Seasonal variability of water mass distribution in the southeastern Beaufort Sea determined by total alkalinity and δ18O

Abstract

We examined the seasonal variability of water mass distributions in the southeastern Beaufort Sea from data collected between September 2003 and August 2004. Salinity, total alkalinity (TA) and isotopic composition (δ18O) of seawater were used together as tracers of freshwater input, i.e., meteoric water and sea ice meltwater. We used an optimum multiparameter analysis to identify the different water masses, including the Mackenzie River, sea ice melt (SIM), winter polar mixed layer (PML), upper halocline water (UHW) with core salinity of 33.1 psu (Pacific origin) and Atlantic Water. Computed values of CO2 fugacity in seawater (fCO2‐sw) show that the surface mixed layer (SML) remains mostly undersaturated (328 ± 55μatm, n = 552) with respect to the average atmospheric CO2 concentration (380 ± 5 μatm) over the study period. The influence of the Mackenzie River (fCO2‐SW > 500 μatm) was relatively small in the southeastern Beaufort Sea, and significant fractions were only observed on the inner Mackenzie Shelf. The contribution of sea ice melt (fCO2‐SW < 300 μatm) to the SML could reach 30% beyond the shelf break and close to the ice pack in autumn. The density of the PML increased through the winter due to cooling and brine rejection. The winter PML reached a maximum depth of 70 m in late April. The UHW (fCO2‐SW > 600 μatm) was usually located between 120 and 180 m depth, but could contribute to the SML during wind‐driven upwelling events, in summer and autumn, and during brine‐driven eddies, in winter.