Transport of terrestrially derived nutrients along the Western Antarctic Peninsula, Anvers Island

Abstract

The mechanisms that supply Fe to the surface waters off the coast of the Western Antarctic Peninsula (WAP) play a key role in the global climate cycle by fueling primary production in this vast and globally important environment. This study investigates the shore-normal mixing rate of nearshore waters using naturally-occurring radioactive isotopes. This mixing could transport nutrients derived from an unevaluated source (i.e., submarine groundwater discharge; SGD) offshore along the WAP. Stable isotopes of water (i.e., ²H, ¹⁸O) and radioactive groundwater tracers (i.e., ²²³,²²⁴,²²⁶,²²⁸Ra, ²²²Rn) were used to evaluate the potential source of these nutrients and nearshore water masses. During the austral summers of 2012-2013 and 2013-2014, seawater samples were collected along the WAP offshore of Anvers Island aboard the R/V Laurence M. Gould (LMG) to observe water-column and tracer dynamics in nearshore and offshore environments in order to evaluate the source and horizontal mixing of water across the continental shelf. Short- and long lived radium (Ra) isotopes and radon-222 (²²²Rn) are used to evaluate the rates that water masses mix in shelf waters. Porewaters collected near Palmer Station were found to be elevated in short-lived Ra isotopes and ²²²Rn, demonstrating that these tracers are valuable to delineating terrestrially derived water masses as has been reported in temperate and tropical shelf systems. Offshore surface waters were depleted in short-lived Ra isotopes and ²²²Rn relative to porewaters, and within the range of those measured in other regions of the WAP and temperate nearshore environments. Using the full suite of parameters measured, comparisons of freshwater delivery to coastal waters are compared across seasons, with increased freshwater observed during the late austral summer, 2014. Horizontal mixing rates of water masses within glacial fjords along the WAP ranged from 570 to 6820 m²s⁻¹. Short-lived Ra isotopes were used to estimate the timing of the most recent sediment-water interaction in surface waters. Estimates ranged between 15-25 days offshore of Anvers Island. Fluorescence was elevated in several nearshore locations and found to be coincident with the high tracer activities used in this study to evaluate the distribution of terrestrial meltwater, suggesting the importance of glacial melt as a source of bio-limiting nutrients.