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As part of the second phase of the Regional Carbon Cycle Assessment and Processes project (RECCAP2), we present an assessment of the carbon cycle of the Atlantic Ocean, including the Mediterranean Sea, between 1985 and 2018 using global ocean biogeochemical models (GOBMs) and estimates based on surface ocean carbon dioxide (CO2) partial pressure (pCO2 products) and ocean interior dissolved inorganic carbon observations. Estimates of the basin-wide long-term mean net annual CO2 uptake based on GOBMs and pCO2 products are in reasonable agreement (−0.47 ± 0.15 PgC yr−1 and −0.36 ± 0.06 PgC yr−1, respectively), with the higher uptake in the GOBM-based estimates likely being a consequence of a deficit in the representation of natural outgassing of land derived carbon. In the GOBMs, the CO2 uptake increases with time at rates close to what one would expect from the atmospheric CO2 increase, but pCO2 products estimate a rate twice as fast. The largest disagreement in the CO2 flux between GOBMs and pCO2 products is found north of 50°N, coinciding with the largest disagreement in the seasonal cycle and interannual variability. The mean accumulation rate of anthropogenic CO2 (Cant) over 1994–2007 in the Atlantic Ocean is 0.52 ± 0.11 PgC yr−1 according to the GOBMs, 28% ± 20% lower than that derived from observations. Around 70% of this Cant is taken up from the atmosphere, while the remainder is imported from the Southern Ocean through lateral transport

For the first time, four dedicated hydrographic cruises—one in each season—took place in 2015 around the Canary Islands to determine the seasonality of the flows at the eastern boundary of the North Atlantic Subtropical Gyre. The Canary Current (CC) is the eastern boundary current of the North Atlantic Subtropical Gyre and links the Azores Current with the North Equatorial Current. The 2015 estimations show that the CC has a seasonal behavior in its path and strength, flowing on its easternmost position in winter (3.4 ± 0.3 Sv), through the Canary Islands in spring (2.1 ± 0.7 Sv) and summer (2.0 ± 0.6 Sv) and on its westernmost position in fall (3.2 ± 0.4 Sv). At the Lanzarote Passage (LP), the dominant flow is southward except in fall, where a northward transport is observed at the surface (1.1 ± 0.3 Sv) and intermediate (1.3 ± 0.2 Sv) layers. Combining all the available transport estimations, a historical composite observational seasonal cycle is constructed which fits the 2015 seasonal cycle. Hence, a solid seasonal cycle is constructed supported by all the available observations in the area. The LP seasonal cycle and its seasonal amplitude match the seasonal cycle and amplitude of the Atlantic Meridional Overturning Circulation (AMOC) measured by the RAPID-MOCHA data array. These results indicate that the seasonal cycle of the AMOC of the RAPID-MOCHA data array is driven by the dynamics of the eastern boundary current system.

The South Atlantic Ocean plays a key role in the heat exchange of the climate system, as it hosts the returning flow of the Atlantic Meridional Overturning Circulation (AMOC). To gain insights on this role, using data from three hydrographic cruises conducted in the South Atlantic Subtropical gyre at 34.5°S, 24°S, and 10°W, we identify water masses and compute absolute geostrophic circulation using inverse modeling. In the upper layers, the currents describe the South Atlantic anticyclonic gyre with the northwest flowing Benguela Current (26.3 ± 2.0 Sv at 34.5°S, and 21.2 ± 1.8 Sv at 24°S) flowing above the Mid-Atlantic Ridge (MAR) between 22.4°S and 28.4°S (−19.2 ± 1.4 Sv), and the southward flowing Brazil Current (−16.5 ± 1.3 Sv at 34.5°S, and −7.3 ± 0.9 Sv at 24°S); the deep layers feature the southward transports of Deep Western Boundary Current (−13.9 ± 3.0 Sv at 34.5°S, and −8.7 ± 3.8 Sv at 24°S) and Deep Eastern Boundary Current (−15.1 ± 3.5 Sv at 34.5°S, and −16.3 ± 4.7 Sv at 24°S), with the interbasin west-to-east flow close to 24°S (7.5 ± 4.4 Sv); the abyssal waters present northward mass transports through the Argentina Basin (5.6 ± 1.1 Sv at 34.5°S, and 5.8 ± 1.5 Sv at 24°S) and Cape Basin (8.6 ± 3.5 Sv at 34.5°S–3.0 ± 0.8 Sv at 24°S) before returning southward (−2.2 ± 0.7 Sv at 24°S to −7.9 ± 3.6 Sv at 34.5°S), without any interbasin exchange across the MAR. In addition, we compute the upper AMOC strength (14.8 ± 1.0 and 17.5 ± 0.9 Sv), the equatorward heat transport (0.30 ± 0.05 and 0.80 ± 0.05 PW), and the freshwater flux (0.18 ± 0.02 and −0.07 ± 0.02 Sv) at 34.5°S and 24°S, respectively

