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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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 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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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〉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: Assessments of ocean data assimilation (DA) systems and observing system design experiments typically rely on identical or nonidentical twin experiments. The identical twin approach has been recognized as yielding biased impact assessments in atmospheric predictions, but these shortcomings are not sufficiently appreciated for oceanic DA applications. Here we present the first direct comparison of the nonidentical and identical twin approaches in an ocean DA application. We assess the assimilation impact for both approaches in a DA system for the Gulf of Mexico that uses the ensemble Kalman filter. Our comparisons show that, despite a reasonable error growth rate in both approaches, the identical twin produces a biased skill assessment, overestimating the improvement from assimilating sea surface height and sea surface temperature observations while underestimating the value of assimilating temperature and salinity profiles. Such biases can lead to an undervaluation of some observing assets (in this case profilers) and thus a misguided distribution of observing system investments.

Description: Gas transfer velocities were measured in two high-speed wind-wave tanks (Kyoto University and the SUSTAIN facility, RSMAS, University of Miami) using fresh water, simulated seawater and seawater for wind speeds between 7 and 85 m s−1. Using a mass balance technique, transfer velocities of a total of 12 trace gases were measured, with dimensionless solubilities ranging from 0.005 to 150 and Schmidt numbers between 149 and 1360. This choice of tracers enabled the separation of gas transfer across the free interface from gas transfer at closed bubble surfaces. The major effect found was a very steep increase of the gas transfer across the free water surface at wind speeds beyond 33 m s−1. The increase is the same for fresh water, simulated seawater and seawater. Bubble-induced gas transfer played no significant role for all tracers in fresh water and for tracers with moderate solubility such as carbon dioxide and dimethyl sulfide (DMS) in seawater, while for low-solubility tracers bubble-induced gas transfer in seawater was found to be about 1.7 times larger than the transfer at the free water surface at the highest wind speed of 85 m s−1. There are indications that the low contributions of bubbles are due to the low wave age/fetch of the wind-wave tank experiments, but further studies on the wave age dependency of gas exchange are required to resolve this issue.

Description: We hypothesized that the overwhelming dominance of cyclonic spirals on satellite images of the sea surface could be caused by some differences between the rotary characteristics of submesoscale cyclonic and anticyclonic eddies. This hypothesis was tested by means of numerical experiments with synthetic floating Lagrangian particles embedded offline in a regional circulation model of the southeastern Baltic Sea with very high horizontal resolution (0.125 nautical mile grid). The numerical experiments showed that the cyclonic spirals can be formed from both a horizontally uniform initial distribution of floating particles and from the initially lined-up particles during an advection time of the order of 1 d. Statistical processing of the trajectories of the synthetic floating particles allowed us to conclude that the submesoscale cyclonic eddies differ from the anticyclonic eddies in three ways favoring the formation of spirals in the tracer field: they can be characterized by (a) a considerably higher angular velocity, (b) a more pronounced differential rotation and (c) a negative helicity.

Description: In December 2002 and January 2003 satellite observations of chlorophyll showed a strong coastal signal along the west African coast between 10 and 22∘ N. In addition, a wavelike pattern with a wavelength of about 750 km was observed from 20 December 2002 and was detectable for 1 month in the open sea, south-west of the Cape Verde Peninsula. Such a pattern suggests the existence of a locally generated Rossby wave which slowly propagated westward during this period. This hypothesis was confirmed by analysing sea surface height provided by satellite altimeter during this period. To decipher the mechanisms at play, a numerical study based on a reduced-gravity shallow-water model has first been conducted. A wind burst, broadly extending over the region where the offshore oceanic signal is observed, is applied for 5 d. A Kelvin wave quickly develops along the northern edge of the cape, then propagates and leaves the area in a few days. Simultaneously, a Rossby wave whose characteristics seem similar to the observed pattern forms and slowly propagates westward. The existence of the peninsula limits the extent of the wave to the north. The spatial extent of the wind burst determines the extent of the response and correspondingly the timescale of the phenomenon (about 100 d in the present case). When the wind burst has a large zonal and small meridional extent, the behaviour of a wave to the north of the peninsula differs from that to the south. These results are corroborated and completed by an analytical study of a linear reduced-gravity model using a non-Cartesian coordinate system. This system is introduced to evaluate the potential impact of the coastline shape. The analytical computations confirm that a period of around 100 d can be associated with the observed wave considering the value of the wavelength; they also show that the role of the coastline remains moderate at such timescales. By contrast, when the period becomes shorter (smaller than 20–30 d), the behaviour of the waves is modified because of the shape of the coast. South of the peninsula, a narrow band of sea isolated from the rest of the ocean by two critical lines appears. Its meridional extent is about 100 km and Rossby waves could propagate there towards the coast.

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 an important driver of the biogeochemical systems within the oceans. Therefore, the accurate calculation of these air–sea gas fluxes is critical if we are to monitor the oceans and assess the impact that these gases are having on Earth's climate and ecosystems. 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. The toolbox has now been considerably updated to allow for its use as a Python library, to enable simplified installation, to ensure verification of its installation, to enable the handling of multiple sparingly soluble gases, and to enable the 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 reanalyse 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 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 calculates air–sea CO2 fluxes using in situ data from a fixed monitoring station in the Baltic Sea. The third case study focuses on nitrous oxide (N2O) and, through a user-defined gas transfer parameterisation, identifies that biological surfactants in the North Atlantic could suppress individual N2O sea–air gas fluxes by up to 13 %. The fourth and 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 study is dedicated to the tidal dynamics in the Sylt-Rømø Bight with a focus on the non-linear processes. The FESOM-C model was used as the numerical tool, which works with triangular, rectangular or mixed grids and is equipped with a wetting/drying option. As the model's success at resolving currents largely depends on the quality of the bathymetric data, we have created a new bathymetric map for an area based on recent studies of Lister Deep, Lister Ley, Højer Deep and Rømø Deep. This new bathymetric product made it feasible to work with high-resolution grids (up to 2 m in the wetting/drying zone). As a result, we were able to study the tidal energy transformation and the role of higher harmonics in the domain in detail. For the first time, the tidal ellipses, maximum tidally induced velocities, energy fluxes and residual circulation maps were constructed and analysed for the entire bight. Additionally, tidal asymmetry maps were introduced and constructed. The full analysis was performed on two grids with different structures and showed a convergence of the results as well as fulfilment of the energy balance. A great deal of attention has been paid to the selection of open-boundary conditions, model validation against tide gauges and recent in situ current data. The tidal residual circulation and asymmetric tidal cycles largely define the circulation pattern, transport and accumulation of sediment, and the distribution of bedforms in the bight; therefore, the results presented in the article are necessary and useful benchmarks for further studies in the area, including baroclinic and sediment dynamics investigations.

