On the seesaw in interannual variability of upper ocean heat advection between the North Atlantic Subpolar Gyre and the Nordic Seas

2021 ◽  
pp. 101263
Author(s):  
Diana A. Iakovleva ◽  
Igor L. Bashmachnikov
Keyword(s):  
Interannual Variability ◽  
North Atlantic ◽  
Upper Ocean ◽  
Subpolar Gyre ◽  
Heat Advection ◽  
Nordic Seas ◽  
The North ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic

Variations of oceanic and atmospheric heat fluxes in the North Atlantic and their link to the North Atlantic Oscillation Index

2020 ◽  
Author(s):  
Diana Iakovleva ◽  
Igor Bashmachnikov
Keyword(s):  
North Atlantic ◽  
Heat Content ◽  
Heat Fluxes ◽  
Upper Ocean ◽  
Subpolar Gyre ◽  
Heat Advection ◽  
Norwegian Sea ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

<p>Interannual variations in the upper ocean heat and freshwater contents in the subpolar North Atlantic has important climatic effect. It affects the intensity of deep convection, which, in turn, forms the link between upper and deep ocean circulation of the global ocean Conveyor Belt.</p><p>The upper ocean heat content is primarily affected by two main process: by the ocean-atmosphere heat exchange and by oceanic heat advection. The intensity of both fluxes in the subpolar gyre is linked to the character of atmospheric circulation, largely determined by the phase of the North Atlantic Oscillation (NAO).</p><p>To study the interannual variability of the oceanic heat advection (in the upper 500<sup>th</sup> meters layer) we compare the results from four different data-sets: ARMOR-3D (1993-2018), SODA3.4.2 and SODA3.12.2 (1980-2017), and ORAS5 (1958-2017). The ocean-atmosphere heat exchange is accessed as the sum of the latent and the sensible heat fluxes, obtained from OAFlux data-set (1958-2016).</p><p>The oceanic heat advection to the Labrador and to the Irminger seas has high negative correlation (-0.79) with that into the Nordic Seas. During the years with high winter NAO Index (NAOI) the oceanic heat advection into the Subpolar Gyre decreases, while to the Nordic Seas – increases. These variations go in parallel with the intensification of the Norwegian, the West Spitsbergen and the slope East Greenland currents and weakening of the West Greenland and the Irminger Currents. During the years with high NAOI, the ocean heat release (both sensible and latent) over the Labrador and Irminger seas increases, but over the Norwegian Sea it decreases.</p><p>In summary, the results show that, during the positive NAO phase, the observed decrease of the heat content in the upper Labrador and Irminger seas is linked to both, a higher oceanic het release and a lower intensity of advection of warm water from the south. In the Norwegian Sea, the opposite sign of variations of the fluxes above leads to a simultaneous warming of the upper ocean.</p><p>The investigation is supported by the Russian Scientific Foundation (RSF), number of project 17-17-01151.</p><p> </p><p> </p>

scholarly journals Circulation adjustment in the Arctic and Atlantic in response to Greenland and Antarctic mass loss

2021 ◽  
Author(s):  
J. van den Berk ◽  
S. S. Drijfhout ◽  
W. Hazeleger
Keyword(s):  
Mass Loss ◽  
North Atlantic ◽  
Subtropical Gyre ◽  
The Arctic ◽  
Subpolar Gyre ◽  
Nordic Seas ◽  
The North ◽  
Freshwater Forcing ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic

