Antarctic phytoplankton and climate change using Holocene sedimentary DNA, fossils and chemical proxies.

The West Antarctic Peninsula (WAP) is one of Earth’s fastest-warming regions, of particular concern given its marine-based ice sheets. Since the 1950s, mean air temperature has risen by ~2°C, and most glaciers are retreating with several ice shelves having already thinned or collapsed. Strengthened westerlies and more frequent incursions of Upper Circumpolar Deep Water (UCDW) have been detected leading to a reduced sea-ice season. Currently the WAP is a highly productive ecosystem, with diatom-rich spring/summer phytoplankton blooms supporting populations of zooplankton and higher trophic levels and driving an efficient biological pump important for the carbon cycle. Current instrumental and satellite records span only recent decades, and microfossil archives under-represent non-siliceous, non-fossilising taxa. High-resolution archives are needed to place recent changes within the last 1–1.5 millennia, to understand if modern changes are unprecedented, and how these climatic changes affect food webs. This thesis applies a high-resolution multiproxy strategy, including sediment geochemistry, diatom assemblages and sedaDNA, to reconstruct late-Holocene environmental change and ecosystem response at Maxwell and Börgen bays. The study interval (~1.5 ka) spans the Neoglacial, the Medieval Climate Anomaly, the Little Ice Age (LIA) and twentieth-century Recent Rapid Warming. There are four aims:. (i) Build new chronologies and multiproxy records of fjord sea ice, sediment input and productivity. (ii) Test the viability of frozen versus chilled cores for sedaDNA and define best practice (iii) Quantify whole-community change, including phytoplankton, zooplankton, viruses and microbes, and coupling to climate. (iv) Compare northern (Maxwell Bay) and southern (Börgen Bay) responses to distinguish between regional and local expressions of climate forcing. Chapter 3 develops a new age model and multiproxy record for Maxwell Bay, revealing ~200-year alternations between colder, stratified, higher-productivity states and warmer, mixed regimes. A LIA expression is identified, which is likely mediated by the Southern Annual Mode (SAM), and since the mid-20th century unprecedented melt and terrigenous influx with reduced diatom biomass. Chapter 4 compares sedaDNA preservation in frozen versus chilled sediments, showing microbial overgrowth in chilled storage, dampened phototroph signals (especially cyanobacteria), and the value of targeted hybridisation capture for chilled archives. Chapter 5 uses authenticated Maxwell Bay sedaDNA to reconstruct whole community turnover, link phytoplankton declines to increases in total viruses and trace benthic–pelagic coupling during warming. Chapter 6 applies the framework to Börgen Bay, where sandy lithologies limit diatom preservation in the older part but sedaDNA reveals recent Phaeocystis dominance and documents very recent phytoplankton turnover associated with enhanced melt. Together, the chapters provide an integrated late-Holocene perspective on how WAP climate forcing reorganises Southern Ocean ecosystems, and how to uncover this history reliably from sedimentary DNA.<p></p>

Author dc:creator

• Charlotte Greenall (21042104)

• Antarctica
• Holocene
• Micropalaeontology
• Sedimentary DNA

Statement dc:rights

• All rights reserved
• Open Access after 2027-04-27

Identifier

10779/exe.32243856.v1

OAI identifier oai:identifier

oai:figshare.com:article/32243856