SURATLANT: a 1993–2017 surface sampling in the central part of the North Atlantic subpolar gyre

Abstract. This paper presents the SURATLANT data set (SURveillance ATLANTique). It consists of individual data of temperature, salinity, parameters of the carbonate system, nutrients, and water stable isotopes (δ18O and δD) collected mostly from ships of opportunity since 1993 along transects between Iceland and Newfoundland (https://doi.org/10.17882/54517). We discuss how the data are validated and qualified, their accuracy, and the overall characteristics of the data set. The data are used to reconstruct seasonal cycles and interannual anomalies, in particular of sea surface salinity (SSS); inorganic nutrients; dissolved inorganic carbon (DIC); and its isotopic composition δ13CDIC, total alkalinity (At), and water isotope concentrations. Derived parameters such as fCO2 and pH are also estimated. The relation between salinity and At is estimated from these data to investigate the possibility to replace missing At when estimating other parameters of the carbonate system. When examining the average seasonal cycle in the deep ocean, in both these data with other climatologies, we find a period of small seasonal change between January and late April. On the Newfoundland shelf and continental slope, changes related with spring stratification and blooms occur earlier. The data were collected in a period of multi-decennial variability associated with the Atlantic multi-decadal variability with warming between 1994 and 2004–2007, and with the recent cooling having peaked in 2014–2016. We also observe strong salinification in 2004–2009 and fresher waters in 1994–1995 as well as since 2010 south of 54° N and in 2016–2017 north of 54° N. Indication of multi-decadal variability is also suggested by other variables, such as phosphate or DIC, but cannot be well resolved seasonally with the discrete sampling and in the presence of interannual variability. As a whole, over the 24 years, the ocean fCO2 trend (+1.9 µatm yr−1) is close to the atmospheric trend and associated with an increase in DIC (+0.77 µmol kg−1 yr−1). The data also revealed a canonical pH decrease of −0.0021 yr−1. There is also a decrease in δ13CDIC between 2005 and 2017 (in winter, −0.014 ‰ yr−1, but larger in summer, −0.042 ‰ yr−1), suggesting a significant anthropogenic carbon signal at play together with other processes (mixing, biological activity).

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SURATLANT: a 1993–2017 surface sampling in the central part of the North Atlantic subpolar gyre

10.5194/essd-2018-50 ◽

2018 ◽

Author(s):

Gilles Reverdin ◽

Nicolas Metzl ◽

Solveig Olafsdotir ◽

Virginie Racapé ◽

Taro Takahashi ◽

...

Keyword(s):

Decadal Variability ◽

Dissolved Inorganic Carbon ◽

Sea Surface Salinity ◽

Total Alkalinity ◽

Surface Sampling ◽

Surface Salinity ◽

Carbonate System ◽

Data Set ◽

The North ◽

Δ18o And Δd

Abstract. This paper presents the SURATLANT dataset (SURveillance ATLANTique), consisting of individual data of temperature, salinity, parameters of the carbonate system, nutrients and water stable isotopes (δ18O and δD) collected mostly from ships of opportunity since 1993 along transects between Iceland and Newfoundland (https://doi.org/10.17882/54517). We discuss how the data are validated, qualified, their accuracy and the overall characteristics of the data set. The data are used to reconstruct seasonal cycles and interannual anomalies, in particular of Sea Surface Salinity (SSS), inorganic nutrients, dissolved inorganic carbon (DIC) and its isotopic composition δ13CDIC, total alkalinity (At), and water isotope concentrations. Derived parameters, such as fCO2 and pH are also estimated. The relation between salinity and At is estimated in these data to investigate the possibility to replace missing At when estimating other parameters of the carbonate system. We compare the seasonal cycle derived from these data with other climatologies. We find a period of small seasonal change between January and late April, except on the Newfoundland shelf/continental slope, when changes related with spring-stratification and blooms occur earlier. The data were collected in a period of multi-decennial variability associated with the Atlantic meridional oscillation with warming between 1994 and 2004–2007, and the recent cooling having peaked in 2014–2016. We also observe strong salinification in 2004–2009 and fresher waters in 1994–1995 as well as since 2010 south of 54° N and in 2016–2017 north of 54° N. Indication of multi-decadal variability is also suggested by other variables, such as phosphate or DIC, but cannot be well resolved seasonally with the discrete sampling and in the presence of interannual variability. As a whole, over the 24 years ocean fCO2 trend (&plus;1.9 µatm yr-1) is close to the atmospheric trend and associated with an increase in DIC (&plus;0.70 μmol kg-1 yr-1). The data also revealed a "canonical" pH decrease of −0.002 yr-1. There is also a decrease in δ13CDIC between 2005 and 2017 (in winter, −0.015 ‰ yr-1, but larger in summer, −0.042 ‰ yr-1), suggesting significant anthropogenic carbon signal at play together with other processes (mixing, biological activity).

