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

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.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0169.1 ◽

2013 ◽

Vol 43 (10) ◽

pp. 2142-2155 ◽

Cited By ~ 33

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.

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Estimation of Oceanic Heat Flux Under Sea Ice in the Arctic Ocean

Journal of Ocean University of China ◽

10.1007/s11802-019-3877-7 ◽

2019 ◽

Vol 18 (3) ◽

pp. 605-614 ◽

Cited By ~ 1

Author(s):

Long Lin ◽

Jinping Zhao

Keyword(s):

Heat Flux ◽

Sea Ice ◽

Arctic Ocean ◽

The Arctic ◽

Oceanic Heat Flux ◽

The Arctic Ocean

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Multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the Arctic Ocean

Journal of Geophysical Research Oceans ◽

10.1002/2012jc008731 ◽

2014 ◽

Vol 119 (1) ◽

pp. 537-547 ◽

Cited By ~ 14

Author(s):

Ruibo Lei ◽

Na Li ◽

Petra Heil ◽

Bin Cheng ◽

Zhanhai Zhang ◽

...

Keyword(s):

Heat Flux ◽

Sea Ice ◽

Arctic Ocean ◽

Mass Balance ◽

The Arctic ◽

Oceanic Heat Flux ◽

Thermal Regimes ◽

The Arctic Ocean ◽

Ice Mass Balance

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Competing Effects of Elevated Vertical Mixing and Increased Freshwater Input on the Stratification and Sea Ice Cover in a Changing Arctic Ocean

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0174.1 ◽

2016 ◽

Vol 46 (5) ◽

pp. 1531-1553 ◽

Cited By ~ 15

Author(s):

Peter E. D. Davis ◽

Camille Lique ◽

Helen L. Johnson ◽

John D. Guthrie

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Mixed Layer ◽

Vertical Mixing ◽

Ice Cover ◽

Atlantic Water ◽

The Arctic ◽

Freshwater Input ◽

Eurasian Basin ◽

Canadian Basin

AbstractThe Arctic Ocean is undergoing a period of rapid transition. Freshwater input is projected to increase, and the decline in Arctic sea ice is likely to drive periodic increases in vertical mixing during ice-free periods. Here, a 1D model of the Arctic Ocean is used to explore how these competing processes will affect the stratification, the stability of the cold halocline, and the sea ice cover at the surface. Initially, stronger shear leads to elevated vertical mixing that causes the mixed layer to warm. The change in temperature, however, is too small to affect the sea ice cover. Most importantly, in the Eurasian Basin, the elevated shear also deepens the halocline and strengthens the stratification over the Atlantic Water thermocline, reducing the vertical heat flux. After about a decade this effect dominates, and the mixed layer begins to cool. The sea ice cover can only be significantly affected if the elevated mixing is sufficient to erode the stratification barrier associated with the cold halocline. While freshwater generally dominates in the Canadian Basin (further isolating the mixed layer from the Atlantic Water layer), in the Eurasian Basin elevated shear reduces the strength of the stratification barrier, potentially allowing Atlantic Water heat to be directly entrained into the mixed layer during episodic mixing events. Therefore, although most sea ice retreat to date has occurred in the Canadian Basin, the results here suggest that, in future decades, elevated vertical mixing may play a more significant role in sea ice melt in the Eurasian Basin.

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The role of sea ice for plastic pollution in the Arctic

10.5194/egusphere-egu21-13366 ◽

2021 ◽

Author(s):

Ilka Peeken ◽

Elisa Bergami ◽

Ilaria Corsi ◽

Benedikt Hufnagl ◽

Christian Katlein ◽

...

