Master of Science
Geography and Environment
Moser, Katrina A.
The overall objective is to determine how responsive lake primary production at the northern treeline is to warming today in comparison to the Holocene Thermal Maximum (HTM) to increase our knowledge of Arctic lake ecosystem sensitivity to climate change. Paleolimnological techniques, including chlorophyll a and biogenic silica to infer overall lake and diatom production, respectively, were measured in 10,000-year sediment records from two tundra lakes, Queen’s and McMaster Lakes, located near Yellowknife, Northwest Territories. Diatoms were enumerated to identify lake ecosystem response to warming. Lake primary production increased at both lakes during the HTM beginning about ~8,400 cal yr BP due to warming temperatures. Recent anthropogenic warming is more rapid than during the HTM and recent increases in lake primary production are unprecedented. Changes in diatom community composition indicate that increased temperatures during both warming periods led to decreased ice-cover duration and increased growing season serving as drivers for increased lake production.
Summary for Lay Audience
Paleolimnology studies the physical, chemical and biological characteristics of lake sediments to determine past changes in lake ecosystems. Our research applies a paleolimnological approach at Queen’s and McMaster Lakes, two unofficially named, Canadian Arctic lakes just north of the northern treeline, to determine if changes in primary production during the Holocene Thermal Maximum (HTM) are similar to how these lakes are responding to the rapid, anthropogenic-driven warming presently occurring in the Arctic. Both lakes are small, however Queen’s Lake is shallower, allowing us to compare responses to warming in deeper versus shallow lakes.
Lake primary production is the amount of carbon that is fixed by algae and aquatic plants during photosynthesis. Chlorophyll a (chlased) is a key pigment used in photosynthesis, so measuring chlased and its degradation products in sediments provides an estimate of overall lake primary production. Primary production was analyzed using various indicators, such as chlased, biogenic silica (BSi), and diatoms. Diatoms are siliceous microfossils preserved in lake sediments that are used as indicators of environmental changes, including shifts in nutrient and habitat availability, while BSi is a measure of total lake diatom production. Total organic carbon (TOC), a measure of carbon compounds such as humic acids, and associated nutrients including nitrogen and phosphorus, was measured to determine if TOC influences lake primary production.
This investigation discovered that during the HTM, all biogeochemical proxies increased at both lakes at the start of the HTM. The increase at the start of the period was likely driven by the onset of warming conditions and catchment vegetation changes over this long-term period. However, halfway through this warmer period all biogeochemical proxies began decreasing at Queen’s Lake, and it is unclear why. During the recent warming period, algal production increased rapidly since 1850 CE at both lakes, however TOC shows little change at either lake. Both lakes show similar changes in the diatom community composition, which are likely driven by prolonged ice-free periods and increased growing seasons in the Arctic. The changes recorded in the sediments at the shallower Queen’s Lake are more striking than at the deeper McMaster Lake. This suggests that shallower Arctic lakes are more responsive to warming, and helps to increase our knowledge of Arctic lake sensitivity to warming.
Brasier, Brittany, "Arctic Lake Response to Warming: A Paleolimnological Investigation in the Northwest Territories, Canada" (2023). Electronic Thesis and Dissertation Repository. 9106.
Available for download on Thursday, January 16, 2025