Fish like it hot? Response of fish and shark communities to abrupt past global warming

The Palaeocene-Eocene Thermal Maximum (PETM) ~56 million years ago, is the largest of a series of abrupt Cenozoic global warming events. During this event, the oceans rapidly warmed by >5 °C and became more acidic, and the world became wetter and stormier with profound consequences for life on land and in the oceans. The PETM was driven by the injection of isotopically light carbon (likely from volcanism) into the atmosphere, and many of the associated environmental changes are similar to those occurring today. Therefore, the PETM is often considered the best geological analogue to understand anthropogenic environmental change and its impacts. However, whilst a large number of studies have investigated PETM biotic and environmental change, very few have investigated the response and long-term impact on marine vertebrates. This is, at least in part, because the body fossil record is patchy, because of a lack of suitable sediments and very poor age control on available sequences to assess short-term biological responses. Yet, resolving the response and resilience of top level trophic consumers to modern anthropogenic change is of vital importance because of predictions of significant reductions in tropical communities productivity, diversity and body size over the coming century with critical implications for many marine-ecosystems and human populations dependent on these resources.

Fortunately, ichthyoliths (= fish teeth and shark denticles, generally <1 mm in size) are pervasive in marine sediments and are an underutilized but powerful resource for generating relatively continuous and highly temporally and spatially resolved records of fish and shark communities through time. The student will utilise this novel archive to compile existing records and generate multiple new records of changes in the productivity and diversity of fish and shark communities across the PETM globally. These data will be integrated with extensive palaeoenvironmental datasets. Key questions that will be addressed include:

- How did shark and fish communities change across the PETM?
- Did high vs low latitude communities respond similarly?
- Was temperature the dominant driver of change in fish and shark communities?