Synchronous Marine and Terrestrial Carbon Cycle Perturbation in the High Arctic During the PETM

Abstract

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ13C) of n‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ13C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chain n‐alkanes (nC19; marine algae/bacteria) with a ∼−5‰ CIE in long‐chain n‐alkanes (nC29 and nC31; plant waxes) during the peak of the PETM. Although δ13Cn‐alkanes values were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ13Cn‐alkanes remain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ13CTOC records. The CIE magnitude of both δ13C n‐C19 and δ13Cn‐C29 can be explained by the elevated influence of 13C‐depleted respired CO2 in the water column and increased water availability on land, elevated pCO2 in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ13C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossil n‐alkanes in the Arctic region.