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The ocean carbonate system is critical to monitor because it plays a major role in regulating Earth's climate and marine ecosystems. It is monitored using a variety of measurements, and it is commonly understood that all components of seawater carbonate chemistry can be calculated when at least two carbonate system variables are measured. However, several recent studies have highlighted systematic discrepancies between calculated and directly measured carbonate chemistry variables and these discrepancies have large implications for efforts to measure and quantify the changing ocean carbon cycle. Given this, the Ocean Carbonate System Intercomparison Forum (OCSIF) was formed as a working group through the Ocean Carbon and Biogeochemistry program to coordinate and recommend research to quantify and/or reduce uncertainties and disagreements in measurable seawater carbonate system measurements and calculations, identify unknown or overlooked sources of these uncertainties, and provide recommendations for making progress on community efforts despite these uncertainties. With this paper we aim to (1) summarize recent progress toward quantifying and reducing carbonate system uncertainties; (2) advocate for research to further reduce and better quantify carbonate system measurement uncertainties; (3) present a small amount of new data, metadata, and analysis related to uncertainties in carbonate system measurements; and (4) restate and explain the rationales behind several OCSIF recommendations. We focus on open ocean carbonate chemistry, and caution that the considerations we discuss become further complicated in coastal, estuarine, and sedimentary environments

In this work, we present, for the first time, the seawater carbonate system measurements of two coastal time-series in the NW Mediterranean Sea, L’Estartit Oceanographic Station (EOS; 42.05°N 3.2542°E) and the Blanes Bay Microbial Observatory (BBMO; 41.665°N 2.805°E). At these two time-series, measurements of total alkalinity (TA), pH, and associated variables, such as dissolved inorganic nutrients, temperature, and salinity, have been performed monthly since 2010 in surface seawater. Seasonality and seasonal amplitude are analogous in both time-series, with seasonality in pHT in situ(pH at in situ seawater conditions on the total hydrogen ion scale) primarily determined by seasonality in sea surface temperature. The evaluated pHT in situtrends at BBMO (-0.0021 ± 0.0003 yr-1) and EOS (-0.0028 ± 0.0005 yr-1) agree with those reported for coastal and open ocean surface waters in the Mediterranean Sea and open ocean surface waters of the global ocean, therefore indicating that these time-series are representative of global ocean acidification signals despite being coastal. The decreases in pHT in situcan be attributed to increases in total dissolved inorganic carbon (DIC; 1.5 ± 0.4 µmol kg-1 yr-1 at BBMO and 1.6 ± 0.6 µmolESkg-1 yr-1 at EOS) and sea surface temperature (0.08 ± 0.02 °C yr-1 at BBMO and 0.08 ± 0.04 °C yr-1 at EOS). The increases in carbon dioxide fugacity (fCO2; 2.4 ± 0.3 µmol kg-1 yr-1 at BBMO and 2.9 ± 0.6 µmol kg-1 yr-1 at EOS) follow the atmospheric CO2 forcing, thus indicating the observed DIC increase is related to anthropogenic CO2 uptake. The increasing trends in TA (1.2 ± 0.3 µmol kg-1 yr-1 at BBMO and 1.0 ± 0.5 µmol kg-1 yr-1 at EOS) buffered the acidification rates, counteracting 60% and 72% of the pHT in situdecrease caused by increasing DIC at EOS and BBMO, respectively. Once accounted for the neutralizing effect of TA increase, the rapid sea surface warming plays a larger role in the observed pH decreases (43% at EOS and 62% at BBMO) than t

