scholarly journals Diagnosing the Observed Seasonal Cycle of Atlantic Subtropical Mode Water Using Potential Vorticity and Its Attendant Theorems

2011 ◽  
Vol 41 (10) ◽  
pp. 1986-1999 ◽  
Author(s):  
Guillaume Maze ◽  
John Marshall
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Gulf Stream ◽  
Seasonal Cycle ◽  
Water Layer ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
Mapping Techniques

Abstract Analyzed fields of ocean circulation and the flux form of the potential vorticity equation are used to map the creation and subsequent circulation of low potential vorticity waters known as subtropical mode water (STMW) in the North Atlantic. Novel mapping techniques are applied to (i) render the seasonal cycle and annual-mean mixed layer vertical flux of potential vorticity (PV) through outcrops and (ii) visualize the extraction of PV from the mode water layer in winter, over and to the south of the Gulf Stream. Both buoyancy loss and wind forcing contribute to the extraction of PV, but the authors find that the former greatly exceeds the latter. The subsequent path of STMW is also mapped using Bernoulli contours on isopycnal surfaces.

scholarly journals Volume and Potential Vorticity Budgets of Eighteen Degree Water

2013 ◽  
Vol 43 (11) ◽  
pp. 2309-2321 ◽  
Author(s):  
Bruno Deremble ◽  
W. K. Dewar
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Mass Flux ◽  
World Ocean ◽  
Water Structure ◽  
Water Dynamics ◽  
Mode Water ◽  
Mode Waters ◽  
The North

Abstract Mode waters are a distinctive baroclinic feature of the World Ocean characterized by relatively weak vertical stratification. They correspond dynamically to low potential vorticity (PV). In the North Atlantic subtropical gyre, the mode waters have become known as Eighteen Degree Water. Their dynamics involves air–sea interaction, diapycnal and isopycnal mixing, and subduction. Understanding mode water dynamics is therefore both challenging and important since it connects several aspects of the ocean circulation. Mass and PV budget of the mode water's core, evaluated in a realistic primitive equation North Atlantic model, are used to characterize mode water maintenance. It is shown that the surface PV flux has very little impact on mode water; the surface buoyancy flux in combination with eddy mass flux is the most important control on mode water structure. A mean PV formalism is used to show that the PV and water-mass formation budgets are intrinsically linked. A decomposition of the budget demonstrates the role of the mean PV field in permitting the eddy mass flux to discharge the net formation to the surrounding fluid.

Enhanced warming of the subtropical mode water in the North Pacific and North Atlantic

2017 ◽  
Vol 7 (9) ◽  
pp. 656-658 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Kimio Hanawa ◽  
Tomowo Watanabe ◽  
Toshio Suga ◽  
Shang-Ping Xie
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
The North Pacific

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

2011 ◽  
Vol 8 (6) ◽  
pp. 12451-12476 ◽  
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.

Interaction of a Glacial Water Outflow with the Gulf Stream

2021 ◽  
Author(s):  
Olivier Marchal ◽  
Alan Condron
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Gulf Stream ◽  
Circulation Model ◽  
Liquid Form ◽  
Sea Levels ◽  
Grand Banks ◽  
The North ◽  
Cape Hatteras ◽  
Water Outflow

