Abstract:
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-[delta]18O 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.