The database provides discrete measurements of seawater carbonate system variables (pH and total alkalinity) and ancillary variables (dissolved inorganic nutrients, temperature, salinity, and pressure) in surface seawater collected at two time-series stations, EOS and BBMO, conducted over 2009–2022. The database compiles all the information, measurements, and analysis performed (including date, location, and equipment used). All chemical analyses were assigned a quality indicator. At the two time-series stations, monthly sampling of surface seawater was performed. BBMO temperature and salinity were measured with a SAIV-A/S-SD204 CTD, while at EOS temperature was measured with reversible thermometers and salinity was measured with two CTDs, a SAIV-A/S-SD204 CTD and a CTD75M. For consistency between BBMO and EOS datasets, the salinity record obtained with the SAIV-A/S-SD204 CTD is considered in this study. When salinity values from the SAIV-A/S-SD204 CTD were missing, salinity values from CTD75M were used. The salinity records obtained with the two CTDs were quality controlled and calibrated to obtain a consistent dataset. Discrete seawater samples for pH, TA, and dissolved inorganic nutrients were taken monthly from a depth of 0.5 m both stations (with a Niskin bottle at EOS and in 10 L polyethylene carboys at BBMO). The biogeochemical variables shown in the database are pH reported on the total hydrogen ion scale at 25 °C (PH_TOT), total alkalinity (ALKALI), and dissolved inorganic nutrients (phosphate, PHSPHT, Silicate, SILCAT, and Nitrate, NITRAT). PH_TOT data were obtained by the spectrophotometric method with m-cresol purple using a Cary 100 UV-vis spectrophotometer containing a 25 °C-thermostated cells holder following Clayton and Byrne (1993). Triplicate samples were taken. At EOS, three cylindrical optical glass cells with a 10 cm path-length were filled directly from the Niskin bottle right after reaching land, ready to be analyzed in the next 3–4 hrs. At BB

Coastal regions exhibit a wide range of pH changes resulting from multiple factors with high spatiotemporal variability, hindering the detection of anthropogenically-driven ocean acidification signals. In this work, we evaluate the seasonal and long-term ocean acidification changes and their drivers in surface waters of two coastal time-series in the northwestern Mediterranean Sea: L'Estartit Oceanographic Station (EOS; 42.05N 3.2542E) and Blanes Bay Microbial Observatory (BBMO; 41.665N 2.805E). These two coastal time-series are located off the coast of Girona (Spain) ~60 km apart, being EOS farther from the coast than BBMO (~3.5 km and ~850 m, respectively), with the former being by a natural reserve and the latter outside a port area; therefore land-ocean interactions and anthropogenic activities should lead to higher variability at BBMO than at EOS. In these two time-series stations, measurements of total alkalinity (TA) and pH and associated variables, such as inorganic nutrients, temperature and salinity, have been performed monthly since 2010. We also assess the impact of distance to land and monitoring frequency on the detection of anthropogenically-driven ocean acidification signals in coastal time-series by comparing our results with those from the French coastal time-series station Point B (43.686N 7.316E; ~400 m from the coast of Villefranche-sur-Mer), also in the northwestern Mediterranean Sea and influenced by the same surface currents as EOS and BBMO, but where total dissolved inorganic carbon and TA are measured weekly

Concentration of ion carbonate has become the fifth measurable variable of the seawater CO2 system since the publication of the work by Byrne and Yao (2008) introducing a spectrophotometric method similar to the standard pH procedure. However, opposite to pH, the ion carbonate method has been refined and updated in a series of works(Easley et al., 2013; Patsavas et al., 2015; Sharp et al., 2017 and Sharp and Byrne, 2019) that introduced modifications in the equations relating the UV absorbance measurements and the final ion carbonate concentration, the reagent used and other details. Except for the USA seminal research group, and the two Spanish teams at the IEO A Coruña and IIM-CSIC, no other oceanographic group has published research data using the ion carbonate spectrophotometric methods. The work by Fajar et al. (2015) used a collection of Spanish cruises from 2009 to 2014 to compare the initial spectrophotometric ion carbonate methods by Byrne and Yao (2008) and Easley et al. (2013)., The current database comprises a set of 9 one-time cruises and one coastal time-series run by the above-mentioned Spanish CO2 research groups, expanding from 2009 to 2020, where ancillary and CO2 measurements (pH, total alkalinity and total inorganic carbon) have been performed, along with spectrophotometric measurements of ion carbonate, which followed the time evolution of the ion carbonate published approaches. The database compiles all the information (cruise identification, time, location, equipment used), measurements and analysis (pressure, temperature, salinity, pH, total alkalinity, total inorganic carbon, silicate and phosphate, UV absorbance ratios for spectrophotometric ion carbonate measurements from two different reagents [PbCl2 and Pb(ClO4)2] needed to perform any CO2 internal consistency analysis. All chemical analysis were assigned a quality indicator

