TY - JOUR

T1 - Weakening of cold halocline layer exposes sea ice to oceanic heat in the eastern Arctic Ocean

AU - Polyakov, Igor

AU - Rippeth, Tom

AU - Fer, Ilker

AU - Alkire, Matthew

AU - Baumann, Till

AU - Carmack, Eddy

AU - Ivanov, Vladimir

AU - Janout, M.A.

AU - Padman, Laurie

AU - Pnyushkov, Andrey

AU - Rember, Robert

N1 - Published verrsion to be used - 6 month embargo

PY - 2020/9/15

Y1 - 2020/9/15

N2 - A 15-year duration record of mooring observations from the eastern (>70oE) 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 (SML) 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 2017-2018 showing AW at only 80 m depth, just below the wintertime surface mixed layer (SML), 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/m2 in 2007-2008 to >10 W/m2 in 2016-2018. This seasonal AW heat loss in the eastern EB is equivalent to a more than a two-fold 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.

AB - A 15-year duration record of mooring observations from the eastern (>70oE) 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 (SML) 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 2017-2018 showing AW at only 80 m depth, just below the wintertime surface mixed layer (SML), 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/m2 in 2007-2008 to >10 W/m2 in 2016-2018. This seasonal AW heat loss in the eastern EB is equivalent to a more than a two-fold 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.

KW - Arctic Sea Ice

KW - atlantification

U2 - 10.1175/JCLI-D-19-0976.1

DO - 10.1175/JCLI-D-19-0976.1

M3 - Article

VL - 33

SP - 8107

EP - 8123

JO - Journal of Climate

JF - Journal of Climate

SN - 0894-8755

IS - 18

ER -