Implications for the branched tetraether membrane lipid temperature proxy in Arctic paleoclimate reconstruction––Evidence over the Holocene from Baffin Island lacustrine sediment

Eaman, Katelyn A.

Undergraduate Honors Thesis

Implications for the branched tetraether membrane lipid temperature proxy in Arctic paleoclimate reconstruction––Evidence over the Holocene from Baffin Island lacustrine sediment Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/7w62f925w

Abstract

This thesis aims to assess the validity of bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) temperature reconstructions in Arctic lake settings from a Holocene (~11,700 BP) lacustrine sediment core from Baffin Island, Eastern Canadian Arctic. The distribution of brGDGTs in peats, soils, and lake sediments has been shown to correlate with mean annual air temperature (MAAT) and this proxy has been widely applied to sedimentary archives for paleotemperature reconstructions. However, the production and distribution of brGDGTs are impacted by confounding environmental variables that are currently not well understood. Here I study the distribution of brGDGTs preserved in a high-Arctic lake setting and apply the most up-to-date brGDGT-inferred temperature reconstruction calibrations. This thesis specifically investigates the role of changing oxygen levels on reconstructed brGDGT paleotemperatures. Comparisons with other soil and lacustrine samples from Baffin Island suggest that brGDGTs in Upper Gnarly are primarily sourced from within the lake over the Holocene, and estimated temperatures from surface sediments using recently published lake-specific calibrations compare favorably with measured summer air and water temperatures from the region. The downcore reconstruction from Upper Gnarly exhibits a trend opposite of what is expected with a cool Early Holocene followed by warming towards the present. Importantly, two intervals of cooler reconstructed temperatures are observed during intervals of supposed suboxia in the lake. Overall, my results present further evidence that suboxic conditions generate a cold-bias in brGDGT paleotemperature reconstructions, and ultimately need to be considered in future research in paleotemperature reconstruction in high-Arctic lake settings.

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