Description: The Arctic Front (AF) in the Norwegian Sea is an important biologically productive region which is well-known for its large feeding schools of pelagic fish. A suite of satellite data, a regional coupled ocean–sea ice data assimilation system (the TOPAZ reanalysis) and atmospheric reanalysis data are used to investigate the variability in the lateral and vertical structure of the AF. A method, known as “singularity analysis”, is applied on the satellite and reanalysis data for 2-D spatial analysis of the front, whereas for the vertical structure, a horizontal gradient method is used. We present new evidence of active air–sea interaction along the AF due to enhanced momentum mixing near the frontal region. The frontal structure of the AF is found to be most distinct near the Faroe Current in the south-west Norwegian Sea and along the Mohn Ridge. Coincidentally, these are the two locations along the AF where the air–sea interactions are most intense. This study investigates in particular the frontal structure and its variability along the Mohn Ridge. The seasonal variability in the strength of the AF is found to be limited to the surface. The study also provides new insights into the influence of the three dominant modes of the Norwegian Sea atmospheric circulation on the AF along the Mohn Ridge. The analyses show a weakened AF during the negative phase of the North Atlantic Oscillation (NAO−), even though the geographical location of the front does not vary. The weakening of AF during NAO− is attributed to the variability in the strength of the Norwegian Atlantic Front Current over the Mohn Ridge associated with the changes in the wind field.

Description: Marine biophysical models can be used to explore the displacement of individuals in and between submarine canyons. Mostly, the studies focus on the shallow hydrodynamics in or around a single canyon. In the northwestern Mediterranean Sea, knowledge of the deep-sea circulation and its spatial variability in three contiguous submarine canyons is limited. We used a Lagrangian framework with three-dimensional velocity fields from two versions of the Regional Ocean Modeling System (ROMS) to study the deep-bottom connectivity between submarine canyons and to compare their influence on the particle transport. From a biological point of view, the particles represented eggs and larvae spawned by the deep-sea commercial shrimp Aristeus antennatus along the continental slope in summer. The passive particles mainly followed a southwest drift along the continental slope and drifted less than 200 km considering a pelagic larval duration (PLD) of 31 d. Two of the submarine canyons were connected by more than 27 % of particles if they were released at sea bottom depths above 600 m. The vertical advection of particles depended on the depth where particles were released and the circulation influenced by the morphology of each submarine canyon. Therefore, the impact of contiguous submarine canyons on particle transport should be studied on a case-by-case basis and not be generalized. Because the flows were strongly influenced by the bottom topography, the hydrodynamic model with finer bathymetric resolution data, a less smoothed bottom topography, and finer sigma-layer resolution near the bottom should give more accurate simulations of near-bottom passive drift. Those results propose that the physical model parameterization and discretization have to be considered for improving connectivity studies of deep-sea species.

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. The amplitude of seasonality decreases with depth and is much larger in temperature and density than in salinity. Time series of temperature and salinity are correlated in the surface but not in the bottom layer. Trends in temperature are large (up to 0.6 ∘C over 10 years), significant through the area, and not sensitive to the sampling interval and time series length. In contrast, trends in salinity are largely small and insignificant and depend on the time series length. The warming of the area is more during spring and summer. Such large temperature trends and their spatial variability emphasize the importance of maintaining regular long-term observations for the proper estimation of thermohaline trends and their variability. This is particularly important in regions which are key for driving thermohaline circulation such as the northern Adriatic, with the potential to affect biogeochemical and ecological properties of the whole Adriatic Sea.

Description: We present the Copernicus in situ ocean dataset of temperature and salinity (version 5.2). Ocean subsurface sampling varied widely from 1950 to 2017 as a result of changes in instrument technology and the development of in situ observational networks (in particular, tropical moorings for the Argo program). Thus, global ocean temperature data coverage on an annual basis grew from 10 % in 1950 (30 % for the North Atlantic basin) to 25 % in 2000 (60 % for the North Atlantic basin) and reached 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 increased 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. Objective analyses (OAs) 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 random-error-induced variability.

Description: Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring–neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being “fished out” by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimize these risks, with u measured by a low-frequency acoustic Doppler current profiler (ADCP) moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the semidiurnal internal tide radiating from the Wyville Thomson Ridge in the North Atlantic. The observed energy flux (4.2±0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by subsampling potential density in an idealized internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

Description: Data on Secchi disc depth (the depth at which a standard white disc lowered into the water just becomes invisible to a surface observer) show that water clarity in the North Sea declined during the 20th century, with likely consequences for marine primary production. However, the causes of this trend remain unknown. Here we analyse the hypothesis that changes in the North Sea's wave climate were largely responsible by causing an increase in the concentrations of suspended particulate matter (SPM) in the water column through the resuspension of seabed sediments. First, we analysed the broad-scale statistical relationships between SPM and bed shear stress due to waves and tides. We used hindcasts of wave and current data to construct a space–time dataset of bed shear stress between 1997 and 2017 across the northwest European Continental Shelf and compared the results with satellite-derived SPM concentrations. Bed shear stress was found to drive most of the inter-annual variation in SPM in the hydrographically mixed waters of the central and southern North Sea. We then used a long-term wave reanalysis to construct a time series of bed shear stress from 1900 to 2010. This shows that bed shear stress increased significantly across much of the shelf during this period, with increases of over 20 % in the southeastern North Sea. An increase in bed shear stress of this magnitude would have resulted in a large reduction in water clarity. Wave-driven processes are rarely included in projections of climate change impacts on marine ecosystems, but our analysis indicates that this should be reconsidered for shelf sea regions.

Description: This study considers ocean–atmosphere influences on marine productivity over the shelf near Cape St. Francis, South Africa. Multiday estimates of chlorophyll fluorescence in the period 2006–2017 with an area outlined by 34.5–33.75∘ S and 24–26.5∘ E provide the basis for evaluation using data from high-resolution reanalyses. Correlations with the mean annual cycle of chlorophyll fluorescence were significant for salinity, linking marine productivity and the coastal hydrology. A strengthened Agulhas Current induces cyclonic shear that lifts water at the shelf edge. Composite high-chlorophyll-fluorescence events were dominated by a large-scale midlatitude atmospheric ridge of high pressure. The resultant easterly winds caused offshore transport and the upwelling of cool nutrient-rich water in multiday events at the beginning and end of austral summer. Environmental controls on interannual fluctuations of the commercial fishery were also explored. Southwestward currents and diminished heat fluxes favored the squid catch, while anchovy and sardine catches were linked with upper northerly wind, consistent with large-scale weather patterns that underpin coastal upwelling and river discharge. Productivity lags a few days behind cyclonic wind and current shear and the upstream coastal hydrology, which shares a common atmospheric driver.

