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- Title
The Transition Layer and Remnant Transition Layer of the Western Arctic Ocean: Stratification, Vertical Diffusivity, and Pacific Summer Water Heat Fluxes.
- Authors
Cole, Sylvia T.; Roemer, Peter A.
- Abstract
The exchange of heat and other tracers between the ocean interior and sea ice cover depends on vertical diffusion through the thin and strongly stratified Arctic Ocean transition layer and remnant transition layer. Ice‐Tethered Profiler observations during 2004–2021 were used to characterize and investigate the active and remnant transition layers in the Beaufort Gyre region. Transition layers evolved seasonally, with the deepest, densest, and warmest transition layers observed in spring. In a composite view, the summer mixed layer shoaled over a timescale of approximately 2 weeks, leaving behind a remnant transition layer whose stratification had already begun to weaken. The stratification maximum of the remnant transition layer continued to weaken and broaden throughout the summer, including changes associated with storm events. The weakening stratification was used to estimate an effective vertical turbulent diffusivity which ranged from 10−8 to 10−6 m2/s for individual ITP records; a value of 6 × 10−7 m2/s is representative of the Beaufort Gyre region. Vertical heat fluxes through the active and remnant transition layers were estimated over 90‐day timescales. Springtime vertical heat fluxes increased from 0.3 ± 0.3 W/m2 during 2006–2011 to 1.1 ± 0.7 W/m2 during 2017–2021. Summertime vertical heat fluxes through the remnant transition layer were somewhat less, but also increased interannually. Vertical gradients of density during spring and summer, and so diffusion of density through the active and remnant transition layers, did not increase interannually. Pacific Summer Water warming has increased ocean to ice heat fluxes, which may continue to become more significant in the future. Plain Language Summary: Heat is stored in the Arctic Ocean tens to hundreds of meters beneath the sea ice cover. A small fraction of this heat can gradually or intermittently reach the sea ice and contribute to its melt in spring or delayed growth in fall. We use observations during 2004–2021 from the most strongly stratified portion of the ocean to investigate the energy barrier that isolates heat at depth. Ocean stratification was seasonally and interannually variable, and weakened in particular over the summer season, including due to storm events. Observations of this weakening are used to derive estimates of the turbulent mixing intensity, which are consistent with other estimates for the Arctic Ocean. Even with no interannual variations in the intensity of ocean mixing, vertical heat transport has increased due to changes in subsurface temperature. Our inferred heat transport in springtime has increased from enough heat to melt 1 cm of ice during 2006–2011 to 3 cm of ice during 2017–2021. Estimated vertical heat transport during summer was somewhat less, but also increased interannually. The role of stored ocean heat on the sea ice cover may become more significant in the future. Key Points: The transition layer varied seasonally, and the remnant transition layer evolved throughout the summer season, including due to storm eventsA representative effective vertical diffusivity for the transition layer and remnant transition layer is estimated to be 6 × 10−7 m2/sDiffusion of heat has increased interannually to values of 1 W/m2 or larger, while diffusion of density has remained constant
- Subjects
HEAT flux; SEA ice; OCEAN; SPRING; OCEANIC mixing; SUMMER
- Publication
Journal of Geophysical Research. Oceans, 2024, Vol 129, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC020059