Exploring the Morphometrics of the Diatom Fragilariopsis Kerguelensis as a Proxy for Paleo-Sea Surface Temperature in the Late Pleistocene-Holocene Southern Ocean

Abstract

The Southern Ocean has played a large role in moderating global climate since its inception in the Oligocene. With the onset of anthropogenic global warming, it is now more necessary than ever that we understand the world’s climate during periods of rapidly fluctuating temperature in the past. Climatic forecasts are informed by paleoenvironmental conditions of the past during these turbulent periods, which we can examine using proxy data. This thesis assesses a potential proxy for Sea Surface Temperature (SST) through morphometric analysis of the Southern Ocean diatom Fragilariopsis kerguelensis in the Amundsen Sea, West Antarctica.

This proxy is based off of research showing that F. kerguelensis populations will display a bimodal morphology, in which relative concentrations of a high and low rectangularity morphotype will fluctuate in a way that has been correlated to SST. Here I examine this relationship by calculating SST in Amundsen Sea surface and Marine Isotope Stage 5 (MIS-5 sediments using three calibrations. I assess how closely each of these calibrations reproduce SST across MIS-5 compared to other SST reconstructions. I find that a calibration produced by Mastro (2020) appears to reconstruct SST in surface sediments that is within the range of the modern Amundsen Sea and that MIS-5 reconstructions align with an Amundsen Sea that is 0-2.5°C warmer than modern, which is supported by other western Southern Ocean studies.

I also compare F. kerguelensis populations in surface sediments between the Amundsen Sea and the Sabrina Coast. I find that F. kerguelensis populations between these two areas display distinctly different populations. This suggests that the dynamics that control F. kerguelensis in Sabrina Coast waters different from those controlling Amundsen Sea populations. It appears that we are able to reasonably calculate SST in the Amundsen Sea using F. kerguelensis morphometry, although the biogeographic discrepancy examined here suggests that the SST-valve morphology relationship is more complex than originally thought.