Description: The long-term theoretical “energy paradox” of whether the final state of two merging anticyclones contains more energy than the initial state is studied by considering two typical merging events of ocean mesoscale eddies. The results demonstrate that the total mass (volume), total circulation (area integration of vorticity), and total angular momentum (AM) are conserved if the orbital AM relative to the center of mass is taken into account as the eddies rotate around the center of mass before merging. For subsurface merging, the mass trapped by the Taylor–Proudman effect above the subsurface eddies should also be included. Both conservation laws of circulation and orbital AM have been overlooked in previous theoretical studies. As a result of fusion during merging, the total eddy kinetic energy decreases slightly. In contrast, the total eddy potential energy (EPE) increases after merging. The increase in EPE is mostly supported by the loss of gravitational potential energy (PE) via eddy sinking below the original level prior to merging. This implies that the merging of eddies requires background gravitational PE to be converted to EPE. In contrast, the vorticity and enstrophy consequently decrease after merging. Thus, the eddy merging effect behaves as a “large-scale energy pump” in an inverse energy cascade. It is noted that eddy conservation and conversion laws depend on the laws of physical dynamics, even if additional degrees of freedom can be provided in a mathematical model.

Description: The dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCEs) dominate the surface circulation of the Gulf of Mexico (GoM) and transport Caribbean Water (CW) into the gulf. In this work, 25 years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll a (Chl a) concentrations from 1998 to 2017, including temporal changes, mean differences, and regional concentration tendencies. The physical variables analyzed are absolute dynamic topography (ADT) and oceanic currents. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of CW with an inward incursion that starts in spring, peaks in the summer, reaches to 28∘ N and 90.45∘ W, and then retreats in winter to approximately 26.5 ∘ N and 88.3 ∘ W. Minimum surface Chl a concentrations ( 0.14 mg m−3. The 3-year running averages of the ADT 40 cm isoline qualitatively reproduce the climatological pattern of 25 years showing that before 2002 CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from the Caribbean Sea have invaded the western GoM and reduced mean surface Chl a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that in the latter time interval, the Chl a concentration above waters deeper than 250 m has decreased significantly.

Description: This work examines the accuracy and validity of two variants of Radon transform and two variants of the two-dimensional fast Fourier transform (2-D FFT) that have been previously used for estimating the propagation speed of oceanic signals such as sea surface height anomalies (SSHAs) derived from satellite-borne altimeters based on time–longitude (Hovmöller) diagrams. The examination employs numerically simulated 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 known ab initio, 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 when its amplitude is smaller than 5 times the amplitude of the other modes and that they successfully detect the phase speed of the dominant input mode only when its amplitude is at least 10 times the amplitude of the other modes. This requirement is an unrealistic limitation on oceanic observations such as SSHA. 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 methods identify a dominant input mode decreases with the increase in the number of modes in the signal. Our findings are relevant to the reliability of phase speed estimates of SSHA observations and the reported “too fast” a phase speed of baroclinic Rossby waves in the ocean.

Description: Persian Gulf Water and Red Sea Water are salty and dense waters flowing at intermediate depths in the Gulf of Oman and the Gulf of Aden, respectively. Their spreading pathways are influence by mesoscale eddies that dominate the surface flow in both semi-enclosed basins. In situ measurements combined with altimetry indicate that Persian Gulf Water is stirred in the form of filaments and submesoscale structures by mesoscale eddies. In this paper, we study the formation and the life cycle of intense submesoscale vortices and their potential impact on the spreading of Persian Gulf Water and Red Sea Water. We use a primitive-equation three-dimensional hydrostatic model at a submesoscale-resolving resolution to study the evolution of submesoscale vortices. Our configuration idealistically mimics the dynamics in the Gulf of Oman and the Gulf of 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. First, intense vorticity filaments are generated over the continental slope due to frictional interactions of the background flow with the sloping topography. These filaments are shed into the ocean interior and undergo horizontal shear instability that leads to the formation of submesoscale coherent vortices. The second mechanism is inviscid and features baroclinic instabilities arising at depth due to the weak stratification. Submesoscale vortices subsequently drift away, merge and form larger vortices. They can also pair with opposite-signed vortices and travel across the domain. They eventually dissipate their energy via several mechanisms, in particular fusion into the larger eddies or erosion on the topography. Since no submesoscale flow clearly associated with the fragments of Persian Gulf Water was observed in situ, we modeled Persian Gulf Water as Lagrangian particles. 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, without 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 potentially important role of submesoscale eddies in spreading Persian Gulf Water and Red Sea Water.

Description: Transparent exopolymer particles (TEPs) are a major source for both organic matter (OM) and carbon transfer in the ocean and into the atmosphere. Consequently, understanding the vertical distribution of TEPs and the processes which impact their movement is important in understanding the OM and carbon pools on a larger scale. Additionally, most studies looking at the vertical profile of TEPs have focused on large depth scales from 5 to 1000 m and have omitted the near-surface environment. Results from a study of TEP enrichment in the sea surface microlayer (SML) in different regions (tropical, temperate) has shown that, while there is a correlation between TEP concentration and primary production (PP) on larger or seasonal scales, such relationships break down on shorter timescales and spatial scales. Using a novel small-scale vertical sampler, the vertical distribution of TEPs within the uppermost 2 m was investigated. For two regions with a total of 20 depth profiles, a maximum variance of TEP concentration of 1.39×106 µg XG eq2 L−2 between depths and a minimum variance of 6×102 µg XG eq2 L−2 was found. This shows that the vertical distribution of TEPs was both heterogeneous and homogeneous at times. Results from the enrichment of TEPs and Chl a between different regions have shown TEP enrichment in the SML to be greater in oligotrophic waters, when both Chl a and TEP concentrations were low, suggesting the importance of abiotic sources for the enrichment of TEPs in the SML. However, considering multiple additional parameters that were sampled, it is clear that no single parameter could be used as a proxy for TEP heterogeneity. Other probable biochemical drivers of TEP transport are discussed.

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. Surface currents, however, are under-resolved in most operational ocean models due to the difficultly of measuring ocean currents close to, or directly at, the air–sea interface 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 Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters, which have draft depths of 60 and 5 cm, respectively. Trajectory data of dense, colocated 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 data reveals that the drifter velocities 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 drifter velocities. During these high wind events, we deconstruct the total drifter velocities of 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 field estimates 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 drifter velocities exhibits a rotation to the right with depth between the velocities measured by undrogued and drogued drifters. We find that the average wind-driven velocity of undrogued drifters (drogued drifters) is ∼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 on the vertical shear present in wind-driven surface currents under high winds, which have vital implications for any surface transport problem.

Description: Low-frequency sea level variability can be a critical factor for several wave energy converter (WEC) systems, for instance, linear systems with 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 finding the most suitable areas for wave energy park installations, this paper describes a study that gives them additional information by exploring the annual and monthly variability of the sea level in the Baltic Sea and adjacent seawaters, with a focus on the Swedish Exclusive Economic Zone. Overall, 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 from a sea level variation viewpoint are found in the Gotland basins and in the Bothnian Sea, where the energy loss due to sea level variations is negligible.