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Improved routines to model the ocean carbonate system: mocsy 1.0

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-2877-2014 ◽

2014 ◽

Vol 7 (3) ◽

pp. 2877-2902 ◽

Cited By ~ 3

Author(s):

J. C. Orr ◽

J.-M. Epitalon

Keyword(s):

Best Practices ◽

Dissolved Inorganic Carbon ◽

Equilibrium Constants ◽

Potential Temperature ◽

Deep Ocean ◽

Total Alkalinity ◽

Carbonate System ◽

Carbon Cycle Model ◽

The North ◽

Ocean Carbon

Abstract. Software used by modelers to compute ocean carbonate chemistry is often based on code from the Ocean Carbon Cycle Model Intercomparison Project (OCMIP), last revised in 2005. As an update, we offer here new publicly available Fortran 95 routines to model the ocean carbonate system (mocsy). Both codes take as input dissolved inorganic carbon CT and total alkalinity AT, the only two tracers of the ocean carbonate system that are unaffected by changes in temperature and salinity and conservative with respect to mixing, properties that make them ideally suited for ocean carbon models. With the same basic thermodynamic equilibria, both codes compute surface-ocean pCO2 in order to simulate air–sea CO2 fluxes. The mocsy package goes beyond the OCMIP code by computing all other carbonate system variables (e.g., pH, CO32−, and CaCO3 saturation states) and by doing so throughout the water column. Moreover, it avoids three common model approximations: that density is constant, that modeled potential temperature is equivalent to in situ temperature, and that depth is equivalent to pressure. These approximations work well at the surface, but total errors in computed variables grow with depth, e.g., reaching −8 μatm in pCO2, +0.010 in pH, and +0.01 in ΩA at 5000 m. Besides the equilibrium constants recommended for best practices, mocsy also offers users three new options: (1) a recent formulation for total boron that increases its ocean content by 4%, (2) an older formulation for KF common to all other such software, and (3) recent formulations for K1 and K2 designed to also include low-salinity waters. More total boron increases borate alkalinity and reduces carbonate alkalinity, which is calculated as a difference from total alkalinity. As a result, the computed surface pCO2 increases by 4 to 6 μatm, while the computed aragonite saturation horizon (ASH) shallows by 60 m in the North Atlantic and by up to 90 m in the Southern Ocean. Changes due to the new formulation for K1 and K2 enhance pCO2 by up to 8 μatm in the deep ocean and in high-latitude surface waters. These changes are comparable in magnitude to errors in the same regions associated with neglecting nutrient contributions to total alkalinity, a common practice in ocean biogeochemical modeling. The mocsy code with the standard options for best practices and none of the 3 approximations agrees with results from the CO2SYS package generally within 0.005%.

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Impact of mesoscale eddies on salinity and CO2 ocean parameters in the western tropical Atlantic in February 2020

10.5194/egusphere-egu21-1253 ◽

2021 ◽

Author(s):

Léa Olivier ◽

Jacqueline Boutin ◽

Nathalie Lefèvre ◽

Gilles Reverdin ◽

Peter Landschützer ◽

...

