Arctic Ocean freshwater composition, pathways andtransformations from a passive tracer simulation

摘要

Freshwater (FW) induced transformations in the upper Arctic Ocean were studied using a coupled regionalsea ice-ocean model driven by winds and thermodynamic forcing from a reanalysis of data during the period19482011, focusing on the mean state during 19682011. Using passive tracers to mark a number ofFW sources and sinks, their mean composition, pathways and export were examined. The distribution of thesimulated FW height reproduced the known features of the Arctic Ocean and volume-integrated FW contentmatched climatological estimates reasonably well. Input from Eurasian rivers and extraction by sea-ice formationdominate the composition of the ArcticFWcontent whilst Pacific water increases in importance in the CanadianBasin. Though pathways generally agreed with previous studies the locus of the Eurasian runoff shelf-basintransport centred at the Alpha-Mendeleyev ridge, shifting the PacificAtlantic front eastwards. A strongcoupling between tracers representing Eurasian runoff and sea-ice formation showed how water modified on theshelf spreads across the Arctic and mainly exits through the Fram Strait. Transformation to salinity dependentcoordinates showed how Atlantic water is modified by both low-salinity shelf and Pacific waters in an estuary-likeoverturning producing water masses of intermediate salinity that are exported to the Nordic Seas. A totalhalocline renewal rate of 1.0 Sv, including both shelf-basin exchange and cross-isohaline flux, was estimated fromthe transports: both components were of equal magnitude. The model’s halocline shelf-basin exchange isdominated by runoff and sea-ice processes at the western shelves (the Barents and Kara seas) and Pacific water atthe eastern shelves (the Laptev, East Siberian and Chukchi seas).