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Long Range ◽

Environmental Concern ◽

Ice Cores ◽

Atlantic Water ◽

The Arctic ◽

Polar Regions ◽

Plastic Pollution ◽

The Arctic Ocean

Marine plastic pollution is a growing worldwide environmental concern as recent reports indicate that increasing quantities of litter disperse into secluded environments, including Polar Regions. Plastic degrades into smaller fragments under the influence of sunlight, temperature changes, mechanic abrasion and wave action resulting in small particles < 5mm called microplastics (MP). Sea ice cores, collected in the Arctic Ocean have so far revealed extremely high concentrations of very small microplastic particles, which might be transferred in the ecosystem with so far unknown consequences for the ice dependant marine food chain.&#160; Sea ice has long been recognised as a transport vehicle for any contaminates entering the Arctic Ocean from various long range and local sources. The Fram Strait is hereby both, a major inflow gateway of warm Atlantic water, with any anthropogenic imprints and the major outflow region of sea ice originating from the Siberian shelves and carried via the Transpolar Drift. The studied sea ice revealed a unique footprint of microplastic pollution, which were related to different water masses and indicating different source regions. Climate change in the Arctic include loss of sea ice, therefore, large fractions of the embedded plastic particles might be released and have an impact on living systems. By combining modeling of sea ice origin and growth, MP particle trajectories in the water column as well as MPs long-range transport via particle tracking and transport models we get first insights &#160;about the sources and pathways of MP in the Arctic Ocean and beyond and how this might affect the Arctic ecosystem.

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Intensification of the Atlantic Water Supply to the Arctic Ocean Through Fram Strait Induced by Arctic Sea Ice Decline

Geophysical Research Letters ◽

10.1029/2019gl086682 ◽

2020 ◽

Vol 47 (3) ◽

Cited By ~ 3

Author(s):

Qiang Wang ◽

Claudia Wekerle ◽

Xuezhu Wang ◽

Sergey Danilov ◽

Nikolay Koldunov ◽

...

Keyword(s):

Sea Ice ◽

Water Supply ◽

Arctic Ocean ◽

Atlantic Water ◽

Arctic Sea Ice ◽

The Arctic ◽

Fram Strait ◽

Sea Ice Decline ◽

Arctic Sea ◽

The Arctic Ocean

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Brine-Driven Eddies under Sea Ice Leads and Their Impact on the Arctic Ocean Mixed Layer

Journal of Physical Oceanography ◽

10.1175/2007jpo3620.1 ◽

2008 ◽

Vol 38 (1) ◽

pp. 146-163 ◽

Cited By ~ 10

Author(s):

Yoshimasa Matsumura ◽

Hiroyasu Hasumi

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Mixed Layer ◽

General Circulation ◽

Salt Transport ◽

Salt Flux ◽

The Arctic ◽

Theoretical Argument ◽

Ocean Mixed Layer ◽

The Arctic Ocean

Abstract Eddy generation induced by a line-shaped salt flux under a sea ice lead and associated salt transport are investigated using a three-dimensional numerical model. The model is designed to represent a typical condition for the wintertime Arctic Ocean mixed layer, where new ice formation within leads is known to be one of the primary sources of dense water. The result shows that along-lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer, and almost all the lead-originated salt is contained inside these eddies. These eddies survive for over a month after closing of the lead and transport the lead-originated salt laterally. Consequently, the lead-origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer. Sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input. This scaling of eddy size is consistent with a theoretical argument based on a linear instability theory. Parameterizing these processes would improve representation of the Arctic Ocean mixed layer in ocean general circulation models.

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Time and space variability of freshwater content, heat content and seasonal ice melt in the Arctic Ocean from 1991 to 2011

Ocean Science Discussions ◽

10.5194/osd-9-2621-2012 ◽

2012 ◽

Vol 9 (4) ◽

pp. 2621-2677 ◽

Cited By ~ 6

Author(s):

