Differentiating freshwater contributions and their variability to the surface and halocline layers of the Arctic and subarctic seas.

摘要

Dramatic and ongoing changes pervading the Arctic and subarctic seas over recent decades have motivated this effort to track and better understand hydrographic variability using chemical tracers. Particular emphasis has been paid to differentiating freshwater contributions to upper layers: namely Pacific water, meteoric water, and sea-ice melt/formation.;Data collected in spring from stations occupied via aircraft in the central Arctic indicate that Pacific origin water partly returned to the mixed and upper halocline layers between 2003 and 2005. The Pacific influence became absent once again from the Makarov Basin between 2006 and 2008. Pacific water appears to be variably entrained into the Transpolar Drift Stream on timescales not clearly linked to Arctic Oscillation indexed atmospheric forcing.;An in-situ ultraviolet spectrophotometer was used to profile nitrate concentrations for the first time in the central Arctic Ocean during 2007-2008 field seasons. Sensor-based nitrate and dissolved oxygen were combined to calculate the NO parameter (NO = 9xNO3 + O2), a quasi-conservative tracer that has been used to define lower halocline water in the literature. The NO minima in the Makarov Basin occurred above lower halocline water and were concomitant with larger Eurasian river runoff fractions. These features suggest respiratory imprinting of East Siberian Sea shelf waters prior to their offshore advection. Vertical, NO profiles in the southern Canada Basin implicate multiple influences on the lower halocline, including Eurasian Basin convective processes, diapycnal mixing near the shelf break and ventilation via brine production associated with recurrent coastal polynyas.;Salinity-delta18O relationships in the Canadian Archipelago and Baffin Bay in late summer in 1997 and 2003 show that a net sea-ice formation signal is inherited from the Arctic Ocean. Local, seasonal sea-ice melt contributions can be estimated by taking this into account. Distributions of freshwater sources are similar to those previously reported using other methods. However, differences in their relative proportions are apparent and suggest variations over time.;Geochemical tracers augment understanding of variability in the formation and circulation of both surface and halocline waters of the Arctic Ocean via quantitative separation of its freshwater components.