scholarly journals Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020 

2021 ◽  
Author(s):  
Christine Provost ◽  
Marylou Athanase ◽  
Maria-Dolores Pérez-Hernández ◽  
Nathalie Sennéchael ◽  
Cécilia Bertosio ◽  
...  
Keyword(s):  
Continental Slope ◽  
Atlantic Water ◽  
Heat Fluxes ◽  
The Arctic ◽  
Buoyancy Frequency ◽  
Interannual Variations ◽  
Good Tool ◽  
Winter Convection ◽  
Yermak Plateau ◽  
Mixed Layers

<div> <div> <div> <p>The Atlantic Water (AW) inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes substantial modifications in the Western Nansen Basin (WNB). Evaluation of the Mercator system in the WNB, using 1,500 independent temperature‐salinity profiles and five years of mooring data, highlighted its performance in representing realistic AW inflow and hydrographic properties. In particular, favorable comparisons with mooring time‐series documenting deep winter mixed layers and changes in AW properties led us to examine winter conditions in the WNB over the 2007–2020 period. The model helped describe the interannual variations of winter mixed layers and documented several processes at stake in modifying AW beyond winter convection: trough outflows and lateral exchange through vigorous eddies. Recently modified AW, either via local convection or trough outflows, were identified as homogeneous layers of low buoyancy frequency. Over the 2007–2020 period, two winters stood out with extreme deep mixed layers in areas that used to be ice‐covered: 2017/18 over the northern Yermak Plateau‐Sofia Deep; 2012/13 on the continental slope northeast of Svalbard with the coldest and freshest modified AW of the 12‐year time series. The northern Yermak Plateau‐Sofia Deep and continental slope areas became “Marginal Convection Zones” in 2011 with, from then on, occasionally ice‐free conditions, 50‐m‐ocean temperatures always above 0 °C and highly variable mixed layer depths and ocean‐to‐atmosphere heat fluxes. In the WNB where observations require considerable efforts and resources, the Mercator system proved to be a good tool to assess Atlantic Water modifications in winter.</p> </div> </div> </div>

Convection in the oceanic waters west of Britain

1986 ◽  
Vol 88 ◽  
pp. 127-139 ◽  
Author(s):  
J. Meincke
Keyword(s):  
Continental Slope ◽  
Vertical Structure ◽  
Spatial Scales ◽  
Atlantic Water ◽  
Maximum Depth ◽  
The Arctic ◽  
Preliminary Results ◽  
Winter Convection ◽  
Arctic Front

SynopsisPreliminary results from a winter and a summer cruise in 1984 to the area west of the U.K. continental slope are presented to discuss the structure and the spatial scales of convection. Winter convection events were found to reach a depth of 630 m with horizontal scales of the order of 50 km. The number of areas with actual convection to maximum depth was small at the particular time of the cruise, but the vertical structure in the investigated area indicated numerous convection events over a longer period. The principal vertical structure of the upper 600 m in winter was preserved until the following summer, which agreed with the age of the summer upper layer water estimated from the tritium/helium ratio. This characterises the area to be one of low advection, which can also be indirectly concluded from the fact that the northward flow of 4 Sverdrup of Atlantic Water through the Faeroe-Shetland Channel is supplied by 2 Sverdrup from the current over the continental slope west of U.K. and 2 Sverdrup of flow along the Arctic Front between Iceland and the Faeroes.

scholarly journals Eastern Arctic Ocean Diapycnal Heat Fluxes through Large Double-Diffusive Steps

2019 ◽  
Vol 49 (1) ◽  
pp. 227-246 ◽  
Author(s):  
Igor V. Polyakov ◽  
Laurie Padman ◽  
Y.-D. Lenn ◽  
Andrey Pnyushkov ◽  
Robert Rember ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Dissipation Rate ◽  
Critical Role ◽  
Density Ratio ◽  
Atlantic Water ◽  
Heat Fluxes ◽  
The Arctic ◽  
Eurasian Basin ◽  
Average Flux ◽  
Double Diffusive