The GEOVIDE cruise was carried out coast to coast between Portugal and Newfoundland via the south tip of Greenland, following the OVIDE line in the eastern part and crossing the Labrador Sea in the western part. The classical hydrographic rosette was cast 163 times at 78 different geographical positions called stations. While the CTD-O2 probe acquired continuous profiles of the “physical” variables (pressure, temperature, salinity and dissolved oxygen), 22 Niskin bottles were closed at different levels during the upcast to provide samples for biogeochemical analysis. After calibration, we find precisions for pressure, temperature, salinity and dissolved oxygen that fit the GO-SHIP international quality requirements. In parallel, but not simultaneously, a trace-metal rosette (TMR) was cast 53 times, also acquiring profiles of physical variables, and equipped with 24 Go-Flo bottles adapted for the sampling of trace metals. Depending on the number of operations, stations were identified as “Short” (one single CTD cast), “Large” (3 CTD casts), “XLarge” (up to 6) and “Super” (up to 11). All along the track of the ship, current magnitude and direction was measured by Ship Acoustic Doppler Current Profilers, down to 1000m depth

The spectrophotometric methodology for carbonate ion determination in seawater was first published in 2008 and has been continuously evolving in terms of reagents and formulations. Although being fast, relatively simple, affordable, and potentially easy to implement in different platforms and facilities for discrete and autonomous observations, its use is not widespread in the ocean acidification community. This study uses a merged overdetermined CO2 system data set (carbonate ion, pH, and alkalinity) obtained from 2009 to 2020 to assess the differences among the five current approaches of the methodology through an internal consistency analysis and discussing the sources of uncertainty. Overall, the results show that none of the approaches meet the climate goal (± 1 % standard uncertainty) for ocean acidification studies for the whole carbonate ion content range in this study but usually fulfill the weather goal (± 10 % standard uncertainty). The inconsistencies observed among approaches compromise the consistency of data sets among regions and through time, highlighting the need for a validated standard operating procedure for spectrophotometric carbonate ion measurements as already available for the other measurable CO2 variables.

The spectrophotometric methodology for carbonate ion determination in seawater was first published in 2008 and has been continuously evolving in terms of reagents and formulations. Although being fast, relatively simple, affordable, and potentially easy to implement in different platforms and facilities for discrete and autonomous observations, its use is not widespread in the ocean acidification community. This study uses a merged overdetermined CO2 system data set (carbonate ion, pH, and alkalinity) obtained from 2009 to 2020 to assess the differences among the five current approaches of the methodology through an internal consistency analysis and discussing the sources of uncertainty. Overall, the results show that none of the approaches meet the climate goal (± 1 % standard uncertainty) for ocean acidification studies for the whole carbonate ion content range in this study but usually fulfill the weather goal (± 10 % standard uncertainty). The inconsistencies observed among approaches compromise the consistency of data sets among regions and through time, highlighting the need for a validated standard operating procedure for spectrophotometric carbonate ion measurements as already available for the other measurable CO2 variables.

