Long-term development and recent dynamics of High Arctic coastal basins

Abstract

This study aimed to understand annual and long-term chemical and physical processes that affect the development and state of coastal lakes in the Canadian High Arctic. The first major research project studied the formation of hypersalinity in a seasonally isolated marine basin (SIMB) located near Shellabear Point, Melville Island, Northwest Territories (75'N, 113'W). To quantify the role of brine rejection from a seasonal ice pan, an annual ice-formation model was applied, which incorporated stable oxygen isotope fractionation. This model complemented seasonal sampling of ionic and isotopic composition and a full-year recording of physical lacustrine parameters. Additionally, a pilot study using radon-222 as a tracer of groundwater seepage was undertaken to quantify the brine seepage from surrounding permafrost into the hypolimnion of the SIMB. Results indicate that brine rejection from the annual formation of lake ice in a SIMB is the major driver of hypersalinity in this system, and that the current chemical constitution may have formed in less than a decade. This study contributes novel hypotheses on the chemical formation of hypersaline lakes, but also coastal meromictic lakes derived from epishelf lakes during the Holocene. The second investigation focused on the seasonal variability of limnological processes in two coastal freshwater lakes in the Canadian Arctic. East and West Lake are located at the Cape Bounty Arctic Watershed Observatory (CBAWO, 75'N, 109'W), Melville Island. From 2006 to 2009, there have been two central changes in the lake systems: 1) an enhanced ionic loading into both lakes since 2007, and 2) a significant increase in the suspended sediment concentration in the lower 15 m of West Lake in 2009. The elevated ionic concentrations are a result of increased active layer thickening during an unusually warm summer in 2007. The high turbidity in 2009 had a substantial impact on annual mixing of West Lake. The suspended sediment produced a density gradient that prevented river-generated density currents from delivering fresh oxygenated water to the bottom of the lake, and prevented thermal warming. The lack of re-oxygenation and nutrient delivery likely had a substantial impact on the benthic ecosystem in the lake.