The South Atlantic Ocean plays a key role in the heat exchange of the climate system, as it hosts the returning flow of the Atlantic Meridional Overturning Circulation (AMOC). To gain insights on this role, using data from three hydrographic cruises conducted in the South Atlantic Subtropical gyre at 34.5°S, 24°S, and 10°W, we identify water masses and compute absolute geostrophic circulation using inverse modeling. In the upper layers, the currents describe the South Atlantic anticyclonic gyre with the northwest flowing Benguela Current (26.3 ± 2.0 Sv at 34.5°S, and 21.2 ± 1.8 Sv at 24°S) flowing above the Mid-Atlantic Ridge (MAR) between 22.4°S and 28.4°S (−19.2 ± 1.4 Sv), and the southward flowing Brazil Current (−16.5 ± 1.3 Sv at 34.5°S, and −7.3 ± 0.9 Sv at 24°S); the deep layers feature the southward transports of Deep Western Boundary Current (−13.9 ± 3.0 Sv at 34.5°S, and −8.7 ± 3.8 Sv at 24°S) and Deep Eastern Boundary Current (−15.1 ± 3.5 Sv at 34.5°S, and −16.3 ± 4.7 Sv at 24°S), with the interbasin west-to-east flow close to 24°S (7.5 ± 4.4 Sv); the abyssal waters present northward mass transports through the Argentina Basin (5.6 ± 1.1 Sv at 34.5°S, and 5.8 ± 1.5 Sv at 24°S) and Cape Basin (8.6 ± 3.5 Sv at 34.5°S–3.0 ± 0.8 Sv at 24°S) before returning southward (−2.2 ± 0.7 Sv at 24°S to −7.9 ± 3.6 Sv at 34.5°S), without any interbasin exchange across the MAR. In addition, we compute the upper AMOC strength (14.8 ± 1.0 and 17.5 ± 0.9 Sv), the equatorward heat transport (0.30 ± 0.05 and 0.80 ± 0.05 PW), and the freshwater flux (0.18 ± 0.02 and −0.07 ± 0.02 Sv) at 34.5°S and 24°S, respectively.

On top of the global sampling efforts carried out since the 1990s under WOCE and GOSHIP programs, the AMOC is being monitored with several mooring arrays in key latitudes. However, the earlier results date back to the year 2000, so these mooring arrays cannot address longer-term decadal changes in the Atlantic Ocean. In contrast, hydrographic data offers the opportunity to understand this longer-term subsurface variability. To address this issue, we have carried out three inverse models in a neutral density framework, one for each of the last three decades (1990-99, 2000-09 and 2010-19). We have used hydrographic data for the entire Atlantic Ocean, covering the whole latitudinal extent of the Atlantic (Figure 1). Answering the question of the slowing of the AMOC is very important, and the contrasting results between in situ observations and model reconstructions is a significant contribution to the debate.