Keyword(s):

Dissolved Inorganic Carbon ◽

Salinity Gradient ◽

Sea Surface Salinity ◽

Amazon River ◽

Tropical Atlantic ◽

Surface Salinity ◽

The North ◽

Brazil Current ◽

North Brazil

Large oceanic eddies are formed by the retroflection of the North Brazil Current (NBC) near 8&#176;N in the western tropical Atlantic. The EUREC4A-OA/Atomic cruise took place in January - February 2020, and extensively documented two NBC rings. The NBC flows northward across the Equator and pass the mouth of the Amazon River, entraining fresh and nutrient-rich water along its nearshore edge. From December to March, the Amazon river discharge is low but a freshwater filament stirred by a NBC ring was nevertheless observed. The strong salinity gradient can be used to delineate the NBC ring during its initial phase and its westward propagation. Using satellite sea surface salinity and ocean color associated to in-situ measurements of salinity, temperature, dissolved inorganic carbon, alkalinity and fugacity of CO2 we characterize the salinity and biogeochemical signature of NBC rings.

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SMOS-based estimation and validation of Total Alkalinity in the Mediterranean basin

10.5194/egusphere-egu2020-20753 ◽

2020 ◽

Author(s):

Roberto Sabia ◽

Estrella Olmedo ◽

Giampiero Cossarini ◽

Aida Alvera-Azcárate ◽

Veronica Gonzalez-Gambau ◽

...

Keyword(s):

Remote Sensing ◽

Mediterranean Sea ◽

Mediterranean Basin ◽

Sea Surface ◽

Sea Surface Salinity ◽

Total Alkalinity ◽

Surface Salinity ◽

Carbonate System ◽

The Mediterranean ◽

The Mediterranean Basin

ESA SMOS satellite [1] has been providing first-ever Sea Surface Salinity (SSS) measurements from space for over a decade now. Until recently, inherent algorithm limitations or external interferences hampered a reliable provision of satellite SSS data in semi-enclosed basin such as the Mediterranean Sea. This has been however overcome through different strategies in the retrieval scheme and data filtering approach [2, 3]. This recent capability has been in turn used to infer the spatial and temporal distribution of Total Alkalinity (TA - a crucial parameter of the marine carbonate system) in the Mediterranean, exploiting basin-specific direct relationships existing between salinity and TA.Preliminary results [4] focused on the differences existing in several parameterizations [e.g, 5] relating these two variables, and how they vary over a seasonal to interannual timescale.Currently, to verify the consistency and accuracy of the derived products, these data are being validated against a proper ensemble of in-situ, climatology and model outputs within the Mediterranean basin. An error propagation exercise is also being planned to assess how uncertainties in the satellite data would translate into the final products accuracy.The resulting preliminary estimates of Alkalinity in the Mediterranean Sea will be linked to the overall carbonate system in the broader context of Ocean Acidification assessment and marine carbon cycle.References:[1] J. Font et al., "SMOS: The Challenging Sea Surface Salinity Measurement From Space," in Proceedings of the IEEE, vol. 98, no. 5, pp. 649-665, May 2010. doi: 10.1109/JPROC.2009.2033096[2] Olmedo, E., J. Martinez, A. Turiel, J. Ballabrera-Poy, and M. Portabella,&#160; &#8220;Debiased non-Bayesian retrieval: A novel approach to SMOS Sea Surface Salinity&#8221;. Remote Sensing of Environment 193, 103-126 (2017).[3] Alvera-Azc&#225;rate, A., A. Barth, G. Parard, J.-M. Beckers, Analysis of SMOS sea surface salinity data using DINEOF, In Remote Sensing of Environment, Volume 180, 2016, Pages 137-145, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2016.02.044.[4] Sabia, R., E. Olmedo, G. Cossarini, A. Turiel, A. Alvera-Azc&#225;rate, J. Martinez, D. Fern&#225;ndez-Prieto, Satellite-driven preliminary estimates of Total Alkalinity in the Mediterranean basin, Geophysical Research Abstracts, Vol. 21, EGU2019-17605, EGU General Assembly 2019, Vienna, Austria, April 7-12, 2019.[5] Cossarini, G., Lazzari, P., and Solidoro, C.: Spatiotemporal variability of alkalinity in the Mediterranean Sea, Biogeosciences, 12, 1647-1658, https://doi.org/10.5194/bg-12-1647-2015, 2015.&#160;&#160;

