Spatial patterns of fossil carbon mobilisation during the Paleocene-Eocene Thermal Maximum

Hollingsworth, Emily, Pancost, Richard D., Dickson, Alexander J., Badger, Marcus P.S., Elling, Felix, Freeman, Katherine H., Baczynski, Allison and Inglis, Gordon (2023) Spatial patterns of fossil carbon mobilisation during the Paleocene-Eocene Thermal Maximum. Goldschmidt, , Lyon, France. 09 - 14 Jul 2023. 1 pp . (doi:10.7185/gold2023.16905).

Abstract

The Paleocene-Eocene Thermal Maximum (56 million years
ago; Ma) is a transient carbon cycle perturbation associated with
rapid global warming and intensification of the hydrological
cycle. These changes will impact various terrestrial carbon cycle
feedbacks and previous studies have found an increase in the
lateral transport of terrigenous sediments from land to sea [1]. If
the mobilised material includes exhumed fossil or ‘petrogenic’
organic carbon (OCpetro), this may oxidise and act as a CO2
source. Existing evidence shows an order-of-magnitude increase
in the delivery of OCpetro to the ocean, ~1-20 thousand years after
the PETM onset, and may explain the prolonged carbon isotope
excursion during the “body” of the PETM [2]. However, this is
limited to only two regions (Atlantic Coastal Plain and Tanzania)
and may not be globally representative. Here, we aim to
determine if: 1. enhanced transport and subsequent burial of
OCpetro in the ocean was a global phenomenon; and 2. whether it
occurred exclusively during the “body”.
To achieve this, we utilise different lipid biomarker thermal
maturity ratios (e.g. hopanes) to fingerprint and quantify OCpetro
in a global compilation of PETM-aged shallow marine sites
(n=9, including 6 new sites). Our results show that OCpetro mass
accumulation rates (MAR) vary spatially, with relatively high
input in the high-latitudes (e.g. Spitsbergen and New Zealand)
and relatively low input in the mid-latitudes (e.g. Atlantic
Coastal Plain). This is consistent with the meridional variability
that is observed in proxy and model-based hydrological
reconstructions [1]. On average, OCpetro MAR increased during
the PETM, but that the magnitude of change was lower than
previously inferred [2]. In addition, a few sites show a decrease
in OCpetro MAR during the PETM (Spitsbergen, SW Pacific, and
New Zealand). Subsequently, its role as a positive feedback may
be less important than previously thought. However, OCpetro
MAR remained elevated during the recovery stages of the
PETM. If some of this OCpetro was oxidised, the rise in
atmospheric CO2 level would require other mechanisms to
stabilise the climate system.

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Contributors

Author: Emily Hollingsworth

Author: Gordon Inglis

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