<p>A popular hypothesis in paleoclimatology posits that the episodic discharges of glacial water from the Laurentide Ice Sheet (LIS) to the North Atlantic caused abrupt changes in ocean circulation and climate during the last (de)glacial periods. Implicit in this hypothesis is that the glacial water spread away from the coast and reached critical sites of deep water formation. Among the processes that could favour the offshore export of glacial water released along the eastern North American coast is the entrainment with the Gulf Stream near Cape Hatteras, where the Stream is observed to detach from the coast in the modern climate, or at other locations between Cape Hatteras and the Grand Banks of Newfoundland.</p><p>Here we investigate the fate of glacial water released in the western North Atlantic from the Laurentian Channel, which geologic evidence suggests to have been the main route of ice discharge from the Québec-Labrador Ice Dome of the LIS. To this end, we conduct numerical experiments with an ocean circulation model with eddy-resolving resolution and configured to represent the region north of Bermuda and west of the Grand Banks. Experiments with different regional sea levels are performed which correspond to different estimates of global sea level since the Last Glacial Maximum. In each experiment, glacial water in liquid form is discharged from the Laurentian Channel, providing a paleoceanographic analogue of the dam-break problem. As expected from the action of the Coriolis force and from the properties of the glacial water inflow, the discharged water turns to the right of the Channel and then produces a narrow buoyant current that flows along the coast to the southwest towards Cape Hatteras. Our presentation will focus on the interaction of this current with the Gulf Stream, particularly with its meanders and rings, and on the role of this interaction both in the seaward export of glacial water and in the modification of the Stream itself.</p>

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

2012 ◽  
Vol 9 (7) ◽  
pp. 2649-2659 ◽  
Author(s):  
N. R. Bates
Keyword(s):  
Carbon Dioxide ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Dissolved Inorganic Carbon ◽  
Co2 Uptake ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
The North ◽  
The North Atlantic

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 subtropical mode water (STMW) of the North Atlantic. STMW 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, but also an increase in ocean acidification indicators such as pH at rates (−0.0022 ± 0.0002 yr−1) higher than the surface ocean (Bates et al., 2012). 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 ± 1.8% of which is due to uptake of Cant). The sink of CO2 into the STMW is 20% of the CO2 uptake in the North Atlantic Ocean between 14°–50° N (Takahashi et al., 2009). 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 during a predominantly 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.

scholarly journals Enhanced mixing across the gyre boundary at the Gulf Stream front

2020 ◽  
Vol 117 (30) ◽  
pp. 17607-17614
Author(s):  
Jacob O. Wenegrat ◽  
Leif N. Thomas ◽  
Miles A. Sundermeyer ◽  
John R. Taylor ◽  
Eric A. D’Asaro ◽  
...  
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Subtropical Gyre ◽  
Freshwater Flux ◽  
Mode Water ◽  
Horizontal Structure ◽  
The North ◽  
Shear Dispersion ◽  
General Importance ◽  
The North Atlantic

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.

Air–Sea Fluxes over the Gulf Stream Region: Atmospheric Controls and Trends

2010 ◽  
Vol 23 (10) ◽  
pp. 2651-2670 ◽  
Author(s):  
Jeffrey Shaman ◽  
R. M. Samelson ◽  
Eric Skyllingstad
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
North Atlantic ◽  
Gulf Stream ◽  
Heat Fluxes ◽  
High Flux ◽  
Mode Water ◽  
The North ◽  
Storm Frequency ◽  
The North Atlantic

Abstract The intraseasonal variability of turbulent surface heat fluxes over the Gulf Stream extension and subtropical mode water regions of the North Atlantic, and long-term trends in these fluxes, are explored using NCEP–NCAR reanalysis. Wintertime sensible and latent heat fluxes from these surface waters are characterized by episodic high flux events due to cold air outbreaks from North America. Up to 60% of the November–March (NDJFM) total sensible heat flux and 45% of latent heat flux occurs on these high flux days. On average 41% (34%) of the total NDJFM sensible (latent) heat flux takes place during just 17% (20%) of the days. Over the last 60 years, seasonal NDJFM sensible and latent heat fluxes over the Climate Variability and Predictability (CLIVAR) Mode Water Dynamic Experiment (CLIMODE) region have increased owing to an increased number of high flux event days. The increased storm frequency has altered average wintertime temperature conditions in the region, producing colder surface air conditions over the North American eastern seaboard and Labrador Sea and warmer temperatures over the Sargasso Sea. These temperature changes have increased low-level vertical wind shear and baroclinicity along the North Atlantic storm track over the last 60 years and may further favor the trend of increasing storm frequency over the Gulf Stream extension and adjacent region.

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