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Project description
Motivation (background):
By the end of this century atmospheric CO2 concentrations may reach levels last seen on Earth during the Eocene greenhouse (56 to 34 million years ago) – an interval characterised by extreme global warmth. Climate during the Eocene also appears to have been highly unstable, as it was punctuated by so-called hyperthermal events, which were rapid warming events lasting for a few 10´s to 100´s of thousand years. This interval of overall warmth and climate instability culminated with the onset of large-scale Antarctic glaciation, approximately 34 million years ago, marking an important step change towards the development of the modern climate system (Taylor et al., 2023). Reconstructing ocean temperatures during these greenhouse climates provides an opportunity to better understand how the Earth system operates under atmospheric carbon dioxide levels similar to those we may see in the future.

Reconstructing past ocean temperatures, however, is challenging and much of our current understanding of Eocene ocean temperatures relies heavily on stable oxygen isotope records from deep-sea benthic foraminifera. Interpreting this record, however, is complicated by the fact that in addition to temperature, the classical oxygen isotope paleothermometer is also influenced by other factors including changes in salinity. Our continued reliance on the classical stable oxygen isotope records thereby remains a principal obstacle to understanding the relationship between carbon cycle changes and climate, and the role and response of the deep ocean to both the extreme warmth of the early Eocene and the establishment of the first continental-scale Antarctic ice sheet in the latest Eocene.

In our group we reconstruct deep ocean temperatures using clumped isotope thermometry, which yields robust temperature information from carbonates based on the ordering ("clumping") of stable isotopes within the molecules (Meckler et al., 2022). Using this approach, this masters project aims to reconstruct independent and robust deep ocean temperatures for a selected time interval in Eocene that will allow disentangling temperature and salinity changes in the existing benthic oxygen isotope record.

The masters 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. Within the Paleocene and Eocene there are many possible time intervals where we can apply this method and, therefore, the exact focus of the master thesis can be discussed with the supervisors based on the interests of the masters student.

Research questions (examples, depends on the final choice of time interval):

• How warm was the deep ocean during peak greenhouse conditions of the early Eocene?
• What is the role and response of deep ocean temperatures to the onset of Antarctic glaciation?
• How variable was deep ocean temperature through time?
• How heterogeneous was deep ocean temperatures during the Paleocene/Eocene?

References:
Meckler, A.N., et al. 2022, Cenozoic evolution of deep ocean temperature from clumped isotope thermometry, Science, 377, 86-90
Taylor, V. E., et al., 2023, Transient Deep Ocean Cooling in the Eastern Equatorial Pacific at the Eocene-Oligocene Transition. Paleoceanography and Paleoclimatology, 38

Photo:

Paul Pearson

Proposed course plan during the master's degree (60 ECTS)
H25:
GEOV222 (10P)
free choice (10P)

V26:
GEOV302 (10P)
GEOV231 (10P)
GEOV342 (10P)
GEOV331 (5P)

H26:
GEOV300 (5P)

Field-, lab- and analysis work
Sediment 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 supervision. The new data will be used in conjunction with other available data from our group and compared to published records from various proxies. The results will also be compared to existing climate model simulations generated within the DOTpaleo project.

Total estimate lab/analysis time: 6 months.

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This project is financed through theÌýDOTpaleo project.

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NB: this project is not yet approved by the program board