In general, CCSM4, GFDL-ESM2M and CMCC-CMS have a stronger capability to capture the PIOAM than that of the other models. The strengths of the PIOAM in the positive phase in less than one-fifth of the models are slightly stronger, and very close to HadISST reanalysis, especially in CCSM4. The interannual variation of PIOAM can be measured by CCSM4, GISS-E2-R and FGOALS-s2. Further analysis indicates that considering the carbon cycle, resolving stratosphere, chemical process or increasing the horizontal resolution of the atmospheric model may effectively improve the performance of the model to simulate the PIOAM.

Description: The mesoscale variability in the Caribbean Sea is dominated by anticyclonic eddies that are formed in the eastern part of the basin. These anticyclones intensify on their path westward while they pass the coastal upwelling region along the Venezuelan and Colombian coast. In this study, we used a regional model to show that this westward intensification of Caribbean anticyclones is driven by the advection of cold upwelling filaments. These dense filaments are advected by the anticyclones, leading to an increase of the horizontal density gradients at the western side of the anticyclones. Following the thermal wind balance, the increased density gradients result in an increase of the vertical shear of the anticyclones and to their westward intensification. To assess the impact of variations in upwelling on the anticyclones, several simulations were performed in which the northward Ekman transport (and thus the upwelling strength) is altered. As expected, stronger (weaker) upwelling is associated with more stronger (weaker) offshore cooling and a more (less) westward intensification of the anticyclones. The simulations with weaker upwelling show farther advection of the Amazon and Orinoco River plumes into the basin. The dispersion of the river plumes affects the formation process of the anticyclones, where the horizontal density gradients were mainly determined by the salinity gradients of the river plume and not by temperature gradients that were associated with upwelling.

Description: Data of CTD transects across continental slope of the Eurasian Basin and the St. Anna Trough performed during NABOS (Nansen and Amundsen Basins Observing System) project in 2003–2015 are used to assess transport and propagation features of the Atlantic Water (AW) in the Arctic Ocean. Estimates of θ-S indices and volume flow rate of the current carrying the AW in the Eurasian Basin were obtained. The assessments were based on the analysis of CTD data including 33 sections in the Eurasian Basin, 4 transects in the St. Anna Trough and 2 transects in the Makarov Basin; additionally a CTD transect of the PolarStern-1996 expedition (PS-96) was considered. Using spatial distributions of temperature, salinity, and density on the transects and applying θ-S analysis, the variability of thermohaline pattern on the AW pathway along the slope of Eurasian Basin was investigated. The Fram Strait branch of the Atlantic Water (FSBW) was satisfactorily identified on all transects, including two transects in the Makarov Basin (along 159° E), while the сold waters, which can be associated with the influence of the Barents Sea branch of the Atlantic water (BSBW), on the transects along 126° E, 142° E and 159° E, were observed in the depth range below 800 m and had a negligible effect on the spatial structure of isopycnic surfaces. Special attention was paid to the variability of the volume flow rate of the AW propagating along the continental slope of the Eurasian Basin. The geostrophic volume flow rate was calculated using the dynamic method. An interpretation of the spatial and temporal variability of hydrological parameters characterizing the flow of the AW in the Eurasian Basin is presented. The geostrophic volume flow rate decreases significantly farther away from the areas of the AW inflow to the Eurasian Basin. Thus, the geostrophic estimate of the volume rate for the AW flow in the Makarov Basin at 159° E was found to be more than an order of magnitude smaller than the estimates of the volume flow rate in the Eurasian Basin, implying that the major part of the AW entering the Arctic Ocean circulates cyclonically within the Nansen and Amundsen Basins. There is an absolute maximum of θmax (AW core temperature) in 2006–2008 time series and a maximum in 2013, but only at 103° E. Salinity S(θmax) (AW core salinity) time series display an increase of the AW salinity in 2006–2008 and 2013 (at 103° E) that can be referred to as a AW salinization in the early 2000-ies. The maxima of θmax and S(θmax) in 2006–2008 and 2013 were accompanied by the volume flow rate highs. Additionally the time average volume rates were calculated for the FSBW flow (in the longitude range 31–92° E), for the BSBW flow in the St. Anna Trough and for a combined FSBW and BSBW flow in longitude range 94–107° E. A detailed discussion of the results is presented.