M. Korhonen ◽

B. Rudels ◽

M. Marnela ◽

A. Wisotzki ◽

J. Zhao

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Mixed Layer ◽

Heat Content ◽

The Arctic ◽

Upper Ocean ◽

Heat Sources ◽

Time And Space ◽

Ice Melt ◽

The Arctic Ocean

Abstract. The Arctic Ocean gains freshwater mainly through river discharge, precipitation and the inflowing low salinity waters from the Pacific Ocean. In addition the recent reduction in sea ice volume is likely to influence the surface salinity and thus contribute to the freshwater content in the upper ocean. The present day freshwater storage in the Arctic Ocean appears to be sufficient to maintain the upper ocean stratification and to protect the sea ice from the deep ocean heat content. The recent freshening has not, despite the established strong stratification, been able to restrain the accelerating ice loss and other possible heat sources besides the Atlantic Water, such as the waters advecting from the Pacific Ocean and the solar insolation warming the Polar Mixed Layer, are investigated. Since the ongoing freshening, oceanic heat sources and the sea ice melt are closely related, this study, based on hydrographic observations, attempts to examine the ongoing variability in time and space in relation to these three properties. The largest time and space variability of freshwater content occurs in the Polar Mixed Layer and the upper halocline. The freshening of the upper ocean during the 2000s is ubiquitous in the Arctic Ocean although the most substantial increase occurs in the Canada Basin where the freshwater is accumulating in the thickening upper halocline. Whereas the salinity of the upper halocline is nearly constant, the freshwater content in the Polar Mixed Layer is increasing due to decreasing salinity. The decrease in salinity is likely to result from the recent changes in ice formation and melting. In contrast, in the Eurasian Basin where the seasonal ice melt has remained rather modest, the freshening of both the Polar Mixed Layer and the upper halocline is mainly of advective origin. While the warming of the Atlantic inflow was widespread in the Arctic Ocean during the 1990s, the warm and saline inflow events in the early 2000s appear to circulate mainly in the Nansen Basin. Nevertheless, even in the Nansen Basin the seasonal ice melt appears independent of the continuously increasing heat content in the Atlantic layer. As no other oceanic heat sources can be identified in the upper layers, it is likely that increased absorption of solar energy has been causing the ice melt prior to the observations.

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Lagrangian measurements in the West Spitsbergen Current by Argo floats

10.5194/egusphere-egu21-13135 ◽

2021 ◽

Author(s):

Waldemar Walczowski ◽

Agnieszka Beszczyńska-Möller ◽

Małgorzata Merchel

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Atlantic Water ◽

Shelf Break ◽

The Arctic ◽

Time Data ◽

The West ◽

Argo Floats ◽

The Arctic Ocean ◽

West Spitsbergen

Almost 4000 operational Argo floats covering the world's ocean provide near-real-time data on its state. The Arctic is less covered than other waters, but observations collected by Argo floats are gaining in importance. By delivering year-round measurements from the water column down to 2000 m (or to the bottom) along float trajectories, they complement and enhance the synoptic data collected during ship campaigns or by fixed moorings. However, oceanographic measurements with autonomous platforms are significantly limited in the Arctic regions by the presence of sea ice.Here we present results obtained by Argo floats deployed in 2012-2020 by the Institute of Oceanology Polish Academy of Sciences (IOPAN) during summer campaigns of RV Oceania. In most years, the Argo floats were launched in the eastern branch (core) and in the western branch of the West Spitsbergen Current (WSC) within the Atlantic water inflow towards the Arctic Ocean. Floats deployed in the WSC core drift predominantly northward over the shelf break and upper slope west of Svalbard. After passing Fram Strait the floats usually turn eastward and continue over the northern Svalbard shelf brake, being advected with the Svalbard Branch of the Atlantic inflow into the Arctic Ocean Boundary Current. The easternmost position reached by the IOPAN Argo float was 39.6&#176;E. Ultimately all deployed floats submerge under the sea ice north of Svalbard or farther to the east and die under the ice. Argo floats deployed in the western WSC branch over the underwater ridges, usually recirculate to the west and continue southward with the East Greenland Current. The float WMO 3901851 that drifted to the Labrador Sea, reached the southernmost latitude of 52.5&#176;N and have been working until now for 4.5 years, which is unusual in the Arctic conditions.&#160;&#160; &#160;The measurements collected in the Marginal Ice Zone are particularly interesting for studying the ocean-atmosphere-ice interactions at the boundary between open and ice-covered ocean as well as they can be used for developing the ice avoidance algorithms for the Argo floats and other under ice sensors and platforms. A number of profiles obtained by Argo floats under the sea ice provide unique measurements in the upper ocean layer that is usually inaccessible from other platforms (e.g., moorings). In 2020 several profiles were collected under the ice cover by Argo floats north of Svalbard and transmitted after the float emerged in the polynya. The eastward flow of warm (up to 4&#176; C at 80 m depth) Atlantic water was observed along the float trajectory over the shelf break. Measurements by Argo floats, revealing the dynamics and transformation of the Atlantic water entering the Arctic Ocean, are compared with ship-borne observations collected during the IOPAN long-term observational program AREX and year-round data from IOPAN moorings deployed north of Svalbard under the A-TWAIN and INTAROS projects.

