T5 Cycles of Climate and Layers of Time I: The Scientific Legacies of Roger Y. Anderson and Walter E. Dean, Jr.

Sunday, 15 October 2023
8:00 AM - 12:10 PM
321

UNDERSTANDING ASTRONOMICALLY FORCED CARBON CYCLE FEEDBACKS THROUGH THE LENS OF AN EARTH SYSTEM MODEL

Paper number: T5-6
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

Astronomical cycles in geological records demonstrates the influence of astronomical forcing on Earth’s climate-carbon dynamics. Proxies suggest that during greenhouse climates such as the early Cenozoic, isotopically light carbon is released during periods of warmth (at eccentricity maxima) and re-sequestered during the following cooling (at eccentricity minima). However, the dominant carbon sources and sinks at play on orbital timescales remain unclear--particularly in absence of large dynamic ice sheets. Methods: In an Earth system model, we apply 4-Myr-long transient astronomical forcing to examine how various climate sensitive (in)organic carbon feedbacks respond and influence the astronomical expression in key oceanographic variables (temperature, pCO2, δ13C of DIC, and wt% CaCO3). Among others, we assess the impact of marine productivity, CaCO3 compensation, terrestrial weathering, organic matter burial, and phosphorus cycling. Results: While most processes are driven by changes in the local conditions -controlled by obliquity and precession, these high frequency signals convert to low frequency eccentricity cycles in pCO2, benthic δ13C, and wt% CaCO3 as a result of the lowpass filtering effect of the ocean carbon and nutrient reservoir. The magnitude of early Cenozoic δ13C variability can be explained by an astronomically forced input-burial fluxes of marine organic carbon, however, it does not explain the presence of the short (100 kyr) eccentricity cycles in benthic δ13C, nor the reduced preservation of CaCO3 during periods of warmth as recorded in the proxy data. In addition, the modelled phasing of the forcing and proxies depends on the paleogeography. Implications: This provides support for the hypothesis that additional feedbacks that are not yet(!) included here (e.g., terrestrial carbon or methane) were likely important controls during greenhouse astronomical climate variability.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-392574

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