AbstractThe diffusive layering (DL) form of double-diffusive convection cools the Atlantic Water (AW) as it circulates around the Arctic Ocean. Large DL steps, with heights of homogeneous layers often greater than 10 m, have been found above the AW core in the Eurasian Basin (EB) of the eastern Arctic. Within these DL staircases, heat and salt fluxes are determined by the mechanisms for vertical transport through the high-gradient regions (HGRs) between the homogeneous layers. These HGRs can be thick (up to 5 m and more) and are frequently complex, being composed of multiple small steps or continuous stratification. Microstructure data collected in the EB in 2007 and 2008 are used to estimate heat fluxes through large steps in three ways: using the measured dissipation rate in the large homogeneous layers; utilizing empirical flux laws based on the density ratio and temperature step across HGRs after scaling to account for the presence of multiple small DL interfaces within each HGR; and averaging estimates of heat fluxes computed separately for individual small interfaces (as laminar conductive fluxes), small convective layers (via dissipation rates within small DL layers), and turbulent patches (using dissipation rate and buoyancy) within each HGR. Diapycnal heat fluxes through HGRs evaluated by each method agree with each other and range from ~2 to ~8 W m−2, with an average flux of ~3–4 W m−2. These large fluxes confirm a critical role for the DL instability in cooling and thickening the AW layer as it circulates around the eastern Arctic Ocean.

scholarly journals Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean

2020 ◽  
Vol 33 (18) ◽  
pp. 8107-8123 ◽  
Author(s):  
Igor V. Polyakov ◽  
Tom P. Rippeth ◽  
Ilker Fer ◽  
Matthew B. Alkire ◽  
Till M. Baumann ◽  
...  
Keyword(s):  
Heat Flux ◽  
Sea Ice ◽  
Arctic Ocean ◽  
Mixed Layer ◽  
Winter Season ◽  
Atlantic Water ◽  
The Arctic ◽  
Surface Mixed Layer ◽  
Winter Convection ◽  
Oceanic Heat Flux

AbstractA 15-yr duration record of mooring observations from the eastern (>70°E) Eurasian Basin (EB) of the Arctic Ocean is used to show and quantify the recently increased oceanic heat flux from intermediate-depth (~150–900 m) warm Atlantic Water (AW) to the surface mixed layer and sea ice. The upward release of AW heat is regulated by the stability of the overlying halocline, which we show has weakened substantially in recent years. Shoaling of the AW has also contributed, with observations in winter 2017–18 showing AW at only 80 m depth, just below the wintertime surface mixed layer, the shallowest in our mooring records. The weakening of the halocline for several months at this time implies that AW heat was linked to winter convection associated with brine rejection during sea ice formation. This resulted in a substantial increase of upward oceanic heat flux during the winter season, from an average of 3–4 W m−2 in 2007–08 to >10 W m−2 in 2016–18. This seasonal AW heat loss in the eastern EB is equivalent to a more than a twofold reduction of winter ice growth. These changes imply a positive feedback as reduced sea ice cover permits increased mixing, augmenting the summer-dominated ice-albedo feedback.

scholarly journals Winter Convection Transports Atlantic Water Heat to the Surface Layer in the Eastern Arctic Ocean*

2013 ◽  
Vol 43 (10) ◽  
pp. 2142-2155 ◽  
Author(s):  
Igor V. Polyakov ◽  
Andrey V. Pnyushkov ◽  
Robert Rember ◽  
Laurie Padman ◽  
Eddy C. Carmack ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Heat Loss ◽  
Mixed Layer ◽  
Atlantic Water ◽  
Velocity Shear ◽  
The Arctic ◽  
Ice Formation ◽  
Surface Mixed Layer ◽  
Winter Convection

