Sea–air CO2 flux in the North Atlantic subtropical gyre: Role and influence of Sub-Tropical Mode Water formation

The Gulf Stream front separates the North Atlantic subtropical and subpolar ocean gyres, water masses with distinct physical and biogeochemical properties. Exchange across the front is believed to be necessary to balance the freshwater budget of the subtropical gyre and to support the biological productivity of the region; however, the physical mechanisms responsible have been the subject of long-standing debate. Here, the evolution of a passive dye released within the north wall of the Gulf Stream provides direct observational evidence of enhanced mixing across the Gulf Stream front. Numerical simulations indicate that the observed rapid cross-frontal mixing occurs via shear dispersion, generated by frontal instabilities and episodic vertical mixing. This provides unique direct evidence for the role of submesoscale fronts in generating lateral mixing, a mechanism which has been hypothesized to be of general importance for setting the horizontal structure of the ocean mixed layer. Along the Gulf Stream front in the North Atlantic, these observations further suggest that shear dispersion at sharp fronts may provide a source of freshwater flux large enough to explain much of the freshwater deficit in the subtropical-mode water budget and a flux of nutrients comparable to other mechanisms believed to control primary productivity in the subtropical gyre.

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Modal composition of the central water in the North Atlantic subtropical gyre

Ocean Science Discussions ◽

10.5194/osd-6-2487-2009 ◽

2009 ◽

Vol 6 (3) ◽

pp. 2487-2506 ◽

Cited By ~ 4

Author(s):

A. Cianca ◽

R. Santana ◽

J. P. Marrero ◽

M. J. Rueda ◽

O. Llinás

Keyword(s):

Time Series ◽

North Atlantic ◽

World Ocean ◽

Average Density ◽

Subtropical Gyre ◽

Mode Water ◽

Data Set ◽

Modal Composition ◽

The North ◽

The North Atlantic

Abstract. The modal composition of the Central Water in the North Atlantic subtropical gyre is not clearly defined, as there are some uncertainties related to mode identification, as well as modes which are not well documented. This study shows that eastern North Atlantic Central Water (eastern NACW) in the subtropical gyre is composed of three modes: The North Atlantic Subpolar Mode Water (NASPMW σt=27.1 to 27.3), the Madeira Mode Water (MMW σt=26.4 to 26.6), and the mode water with a σt near 27.0, which is currently not well documented. We confirmed this mode based on the similarities found between it and the mode waters already reported. The similarities were determined from comparative analyses of the temperature/salinity standard curves and the gradients of the potential density anomalies of two concurrent data sets from two subtropical time-series stations (Bermuda Atlantic Time-series Study, BATS, in the west, and European Station for Time-series in the Ocean Canary Islands, ESTOC, in the east). In order to establish the outcropping regions, the corresponding pycnostads were determined using another climatologic data set (World Ocean Database, WOD2005). In this case, the pycnostads were located based on the presence of standard deviation minima from the average density anomalies. Finally, we confirmed that the pycnostads corresponded to the temperature values related to the modes by overlaying the characteristic modal isotherm of each of the modes in the geographic distribution of the pycnostads. Sea surface temperature data (SST) from the Ocean Pathfinder Program (OPP) were used to estimate the isotherms. The results showed a clear correspondence between the modal isotherms and the pycnostads, for both the modes that have already been documented and the mode confirmed in this study.

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Multi-decadal uptake of carbon dioxide into subtropical mode water of the North Atlantic Ocean

Biogeosciences Discussions ◽

10.5194/bgd-8-12451-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 12451-12476 ◽

Cited By ~ 4

Author(s):

N. R. Bates

Keyword(s):

Carbon Dioxide ◽

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Dissolved Inorganic Carbon ◽

Mode Water ◽

Subtropical Mode Water ◽

The North ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract. Natural climate variability impacts the multi-decadal uptake of anthropogenic carbon dioxide (Cant) into the North Atlantic Ocean subpolar and subtropical gyres. Previous studies have shown that there is significant uptake of CO2 into the subtropical mode water (STMW) that forms south of the Gulf Stream in winter and constitutes the dominant upper-ocean water mass in the subtropical gyre of the North Atlantic Ocean. Observations at the Bermuda Atlantic Time-series Study (BATS) site near Bermuda show an increase in dissolved inorganic carbon (DIC) of +1.51 ± 0.08 μmol kg−1 yr−1 between 1988 and 2011. It is estimated that the sink of CO2 into STMW was 0.985 ± 0.018 Pg C (Pg = 1015 g C) between 1988 and 2011 (~70 % of which is due to uptake of Cant). However, the STMW sink of CO2 was strongly coupled to the North Atlantic Oscillation (NAO) with large uptake of CO2 into STMW during the 1990s (NAO positive phase). In contrast, uptake of CO2 into STMW was much reduced in the 2000s during the NAO neutral/negative phase. Thus, NAO induced variability of the STMW CO2 sink is important when evaluating multi-decadal changes in North Atlantic Ocean CO2 sinks.