Understanding the ocean carbon sink and its future acidification-derived changes requires accurate and precise measurements with good spatiotemporal coverage. In addition, a deep knowledge of the thermodynamics of the seawater carbonate system is key to interconverting between measured and calculated variables. To gain insights into the remaining inconsistencies in the seawater carbonate system, we assess discrete water column measurements of carbon dioxide fugacity (fCO2), dissolved inorganic carbon (DIC), total alkalinity (TA), and pH measured with unpurified indicators, from hydrographic cruises in the Atlantic, Pacific, and Southern Oceans included in GLODAPv2.2020 (19,013 samples). An agreement of better than ± 3% between fCO2 measured and calculated from DIC and pH is obtained for 94% of the compiled dataset, while when considering fCO2 measured and calculated from DIC and TA, the agreement is better than ± 4% for 88% of the compiled dataset, with a poorer internal consistency for high-CO2 waters. Inspecting all likely sources of uncertainty from measured and calculated variables, we conclude that the seawater carbonate system community needs to (i) further refine the thermodynamic model of the seawater carbonate system, especially K2, including the impact of organic compounds and other acid-base systems on TA; (ii) update the standard operating procedures for the seawater carbonate system measurements following current technological and analytical advances, paying particular attention to the pH methodology that is the one that evolved the most; (iii) encourage measuring discrete water column fCO2 to further check the internal consistency of the seawater carbonate system, especially given the new era of sensor-based seawater measurements; and (iv) develop seawater Certified Reference Materials (CRMs) for fCO2 and pH together with seawater CRMs for TA and DIC over the range of values encountered in the global ocean. Our conclusions also suggest the need for a r

The global ocean has mediated the atmospheric CO2 increase derived from human activities by absorbing about 30% of the anthropogenic emissions since the industrial revolution. CO2 enters the surface ocean through air-sea gas exchange and its uptake rate is limited by the upper-ocean-to-interior transport, i.e., the large-scale dynamics that control the ventilation of the interior ocean. Hence, the high-latitude oceans, where deep convective overturning and subduction occur, are the areas of strongest CO2 uptake and deep-ocean CO2 sequestration. Amongst those high-latitude oceans, the North Atlantic is one of the most important CO2 sinks thanks to the Atlantic meridional overturning circulation, where the deep-water formation provides the pathway for CO2 into the interior ocean. Here a database analysis is used to study the long-term trends in ocean acidification in the different water masses. I will also discuss the physical and chemical drivers of the ocean acidification and the expected changes for future increases in atmospheric CO2. Finally, I will present my Severo Ochoa postdoctoral project, which focuses on assessing the changes in alkalinity naturally occurring in the Mediterranean Sea and how they affect the ocean acidification signal in the Mediterranean Sea and the North Atlantic

The pH spectrophotometric method is the gold standard to measure pH in the ocean and detect ocean acidification trends due to the anthropogenic carbon uptake from the atmosphere into the ocean. The pH method has an accuracy of about 0.003 and a precision of about 0.0004 pH units. The method has evolved since the 1990s when defined using manual approaches and unpurified dyes to currently automated methods using expensive and cumbersome to obtain purified dyes. From a collection of about 300 paired measurements of unpurified and purified pH measurements along with DIC and TA from natural samples in the Eastern North Atlantic and Mediterranean Sea we find that contrary to expected, unpurified and purified pH measurements calculated with the proper corresponding functions agree to within 0.003 pH units for waters with pH >7.95, while waters with lower pH, calculated unpurified pH is higher than purified pH. Applying the purposed correction from unpur to pur pH as explained in the literature is not straight forward, the community risks for an incoherence in the pH time series. Clearly, we need a definition and evaluation of the unpur to pur correction on real seawater samples by different labs, and look for a consensus agreement on seawater pH definition (scales!, ionic model), metrology, and on the Standard Operational Procedure, where loose issues are still present

