Isotopic analyses (¹⁸O, ¹³C, ¹⁴C) of two meromictic lakes in the Canadian Arctic Archipelago1

Abstract

Meromictic Lakes Garrow and Sophia in the Canadian Arctic Archipelago were sampled to establish the origin and age of their waters by isotopic studies. The ?&,OW*8O values reflect the permanent stratification of the waters in both lakes. The mixolimnia contain waters with an isotopic signal between -13.16 and -2 1.98o/oo, coherent with the values for precipitation in these high latitudes. The short residence time of the water in this layer makes it possible to record episodic variations of the freshwater inputs to the lakes. In the chemoclines, the Al80 values increase to -10% concomitantly with a rise in chloride content to 42 g-liter-'. This corresponds to a conservative mixing of surficial and deep waters. In the monimolimnia, hypersaline waters (up to 2.5 times the salinity of seawater) show negative 6180 values (ca. -8%~). These waters result from brine production during permafrost growth in the watershed, according to a Rayleigh process. The brines drained toward the deepest part of each lake, after postglacial uplift, and became isolated. 14C dating of total inorganic carbon in the Lake Garrow monimolimnion gave an age of 2,580 + 260 years B.P. In Lake Sophia, the deep waters exhibit recent 14C activity (12 1.4% modern carbon) that suggests recent infiltration of seawater into the lake basin.

The comparative limnology of high arctic, coastal, meromictic lakes

“…Further south, three additional meromictic lakes have been described, Sophia Lake on Cornwallis Island, Garrow Lake on Little Cornwallis Island (Pag6 et al, 1984;Pag~ et al, 1987;Stewart & Platford, 1986) and Romulus Lake on the Fosheim Peninsula (Davidge, 1994). Their sharp chemoclines and strongly hypersaline monimolimnia were distinctly different from the same features in most of the more northerly lakes.…”

The chemical development of a hypersaline coastal basin in the High Arctic

“…Alternatively, it has been hypothesized that hypersalinity develops from groundwater seeping through intra-and subpermafrost aquifers (Pagé et al 1984). It has been widely assumed that permafrost presents an impermeable barrier to water flow, effectively acting as an aquiclude and preventing subsurface flow (Woo 1990).…”

“…Theoretically, groundwater seepage should occur in recently uplifted areas where permafrost is absent because of past insulation from ocean waters, and where the ground is saturated with marine waters. As the permafrost forms, rejected salt migrates to lake basins through sublacustrine taliks (Pagé et al 1984(Pagé et al , 1987. Therefore, all sufficiently large coastal lakes in the Arctic Archipelago should experience high-conductivity bottom waters (Stewart and Platford 1986).…”

“…In the examination of Garrow and Sophia lakes, Pagé et al (1984) attribute d 18 O depletion in the hypolimnia to a freezing mechanism. As the formation of a shallow ice pack (, 2 m) could not have produced such concentrated, isotopically depleted brine in one season, it is concluded that the freezing mechanism is brine rejection from unfrozen permafrost that seeps into the lake.…”

An isolated population of fourhorn sculpins (Myoxocephalus quadricornis, family Cottidae) in a hypersaline high arctic Canadian lake

“…As a consequence, Garrow Lake, which separated from the sea some 3000 years ago, serves as an excellent `laboratory' for studying evolutionary changes in this sculpin . The age of the lake was based on carbon-14 dates of the fossil pelecypods from raised beaches around the lake and from observations of rates of isostatic rebound in the area as reported by Dickman &Ouellet 1983 andPage et al 1984 . During the last 3000 years, the surface waters of Garrow Lake have freshened and its sculpins have apparently adapted to this top down freshening by occupying a depth where the salinity of the lake approaches that of sea water.…”