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Long-term ventilation changes of Subpolar Mode Waters in the North Atlantic Ocean and its impact on the oxygen distribution

10.5194/egusphere-egu21-847 ◽

2021 ◽

Author(s):

Ilaria Stendardo ◽

Bruno Buongiorno Nardelli ◽

Sara Durante

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Horizontal Resolution ◽

Late Winter ◽

Mode Water ◽

Mode Waters ◽

The North ◽

The North Atlantic ◽

The Impact

<p>In the subpolar North Atlantic Ocean, Subpolar Mode Waters (SPMWs) are formed during late winter convection following the cyclonic circulation of the subpolar gyre. SPMWs participate in the upper flow of the Atlantic overturning circulation (AMOC) and provide much of the water that is eventually transformed into several components of the North Atlantic deep water (NADW), the cold, deep part of the AMOC. In a warming climate, an increase in upper ocean stratification is expected to lead to a reduced ventilation and a loss of oxygen. Thus, understanding how mode waters are affected by ventilation changes will help us to better understand the variability in the AMOC. In particular, we would like to address how the volume occupied by SPMWs has varied over the last decades due to ventilation changes, and what are the aspects driving the subpolar mode water formation, their interannual variations as well as the impact of the variability in the mixing and subduction and vertical dynamics on ocean deoxygenation. For this purpose, we use two observation-based 3D products from Copernicus Marine Service (CMEMS), the ARMOR3D and the OMEGA3D datasets. The first consists of 3D temperature and salinity fields, from the surface to 1500 m depth, available weekly over a regular grid at 1/4&#176; horizontal resolution from 1993 to present. The second consists of observation-based quasi-geostrophic vertical and horizontal ocean currents with the same temporal and spatial resolution as ARMOR3D.</p>

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Meridional variability in dissolved organic matter stocks and diagenetic state within the euphotic and mesopelagic zone of the North Atlantic subtropical gyre

Marine Chemistry ◽

10.1016/j.marchem.2009.12.002 ◽

2010 ◽

Vol 119 (1-4) ◽

pp. 9-21 ◽

Cited By ~ 16

Author(s):

Stuart J. Goldberg ◽

Craig A. Carlson ◽

Brandon Bock ◽

Norm B. Nelson ◽

David A. Siegel

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

North Atlantic ◽

Subtropical Gyre ◽

The North ◽

Mesopelagic Zone ◽

The North Atlantic

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Changes across 66°W, the Caribbean Sea and the Western boundaries of the North Atlantic Subtropical Gyre

Progress In Oceanography ◽

10.1016/j.pocean.2018.09.013 ◽

2018 ◽

Vol 168 ◽

pp. 296-309 ◽

Cited By ~ 3

Author(s):

M. Casanova-Masjoan ◽

T.M. Joyce ◽

M.D. Pérez-Hernández ◽

P. Vélez-Belchí ◽

A. Hernández-Guerra

Keyword(s):

North Atlantic ◽

Caribbean Sea ◽

Subtropical Gyre ◽

The North ◽

The Caribbean ◽

The North Atlantic

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Climate extremes in Loess of China coupled with the strength of deep-water formation in the North Atlantic

Global and Planetary Change ◽

10.1016/s0921-8181(98)00010-1 ◽

1998 ◽

Vol 18 (3-4) ◽

pp. 113-128 ◽

Cited By ~ 179

Author(s):

Zhengtang Guo ◽

Tungsheng Liu ◽

Nicolas Fedoroff ◽

Lanying Wei ◽

Zhongli Ding ◽

...

Keyword(s):

North Atlantic ◽

Deep Water ◽

Climate Extremes ◽

Deep Water Formation ◽

The North ◽

Water Formation ◽

The North Atlantic

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The spiralling North Atlantic Subtropical Gyre

10.5194/egusphere-egu2020-1459 ◽

2020 ◽

Author(s):

Kristofer Döös ◽

Sara Berglund ◽

Trevor Mcdougall ◽

Sjoerd Groeskamp

Keyword(s):

North Atlantic ◽

Gulf Stream ◽

Subtropical Gyre ◽

The South ◽

Spiral Flow ◽

The North ◽

Saline Waters ◽

Downward Spiral ◽

Meridional Overturning ◽

The North Atlantic

<p>The North Atlantic Subtropical Gyre is shown to have a downward spiral flow beneath the mixed layer, where the water slowly gets denser, colder and fresher as it spins around the gyre. This path is traced with Lagrangian trajectories as they enter the Gyre in the Gulf Stream from the south until they exit through the North Atlantic Drift. The preliminary results indicate that these warm, saline waters from the south gradually becomes fresher, colder and denser due to mixing with waters originating from the North Atlantic. There are indications that there is also a diapycnal mixing, in the eastern part of the gyre due to mixing with the saline Mediterranean Waters, which would then be crucial for the Atlantic Meridional Overturning. The mixing in the rest of the gyre is dominated by isopycnic mixing, which transforms gradually the water into colder and fresher water as it spins down the gyre into the abyssal ocean before heading north.</p>

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