To access this work you must either be on the Smith College campus OR have valid Smith login credentials.

On Campus users: To access this work if you are on campus please Select the Download button.

Off Campus users: To access this work from off campus, please select the Off-Campus button and enter your Smith username and password when prompted.

Non-Smith users: You may request this item through Interlibrary Loan at your own library.

Publication Date

2025-5

First Advisor

Gregory de Wet

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Keywords

brGDGT, climate change, temperature reconstruction, arctic, climate model, sediment traps, environmental monitoring, bacterial communities, proxy, lakes, lake sediment, sediment core

Abstract

Quantitative paleotemperature proxies are essential to contextualize ongoing climate change properly. Today, we need numerical paleoclimate proxies present before the last interglacial to predict how the climate will continue to change. Distributions of brGDGTs, bacterial lipids produced in many environments globally, have a strong relationship to temperature in lake sediment archives. They hold great potential as a lacustrine climate proxy as they can record continental climate changes and generate quantitative temperature reconstructions. However, in some environments, brGDGTs also correlate with environmental conditions other than temperature, such as dissolved oxygen (DO), conductivity, and pH. The bacterial responses to these environmental stimuli can confound the temperature signal generated by brGDGT calibrations. Additionally, different bacteria may respond to the same environmental stimuli by producing different brGDGTs, further clouding calibration attempts. This leads to the question of whether accurate brGDGT temperature reconstructions are possible to obtain in all environments around the world, or if a specific set of environmental requirements needs to be met to ensure a verifiable reconstruction. To assess this question, we have studied Kongressvatnet, a high Arctic lake in Svalbard. We have collected two years of bacterial DNA data and four years of brGDGT sediment trap data alongside conductivity, DO, and temperature data, all of which span the water column. Kongressvatnet is 55 m deep, meromictic, and stratified. In the summer, it has chemoclines at 12 and 44 m, an oxycline at 35 m, and a thermocline at 10 m. Preliminary DNA data show different bacterial communities throughout the lake water column that can vary greatly from year to year, with low concentrations of acidobacteria, a known producer of brGDGTs. Additionally, the sediment traps show changing brGDGT compositions across the oxy- and chemoclines that can not consistently reconstruct accurate air temperatures. Additionally, MAF air temperatures do not strongly relate to brGDGTs that are common in temperature reconstructions. This lack of consistency indicates that temperature may not be the primary control on brGDGT response in this lake. Our results imply that data about the lake conditions must be known and assessed for confounding factors before a brGDGT-based temperature calibration can be confidently utilized

Rights

©2025 Beth Christensen. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

vi, 89 pages : color illustrations, charts. Includes bibliographical references (pages 81-89).

Download

Smith Only:
Off Campus Download

Share

COinS