The change in anthropogenic CO2 (Canth) in the Atlantic Ocean is linked to the Atlantic Meridional Overturning Circulation (AMOC), that redistributes Canth meridionally and in depth. We have employed direct biogeochemical measurements and hydrographic data from the last 30 years, adjusted using inverse models for each decade with both physical and biogeochemical constraints. We then have computed the meridional transports and the vertical transports between two sections at the interphases by advection and diffusion. We have focused on the repeated sections at three latitudes—30°S, 24, and 55°N, dividing the Atlantic into two boxes. We have divided the net transport into upper, deep and abyssal layers, with an upper and abyssal northward transport of Canth and a southward component in deep layers. The change in time in the net transports of Canth appears to be mainly due to modifications in the transport of upper layers. The lower layer of the AMOC, a combination of deep and abyssal waters, maintain more consistent transports in time. Vertical advection plays an important role in the North Atlantic, exporting Canth from upper to deep layers. In the South Atlantic, the newly formed Antarctic Bottom Water exports Canth from abyssal to deep layers. The strong gradient in Canth concentration at the interphase of upper and deep layers results in a strong vertical diffusion

The meridional circulation and transport at 32°S in the Pacific Ocean in 1992 and 2017 are compared with analogous data from 2003 and 2009 computed by Hernández-Guerra and Talley (2016). The hydrographic data come from the GO-SHIP database and an inverse box model has been applied with similar constraints as in Hernández-Guerra and Talley (2016). In 1992, 2003 and 2017 the pattern of the overturning streamfunction and circulation are similar, but in 2009 the pattern of the circulation changes in the whole water column. The horizontal distribution of mass transports at all depths in 1992 and 2017 resembles the familiar shape of the “classical gyre” also observed in 2003 and is notably different to the “bowed gyre” found in 2009. The hydrographic data have been compared with data obtained from the numerical modelling outputs of ECCO, SOSE, GLORYS, and MOM. Results show that none of these models properly represents the “bowed gyre” circulation in 2009, and this change in circulation pattern was not observed during the entire length of model simulations. Additionally, the East Australian Current in the western boundary presents higher mass transport in the hydrographic data than in any numerical modelling output. Its poleward mass transport ranges from −35.1 ± 2.0 Sv in 1992 to −54.3 ± 2.6 Sv in 2003. Conversely, the Peru-Chile Current is well represented in models and presents an equatorward mass transport from 2.3 ± 0.8 Sv in 2009 to 4.4 ± 1.0 Sv in 1992. Furthermore, the Peru-Chile Undercurrent presents a more intense poleward mass transport in 2009 (−3.8 ± 1.2 Sv). In addition, the temperature and freshwater transports in 1992 (0.42 ± 0.12 PW and 0.26 ± 0.08 Sv), 2003 (0.38 ± 0.12 PW and 0.25 ± 0.02 Sv), and 2017 (0.42 ± 0.12 PW and 0.34 ± 0.08 Sv) are similar, but significantly different from those in 2009 (0.16 ± 0.12 PW and 0.50 ± 0.03 Sv, respectively). To clarify the causes of these different circulation schemes, a linear Rossby wave model is adopted, which inc

Four Pressure-equipped Inverted Echo Sounders (PIES) were deployed at about 10°W, between 19 and 35°S, the South Atlantic Gateway (SAGA), in order to determine the zonal flows in the South Atlantic. Those PIES will allow to observe the circulation of two water masses, the South Atlantic Central Water (SACW) and the North Atlantic Deep Water (NADW), that flow in opposite directions across the South Atlantic, between Cape town and Brazil, through the SAGA. The measurements from the PIES, together with historical hydrographic data, permit to estimate the profiles of temperature and salinity of the water column, and therefore the density. Besides, using the thermal-wind equation, it is possible to retrieve the geostrophic velocity from an array of PIES. In order to get those estimations of temperature and salinity, it is necessary to determine the Gravest Empirical Mode (GEM), a relationship between the acoustic travel time observed by the PIES and the historical observations of salinity and temperature in the study area. In this work, we will show the GEM estimated for the SAGA, calculated using historical hydrographic data from CTDs and Argo Float, as well as, the estimations of the error in the geostrophic transport.