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OceanSODA-ETHZ: A global gridded data set of the surface ocean carbonate system for seasonal to decadal studies of ocean acidification

10.5194/essd-2020-300 ◽

2020 ◽

Author(s):

Luke Gregor ◽

Nicolas Gruber

Keyword(s):

Ocean Acidification ◽

Dissolved Inorganic Carbon ◽

Total Error ◽

Total Alkalinity ◽

Global Ocean ◽

Carbonate System ◽

Data Set ◽

Saturation State ◽

Mean Squared Errors ◽

Surface Ocean

Abstract. Ocean acidification has altered the ocean's carbonate chemistry profoundly since preindustrial times, with potentially serious consequences for marine life. Yet, no long-term global observation-based data set exists that permits to study changes in ocean acidification for all carbonate system parameters over the last few decades. Here, we fill this gap and present a methodologically consistent global data set of all relevant surface ocean parameters, i.e., dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2 (pCO2), pH, and the saturation state with respect to mineral CaCO3 (Ω) at monthly resolution over the period 1985 through 2018 at a spatial resolution of 1 × 1°. This data set, named OceanSODA-ETHZ, was created by extrapolating in time and space the surface ocean observations of pCO2 (from the Surface Ocean CO2 ATlas (SOCAT)) and total alkalinity (TA, from the Global Ocean Data Analysis Project (GLODAP)) using the newly developed Geospatial Random Cluster Ensemble Regression (GRaCER) method. This method is based on a two-step (cluster-regression) approach, but extends it by considering an ensemble of such cluster-regressions, leading to higher robustness. Surface ocean DIC, pH, and Ω were then computed from the globally mapped pCO2 and TA using the thermodynamic equations of the carbonate system. For the open ocean, the cluster regression method estimates pCO2 and TA with global near-zero biases and root mean squared errors of 12 µatm and 13 µmol kg−1, respectively. Taking into account also the measurement and representation errors, the total error increases to 14 µatm and 21 µmol kg−1, respectively. We assess the fidelity of the computed parameters by comparing them to direct observations from GLODAP, finding surface ocean pH and DIC global biases of near zero, and root mean squared errors of 0.023 and 16 µmol kg−1, respectively. These errors are very comparable to those expected by propagating the total errors from pCO2 and TA through the thermodynamic computations, indicating a robust and conservative assessment of the errors. We illustrate the potential of this new dataset by analyzing the climatological mean seasonal cycles of the different parameters of the surface ocean carbonate system, highlighting their commonalities and differences. The OceanSODA-ETHZ data can be downloaded from https://doi.org/10.25921/m5wx-ja34 (Gregor and Gruber, 2020).

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North Atlantic subpolar gyre along predetermined ship tracks since 1993: a monthly data set of surface temperature, salinity, and density

Earth System Science Data ◽

10.5194/essd-10-1403-2018 ◽

2018 ◽

Vol 10 (3) ◽

pp. 1403-1415 ◽

Cited By ~ 6

Author(s):

Gilles Reverdin ◽

Hedinn Valdimarsson ◽

Gael Alory ◽

Denis Diverres ◽

Francis Bringas ◽

...

