Palaeoceanographic change during the Palaeocene/Eocene thermal maximum in Arctic Spitzbergen

Abstract

The interaction of the ocean, atmosphere and ice in the Arctic region plays a critical role in modulating global climate. However, recent observations have illustrated the region is changing rapidly in response to anthropogenically-induced warming. Given the uncertainty in climate model predictions, one way to analyse the response of the Arctic to warming is to generate records through transient warm intervals from the geological past. However, the most pronounced warming event of the Cenozoic, known as the Palaeocene/Eocene thermal maximum (PETM), is poorly documented in the Arctic region.

Therefore, in order to place further constraints on environmental conditions in the high Arctic during the PETM, this thesis documents results from two new PETM localities in the Spitsbergen Central Basin, the BH9/05 core and the Bergmanfjellet outcrop section. Results from sedimentological, palynofacies and dinoflagellate cyst (dinocyst) analyses have been compared to previous results from the Longyearbyen section (Spitsbergen) and Integrated Ocean Drilling Project Site 302-4A in order to analyse spatial and temporal changes across the event in this high Arctic setting. Analysis of Fe and Mn XRF time-series from core BH9/05 has been used to construct a cyclostratigraphic age model to constrain temporal changes. Together with radio-isotopic dating of a bentonite layer within the PETM, the cyclostratigraphic age model implies that the onset of the event occurred on a falling limb of the 405 kyr eccentricity cycle (between 55.728 and 55.964 Ma). Given that other early Palaeogene transient warming events (hyperthermals) have consistently been documented at the peak of both 100 and 405 kyr eccentricity cycles, or on the rising limb of such cycles, this suggests the PETM may have been initiated by a different mechanism compared to other hyperthermals.

Furthermore, comparison of dinocyst assemblages across the Spitsbergen Central Basin illustrates a pronounced influx of the low salinity tolerant taxon Senegalinium during the PETM, consistent with a regime of enhanced precipitation and runoff. Such conditions led to salinity stratification, which together with elevated productivity and the warming of Arctic waters led to sedimentary anoxia and enhanced burial of marine organic matter. As the mechanisms driving anoxia and elevated productivity seen in the Central Basin would be expected to occur across the Arctic region, it is probable that the enhanced burial of contemporary marine organic matter was a pan-Arctic phenomenon in marginal settings. Given the burial of this type of organic matter sequesters carbon directly from the exogenic system, this suggests that the Arctic would have been a significant carbon sink during the PETM.

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Identifiers

ORCID for Ian Harding: orcid.org/0000-0003-4281-0581

ORCID for John Marshall: orcid.org/0000-0002-9242-3646

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