AbstractFollowing a high-end projection for mass loss from the Greenland and Antarctic ice-sheets, a freshwater forcing was applied to the ocean surface in the coupled climate model EC-Earthv2.2 to study the response to meltwater release assuming an RCP8.5 emission scenario. The meltwater forcing results in an overall freshening of the Atlantic that is dominated by advective changes, strongly enhancing the freshening due to dilution by Greenland meltwater release. The strongest circulation change occurs in the western North Atlantic subpolar gyre and in the gyre in the Nordic Seas, leaving the North Atlantic subpolar gyre the region where most advective salt export occurs. Associated with counteracting changes in both gyre systems, the response of the Atlantic Meridional Overturning Circulation is rather weak over the 190 years of the experiment; it reduces with only 1 Sv ($$= 10^6$$ = 10 6 m $$^3$$ 3 s $$^{-1}$$ - 1 ), compared to changes in the subpolar gyre of 5 Sv. This relative insensitivity of the AMOC to the forcing is attributed to enhanced convection in the Nordic Seas and stronger overflows that compensate reduced convection in the Labrador and Irminger Seas, and lead to higher sea surface temperatures (SSTs) in the former and lower SSTs in the latter region. The weakened subpolar gyre in the west also shifts the North Atlantic Current and the subpolar-subtropical gyre boundary; with the subtropical gyre expanding, and the western subpolar gyre contracting. The SST changes are associated with obduction of Atlantic waters in the Nordic Seas that would otherwise obduct in the western subpolar gyre. The anomalous SSTs also induce a coupled ocean-atmosphere feedback that further strengthens the Nordic Seas circulation and weakens the western subpolar gyre. This occurs because the anomalous SST-gradient enhances the westerlies, especially between 65$$^{\circ }$$ ∘ N and 70$$^{\circ }$$ ∘ N; the associated increase in windstress curl consequently enhances the gyre in the Nordic Seas. This feedback is driven by the Greenland mass loss; Antarctic meltwater discharge causes a weaker, opposite response and more particularly affects the South Atlantic salinity budget through northward advection of low-salinity waters from the Southern Ocean. This effect, however, becomes visible only hundred years after the onset of Antarctic mass loss. We conclude that the response to freshwater forcing from both ice caps can lead to a complex response in the Atlantic circulation systems with opposing effects in different subbasins. The relative strength of the response is time-dependent and largely governed by internal feedbacks; the forcing acts mainly as a trigger and is decoupled from the response.

scholarly journals Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

2019 ◽  
Author(s):  
Mathieu Le Corre ◽  
Jonathan Gula ◽  
Anne-Marie Tréguier
Keyword(s):  
North Atlantic ◽  
Subpolar Gyre ◽  
Bottom Pressure ◽  
First Order ◽  
The North ◽  
Sverdrup Balance ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic ◽  
Barotropic Vorticity ◽  
Vorticity Balance

Abstract. The circulation in the North Atlantic Subpolar gyre is complex and strongly influenced by the topography. The gyre dynamics is traditionally understood as the result of a topographic Sverdrup balance, which corresponds to a first order balance between the planetary vorticity advection, the bottom pressure torque and the wind stress curl. However, this dynamics has been studied mostly with non-eddy-resolving models and a crude representation of the bottom topography. Here we revisit the barotropic vorticity balance of the North Atlantic Subpolar gyre using a high resolution simulation (≈ 2-km) with topography-following vertical coordinates to better represent the mesoscale turbulence and flow-topography interactions. Our findings highlight that, locally, there is a first order balance between the bottom pressure torque and the nonlinear terms, albeit with a high degree of cancellation between each other. However, balances integrated over different regions of the gyre – shelf, slope and interior – still highlight the important role played by nonlinearities and the bottom drag curls. In particular the topographic Sverdrup balance cannot describe the dynamics in the interior of the gyre. The main sources of cyclonic vorticity are the nonlinear terms due to eddies generated along eastern boundary currents and the time-mean nonlinear terms from the Northwest Corner. Our results suggest that a good representation of the mesoscale activity along with a good positioning of the Northwest corner are two important conditions for a better representation of the circulation in the North Atlantic Subpolar Gyre.

scholarly journals The seasonal cycle of δ<sup>3</sup>C<sub>DIC</sub> in the North Atlantic subpolar gyre

2014 ◽  
Vol 11 (6) ◽  
pp. 1683-1692 ◽  
Author(s):  
V. Racapé ◽  
N. Metzl ◽  
C. Pierre ◽  
G. Reverdin ◽  
P. D. Quay ◽  
...  
Keyword(s):  
North Atlantic ◽  
Dissolved Inorganic Carbon ◽  
Ocean Dynamics ◽  
Subpolar Gyre ◽  
The North ◽  
Winter Convection ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic ◽  
First Time ◽  
Negative Linear Relationship