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Atlantic ◽

Sea Surface ◽

Sea Surface Salinity ◽

Subpolar Gyre ◽

Surface Salinity ◽

Data Set ◽

The North ◽

North Atlantic Subpolar Gyre

Abstract. We present a binned product of sea surface temperature, sea surface salinity, and sea surface density data in the North Atlantic subpolar gyre from 1993 to 2017 that resolves seasonal variability along specific ship routes (https://doi.org/10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work were collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The data were binned along a selected usable transect. The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal timescales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the West Greenland Shelf. Variability in sea surface salinity increases towards Newfoundland south of 54∘ N, as well as in the western Iceland Basin along 59∘ N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.

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Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

Biogeosciences Discussions ◽

10.5194/bgd-10-8283-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 8283-8311 ◽

Cited By ~ 1

Author(s):

M. Wakita ◽

S. Watanabe ◽

M. Honda ◽

A. Nagano ◽

K. Kimoto ◽

...

Keyword(s):

Ocean Acidification ◽

Mixed Layer ◽

North Pacific ◽

Dissolved Inorganic Carbon ◽

North Pacific Ocean ◽

Total Alkalinity ◽

Co2 Uptake ◽

The North ◽

Western Subarctic Gyre ◽

Calcite Saturation

Abstract. Rising atmospheric CO2 contents have led to greater CO2 uptake by the oceans, lowering both pH due to increasing hydrogen ions and CaCO3 saturation states due to declining carbonate ion (CO32−). Here, we used previously compiled data sets and new data collected in 2010 and 2011 to investigate ocean acidification of the North Pacific western subarctic gyre. In winter, the western subarctic gyre is a source of CO2 to the atmosphere because of convective mixing of deep waters rich in dissolved inorganic carbon (DIC). We calculated pH in winter mixed layer from DIC and total alkalinity (TA), and found that it decreased at the rate of −0.001 ± 0.0004 yr−1 from 1997 to 2011. This decrease rate is slower than that expected under condition of seawater/atmosphere equilibration, and it is also slower than the rate in the subtropical regions (−0.002 yr−1). The slow rate is caused by a reduction of CO2 emission in winter due to an increase in TA. Below the mixed layer, the calcite saturation horizon (~185 m depth) shoaled at the rate of 2.9 ± 0.9 m yr−1 as the result of the declining CO32− concentration (−0.03 ± 0.01 μmol k−1yr−1). Between 200 m and 300 m depth, pH decline during the study period (−0.0051 ± 0.0010 yr−1) was larger than ever reported in the open North Pacific. This enhanced acidification rate below the calcite saturation horizon reflected not only the uptake of anthropogenic CO2 but also the increase in the decomposition of organic matter evaluated from the increase in AOU, which suggests that the dissolution of CaCO3 particles increased.

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Sea-surface salinity variations in the Northern Caribbean Sea across the mid-Pleistocene transition

Climate of the Past Discussions ◽

10.5194/cpd-6-1229-2010 ◽

2010 ◽

Vol 6 (3) ◽

pp. 1229-1265

Author(s):

S. Sepulcre ◽

L. Vidal ◽

K. Tachikawa ◽

F. Rostek ◽

E. Bard

Keyword(s):

Temperature Gradient ◽

Planktonic Foraminifera ◽

Caribbean Sea ◽

Meridional Overturning Circulation ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

Inter Tropical Convergence Zone ◽

The North ◽

The Difference

Abstract. This study aimed at documenting climate changes in tropical area in response to the Mid-Pleistocene Transition (MPT) by reconstructing past hydrologic variations in the Northern Caribbean Sea and its influence on the stability of the Atlantic Meridional Overturning Circulation (AMOC) during the last 940 kyr. Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δδ18O, the difference between the modern and the past δ18O of seawater (obtained by combining alkenone thermometer data with the δ18O of the planktonic foraminifera Globigerinoides ruber (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in the studied area are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δδ18O record exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 kyr, indicating increased SSS. At a longer timescale, the Δδ18O exhibits a shift toward lower values for interglacial periods during the last 450 kyr, when compared to interglacial stages older than 650 kyr. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper interhemispheric temperature gradient and associated with reduced northward cross equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 kyr. Following the MPT, lower salinities during the last five interglacial stages indicate a northernmost ITCZ location, forced by changes in the interhemispheric temperature gradient that is associated with the poleward position of Southern Oceanic Fronts that amplified the transport of heat and moisture to the North Atlantic. These processes may have contributed to amplification of the climate cycles that followed the MPT.

