Meltwaters in Antarctica: Delineating and Quantifying Sources of Freshwater along the Western Antarctic Peninsula

Abstract:

The importance of freshwater discharge from glaciers and ice sheets along the Western Antarctic Peninsula (WAP) is now evident, but quantifying the source of freshwater inputs (e.g., calving, ice sheet basal melt, and/or subglacial flow) directly and the associated constituent fluxes have been limited. The mode of freshwater contribution in glacier marine environments can be important to understanding glacial melt dynamics related to climate change and overall influences on the coastal ecosystem. As part of an NSF funded project, we are attempting to quantify for the first time using land-based measurements the rate of freshwater input and the associated flux of nutrients and iron to the coastal waters of the WAP, and the mixing of these constituents across the continental shelf. This research is combining geophysical measurements with established radio- (radium quartet and ²²²Rn) and stable tracer (¹⁸O and ²H) techniques to quantify submarine groundwater discharge (SGD), particularly the freshwater contributions, to the coast and delineate the source of water and dissolved constituents.

Nearshore surface water and end member (e.g., streams, groundwater, etc.) tracer data suggest a means of discerning the source of freshwater, with up to 50% of freshwater input from subsurface flow. Time series tracer data in combination with electrical resistivity measurements provide clear observations of SGD and provide insights into tidal influences and the rapid response of subsurface fluid interactions. More broadly, ²²³Ra and ²²⁴Ra activities are elevated in porewaters and glacial meltwaters and decreased in surface water with distance from shore. A preliminary mass balance model estimates SGD at approximately 200 m³ d^-1 per m of shoreline during austral summer, comparable to temperate environments.

Across the shelf, surface water tracer concentrations suggest rapid cross-shelf mixing (730-14000 m²s^-1) that could increase delivery of nearshore freshwater and dissolved constituents further afield. Primary production in iron-limited waters offshore of the WAP is believed to be fueled by continentally-derived sediments. Based on these measurements, SGD could potentially be an important and unaccounted source of iron to continental shelf waters.