Shelf-basin exchange in the Laptev Sea in the warming climate: a model study

Abstract

GCM-based forecast simulations predict continuously increasing seasonality of the sea ice cover and an almost ice-free, summer-time, Arctic Ocean within several decades from the present. In this study we use a primitive equation ocean model: NEMO, coupled with the sea ice model LIM2, to test the hypothesis that under such an increased range in seasonal ice cover the intensity of shelf-basin water exchange will significantly increase. We use the simulated results for the Laptev Sea from a global model run 1958–2007 and compare results for two years with anomalously high and low summer sea ice extents: 1986–1987 and 2006–2007. The shelf–basin fluxes of volume, heat and salt during specific seasons are evaluated and attributed to plausible driving processes, with particular attention to dense water cascading. Analyses of the model temperature distribution at the depth of the intermediate maximum, associated with Atlantic Water, have shown a marked increase of the amount of the local origin cold water in late winter 2007 in the region, where dense water typically appears as a result of its formation on the shelf and subsequent downslope leakage. Calculation of the shelf-basin exchange during March-May in both years confirmed a substantial increase (a factor of two) of fluxes in “ice-free” 2007 compared to the “icy” 1987. According to several past model studies, dense water production on Arctic shelves in winter driven by ice freezing and brine rejection is not likely to cease in a warmer climate, but rather to increase. There is also observational evidence that cascading in the seasonally ice covered seas (e.g. the Barents Sea) is much more efficient than it is in the permanently ice covered Arctic Ocean, which supports these model results.

Keywords:

• Shelf-basin exchange
• Dense water cascading
• Arctic Ocean
• Sea ice
• Climate change

Acknowledgements

The authors would like to express their deep respect to Professor John Huthnance, M.B.E. of the National Oceanographic Centre (NOC), whose fundamental contribution to the theory of dense water cascading in the World Ocean inspired this investigation. We would like to thank our former colleague Beverly de Cuevas from the NOC for performing the model experiments. From the Russian side this study was supported by the Russian Science Foundation (grant #14-37-00053). At the NOC this study was supported by the UK Natural Environment Research Council through the Marine Centres’ Strategic Research Programmes and is a contribution to the Arctic Research Programme TEA-COSI project (Project ID: NE/I028947/1). The NOCS-ORCA simulations were undertaken as part of the DRAKKAR collaboration (Barnier et al. 2006). NOC also acknowledges the use of UK National High Performance Computing Resource. V. Ivanov is grateful to IARC director Larry Hinzman for the opportunity to finalise this paper during his visit in Fairbanks.

Disclosure statement

No potential conflict of interest was reported by the authors.