Description: Sea surface waves are important for marine safety and coastal engineering, but mapping the wave properties at complex shorelines, such as coastal archipelagos, is challenging. The wave spectrum, E(f), contains a majority of the information about the wave field, and its properties have been studied for decades. Nevertheless, any systematic research into the wave spectrum in archipelagos has not been made. In this paper we present wave buoy measurements from 14 locations in the Finnish archipelago. The shape of the wave spectrum showed a systematic transition from a single-peaked spectrum to a spectrum with a wide frequency range having almost constant energy. The exact shape also depended on the wind direction, since the fetch, island, and bottom conditions are not isotropic. The deviation from the traditional spectral form is strong enough to have a measurable effect on the definitions of the significant wave height. The relation between the two definitions in the middle of the archipelago was H1/3=0.881Hs, but the ratio varied with the spectral width (Hs was defined using the variance). At this same location the average value of the single highest wave, Hmax∕Hs, was only 1.58. A wider archipelago spectrum was also associated with lower confidence limits for the significant wave height compared to the open sea (6 % vs. 9 %). The challenges caused by the instability of the peak frequency for an archipelago spectrum are presented, and the mean frequency, weighted with E(f)4, is proposed as a compromise between stability and bias with respect to the peak frequency. The possibility of using the frequency and width parameters of this study as a starting point for a new analytical parameterisation of an archipelago type spectrum is discussed.

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 steered by the advection of cold upwelling filaments. Following the thermal wind balance, the increased horizontal density gradients result in an increase in the vertical shear of the anticyclones and in 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 stronger (weaker) offshore cooling and a stronger (weaker) westward intensification of the anticyclones. Moreover, the simulations with weaker upwelling show farther advection of the Amazon and Orinoco River plumes into the basin. As a result, in these simulations the horizontal density gradients were predominantly set by horizontal salinity gradients. The importance of the horizontal density gradients driven by temperature, which are associated with the upwelling, increased with increasing upwelling strength. The results of this study highlight that both upwelling and the advection of the river plumes affect the life cycle of mesoscale eddies in the Caribbean Sea.

Description: We analyze extreme sea levels (ESLs) and related uncertainty in an ensemble of regional climate change scenarios for the Baltic Sea. The ERA-40 reanalysis and five Coupled Model Intercomparison Project phase 5 (CMIP5) global general circulation models (GCMs) have been dynamically downscaled with the coupled atmosphere–ice–ocean model RCA4-NEMO (Rossby Centre regional atmospheric model version 4 – Nucleus for European Modelling of the Ocean). The 100-year return levels along the Swedish coast in the ERA-40 hindcast are within the 95 % confidence limits of the observational estimates, except those on the west coast. The ensemble mean of the 100-year return levels averaged over the five GCMs shows biases of less than 10 cm. A series of sensitivity studies explores how the choice of different parameterizations, open boundary conditions and atmospheric forcing affects the estimates of 100-year return levels. A small ensemble of different regional climate models (RCMs) forced with ERA-40 shows the highest uncertainty in ESLs in the southwestern Baltic Sea and in the northeastern part of the Bothnian Bay. Some regions like the Skagerrak, Gulf of Finland and Gulf of Riga are sensitive to the choice of the RCM. A second ensemble of one RCM forced with different GCMs uncovers a lower sensitivity of ESLs against the variance introduced by different GCMs. The uncertainty in the estimates of 100-year return levels introduced by GCMs ranges from 20 to 40 cm at different stations and includes the estimates based on observations. It is of similar size to the 95 % confidence limits of 100-year return levels from tide gauge records.

Description: We have designed a method for testing the quality of multidecadal analyses of sea surface temperature (SST) in regional seas by using a set of high-quality local SST observations. In recognizing that local data may reflect local effects, we focus on the dominant empirical orthogonal functions (EOFs) of the local data and of the localized data of the gridded SST analyses. We examine the patterns, variability, and trends of the principal components. This method is applied to examine three different SST analyses, i.e., HadISST1, ERSST, and COBE SST. They have been assessed using a newly constructed high-quality dataset of SST at 26 coastal stations along the Chinese coast in 1960–2015, which underwent careful examination with respect to quality and a number of corrections for inhomogeneities. The three gridded analyses perform generally well from 1960 to 2015, in particular since 1980. However, for the pre-satellite period prior to the 1980s, the analyses differ among each other and show some inconsistencies with the local data, such as artificial break points, periods of bias, and differences in trends. We conclude that gridded SST analyses need improvement in the pre-satellite period (prior to the 1980s) by reexamining in detail archives of local quality-controlled SST data in many data-sparse regions of the world.

Description: As part of the Copernicus Marine Environment Monitoring Service (CMEMS), a physical–biogeochemical coupled model system has been developed to monitor and forecast the ocean dynamics and marine ecosystem of the European waters and more specifically on the Iberia–Biscay–Ireland (IBI) area. The CMEMS IBI coupled model 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. The coupled system has been providing 7 d weekly ocean forecasts for CMEMS since April 2018. Prior to its operational launch, a pre-operational qualification simulation (2010–2016) has allowed assessing the model's capacity to reproduce the main biogeochemical and ecosystem features of the IBI area. The objective of this paper is then to describe the consistency and skill assessment of the PISCES biogeochemical model using this 7-year qualification simulation. The model results are compared with available satellite estimates as well as in situ observations (ICES, EMODnet and BGC-Argo). The simulation successfully reproduces the spatial distribution and seasonal cycles of oxygen, nutrients, chlorophyll a and net primary production, and confirms that PISCES is suitable at such a resolution and can be used for operational analysis and forecast applications. This model system can be a useful tool to better understand the current state and changes in the marine biogeochemistry of European waters and can also provide key variables for developing indicators to monitor the health of marine ecosystems. These indicators may be of interest to scientists, policy makers, environmental agencies and the general public.

Description: The predictability of the sea surface height expression of baroclinic tides is examined with 96 h 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 time-variable mesoscale stratification and currents, may be identified from residual sea level anomalies (SLAs) 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, T+60, or T+84 h – 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 subtidal (mesoscale) SLA. Root mean square values of the former range from 0.5 to 2 cm, while the latter ranges from 1 to 6 cm, for a typical 84 h 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: For more than 20 years, the multi-satellite Data Unification and Altimeter Combination System (DUACS) has been providing near-real-time (NRT) and delayed-time (DT) altimetry products. DUACS datasets range from along-track measurements to multi-mission sea level anomaly (SLA) and absolute dynamic topography (ADT) maps. The DUACS DT2018 ensemble of products is the most recent and major release. For this, 25 years of altimeter data have been reprocessed and are available through the Copernicus Marine Environment Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S). Several changes were implemented in DT2018 processing in order to improve the product quality. New altimetry standards and geophysical corrections were used, data selection was refined and optimal interpolation (OI) parameters were reviewed for global and regional map generation. This paper describes the extensive assessment of DT2018 reprocessing. The error budget associated with DT2018 products at global and regional scales was defined and improvements on the previous version were quantified (DT2014; Pujol et al., 2016). DT2018 mesoscale errors were estimated using independent and in situ measurements. They have been reduced by nearly 3 % to 4 % for global and regional products compared to DT2014. This reduction is even greater in coastal areas (up to 10 %) where it is directly linked to the geophysical corrections applied to DT2018 processing. The conclusions are very similar concerning geostrophic currents, for which error was globally reduced by around 5 % and as much as 10 % in coastal areas.

