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 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>

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.

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>

Modifications of Atlantic inflow along the Fram Strait Branch to the Arctic Ocean and its variability north of Svalbard from ship-borne and moored observations in the last two decades.

2021 ◽  
Author(s):  
Agnieszka Beszczynska-Möller ◽  
Waldemar Walczowski ◽  
Agata Grynczel
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Vertical Structure ◽  
Heat Content ◽  
Atlantic Water ◽  
Ocean Heat Content ◽  
The Arctic ◽  
Fram Strait ◽  
Ocean Atmosphere ◽  
The Arctic Ocean

<p>Understanding variable properties and dynamics of the Atlantic water (AW) inflow into the Arctic Ocean, and their impacts on ocean heat content, ocean-atmosphere-sea ice exchanges, changing sea ice cover and propagation of anomalies are key prerequisites to elucidate drivers and mechanisms behind the new, warmer regime of the Arctic Ocean. As the AW progress northwards, its properties are modified by ocean-atmosphere interactions, mixing and lateral exchanges. Warm anomalies reaching the Arctic Ocean can result from smaller heat loss during the AW northward passage through Fram Strait, and/or from an increased oceanic advection. Vertical structure of the Atlantic water layer implies the depth of winter convection and access to oceanic heat carried northward by the inflow.</p><p>During the last two decades warming of the Atlantic inflow has been reported to progress into the Arctic Ocean, however with strong interannual variations and quasi-periodic pulses of water with extraordinary high temperature. Here we present results from 20 years of annual hydrographic surveys, covering the Atlantic water inflow in the eastern Norwegian and Greenland seas, Fram Strait up to the southern Nansen Basin. Interannual changes in the AW properties and transport are analyzed with a focus on the en route modifications of AW inflow in the Fram Strait Branch and changes in the integrated ocean heat content.</p><p>After leaving Fram Strait, the part of AW continues eastward and enters the Arctic Ocean boundary current along different pathways north of Svalbard. The strongest ocean-atmosphere-sea ice interactions and lateral oceanic exchanges in this region lead to substantial local modification of the Atlantic inflow before it continues farther eastward around the rim of the Arctic Ocean. Observations from year-round moorings deployed since 2013 north of Svalbard are used to describe changes in the Atlantic water properties, vertical structure, and dynamics on monthly to seasonal and interannual time scales and their links to the upstream conditions and local and regional atmospheric forcing. Vertical heat fluxes from the Atlantic layer are derived to evaluate the ocean-air and ocean-sea ice exchanges in the only region of the Arctic Ocean where Atlantic-origin water has still contact with sea ice cover.</p>

scholarly journals The Arctic Front and its variability in the Norwegian Sea

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1729-1744 ◽  
Author(s):  
Roshin P. Raj ◽  
Sourav Chatterjee ◽  
Laurent Bertino ◽  
Antonio Turiel ◽  
Marcos Portabella
Keyword(s):  
Vertical Structure ◽  
Geographical Location ◽  
Singularity Analysis ◽  
Reanalysis Data ◽  
The Arctic ◽  
Horizontal Gradient ◽  
Norwegian Sea ◽  
The North ◽  
Frontal Structure ◽  
Arctic Front

Abstract. The Arctic Front (AF) in the Norwegian Sea is an important biologically productive region which is well-known for its large feeding schools of pelagic fish. A suite of satellite data, a regional coupled ocean–sea ice data assimilation system (the TOPAZ reanalysis) and atmospheric reanalysis data are used to investigate the variability in the lateral and vertical structure of the AF. A method, known as “singularity analysis”, is applied on the satellite and reanalysis data for 2-D spatial analysis of the front, whereas for the vertical structure, a horizontal gradient method is used. We present new evidence of active air–sea interaction along the AF due to enhanced momentum mixing near the frontal region. The frontal structure of the AF is found to be most distinct near the Faroe Current in the south-west Norwegian Sea and along the Mohn Ridge. Coincidentally, these are the two locations along the AF where the air–sea interactions are most intense. This study investigates in particular the frontal structure and its variability along the Mohn Ridge. The seasonal variability in the strength of the AF is found to be limited to the surface. The study also provides new insights into the influence of the three dominant modes of the Norwegian Sea atmospheric circulation on the AF along the Mohn Ridge. The analyses show a weakened AF during the negative phase of the North Atlantic Oscillation (NAO−), even though the geographical location of the front does not vary. The weakening of AF during NAO− is attributed to the variability in the strength of the Norwegian Atlantic Front Current over the Mohn Ridge associated with the changes in the wind field.

scholarly journals The Arctic Front and its variability in the Norwegian Sea

2019 ◽  
Author(s):  
Roshin P. Raj ◽  
Sourav Chatterjee ◽  
Laurent Bertino ◽  
Antonio Turiel ◽  
Marcos Portebella
Keyword(s):  
Vertical Structure ◽  
Geographical Location ◽  
Singularity Analysis ◽  
Reanalysis Data ◽  
The Arctic ◽  
Horizontal Gradient ◽  
Norwegian Sea ◽  
The North ◽  
Frontal Structure ◽  
Arctic Front

Abstract. The Arctic Front (AF) in the Norwegian Sea is an important biologically productive region which is well-known for its large feeding schools of pelagic fish. A suite of satellite data, a regional coupled ocean-sea ice data assimilation system (the TOPAZ reanalysis) and atmospheric reanalysis data is used to investigate the variability in the lateral and vertical structure of the AF. A method, the so-called Singularity Analysis, is applied on the satellite and reanalysis data for 2D spatial analysis of the front, whereas for the vertical structure, a horizontal gradient method is used. We present new evidences of active air-sea interaction along the AF due to enhanced momentum mixing near the frontal region. The frontal structure of the AF is found to be most distinct near the Faroe Current in the southwest Norwegian Sea and along the Mohn Ridge. Coincidentally, these are the two locations along the AF where the air-sea interactions are most intense. This study investigates in particular the frontal structure along the Mohn Ridge and provides new insights on the influence of the three dominant modes of the Norwegian Sea atmospheric circulation on the AF along the Mohn Ridge. The analyses show a weakened AF during the negative phase of the North Atlantic Oscillation (NAO-), even though the geographical location of the front does not vary. The weakening of AF during NAO- is attributed to the variability in the strength of the Norwegian Atlantic Front Current over the Mohn Ridge associated with the changes in the wind field.

scholarly journals Holocene polynya dynamics and their interaction with oceanic heat transport in northernmost Baffin Bay

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rebecca Jackson ◽  
Anna Bang Kvorning ◽  
Audrey Limoges ◽  
Eleanor Georgiadis ◽  
Steffen M. Olsen ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Active Role ◽  
Atlantic Water ◽  
The Arctic ◽  
Negative Consequences ◽  
Baffin Bay ◽  
The North ◽  
North Water ◽  
History Of ◽  
Ocean Conditions

AbstractBaffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.

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