Institutt for geovitenskap
Masterprosjekt - Klima

North Atlantic circulation changes across the Eocene-Oligocene Transition

This project was allocated to the student Malene Vold when she started her Master's Program in Earth Sciences, UiB, Autumn 2022.



Motivation (background):
Approximately 34 million years ago, across the Eocene-Oligocene Transition (EOT), Earth’s climate cooled, leading to the onset of large-scale Antarctic glaciation (Coxall et al., 2005). Two mechanisms have been proposed for triggering Antarctic glaciation: (1) thermal isolation of Antarctica through the opening of Southern Ocean gateways (Kennett and Shackleton, 1976), and (2) a decrease in atmospheric CO2 concentrations (DeConto and Pollard, 2003). Recent studies suggest a link between these leading hypotheses by advocating for climate system preconditioning through late Eocene ocean circulation change (Elsworth et al., 2017). Central to this school of thought is the onset and/or invigoration of North Atlantic deep-water formation, driving heat piracy from southern to northern high latitudes. Tectonic changes in the Arctic-Atlantic connection likely played a key role in the onset and/or invigoration of early North Atlantic deep-water formation, with tectonic isolation of the Arctic enabling progressive salinification of the North Atlantic relative to the North Pacific (Hutchinson et al., 2019).  This is supported by multi-proxy records from ODP Site 647 in the southern Labrador Sea (Coxall et al., 2018). These records have been interpreted to suggest a progressive southward export of a high nutrient, low salinity, Arctic-imprinted northern-sourced deep water from the latest Eocene to earliest Oligocene (Coxall et al., 2018). Reconstructing deep-sea temperatures associated with this water mass is challenging because the traditional deep-sea temperature proxy (Mg/Ca) is influenced by several non-thermal factors. We have been working on reconstructing deep ocean temperatures using clumped isotope thermometry; a relatively new approach to derive robust temperature information from carbonates based on the ordering ("clumping") of stable isotopes within the molecules (Eiler, 2011). Our preliminary results in the North Atlantic suggest that transient deep-sea cooling and freshening events may have occurred both in both the latest Eocene and earliest Oligocene. We hypothesise that these events may relate to changes in the connectivity of the Arctic and North Atlantic, which could have had far-reaching implications for ocean circulation and climate. To test this hypothesis, constraints on deep-sea temperatures and seawater d18O (regionally, a function of salinity) in the southern Labrador Sea are required.

The goal of this master thesis is to contribute to existing and ongoing work in the North Atlantic by generating a benthic foraminiferal clumped isotope record from the late Eocene to early Oligocene at ODP Site 647. These data will be used to: (i) characterise deep-sea temperatures and seawater d18O values in the southern Labrador Sea, and (ii) help to characterise the role and response of the North Atlantic to the onset of large-scale Antarctic glaciation at the EOT. To assess the effect of changes in Arctic-Atlantic connections on deep-water formation and temperatures in the North Atlantic, both the new and existing data will be compared to existing climate model simulations. The master student will join the DOTpaleo project team who are studying Paleocene to Eocene climate through a combination of clumped isotope-based temperature reconstructions and Earth System modelling.

Research question:
How did deep-sea temperatures in the North Atlantic evolve from the late Eocene to early Oligocene and to what extent can these deep-sea temperature variations be explained by tectonic changes in the connectivity between the Arctic and the North Atlantic?

Test (work):
New samples from ODP Site 647 will be taken at the IODP Bremen core repository to supplement existing samples from collaborators. Samples will be wet-sieved and benthic foraminifera picked from the dried coarse fraction. Benthic foraminifera will be cleaned and analysed using a clumped isotope mass spectrometer, under guidance, to generate 5–6 temperature data points. The results will be compared to existing data from ODP Site 647 (e.g., benthic and planktic foraminiferal stable isotopes, benthic foraminiferal Mg/Ca, and fossil fish tooth neodymium isotope records; Coxall et al., 2018), in addition to our existing clumped isotope-derived temperature records from the wider North Atlantic Ocean. These results will also be compared to existing NorESM simulations in collaboration with Postdoc Eivind Straume (NORCE). Total estimated lab/analysis time: 6 months.

Field, lab and analysis:
No fieldwork, labwork app. 6 months. 

Foreslåtte emner i spesialiseringen (60 sp): 
A suggestion, can be discussed (+10P etter eget ønske):

Autumn semester:
GEOV222 (10P)
GEOV228 (10P)
GEOV300 (5P)

Spring semester:
GEOV302 (10P)
GEOV231 (10P)
GEOV331 (5P)