Description: Spatio-temporal variations in the partial pressure of CO2 (pCO2) were studied during eight oceanographic cruises conducted between March 2014 and February 2016 in surface waters of the eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) between the Guadalquivir river and Cape Trafalgar. pCO2 presents a range of variation between 320.6 and 513.6 µatm with highest values during summer and autumn and lowest during spring and winter. For the whole study, pCO2 shows a linear dependence with temperature, and spatially there is a general decrease from coastal to offshore stations associated with continental inputs and an increase in the zones deeper than 400 m related to the influence of the eastward branch of the Azores Current. The study area acts as a 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 transects, the CO2 fluxes decrease towards offshore, whereas in the Trafalgar transect fluxes increase due to the presence of an upwelling. The annual uptake capacity of CO2 in the Gulf of Cádiz is 4.1 Gg C yr−1.

Description: Recently two gridded sea surface salinity (SSS) products that cover the Arctic Ocean have been derived from the European Space Agency (ESA)'s Soil Moisture and Ocean Salinity (SMOS) mission: one developed by the Barcelona Expert Centre (BEC) and the other developed by the Ocean Salinity Expertise Center of the Centre Aval de Traitement des Données SMOS at IFREMER (The French Research Institute for Exploitation of the Sea) (CEC). The uncertainties of these two SSS products are quantified during the period of 2011–2013 against other SSS products: one data assimilative regional reanalysis; one data-driven reprocessing in the framework of the Copernicus Marine Environment Monitoring Services (CMEMS); two climatologies – the 2013 World Ocean Atlas (WOA) and the Polar science center Hydrographic Climatology (PHC); and in situ datasets, both assimilated and independent. The CMEMS reanalysis comes from the TOPAZ4 system, which assimilates a large set of ocean and sea-ice observations using an ensemble Kalman filter (EnKF). Another CMEMS product is the Multi-OBservations reprocessing (MOB), a multivariate objective analysis combining in situ data with satellite SSS. The monthly root mean squared deviations (RMSD) of both SMOS products, compared to the TOPAZ4 reanalysis, reach 1.5 psu in the Arctic summer, while in the winter months the BEC SSS is closer to TOPAZ4 with a deviation of 0.5 psu. The comparison of CEC satellite SSS against in situ data shows Atlantic Water that is too fresh in the Barents Sea, the Nordic Seas, and in the northern North Atlantic Ocean, consistent with the abnormally fresh deviations from TOPAZ4. When compared to independent in situ data in the Beaufort Sea, the BEC product shows the smallest bias (

Description: Oceanic dissolved organic carbon (DOC) represents one of the largest carbon reservoirs on Earth, and its distribution and biogeochemical cycles play important roles in carbon cycling and other biogeochemical processes in the ocean. We report the distribution and concentrations of DOC for water samples collected from the shelf-edge and slope regions in the East China Sea (ECS) and the Kuroshio Extension (KE) in the northwestern North Pacific during two cruises in 2014–2015. The DOC concentrations were 45–88 µM in the ECS and 35–65 µM in the KE. In addition to biological processes that are estimated to account for 7 % and 8 %–20 % in shaping the DOC distribution in the ECS and KE regions, respectively, the DOC distribution is largely controlled by hydrodynamic mixing of different water masses. By comparing the DOC results with dissolved inorganic carbon (DIC) and dissolved inorganic radiocarbon (Δ14C-DIC) measured from the same water samples, we further demonstrate that the intrusion of the Kuroshio Current could dilute the DOC concentrations at stations in the outer shelf and slope regions of the ECS. The concentrations of DOC in the KE were significantly lower in surface waters than in the ECS, and a relatively low and stable DOC level (∼40 µM) was found in deep water (below 1500 m) at all stations. Based on the previously reported DIC and Δ14C-DIC values for the stations, the observed spatial variations of DOC in the upper 700 m among the stations in the KE were mainly influenced by mixing of the two water masses carried by the Kuroshio and Oyashio, the two dominant western boundary currents in the region. The hydrodynamic processes are thus important factors in the distribution and dynamics of DOC in the KE region.

Description: In the Southern Hemisphere, macroscale atmospheric systems such as westerly winds and the southeast Pacific subtropical anti-cyclone (SPSA) influence the wind regime of the eastern austral Pacific Ocean. The average and seasonal behaviors of these systems are well known, although wind variability at different time and distance scales remains largely unexamined. Therefore, the main goal of this study was to determine the variabilities of surface winds on a spatiotemporal scale from 40 to 56∘ S, using QuikSCAT, Advanced Scatterometer (ASCAT), and the fifth major global European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) surface-wind information complemented with in situ meteorological data. In addition, interactions between the atmospheric systems, together with the ocean–atmosphere response, were evaluated for the period 1999–2018. The empirical orthogonal function detected dominance at the synoptic scale in mode 1, representing approximately 30 % of the total variance. In this mode, low and high atmospheric pressure systems characterized wind variability for a 16.5 d cycle. Initially, mode 2 – which represents approximately 22 % of the variance – was represented by winds from the west/east (43–56∘ S), occurring mostly during spring and summer/fall and winter at an annual timescale (1999–2008) until they were replaced by systems cycling at 27.5 d (2008–2015). This reflects the influence of the baroclinic annular mode in the Southern Hemisphere. Mode 3, representing approximately 15 % of the variance, involved the passage of small-scale low and high atmospheric pressure (LAP and HAP) systems throughout Patagonia. Persistent Ekman suction occurred throughout the year south of the Gulf of Penas and beyond the Pacific mouth of the Strait of Magellan. Easterly Ekman transport (ET) piled these upwelled waters onto the western shore of South America when winds blew southward. These physical mechanisms were essential in bringing nutrients to the surface and then transporting planktonic organisms from the oceanic zone to Patagonian fjords and channels. In the zonal band between 41 and 43∘ S, the latitude of Chiloé Island, upward Ekman pumping and Ekman transport during spring and summer favored a reduced sea surface temperature and increased chlorophyll a (Chl a) levels; this is the first time that such Ekman upwelling conditions have been reported so far south in the eastern Pacific Ocean. The influence of the northward-migrating LAP systems on the ocean–atmosphere interphase allowed us to understand, for the first time, their direct relationship with recorded nighttime air temperature maxima (locally referred to as “nighttime heatwave events”). In the context of global climate change, greater attention should be paid to these processes based on their possible impact on the rate of glacier melting and on the austral climate.

Description: Rapid evolution of operational ocean forecasting systems is driven by advances in numerics and data assimilation schemes, and increase of in situ and satellite observations. 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 sea surface height (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 2013–2016 period. 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 3-D 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. The mesoscale data provided here may be of interest to CMEMS users and in the future could be a useful addition to a more diverse CMEMS catalogue.