About 30% of the carbon dioxide derived from human activities (CANTH) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Friedlingstein et al., 2021), with the North Atlantic (NA) being one of the largest CANTH sinks per unit area (Khatiwala et al., 2013; Sabine et al., 2004). In the NA, oceanic CANTH uptake strongly relies on the meridional overturning circulation and the associated regional winter deep convection. In fact, the formation and deep spreading of Labrador Sea Water stands as a critical CANTH gateway to intermediate and abyssal depths. The NA CANTH uptake has fluctuated over the years according to changes in the North Atlantic Oscillation. Biennial observation of the marine carbonate system along the Go-Ship A25-OVIDE section has allowed us assessing the decadal and interannual variability of the CANTH storage in the subpolarNA from 2002 to 2021. In this study, we investigate 1) the trend of CANTH and 2) the relationship between the CANTH saturation, the apparent oxygen utilization, and the ventilation of the water masses between the A25-OVIDE section and the Greenland-Iceland-Scotland sills during 2002-2021. We divided the A25-OVIDE section into three main basins (Irminger, Iceland, and Eastern NA). Our results show that the Irminger Basin presents a more homogenous CANTH profile and higher CANTH saturation values at depth than the other two basins, which is related to the pronounced convective activity in the Irminger Basin. In contrast, the Eastern NA Basin has higher CANTH values at the surface due to its higher surface temperature, but its deep water masses show the lowest CANTH values since they are the less ventilated in the section. Our analysis also reveals that, overall, the NA CANTH storage has increased during 2002-2021, but varied according to the ventilation changes. While the Eastern NA water masses experienced a relatively constant, although shallower, average ventilation, the Irminger and Iceland Basins underwent a less

Despite covering only 15% of the global oceanic area, the North Atlantic (NA) accumulates one of the highest contents of anthropogenic CO2 (CANTH) in the ocean, storing 23% of the oceanic CANTH (Sabine et al., 2004). In terms of CANTH increase, large regions of the NA recorded average rates of 1.2 ± 0.1 mol m-2 yr-1 during 1994-2007, doubling the global oceanic rate of CANTH increase of 0.65 ± 0.08 mol m-2 yr-1 (Gruber et al., 2019). In the NA, high CANTH concentrations penetrate to mid and abyssal depths as a result of the formation and deep spreading of Labrador Sea Water. These processes are linked to the meridional overturning circulation and winter convection occurring in the NA subpolar gyre. Differences in CANTH storage rates have been observed between different phases of the NA Oscillation (NAO), attributed to both changes in CANTH concentration and decreases in volumetric water mass census (Fröb et al., 2018). There has been a 50% slowdown in the rate of CANTH increase in the NA subpolar gyre between 1994 and 2007, coinciding with a period of low NAO. Biennial observation of the marine carbonate system along the GOSHIP A25-OVIDE section has allowed assessing the long-term and interannual variability of the CANTH storage in the subpolar NA from 2002 to 2018. In this research, we determined the increases of CANTH in the water masses present between the OVIDE section and the Nordic sills. The average accumulation rate CANTH in the water column between the A25-OVIDE section and the sills was 0.90 ± 0.08 mol m-2 yr-1 (0.041 ± 0.003 Pg-C yr-1) for 2002-2021, being 61% higher than the 0.54 ± 0.06 mol m-2 yr-1 observed for 1997-2006 (low NAO). The increase in the CANTH accumulation rate during 2002-2021 is mainly found in the Irminger and Iceland basins and is mainly associated with the period of high NAO that occurred after 2014. In these two basins, the CANTH accumulation rates during the high NAO double those found during the low NAO

The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this special issue (https://www.biogeosciences.net/special-issue900.html), results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 18 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