Abstract A 1-yr (2009/10) record of temperature and salinity profiles from Ice-Tethered Profiler (ITP) buoys in the Eurasian Basin (EB) of the Arctic Ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer. The upper pycnocline in the central EB is fed by the upward flux of heat from the intermediate-depth (~150–900 m) Atlantic Water (AW) layer; this flux is estimated to be ~1 W m−2 averaged over one year. Release of heat from the upper pycnocline, through the cold halocline layer to the surface mixed layer is, however, seasonally intensified, occurring more strongly in winter. This seasonal heat loss averages ~3–4 W m−2 between January and April, reducing the rate of winter sea ice formation. This study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine-driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer (SML), enhanced by atmospheric storms and the seasonal reduction in density difference between the SML and underlying pycnocline.

scholarly journals The coherence of the oceanic heat transport through the Nordic seas: oceanic heat budget and interannual variability

2020 ◽  
Author(s):  
Anna V. Vesman ◽  
Igor L. Bashmachnikov ◽  
Pavel A. Golubkin ◽  
Roshin P. Raj
Keyword(s):  
Heat Budget ◽  
Atlantic Water ◽  
Heat Fluxes ◽  
The Arctic ◽  
Ekman Pumping ◽  
Sea Ice Extent ◽  
Weather Types ◽  
Study Region ◽  
Nordic Seas ◽  
Local Climate

Abstract. Atlantic Water is the main source of the heat and salt in the Arctic. On the way to the Arctic Ocean via the Nordic Seas, it interacts and mixes with other water masses which affects sea ice extent and deep water formation. The Atlantic Water heat transported into the Nordic Seas has a significant impact on the local climate and is investigated here along with its inter-annual variability using the ARMOR3D dataset, which is a collection of 3D monthly temperature, salinity and geostrophic velocities fields, derived from in situ and satellite data on a regular grid since 1993. The study region includes the eastern part of the Nordic seas, i.e., seven latitudinal transects from Svinoy section (65° N) to the northern part of the Fram Strait (78.8° N). The Atlantic Water heat advection decreases northwards, as a significant amount of heat is lost to the atmosphere and due to mixing with surrounding waters. As observed, the imbalance of heat fluxes in the upper layer leads to an increase in the upper ocean mean temperature over most of the study region. The correlations of the interannual variations of the advective heat fluxes rapidly drop from Svinoy to Jan Mayen sections and between Bear Island and Sorkapp sections. This is a result of a differential damping of periodicities (the 2–3 year and 5–6 year oscillations), as well as of different signs of the tendencies over the latest decades. The heat fluxes at all sections show a consistent change with meridional (C) and western (W) weather types, which is due to the different direction of the Ekman pumping associated with each of the weather types. A certain link to the NAO, AO and EA atmospheric indices is observed only at the southern sections.

scholarly journals Tidal forcing, energetics, and mixing near the Yermak Plateau

Ocean Science ◽  
2015 ◽  
Vol 11 (2) ◽  
pp. 287-304 ◽  
Author(s):  
I. Fer ◽  
M. Müller ◽  
A. K. Peterson
Keyword(s):  
Energy Conversion ◽  
Arctic Ocean ◽  
Atlantic Water ◽  
The Arctic ◽  
Fram Strait ◽  
Topographic Feature ◽  
Dissipation Rates ◽  
Conversion Rates ◽  
The Arctic Ocean ◽  
Yermak Plateau