The Atlantic Meridional Circulation (AMOC) plays a major role in the life cycle of nutrients and chemical species in the ocean, as they are introduced into the ocean by deep water formation and resurface as part of the upwelling. We aim to obtain decadal changes in the latitudinal and vertical distribution of nutrients and carbon species in the Atlantic Ocean, using data from three inverse models carried out for the 1990-99, 2000-09 and 2010-19. We have used in situ quality-controlled data from GLODAPv2, the neural network CANYON-B for nutrients, and total alkalinity and dissolved inorganic carbon. We then compute the transport of each property, taking into account the results of mass transport balance from the inverse model for each decade. The inverse model has been applied to the whole Atlantic basin with 11 neutral density layers. With these results, we will be able to find out if the CO2 variability arises from changes in circulation or from other processes. On top of that, the availability of several zonal sections for the Atlantic enables the latitudinal division in boxes in which we may find differences in the regional anthropogenic carbon uptake. Our results will allow us to estimate how much anthropogenic carbon is being released or captured within each box, as well as the balance for other variables related to the carbon cycle

Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems with high species diversity, and in some cases, are densely populated by benthic organisms, such corals, gorgonians, and sponges. In this study, we describe the oceanographic conditions over seamounts and other underwater features in the path of the Mediterranean Outflow Water (MOW), where populations of benthic suspensions feeders have been observed. Using CTD, LADPC and biochemical measurements carried out in the Ormonde and Formigas seamounts and the Gazul mud volcano (Northeast Atlantic), we show that Taylor caps were not observed in any of the sampled features. However, we point out that the relatively high values of the Brunt–Väisälä frequency in the MOW halocline, in conjunction with the slope of the seamount flanks, set up conditions for the breakout of internal waves and amplification of the currents. This may enhance the vertical mixing, resuspending the organic material deposited on the seafloor and, therefore, increasing the food availability for the communities dominated by benthic suspension feeders. Thus, we hypothesize that internal waves could be improving the conditions for benthic suspension feeders to grow on the slope of seamounts.

Seamounts constitute an obstacle to the free ocean flow giving rise to a variety of hydrodynamical processes and phenomena such as, among others, Taylor columns/caps. As a consequence of that, seamounts may turn into very productive ecosystems with high biodiversity, which provide a particularly good environment for the settle of some organisms, acting as stepping stones and contributing to its dispersal. In this study, we verify if these oceanographic effects explain the presence of cold-water corals of Mediterranean origin in the Atlantic. To achieve this, CTD, LADPC and biochemical measurements were carried out in three seamounts in the path of the Mediterranean Outflow Water (MOW): the Gazul mud volcano, and the Ormonde and Formigas seamounts. Taylor columns were not observed in any of the three sampled areas. In fact, the oceanographic processes in those areas are more influenced by the vertical distribution of water masses, which determine the stability of the water column. Moreover, the high values of the Brunt-Väisälä frequency around the MOW halocline can lead to the formation of internal waves. These perturbations in the water column can enhance the vertical mixing, producing suspension, which, in turn, could affect the vertical distribution of cold-water corals.

Seamounts constitute an obstacle to the free ocean flow, modifying the patter of circulation. As a result of these alterations, a variety of hydrodynamical processes and phenomena may take place in seamounts, among others, Taylor columns/caps. These oceanographic effects may turn seamounts into very productive ecosystems with high biodiversity. Under these conditions seamounts provide a particularly good environment for the settle of some organisms, acting as stepping stones and contributing to its dispersal. In this study, we verify if these oceanographic effects explain the presence of cold-water corals of Mediterranean origin in the Atlantic. To achieve this, three seamounts in the path of the Mediterranean Outflow Water (MOW) through the Eastern North Atlantic were selected: the Gazul mud volcano, and the Ormonde and Formigas seamounts. In order to determine the hydrographic and dynamical conditions in each one of the three locations, CTD, LADPC and biochemical observations were carried out. Taylor columns were not observed in any of the three sampled areas. Although we found suggestions of upwelling/downwelling systems, their effect was barely noticed in the circulation pattern. The oceanographic processes in those areas are more influenced by the vertical distribution of water masses, which determine the stability of the water column. Moreover, the high values of the Brunt-Väisälä frequency around the MOW halocline can lead to the formation of internal waves. These perturbations in the water column can enhance the vertical mixing, producing suspension, which, in turn, could affect the vertical distribution of cold-water corals.