Pathways and timescales of water mass transport in the subpolar North Atlantic Ocean (SPNA) have been investigated by many studies due to their importance for the meridional overturning circulation and thus for the global ocean. In this sense, observational data on geochemical tracers provide complementary information to improve the current understanding of the circulation in the SPNA. To this end, we present the first simultaneous distribution of artificial 129I and 236U in 14 depth profiles and in surface waters along the GEOVIDE section covering a zonal transect through the SPNA in spring 2014. Our results show that the two tracers are distributed following the water mass structure and that their presence is largely influenced by the global fallout (GF) and liquid effluents discharged to north-western European coastal waters by the Sellafield and La Hague nuclear reprocessing plants (NRPs). As a result, 129I concentrations and 236Uĝ•238U atom ratios and 129Iĝ•236U atom ratios display a wide range of values: (0.2-256) × 107 at kgĝ'1 (40-2350) × 10ĝ'12 and 0.5-200, respectively. The signal from NRPs, which is characterised by higher 129I concentrations and 129Iĝ•236U atom ratios compared to GF, is transported by Atlantic Waters (AWs) into the SPNA, notably by the East Greenland Current (EGC)/Labrador Current (LC) at the surface and by waters overflowing the Greenland-Scotland passage at greater depths. Nevertheless, our results show that the effluents from NRPs may also directly enter the surface of the eastern SPNA through the Iceland-Scotland passage or the English Channel/Irish Sea. The use of the 236Uĝ•238U and 129Iĝ•236U dual tracer approach further serves to discern Polar Intermediate Water (PIW) of Canadian origin from that of Atlantic origin, which carries comparably higher tracer levels due to NRPs (particularly 129I). The cascading of these waters appears to modify the water mass composition in the bottom of the Irminger and Labrador seas, which are dom

The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this special issue (https://www.biogeosciences.net/special_issue900.html), results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 18 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 15 (2018): 3027-3048, doi:10.5194/bg-15-3027-2018., We report detailed sections of radium-226 (226Ra, T1∕2 = 1602 years) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the international GEOTRACES program (GA01 section – GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, a pattern that may reflect their similar chemical behavior. Because 226Ra and Ba have been widely used as tracers of water masses and ocean mixing, we investigated their behavior more thoroughly in this crucial region for thermohaline circulation, taking advantage of the contrasting biogeochemical patterns existing along the GA01 section. We used an optimum multiparameter (OMP) analysis to distinguish the relative importance of physical transport (water mass mixing) from nonconservative processes (sedimentary, river or hydrothermal inputs, uptake by particles and dissolved–particulate dynamics) on the 226Ra and Ba distributions in the North Atlantic. Results show that the measured 226Ra and Ba concentrations can be explained by conservative mixing for 58 and 65 % of the samples, respectively, notably at intermediate depth, away from the ocean interfaces. 226Ra and Ba can thus be considered conservative tracers of water mass transport in the ocean interior on the space scales considered here, namely, on the order of a few thousand kilometers. However, regions in which 226Ra and Ba displayed nonconservative behavior and in some cases decoupled behaviors were also identified, mostly at the ocean boundaries (seafloor, continental margins and surface waters). Elevated 226Ra and Ba concentrations found in deepwater in the West European Basin suggest that lower Northeast Atlantic Deep Water (NEADWl) accumulates 226Ra and Ba from sediment diffusion and/or particle dissolution during transport. In the upper 1500 m of the West European Basin, deficiencies in 226Ra and Ba are likely explained by their incorporation in planktonic calcareous, The present research and Emilie Le Roy’s fellowship are co-funded by the European Union and the Région Occitanie-Pyrénées-Méditerranée (European Regional Development Fund). This work was also co-funded by the French national program LEFE/INSU “REPAP” (PI Stéphanie H. M Jacquet) and the US National Science Foundation (PI Matthew A. Charette, OCE-1458305; OCE-1232669). For this work Maribel I. García-Ibáñez and Fiz F. Pérez were supported by the Spanish Ministry of Economy and Competitiveness through the BOCATS (CTM2013-41048-P) project co-funded by the Fondo Europeo de Desarrollo Regional 2014–2020 (FEDER).

The GEOVIDE cruise, a collaborative project within the framework of the international GEOTRACES programme, was conducted along the French-led section in the North Atlantic Ocean (Section GA01), between 15 May and 30 June 2014. In this special issue (https://www.biogeosciences.net/special_issue900.html), results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 18 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

The stable isotope composition of dissolved silicon in seawater ( 30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60 N) and Labrador Sea. Variations in 30SiDSi below 500m were closely tied to the distribution of water masses. Higher 30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower 30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest 30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the 30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high 30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both 30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower DeepWater. The GEOVIDE 30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/ polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local 30SiDSi distribution