Evidence for PETM carbon cycle disruption in the high Arctic: Results of the WUN-pACE initiative

Category Climate system
Group GSI.IR
Location International Geological Congress,oslo 2008
Author White, Tim; Kump, Lee; Junium, Chris
Holding Date 05 October 2008

A recent Worldwide Universities Network (WUN) expedition to Svalbard, under the aegis of the paleo-Arctic Climates and Environments initiative (pACE), has identified over 450 m of core spanning the Paleocene-Eocene boundary and extending well into the Eocene. The core material consists of mostly dark grey to black shale and siltstone deposited in a nearshore and shelf environment of the evolving Paleogene foreland basin of Svalbard. Our work is part of a larger effort to understand the nature of the high-latitude environmental response to the Paleocene-Eocene Thermal Maximum (PETM) event. The isotopic and geochemical results presented here are based on reconnaissance-scale (~ 10m spacing) sampling of the cores and represent our contribution to the WUN-pACE initiative; others are studying the palynology, sedimentology, paleobotany, micropaleontology, and organic geochemistry of this highly expanded section of a key interval in Earth history.
We have performed analyses of major oxide elemental analysis, total organic carbon (TOC) and nitrogen abundance, and organic carbon and nitrogen isotopic composition. The results clearly identify the negative carbon isotopic excursion at the PETM, with an overall magnitude of -4 per mil through 50 m of section. A second negative excursion may be correlable to the ELMO event identified elsewhere. TOC values range between 1-2 wt. %, and organic C/N ratios range between 10 and 15. The nitrogen isotopic values range between 3-4 per mil but trend downward through the upper 100 m of the study interval (poorly dated, ELMO?). The chemical index of alteration (CIA) peaks in the PETM at 77% and then declines monotonically through the rest of the section, to a minimum of 70%.
Our preliminary interpretations are that 1) the amplitude of the PETM carbon isotope excursion in Svalbard is comparable to that of the best-preserved open-marine sections though smaller than that reported for the ACEX core (North Pole) and some terrestrial sections; 2) C/N ratios are consistent with a predominantly marine source for the organic matter, but further organic geochemical and petrologic analyses are ongoing; 3) the organic N isotope trends could indicate a temporal shift from nitrate assimilation predominating in the latest Paleocene and earliest Eocene toward nitrogen fixation later in the Eocene; 4) intensified chemical weathering in the Arctic accompanied the PETM climate shifts.