Description: The North-West European Shelf ocean forecasting system has been providing oceanographic products for the European continental shelf seas for more than 15 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 operation, an eddy-resolving model at 1.5 km (AMM15), replaces the 7 km model (AMM7) that has been used for 8 years to deliver forecast products to the Copernicus Marine Environment Monitoring Service and its precursor projects. 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 with data assimilation is based on the results of 2 years (2016–2017) of 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 penalized 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: Diatoms account for up to 50 % 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 the following: (1) if and how bulk diatom communities respond to elevated CO2 with respect to abundance or biomass and (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 bulk 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 favours larger species as 12 out of 13 experiments which investigated cell size found a shift towards larger species. Unravelling winners and losers with respect to taxonomic affiliation was difficult due to a limited database. The OA-induced changes in diatom competitiveness and assemblage structure may alter key ecosystem services due to the pivotal role diatoms play in trophic transfer and biogeochemical cycles.

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 described or are insufficiently 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 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 parameterise 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 the GOTM and improve upon existing parameterisations, showing the potential of this method for use in data assimilation systems.

Description: The quality of the upgraded version of the Copernicus Marine Environment Monitoring Service (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, and literature. We show that the quality of the MedBFM system has been improved in the previous 10 years. We demonstrate that a set of metrics based on the GODAE (Global Ocean Data Assimilation Experiment) paradigm can be efficiently applied to validate an operational model system for biogeochemical and ecosystem forecasts. The accuracy of the CMEMS biogeochemical products for the Mediterranean Sea can be achieved from basin-wide and seasonal scales to mesoscale and weekly scales, and its level depends on the specific variable and the availability of reference data, the latter being an important prerequisite to build robust statistics. In particular, the use of the Biogeochemical Argo floats data proved to significantly enhance the validation framework of operational biogeochemical models. New skill metrics, aimed to assess key biogeochemical processes and dynamics (e.g. deep chlorophyll maximum depth, nitracline depth), can be easily implemented to routinely monitor the quality of the products and highlight possible anomalies through the comparison of near-real-time (NRT) forecasts skill with pre-operationally defined seasonal benchmarks. Feedbacks to the observing autonomous systems in terms of quality control and deployment strategy are also discussed.

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∘ at the Equator) to quantify this sinking. To this end we have calculated the Eulerian net vertical transport (W∑) from the modeled 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 W∑ 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 shelf: one within the first 90 km and onto the bathymetric slope at around the peak of the boundary current speed (regime I), the second between 90 and 250 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 at larger distances from the shelf where W∑ 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 W∑ in marginal seas located far from the overflow areas, although the regime boundaries can shift a few tens of kilometers 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, seasonal variability, and depth at which W∑ peaks vary for each region, thus revealing a complex picture of sinking in the subpolar North Atlantic.

Description: The harmonic representation of inequalities (HRoI) is a procedure for tidal analysis and prediction that combines aspects of the non-harmonic and the harmonic method. With this technique, the deviations of heights and lunitidal intervals, especially of high and low waters, from their respective mean values are represented by superpositions of long-period tidal constituents. This article documents the preparation of a constituents list for the operational application of the harmonic representation of inequalities. Frequency analyses of observed heights and lunitidal intervals of high and low water from 111 tide gauges along the German North Sea coast and its tidally influenced rivers have been carried out using the generalized Lomb–Scargle periodogram. One comprehensive list of partial tides is realized by combining the separate frequency analyses and by applying subsequent improvements, e.g. through manual inspections of long time series data. The new set of 39 partial tides largely confirms the previously used set with 43 partial tides. Nine constituents are added and 13 partial tides, mostly in the close neighbourhood of strong spectral components, are removed. The effect of these changes has been studied by comparing predictions with observations from 98 tide gauges. Using the new set of constituents, the standard deviations of the residuals are reduced on average by 2.41 % (times) and 2.30 % (heights) for the year 2016. The new set of constituents will be used for tidal analyses and predictions starting with the German tide tables for the year 2020.

Description: Marine waters can be highly heterogeneous both on a spatial and temporal scale, yet monitoring programs currently rely primarily on low-resolution methods. This potentially leads to undersampling. This study explores the potential of two high-resolution methods for monitoring phytoplankton dynamics: fast repetition rate fluorometry for information on phytoplankton photosynthesis and productivity and automated scanning flow cytometry for information on phytoplankton abundance and community composition. These methods were tested in combination with an underway Ferrybox system during four cruises on the Dutch North Sea in April, May, June, and August 2017. The high-resolution methods were able to visualize both the spatial and temporal variability of the phytoplankton community in the Dutch North Sea. Spectral cluster analysis was applied to objectively interpret the multitude of parameters and visualize potential spatial patterns. This resulted in the identification of biogeographic regions with distinct phytoplankton communities, which varied per cruise. Our results clearly show that the sampling based on fixed stations does not give a good representation of the spatial patterns, showing the added value of underway high-resolution measurements. To fully exploit the potential of the tested high-resolution measurement setup, methodological constraints need further research. Among these constraints are accounting for the diurnal cycle in photophysiological parameters concurrent to the spatial variation, better predictions of the electron requirement for carbon fixation to estimate gross primary productivity, and the identification of more flow cytometer clusters with informative value. Nevertheless, the richness of additional information provided by high-resolution methods can improve existing low-resolution monitoring programs towards a more precise and ecosystemic ecological assessment of the phytoplankton community and productivity.

Description: The Galápagos Archipelago and Galápagos Marine Reserve lie 1000 km off the coast of Ecuador and are among the world's most iconic wildlife refuges. However, plastic litter is now found even in this remote 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 sources of plastic pollution are also fairly localised and limited to nearby fishing regions and South American 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 plastic origin and fate using pathways and connectivity between the Galápagos region and the coastlines as well as known fishery locations 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 region. 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: The development of coupled atmosphere–ocean prediction systems with utility on 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 the 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: There is a need for cost-efficient tools to explore deep-ocean ecosystems to collect baseline biological observations on pelagic fauna (zooplankton and nekton) and establish the vertical ecological zonation in the deep sea. The Pelagic In situ Observation System (PELAGIOS) is a 3000 m rated slowly (0.5 m s−1) towed camera system with LED illumination, an integrated oceanographic sensor set (CTD-O2) and telemetry allowing for online data acquisition and video inspection (low definition). The high-definition video is stored on the camera and later annotated using software and related to concomitantly recorded environmental data. The PELAGIOS is particularly suitable for open-ocean observations of gelatinous fauna, which is notoriously under-sampled by nets and/or destroyed by fixatives. In addition to counts, diversity, and distribution data as a function of depth and environmental conditions (T, S, O2), in situ observations of behavior, orientation, and species interactions are collected. Here, we present an overview of the technical setup of the PELAGIOS as well as example observations and analyses from the eastern tropical North Atlantic. Comparisons to data from the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) net sampling and data from the Underwater Vision Profiler (UVP) are provided and discussed.