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Sea surface salinity reemergence in an updated North Atlantic in-situ salinity data set

Journal of Climate ◽

10.1175/jcli-d-20-0840.1 ◽

2021 ◽

pp. 1-49

Author(s):

Claude Frankignoul ◽

Elodie Kestenare ◽

Gilles Reverdin

Keyword(s):

Large Scale ◽

Cold Season ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

Data Set ◽

Salinity Data ◽

Deep Mixed Layer ◽

Geostrophic Advection

AbstractMonthly sea surface salinity (SSS) fields are constructed from observations, using objective mapping on a 1°x1° grid in the Atlantic between 30°S and 50°N in the 1970-2016 period in an update of the data set of Reverdin et al. (2007). Data coverage is heterogeneous, with increased density in 2002 when Argo floats become available, high density along Voluntary Observing Ship lines, and low density south of 10°S. Using lag correlation, the seasonal reemergence of SSS anomalies is investigated between 20°N and 50°N in 5°x5° boxes during the 1993-2016 period, both locally and remotely following the displacements of the deep mixed-layer waters estimated from virtual float trajectories derived from the daily AVISO surface geostrophic currents. Although SSS data are noisy, local SSS reemergence is detected in about half of the boxes, notably in the northeast and southeast, while little reemergence is seen in the central and part of the eastern subtropical gyre. In the same period, sea surface temperature (SST) reemergence is found only slightly more frequently, reflecting the short data duration. However, taking geostrophic advection into account degrades the detection of remote SSS and even SST reemergence. When anomalies are averaged over broader areas, robust evidence of a second and third SSS reemergence peak is found in the northeastern and southeastern parts of the domain, indicating long cold-season persistence of large-scale SSS anomalies, while only a first SST reemergence is seen. An oceanic reanalysis is used to confirm that the correlation analysis indeed reflects the reemergence of subsurface salinity anomalies.

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Development of a Biogeochemical and Carbon Model Related to Ocean Acidification Indices with an Operational Ocean Model Product in the North Western Pacific

Sustainability ◽

10.3390/su11092677 ◽

2019 ◽

Vol 11 (9) ◽

pp. 2677 ◽

Cited By ~ 3

Author(s):

Miho Ishizu ◽

Yasumasa Miyazawa ◽

Tomohiko Tsunoda ◽

Xinyu Guo

Keyword(s):

Ocean Acidification ◽

General Circulation ◽

Inorganic Carbon ◽

Dissolved Inorganic Carbon ◽

Ocean Model ◽

Western Pacific ◽

Total Alkalinity ◽

The North ◽

North Western ◽

North Western Pacific

We developed a biogeochemical and carbon model (JCOPE_EC) coupled with an operational ocean model for the North Western Pacific. JCOPE_EC represents ocean acidification indices on the background of the risks due to ocean acidification and our model experiences. It is an off-line tracer model driven by a high-resolution regional ocean general circulation model (JCOPE2M). The results showed that the model adequately reproduced the general patterns in the observed data, including the seasonal variability of chlorophyll-a, dissolved inorganic nitrogen/phosphorus, dissolved inorganic carbon, and total alkalinity. We provide an overview of this system and the results of the model validation based on the available observed data. Sensitivity analysis using fixed values for temperature, salinity, dissolved inorganic carbon and total alkalinity helped us identify which variables contributed most to seasonal variations in the ocean acidification indices, pH and Ωarg. The seasonal variation in the pHinsitu was governed mainly by balances of the change in temperature and dissolved inorganic carbon. The seasonal increase in Ωarg from winter to summer was governed mainly by dissolved inorganic carbon levels.

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