ASSESSING THE STRATIGRAPHIC INTEGRITY OF PLANKTIC AND BENTHIC 14C RECORDS IN THE WESTERN PACIFIC FOR Δ14C RECONSTRUCTIONS AT THE LAST GLACIAL TERMINATION

Lowell D Stott

doi:10.1017/rdc.2020.82

Abstract

ABSTRACTThere is a growing database of radiocarbon (14C) reconstructions from biogenic carbonate taken from marine sediment cores being used to investigate changing ocean circulation and carbon cycling at the end of the last great ice age. Reported here are 14C results from a marine core taken in the Makassar Straits of the western equatorial Pacific that was intended to test whether there was evidence of geologic carbon release to the ocean during the glacial termination. A thorough investigation of planktic and benthic 14C ages with stable isotopes and CT-scans revealed extensive burrowing in the upper 2 m of the core that displaced younger sediments downward by more than half a meter into the glacial section of the core. The vertical displacement is evident in both planktic and benthic fossils. However, the extent of displacement and the stratigraphic disturbance became evident only after multiple measurements of different species and genera. A CT-scan prior to sampling would be an effective screening tool to avoid sampling problem cores such as this.

Highlights

Considerable effort and expense have been devoted to reconstructions of radiocarbon activity (Δ14C) of biogenic carbonates from marine sediments to evaluate how the global-scale overturning circulation responded to climate changes in the past
The first hypothesis called upon enhanced bottom water stratification and the isolation of an abyssal water mass that accumulated respired metabolic carbon during glaciations (Toggweiler 1999) and the aged, 14C-depleted abyssal waters were ventilated during the Mystery Interval (Broecker 2009)
During deglaciation, as ventilation rates increased, the residence time of deep water decreased (Sigman and Boyle 2000; Anderson et al 2009, 2019; Kwon et al 2011; Jacobel et al 2019; Menviel et al 2018). This hypothesis makes specific predictions about Δ14C change in the ocean during the deglaciation. It predicts that the Δ14C of deep waters throughout the ocean would increase as older (14C-depleted) waters from the glacial ocean were replaced by younger

Summary

Introduction

Considerable effort and expense have been devoted to reconstructions of radiocarbon activity (Δ14C) of biogenic carbonates from marine sediments to evaluate how the global-scale overturning circulation responded to climate changes in the past. Similar studies using cores from the eastern equatorial Pacific have documented large benthic-planktic (B-P) 14C age increases at the last glacial termination (Stott et al 2009). With these results in hand it appeared appropriate to proceed with the second phase of the study, to develop planktic and benthic 14C ages to investigate whether there was increased benthic-planktic 14C age differences at the glacial termination as seen in other shallow-intermediate depth cores (see Table 2).

Results

Conclusion