Description: The Data Unification and Altimeter Combination System (DUACS) produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, and geophysics and biology communities. These maps are generated using an optimal interpolation method applied to altimeter observations. They 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 does not have full 1∕4∘ spatial and 1 d temporal resolutions 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 (a.k.a. DUACS-DT2018). Our approach is based on the ratio between the spectral content of the mapping error and the spectral content of independent true signals (along-track and tide gauge observations), also known as the noise-to-signal ratio. 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 ∼34 d. The mean effective spatial resolution at midlatitude is estimated to be ∼200 km. The mean effective spatial resolution is ∼130 km for the regional Mediterranean Sea and for the regional Black Sea products. An intercomparison with previous DUACS reprocessing systems (a.k.a., 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 in resolving capabilities and accuracies in the DUACS maps with the number of missions.

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, n=24, 0.16±0.04 µmol L−1), chromophoric (CDOM, n=76, 0.152±0.03), and fluorescent dissolved organic matter (FDOM, n=35), from the Peruvian upwelling region (Guayaquil, Ecuador to Antofagasta, Chile, October 2015). OCS was measured continuously with an equilibrator connected to an off-axis integrated cavity output spectrometer at the surface (29.8±19.8 pmol L−1) and at four profiles ranging down to 136 m. CS2 was measured at the surface (n=143, 17.8±9.0 pmol L−1) and below, ranging down to 1000 m (24 profiles). These observations were 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. Quantifying OCS photoproduction using a specific humic-like FDOM component as proxy, together with an updated parameterization for dark production, improves agreement with observations in a 1-D biogeochemical model. Our results will help to better predict oceanic concentrations and emissions of both gases on regional and, potentially, global scales.

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 (GoC) 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 Water (MW), 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 in terms of 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: Methane (CH4) in marine sediments has the potential to contribute to changes in the ocean and climate system. Physical and biochemical processes that are difficult to quantify with current standard methods such as acoustic surveys and discrete sampling govern the distribution of dissolved CH4 in oceans and lakes. Detailed observations of aquatic CH4 concentrations are required for a better understanding of CH4 dynamics in the water column, how it can affect lake and ocean acidification, the chemosynthetic ecosystem, and mixing ratios of atmospheric climate gases. Here we present pioneering high-resolution in situ measurements of dissolved CH4 throughout the water column over a 400 m deep CH4 seepage area at the continental slope west of Svalbard. A new fast-response underwater membrane-inlet laser spectrometer sensor demonstrates technological advances and breakthroughs for ocean measurements. We reveal decametre-scale variations in dissolved CH4 concentrations over the CH4 seepage zone. Previous studies could not resolve such heterogeneity in the area, assumed a smoother distribution, and therefore lacked both details on and insights into ongoing processes. We show good repeatability of the instrument measurements, which are also in agreement with discrete sampling. New numerical models, based on acoustically evidenced free gas emissions from the seafloor, support the observed heterogeneity and CH4 inventory. We identified sources of CH4, undetectable with echo sounder, and rapid diffusion of dissolved CH4 away from the sources. Results from the continuous ocean laser-spectrometer measurements, supported by modelling, improve our understanding of CH4 fluxes and related physical processes over Arctic CH4 degassing regions.

Description: We present consistent annual mean atmospheric histories and growth rates for the mainly anthropogenic halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116, which are all potentially useful oceanic transient tracers (tracers of water transport within the ocean), for the Northern and Southern Hemisphere with the aim of providing input histories of these compounds for the equilibrium between the atmosphere and surface ocean. We use observations of these halogenated compounds made by the Advanced Global Atmospheric Gases Experiment (AGAGE), the Scripps Institution of Oceanography (SIO), the Commonwealth Scientific and Industrial Research Organization (CSIRO), the National Oceanic and Atmospheric Administration (NOAA) and the University of East Anglia (UEA). Prior to the direct observational record, we use archived air measurements, firn air measurements and published model calculations to estimate the atmospheric mole fraction histories. The results show that the atmospheric mole fractions for each species, except HCFC-141b and HCFC-142b, have been increasing since they were initially produced. Recently, the atmospheric growth rates have been decreasing for the HCFCs (HCFC-22, HCFC-141b and HCFC-142b), increasing for the HFCs (HFC-134a, HFC-125, HFC-23) and stable with little fluctuation for the PFCs (PFC-14 and PFC-116) investigated here. The atmospheric histories (source functions) and natural background mole fractions show that HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125 and HFC-23 have the potential to be oceanic transient tracers for the next few decades only because of the recently imposed bans on production and consumption. When the atmospheric histories of the compounds are not monotonically changing, the equilibrium atmospheric mole fraction (and ultimately the age associated with that mole fraction) calculated from their concentration in the ocean is not unique, reducing their potential as transient tracers. Moreover, HFCs have potential to be oceanic transient tracers for a longer period in the future than HCFCs as the growth rates of HFCs are increasing and those of HCFCs are decreasing in the background atmosphere. PFC-14 and PFC-116, however, have the potential to be tracers for longer periods into the future due to their extremely long lifetimes, steady atmospheric growth rates and no explicit ban on their emissions. In this work, we also derive solubility functions for HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116 in water and seawater to facilitate their use as oceanic transient tracers. These functions are based on the Clark–Glew–Weiss (CGW) water solubility function fit and salting-out coefficients estimated by the poly-parameter linear free-energy relationships (pp-LFERs). Here we also provide three methods of seawater solubility estimation for more compounds. Even though our intention is for application in oceanic research, the work described in this paper is potentially useful for tracer studies in a wide range of natural waters, including freshwater and saline lakes, and, for the more stable compounds, groundwaters.

Description: Although tide gauges are the primary source of data used to calculate multi-decadal- to century-scale rates of relative sea-level change, we question the usefulness of tide-gauge data in rapidly subsiding low-elevation coastal zones (LECZs). Tide gauges measure relative sea-level rise (RSLR) with respect to the base of associated benchmarks. Focusing on coastal Louisiana, the largest LECZ in the United States, we find that these benchmarks (n=35) are anchored an average of 21.5 m below the land surface. Because at least 60 % of subsidence occurs in the top 5 m of the sediment column in this area, tide gauges in coastal Louisiana do not capture the primary contributor to RSLR. Similarly, global navigation satellite system (GNSS) stations (n=10) are anchored an average of 〉 14.3 m below the land surface and therefore also do not capture shallow subsidence. As a result, tide gauges and GNSS stations in coastal Louisiana, and likely in LECZs worldwide, systematically underestimate rates of RSLR as experienced at the land surface. We present an alternative approach that explicitly measures RSLR in LECZs with respect to the land surface and eliminates the need for tide-gauge data in this context. Shallow subsidence is measured by rod surface-elevation table–marker horizons (RSET-MHs) and added to measurements of deep subsidence from GNSS data, plus sea-level rise from satellite altimetry. We show that for an LECZ the size of coastal Louisiana (25 000–30 000 km2), about 40 RSET-MH instruments suffice to collect useful data. Rates of RSLR obtained from this approach are substantially higher than rates as inferred from tide-gauge data. We therefore conclude that LECZs may be at higher risk of flooding within a shorter time horizon than previously assumed.

