Evolution of Southern Ocean temperature and Antarctic circumpolar circulation.

Project Rationale:

The flow of the Antarctic Circumpolar Current (ACC) through the Drake Passage is the primary conduit for modern surface and deep-water communication between the Pacific and Atlantic oceans. This connection is an essential component of global overturning circulation and significantly impacts climate on both regional and global scales. The tectonic history the Scotia Sea between South America and the Antarctic Peninsula is complex [1], and the timing of the opening of the Drake Passage through the Scotia Sea is highly uncertain due to controversy in tectonic reconstructions and seafloor ages – with estimates spanning the middle Eocene to middle Miocene (~10 to 45 million years ago). This uncertainty, combined with unreliable temperature records across the same time interval, makes it impossible to rigorously assess the impact of Drake Passage opening on Southern Ocean cooling and the onset of Antarctic glaciation.

This project aims to construct robust Southern Ocean temperature records for the Eocene-to-Miocene interval in combination with determining the precise timing of increased transport of circumpolar deep waters through the Drake Passage. The results of the project will test long-standing hypotheses proposing direct links between Southern Ocean gateway opening, ACC development, and Antarctic ice-sheet development as a result of cooling.

Methodology:

The project will focus on the application of two primary methods: (i) benthic foraminiferal Mg/Ca temperature reconstructions at Southern Ocean pelagic drillsites, and (ii) deep-water mass characterisation using neodymium isotopes at Southwest Atlantic drillsites. For the trace element work, we will target pelagic carbonate ooze deposits at Ocean Drilling Project (ODP) sites on Maud Rise, the Kerguelen Plateau, and in the Georgia Basin. Neodymium isotope work will use cores from the Falkland Plateau and Georgia Basin recovered by the Deep Sea Drilling Project and ODP and recently recovered piston cores from RRS Discovery cruise DY087.

Benthic foraminiferal Mg/Ca study at Southern Ocean sites will involve method development to better identify species that record deep-water temperature information. Specifically, we will test whether infaunal species are less susceptible to bottom-water carbonate ion effects, such as successfully done in younger time intervals [2].

Neodymium isotope analysis will be performed on fossil fish teeth to investigate the influx of Pacific-sourced waters into the South Atlantic at sites adjacent to the Drake Passage. Previous work in the South Atlantic has documented shallow through-flow across the Drake Passage beginning ~40 million years ago [3], but the timing of onset off a sustained deep connection, and whether early deep through-flow was pulsed, is not well constrained.

Training:

All doctoral candidates will enrol in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas). Specific training will include:

● Chronology and stratigraphy of Southern Ocean drillcores
● Preparation of marine drillcore samples for geochemical studies
● Foraminiferal trace element preparation and cleaning techniques and inductively coupled plasma-mass spectrometer analysis
● Foraminiferal oxygen and carbon isotope analysis, involving day-to-day operation of gas-source isotope ratio mass spectrometers
● Correlation, integration, and interpretation of multi-proxy datasets from deep-sea cores for palaeoclimatic and palaeoceanographic reconstructions

As part of this project, there will be opportunities to travel to Germany and the US for collaborative work and sample collection at drillcore repositories. Travel to international scientific meetings to present project results will also be encouraged and supported.