Abstract. This study introduces for the first time the δ13CDIC seasonality in the North Atlantic subpolar gyre (NASPG) using δ13CDIC data obtained in 2005–2006 and 2010–2012 with dissolved inorganic carbon (DIC) and nutrient observations. On the seasonal scale, the NASPG is characterized by higher δ13CDIC values during summer than during winter, with a seasonal amplitude between 0.70 ± 0.10‰ (August 2010–March 2011) and 0.77 ± 0.07‰ (2005–2006). This is mainly attributed to photosynthetic activity in summer and to a deep remineralization process during winter convection, sometimes influenced by ocean dynamics and carbonate pumps. There is also a strong and negative linear relationship between δ13CDIC and DIC during all seasons. Winter data also showed a large decrease in δ13CDIC associated with an increase in DIC between 2006 and 2011–2012, but the observed time rates (−0.04‰ yr−1and +1.7 μmol kg−1 yr−1) are much larger than the expected anthropogenic signal.

scholarly journals Ocean carbonate system variability in the North Atlantic Subpolar surface water (1993–2017)

2020 ◽  
Vol 17 (9) ◽  
pp. 2553-2577
Author(s):  
Coraline Leseurre ◽  
Claire Lo Monaco ◽  
Gilles Reverdin ◽  
Nicolas Metzl ◽  
Jonathan Fin ◽  
...  
Keyword(s):  
Surface Water ◽  
Ocean Acidification ◽  
North Atlantic ◽  
Subpolar Gyre ◽  
The North ◽  
Short Period ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic ◽  
Co2 Sink

Abstract. The North Atlantic is one of the major ocean sinks for natural and anthropogenic atmospheric CO2. Given the variability of the circulation, convective processes or warming–cooling recognized in the high latitudes in this region, a better understanding of the CO2 sink temporal variability and associated acidification needs a close inspection of seasonal, interannual to multidecadal observations. In this study, we investigate the evolution of CO2 uptake and ocean acidification in the North Atlantic Subpolar Gyre (50–64∘ N) using repeated observations collected over the last 3 decades in the framework of the long-term monitoring program SURATLANT (SURveillance de l'ATLANTique). Over the full period (1993–2017) pH decreases (−0.0017 yr−1) and fugacity of CO2 (fCO2) increases (+1.70 µatm yr−1). The trend of fCO2 in surface water is slightly less than the atmospheric rate (+1.96 µatm yr−1). This is mainly due to dissolved inorganic carbon (DIC) increase associated with the anthropogenic signal. However, over shorter periods (4–10 years) and depending on the season, we detect significant variability investigated in more detail in this study. Data obtained between 1993 and 1997 suggest a rapid increase in fCO2 in summer (up to +14 µatm yr−1) that was driven by a significant warming and an increase in DIC for a short period. Similar fCO2 trends are observed between 2001 and 2007 during both summer and winter, but, without significant warming detected, these trends are mainly explained by an increase in DIC and a decrease in alkalinity. This also leads to a pH decrease but with contrasting trends depending on the region and season (between −0.006 and −0.013 yr−1). Conversely, data obtained during the last decade (2008–2017) in summer show a cooling of surface waters and an increase in alkalinity, leading to a strong decrease in surface fCO2 (between −4.4 and −2.3 µatm yr−1; i.e., the ocean CO2 sink increases). Surprisingly, during summer, pH increases up to +0.0052 yr−1 in the southern subpolar gyre. Overall, our results show that, in addition to the accumulation of anthropogenic CO2, the temporal changes in the uptake of CO2 and ocean acidification in the North Atlantic Subpolar Gyre present significant multiannual variability, not clearly directly associated with the North Atlantic Oscillation (NAO). With such variability it is uncertain to predict the near-future evolution of air–sea CO2 fluxes and pH in this region. Thus, it is highly recommended to maintain long-term observations to monitor these properties in the next decade.

scholarly journals Extreme air–sea interaction over the North Atlantic subpolar gyre during the winter of 2013–2014 and its sub-surface legacy

2015 ◽  
Vol 46 (11-12) ◽  
pp. 4027-4045 ◽  
Author(s):  
Jeremy P. Grist ◽  
Simon A. Josey ◽  
Zoe L. Jacobs ◽  
Robert Marsh ◽  
Bablu Sinha ◽  
...  
Keyword(s):  
North Atlantic ◽  
Subpolar Gyre ◽  
The North ◽  
North Atlantic Subpolar Gyre ◽  
The North Atlantic
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