Abstract. The Yermak Plateau (YP), located northwest of Svalbard in Fram Strait, is the final passage for the inflow of warm Atlantic Water into the Arctic Ocean. The region is characterized by the largest barotropic tidal velocities in the Arctic Ocean. Internal response to the tidal flow over this topographic feature locally contributes to mixing that removes heat from the Atlantic Water. Here, we investigate the tidal forcing, barotropic-to-baroclinic energy conversion rates, and dissipation rates in the region using observations of oceanic currents, hydrography, and microstructure collected on the southern flanks of the plateau in summer 2007, together with results from a global high-resolution ocean circulation and tide model simulation. The energetics (depth-integrated conversion rates, baroclinic energy fluxes and dissipation rates) show large spatial variability over the plateau and are dominated by the luni-solar diurnal (K1) and the principal lunar semidiurnal (M2) constituents. The volume-integrated conversion rate over the region enclosing the topographic feature is approximately 1 GW and accounts for about 50% of the M2 and approximately all of the K1 conversion in a larger domain covering the entire Fram Strait extended to the North Pole. Despite the substantial energy conversion, internal tides are trapped along the topography, implying large local dissipation rates. An approximate local conversion–dissipation balance is found over shallows and also in the deep part of the sloping flanks. The baroclinic energy radiated away from the upper slope is dissipated over the deeper isobaths. From the microstructure observations, we inferred lower and upper bounds on the total dissipation rate of about 0.5 and 1.1 GW, respectively, where about 0.4–0.6 GW can be attributed to the contribution of hot spots of energetic turbulence. The domain-integrated dissipation from the model is close to the upper bound of the observed dissipation, and implies that almost the entire dissipation in the region can be attributed to the dissipation of baroclinic tidal energy.

scholarly journals Water mass distribution in Fram Strait and over the Yermak Plateau in summer 1997

2000 ◽  
Vol 18 (6) ◽  
pp. 687-705 ◽  
Author(s):  
B. Rudels ◽  
R. Meyer ◽  
E. Fahrbach ◽  
V. V. Ivanov ◽  
S. Østerhus ◽  
...  
Keyword(s):  
Arctic Ocean ◽  
Water Mass ◽  
Atlantic Water ◽  
The Arctic ◽  
Fram Strait ◽  
The West ◽  
The Arctic Ocean ◽  
Yermak Plateau ◽  
Eurasian Basin ◽  
West Spitsbergen

Abstract. The water mass distribution in northern Fram Strait and over the Yermak Plateau in summer 1997 is described using CTD data from two cruises in the area. The West Spitsbergen Current was found to split, one part recirculated towards the west, while the other part, on entering the Arctic Ocean separated into two branches. The main inflow of Atlantic Water followed the Svalbard continental slope eastward, while a second, narrower, branch stayed west and north of the Yermak Plateau. The water column above the southeastern flank of the Yermak Plateau was distinctly colder and less saline than the two inflow branches. Immediately west of the outer inflow branch comparatively high temperatures in the Atlantic Layer suggested that a part of the extraordinarily warm Atlantic Water, observed in the boundary current in the Eurasian Basin in the early 1990s, was now returning, within the Eurasian Basin, toward Fram Strait. The upper layer west of the Yermak Plateau was cold, deep and comparably saline, similar to what has recently been observed in the interior Eurasian Basin. Closer to the Greenland continental slope the salinity of the upper layer became much lower, and the temperature maximum of the Atlantic Layer was occasionally below  0.5 °C, indicating water masses mainly derived from the Canadian Basin. This implies that the warm pulse of Atlantic Water had not yet made a complete circuit around the Arctic Ocean. The Atlantic Water of the West Spitsbergen Current recirculating within the strait did not extend as far towards Greenland as in the 1980s, leaving a broader passage for waters from the Atlantic and intermediate layers, exiting the Arctic Ocean. A possible interpretation is that the circulation pattern alternates between a strong recirculation of the West Spitsbergen Current in the strait, and a larger exchange of Atlantic Water between the Nordic Seas and the inner parts of the Arctic Ocean.Key words: Oceanography: general (Arctic and Antarctic oceanography; water masses) - Oceanography: physical (general circulation)

Topographically trapped waves along the continental slope north of Svalbard

2020 ◽  
Author(s):  
Kjersti Kalhagen ◽  
Frank Nilsen ◽  
Ragnheid Skogseth ◽  
Ilker Fer ◽  
Zoé Koenig ◽  
...  
Keyword(s):  
Heat Exchange ◽  
Arctic Ocean ◽  
Continental Slope ◽  
Atlantic Water ◽  
The Arctic ◽  
Boundary Current ◽  
Trapped Waves ◽  
Current Time ◽  
The Arctic Ocean ◽  
Lateral Exchange