The deep water thermohaline anomaly, named Western Mediterranean Transition (WMT) (CIESM, 2009) was first observed in winter 2005 (López-Jurado et al. 2005) NE of Menorca, at a deep station (2500 m water depth) sampled on a seasonal basis since 2001, within the RADMED Program (López-Jurado et al. 2015). To improve the knowledge of the evolution of this thermohaline anomaly, an instrumented mooring was deployed in 2015 at the same station during the ATHAPOC Project. This mooring is composed of 5 current meters, 8 CTDs, 8 thermistors and covers most of the water column, allowing for a continuous record of salinity, temperature and currents that characterize the different water masses present in the region, including those that contribute to the anomaly. The mooring also includes 1 turbidity sensor and 2 sediment traps to evaluate the sediment dynamics and the associated particle fluxes. Designed to be operative at least during two years, this contribution presents the preliminary results of the first 9 months of deployment, when 40 days period oscillations are observed from the sea bottom to 400 m below the surface

The MEDWAVES, The MEDWAVES (MEDiterranean out flow WAter and Vulnerable EcosystemS) cruise was developed in the framework of the ATLAS project, with the main objective of determining areas under the influence of the Mediterranean Overflow Water within the Mediterranean and Atlantic areas. MEDWAVES cruise (LEG 1: Cadiz – Punta Delgada and LEG 2: Punta Delgada – Málaga) was completed between September-October 2016 on board the Spanish R/V Sarmiento de Gamboa. Within the specific aim of evaluating the biogeochemichal role of the Mediterranean Water, over and around the Formigas, Ormonde and Seco de los Olivos seamounts, and the Gazul Mud volcano, some CO2 system variables were measured on board (pH, total alkalinity and carbonate ion concentration) together with dissolved oxygen samples. The chemistry of the CO2 in the Mediterranean Sea is very particular, characterised by warm, salty and high alkalinity waters [1]. The Mediterranean Water goes into the Atlantic Ocean through the strait of Gibraltar, being clearly identified as the most saline water of the water column located at approximately 1000 dbar [2]. Apart from the water mass characteristic, other properties and organism characteristics of the Mediterranean Sea are spilt into the Atlantic. According to the objectives of MEDWAVES cruise and taking into account the fine scale sampling made over the 400m above the bottom, we will characterise the CO2 system of the four different areas, trying to distinguish the signature of the Mediterranean Water in each seamount. The presence of depth cold water coral in those seamounts is poorly known and we would like to connect those of Mediterranean Sea with those of the continental shelf of Portugal, the Azores and the Mid-Atlantic Ridge with the CO2 variables. Hence, a second step will be to evaluate the connexion between the cold water corals and the CO2 system.