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Drivers of sea ice decline in the Fram Strait and north of Svalbard

10.5194/egusphere-egu21-13529 ◽

2021 ◽

Author(s):

Agata Grynczel ◽

Agnieszka Beszczynska-Moeller ◽

Waldemar Walczowski

Keyword(s):

Sea Ice ◽

Arctic Ocean ◽

Ice Cover ◽

Atlantic Water ◽

The Arctic ◽

Fram Strait ◽

Atmospheric Conditions ◽

The North ◽

The Arctic Ocean ◽

Atlantic Origin

The Arctic Ocean is undergoing rapid change. Satellite observations indicate significant negative Arctic sea ice extent trends in all months and substantial reduction of winter sea ice in the Atlantic sector. One of the possible reasons can be sought in the observed warming of Atlantic water, carried through Fram Strait into the Arctic Ocean. Fram Strait, as well as the region north of Svalbard, play a key role in controlling the amount of oceanic heat supplied to the Arctic Ocean and are the place of dynamic interaction between the ocean and sea ice. Shrinking sea ice cover in the southern part of Nansen Basin (north of Svalbard) and shifting the ice edge in Fram Strait are driven by the interplay between increased advection of oceanic heat in the Atlantic origin water and changes in the local atmospheric conditions.Processes related to the loss of sea ice and the upward transport of heat from the layers of the Arctic Ocean occupied by the Atlantic water are still not fully explored, but higher than average temperature of Atlantic inflow in the Nordic Seas influence the upper ocean stratification and ice cover in the Arctic Ocean, in particular in the north of Svalbard area. The regional sea ice cover decline is statistically signifcant in all months, but the largest changes in the Nansen Basin are observed in winter season. The winter sea ice loss north of Svalbard is most pronounced above the core of the inflow warm Atlantic water. The basis for this hypothesis of the research is that continuously shrinking sea ice cover in the region north of Svalbard and withdrawal of the sea ice cover towards the northeast are driven by the interplay between increased oceanic heat in the Atlantic origin water and changes in the local atmospheric conditions, that can result in the increased ocean-air-sea ice exchange in winter seasons. In the current study we describe seasonal, interannual and decadal variability of concentration, drift, and thickness of sea ice in two regions, the north of Svalbard and central part of the Fram Strait, based on the satellite observations. To analyze the observed changes in the sea ice cover in relation to Atlantic water variability and atmospheric forcing we employ hydrographic data from the repeated CTD sections and new atmospheric reanalysis from ERA5. Atlantic water variability is described based on the set of summer synoptic sections across the Fram Strait branch of the Atlantic inflow that have been occupied annually since 1996 under the long-term observational program AREX of the Institute of Oceanology PAS. To elucidate driving mechanisms of the sea ice cover changes observed in different seasons in Fram Strait and north of Svalbard we analyze changes in the temperature, heat content and transport of the Atlantic water and describe their potential links to variable atmospheric forcing, including air temperature, air-ocean fluxes, and changes in wind pattern and wind stress.

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