<p>On the continental slope north of Svalbard, Atlantic Water is transported eastward as a part of the Arctic Circumpolar Boundary Current. As inflow of Atlantic Water through the Fram Strait is the largest oceanic heat source to the Arctic Ocean, it is important to improve our knowledge about the dynamics and processes that govern the heat exchange between Atlantic Water and water masses of Arctic origin. This includes processes that enable lateral exchange across the shelf break or into the interior of the deep basin. Here, we study the vorticity dynamics on the slope and its contribution to the water mass modifications and heat exchange. Focusing on topographically trapped waves – sub-inertial oscillations trapped to follow the continental slope – we establish their existence and properties on the northern slope of Svalbard using a free baroclinic wave model. Their dependence on background stratification and current properties is explored in sensitivity analysis. Next, we discuss their contribution to lateral exchange from the boundary current on the slope to the continental shelf, troughs, and the deep Nansen Basin in the Arctic Ocean, including exchange associated with instabilities and resulting eddy shedding off the vorticity waves. Hydrographic and current time series from 2018-19 at two mooring arrays crossing the slope north of Svalbard (The Nansen Legacy project) are used to associate the observed physical environment with model-predicted topographic waves. Analysis of the in-situ data will determine which wave mode that can exist over the sloping seafloor and the observed hydrography and flow, and the model will give the corresponding spatial characteristics for the given frequencies and wave numbers. Energetic oscillations present in the observations are analyzed in light of the model results. Of special interest are the seasonal variability in hydrography and current strength and the resulting modification of the wave characteristics. Moreover, the interaction between the vorticity waves and tidal oscillations in the diurnal band is emphasized.</p>

Mixed layers along the Atlantic water path in the Nordic seas in HighResMIP models

2021 ◽  
Author(s):  
Anne Marie Tréguier ◽  
Torben Koenigk ◽  
Iovino Doroteaciro ◽  
Lique Camille ◽  
David Docquier
Keyword(s):  
High Resolution ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Atlantic Water ◽  
The Arctic ◽  
Greenland Sea ◽  
Layer Depth ◽  
Nordic Seas ◽  
Heat Exchanges ◽  
Mixed Layers

<p>Atlantic water flows over the Greenland-Iceland-Scotland Ridge into the Norwegian Sea. Along its path towards the Arctic, the Atlantic water is cooled by strong air-sea fluxes. Deep winter mixed layers modify the stratification and properties of the Atlantic water and precondition its flow into the Arctic, thus influencing Arctic sea ice and climate. Atlantic water also recirculates in the Greenland sea where deep water formation contributes to the dense limb of the Atlantic Meridional Overturning Circulation. It is thus of paramount importance to represent mixed layer deepening and lateral heat exchanges processes in the Nordic Seas in climate models.</p><p>Heat exchanges in the Nordic Seas are influenced by narrow current branches, instabilities and eddies, which are not accurately represented in low resolution climate model (with grid ~ 50-100km).  Here we examine the mixed layer dynamics and heat exchanges using the latest generation of European high resolution global coupled models in the framework of HighResMip (5-15km grids in the Nordic Seas). We investigate in detail the effect of model resolution on the mixed layer depth and water mass formation in relation with the Atlantic water circulation and modification between the Norwegian and the Greenland Sea. First results show an increased northward ocean heat transport, a more realistic representation of the ocean current system in the Nordic Seas, and consequently an improved spatial distribution of the turbulent surface heat flux compared to standard resolution CMIP6 models. The mixed layer depth itself however varies strongly between different HighResMIP models. Summarizing, our assessment of the high resolution coupled simulations of the historical period demonstrates that future climate projections at high resolution have a huge potential, but also limitations.</p>

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