The MEDWAVES (MEDiterranean out flow WAter and Vulnerable EcosystemS) cruise targeted areas under the potential influence of the MOW within the Mediterranean and Atlantic realms. These include seamounts where Cold-water corals (CWCs) have been reported but that are still poorly known, and which may act as essential “stepping stones” connecting fauna of seamounts in the Mediterranean with those of the continental shelf of Portugal, the Azores and the Mid-Atlantic Ridge. During MEDWAVES sampling has been conducted in two of the case studies of ATLAS: Case study 7 (Gulf of Cádiz-Strait of Gibraltar-Alboran Sea) and Case study 8 (Azores). The initially targeted areas in the Atlantic were: the Gazul Mud volcano, in the Gulf of Cádiz (GoC) area, included in the case study 7, and the Atlantic seamounts Ormonde (Portuguese shelf) and Formigas (by Azores), both part of the case study 8. In the Mediterranean the targeted areas were The Guadiaro submarine canyon and the Seco de los Olivos (also known as Chella Bank) seamount. Unfortunately it was not possible to sample in Guadiaro due to time constraints originated by adverse meteorological conditions which obligate us to reduce the time at sea focusing only in 4 of the 5 initially planned areas. MEDWAVES was structured in two legs; the first leg took place from the 21st September (departure from Cádiz harbour in Spain) to the 13th October 2016 (arrival in Ponta Delgada, São Miguel, Azores, Portugal took place the 8th of October due to the meteorological conditions that obligated to conclude the first leg earlier as planned). during the Leg 1 sampling was carried out in Gazul, Ormonde and Formigas. The second leg started the 14th October (departure from Ponta Delgada) and finished the 26th October (arrival in Málaga harbour, Spain). MEDWAVES had a total of 30 effective sampling days, being 6 days not operative due to the adverse meteorological conditions experienced during the first leg which forced us to stay in Ponta Delgada

High resolution grain-size results of core KTA-GC-05 are presented in order to infer millennial and submillennial changes of open ocean transport processes. The core was collected using a gravity corer on board the B/O Sarmiento de Gamboa during PALEOACID cruise of CATARINA project in August 2012. It is located in the eastern basin of the North Atlantic Ocean at 46º 11.157¿N and 18º 18.837¿W, at a depth of 3939 meters. The core length reaches 337 cm and an expected age of around 120 ka. Grain-size analyses were performed on both the total fraction (organic matter removed with 10% H2O2) and the non-carbonate fraction (both organic matter and carbonate were removed with H2O2 and HCl, respectively). Grain-size distributions were measured with a Beckman Coulter LS 13 320 laser particle size analyser (CLS), which determines particle grain-sizes between 0.04 and 2000 m as volume percentages based on diffraction laws (McCave et al., 1986; Agrawal et al., 1991). Results for every sample include the median (D50), the mean and the first mode. Also percentages of sand, silt and clay fractions are shown. In addition, the UP10 size (i.e. particles coarser than 10 m) is considered, which adds the fine sand subpopulation to the sortable silt size fraction (SS, 10-63 m). The sortable silt size (SS) has been broadly used as a proxy to infer the intensity of deep water currents (McCave et al., 1995). However, since strong currents are also able to rework particles coarser than 63 m, the UP10 fraction has been also considered for the study of paleocurrent intensity (Frigola et al., 2008). Median and mean values of bulk and non-carbonated sediment fractions show different features thus pointing to different processes controlling the deposition of both fractions. Nevertheless, the noncarbonate fraction better represents the intensity of bottom currents (McCave et al., 1995) or the influence of iceberg discharge. Clear differences of sedimentological data between the Last Glaciation (MIS

Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems with high species diversity, and in some cases, are densely populated by benthic organisms, such corals, gorgonians, and sponges. In this study, we describe the oceanographic conditions over seamounts and other underwater features in the path of the Mediterranean Outflow Water (MOW), where populations of benthic suspensions feeders have been observed. Using CTD, LADPC and biochemical measurements carried out in the Ormonde and Formigas seamounts and the Gazul mud volcano (Northeast Atlantic), we show that Taylor caps were not observed in any of the sampled features. However, we point out that the relatively high values of the Brunt–Väisälä frequency in the MOW halocline, in conjunction with the slope of the seamount flanks, set up conditions for the breakout of internal waves and amplification of the currents. This may enhance the vertical mixing, resuspending the organic material deposited on the seafloor and, therefore, increasing the food availability for the communities dominated by benthic suspension feeders. Thus, we hypothesize that internal waves could be improving the conditions for benthic suspension feeders to grow on the slope of seamounts.