C033-09
High Resolution Measurements of CH4 and δ15N-N2 in the GISP2 Ice Core Across Heinrich Events H1 Through H5

Thursday, 10 December 2020: 10:54
Virtual
Kaden Martin1, Christo Buizert2, Edward J Brook2, Michael Kalk2, Jon Shelley Edwards2, Benjamin Young1, Jeffrey P Severinghaus3 and Ross Beaudette3, (1)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (2)Oregon State University, College of Ocean, Earth, and Atmospheric Sciences, Corvallis, OR, United States, (3)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States
Abstract:
Heinrich events, observed as periods of ice-rafted debris deposition in North Atlantic marine sediments, are thought to reflect extremely cold conditions in the North Atlantic. Heinrich events are further associated with perturbations to Atlantic Meridional Overturning Circulation (AMOC), changes in tropical hydrology, and a southward displacement of the ITCZ. Despite the large global impact of Heinrich events, detection of a climate response within Greenland ice cores has remained elusive. Greenland δ15N-N2 is a sensitive recorder of abrupt climate change and responds only to processes within the firn column, such as the surface temperature and accumulation rate, making it the ideal proxy to identify the impact of Heinrich events on Greenland climate. Work by Rhodes et al. (2015) on the Antarctic WAIS Divide ice core has shown that Hudson Strait sourced Heinrich events leave a clear imprint on atmospheric CH4. This provides a unique way to study the impact of Heinrich events on Greenland climate from co-registered CH4 and δ15N analyses. As both are measured in the gas phase, there is no relative age uncertainty between observed CH4and δ15N signals. Here we present high resolution (7-67 yr) measurements of CH4 and δ15N-N2 in the GISP2 ice core from 12.5 to 50 ka B.P. with the goal of identifying the imprint of Heinrich events H1-H5 on Greenland climate. We observe a significant and abrupt decrease in δ15N at the onset of Heinrich stadial 1 (HS1, ~17.8ka BP), not previously reported, that suggests a modest cooling of ~2oC. This is in agreement with features in Antarctic ice core δ18O and North Atlantic 231Pa/230Th sediment proxies, suggesting a cooling in Greenland coincident with Antarctic warming via the bipolar seesaw at the onset of HS1. During Heinrich stadials, we observe a gradual increase in δ15N corresponding to increases in atmospheric CH4. There are no significant abrupt features in δ15N coincident with the events identified by Rhodes et al. (2015) from H1 to H5. This suggests that Heinrich events themselves do not have a strong impact on Greenland climate, and/or that their effect is too short lived to be recorded in the decadally-smoothed ice core δ15N record.
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