Description: The sei whale (Balaenoptera borealis) is one of the least known whale species. Information on sei whale distributions and its regional variability in the south-eastern Pacific Ocean are even more scarce than that from other areas. Vocalizations of sei whales from this region are not described yet. This research presents the first characterization of sei whale sounds recorded in Chile during the austral autumn of 2016 and 2017. Recordings were done opportunistically. A total of 41 calls were identified to be sei whale downsweeps. In 2016, calls ranged from an average maximum frequency of 105.3 Hz down to an average minimum of 35.6 Hz over 1.6 s with a peak frequency of 65.4 Hz. During 2017, calls ranged from an average maximum frequency of 93.3 down to 42.2 Hz (over 1.6 s) with a peak frequency of 68.3 Hz. The absolute minimum frequency recorded was 30 Hz and the absolute maximum frequency was 129.4 Hz. Calls generally occurred in pairs, but triplets or singles were also registered. These low-frequency sounds share characteristics with recordings of sei whales near the Hawai'ian Islands but with differences in the maximum frequencies and duration. These calls distinctly differ from sounds previously described for sei whales in the Southern Ocean and are the first documented sei whale calls in the south-eastern Pacific.

Description: A diagnostic analysis of the climatological annual mean and seasonal cycle of the Angola–Benguela Frontal Zone (ABFZ) is performed by applying an ocean frontogenetic function (OFGF) to the ocean mixing layer (OML). The OFGF reveals that the meridional confluence and vertical tilting terms are the most dominant contributors to the frontogenesis of the ABFZ. The ABFZ shows a well-pronounced semiannual cycle with two maximum (minimum) peaks in April–May and November–December (February–March and July–August). The development of the two maxima of frontogenesis is due to two different physical processes: enhanced tilting from March to April and meridional confluence from September to October. The strong meridional confluence in September to October is closely related to the seasonal southward intrusion of tropical warm water to the ABFZ that seems to be associated with the development of the Angola Dome northwest of the ABFZ. The strong tilting effect from March to April is attributed to the meridional gradient of vertical velocities, whose effect is amplified in this period due to increasing stratification and shallow OML depth. The proposed OFGF can be viewed as a tool to diagnose the performance of coupled general circulation models (CGCMs) that generally fail at realistically simulating the position of the ABFZ, which leading to huge warm biases in the southeastern Atlantic.

Description: The Mediterranean near-real-time multi-sensor processing chain has been set up and is operational in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). This work describes the main steps operationally performed to enable single ocean colour sensors to enter the multi-sensor processing applied to the Mediterranean Sea by the Ocean Colour Thematic Assembly Centre within CMEMS. Here, the multi-sensor chain takes care of reducing the inter-sensor bias before data from different sensors are merged together. A basin-scale in situ bio-optical dataset is used both to fine tune the algorithms for the retrieval of phytoplankton chlorophyll and the attenuation coefficient of light, Kd, and to assess the uncertainty associated with them. The satellite multi-sensor remote sensing reflectance spectra agree better with the in situ observations than those of the single sensors. Here, we demonstrate that the operational multi-sensor processing chain compares sufficiently well with the historical in situ datasets to also confidently be used for reprocessing the full data time series.

Description: An established tidal model, validated for present-day conditions, is used to investigate the effect of large levels of sea-level rise (SLR) on tidal characteristics around Australasia. SLR is implemented through a uniform depth increase across the model domain, with a comparison between the implementation of coastal defences or allowing low-lying land to flood. The complex spatial response of the semi-diurnal M2 constituent does not appear to be linear with the imposed SLR. The most predominant features of this response are the generation of new amphidromic systems within the Gulf of Carpentaria and large-amplitude changes in the Arafura Sea, to the north of Australia, and within embayments along Australia's north-west coast. Dissipation from M2 notably decreases along north-west Australia but is enhanced around New Zealand and the island chains to the north. The diurnal constituent, K1, is found to decrease in amplitude in the Gulf of Carpentaria when flooding is allowed. Coastal flooding has a profound impact on the response of tidal amplitudes to SLR by creating local regions of increased tidal dissipation and altering the coastal topography. Our results also highlight the necessity for regional models to use correct open boundary conditions reflecting the global tidal changes in response to SLR.

Description: A quantitative definition for the land–sea (coastal) transitional area is proposed here for wave-driven areas, based on the variability and isotropy of met-ocean processes. Wind velocity and significant wave height fields are examined for geostatistical anisotropy along four cross-shore transects on the Catalan coast (north-western Mediterranean), illustrating a case of significant changes along the shelf. The variation in the geostatistical anisotropy as a function of distance from the coast and water depth has been analysed through heat maps and scatter plots. The results show how the anisotropy of wind velocity and significant wave height decrease towards the offshore region, suggesting an objective definition for the coastal fringe width. The more viable estimator turns out to be the distance at which the significant wave height anisotropy is equal to the 90th percentile of variance in the anisotropies within a 100 km distance from the coast. Such a definition, when applied to the Spanish Mediterranean coast, determines a fringe width of 2–4 km. Regarding the probabilistic characterization, the inverse of wind velocity anisotropy can be fitted to a log-normal distribution function, while the significant wave height anisotropy can be fitted to a log-logistic distribution function. The joint probability structure of the two anisotropies can be best described by a Gaussian copula, where the dependence parameter denotes a mild to moderate dependence between both anisotropies, reflecting a certain decoupling between wind velocity and significant wave height near the coast. This wind–wave dependence remains stronger in the central bay-like part of the study area, where the wave field is being more actively generated by the overlaying wind. Such a pattern controls the spatial variation in the coastal fringe width.

Description: The North Balearic Front forms the southern branch of the cyclonic gyre in the northwestern Mediterranean Sea. Its dynamics exhibit significant seasonal variability. During autumn, the front spreads northward during the calm wind periods and rapidly moves back southward when it is exposed to strong northerly wind events such as the tramontane and mistral. These strong winds considerably enhance the air–sea exchanges. To investigate the role of air–sea exchanges in the dynamics of the North Balearic front, we used observations and a high-resolution air–sea coupled modelling system. We focused on a strong-wind event observed in late October 2012, which was well-documented during the Hydrological Cycle Mediterranean Experiment. The coupled model was able to correctly reproduce the 4 ∘C sea surface temperature drop recorded in the frontal zone together with the observed southwestward displacement of the front. The comparison between the weak wind period preceding the event and the strong-wind event itself highlighted the impact of the wind regime on the air–sea coupling. During the low-wind period the coupling is thermal and dynamical whereas during the strong-wind period the coupling is mainly thermal. The effect of air–sea exchanges on the stratification variations in the frontal zone was investigated with a stratification budget diagnosis. The stratification variations are controlled by diabatic air–sea buoyancy flux, adiabatic Ekman buoyancy flux, and advective processes. During the strong-wind period, the Ekman buoyancy flux was found to be 3 times greater than the air–sea buoyancy flux and thus played a major role in the de-stratification of the frontal zone. The role of Ekman pumping and inertial wave in the advective processes is also discussed.