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1. Carbon isotope budget indicates biological disequilibrium dominated ocean carbon storage at the Last Glacial Maximum.

Author

Omta, Anne Willem, Follett, Christopher L., Lauderdale, Jonathan M., and Ferrari, Raffaele

Subjects
LAST Glacial Maximum, ATMOSPHERIC carbon dioxide, GLACIAL climates, CARBON isotopes, ISOTOPIC signatures
Abstract

Understanding the causes of the ~90 ppmv atmospheric CO2 swings between glacial and interglacial climates is an important open challenge in paleoclimate research. Although the regularity of the glacial-interglacial cycles hints at a single driving mechanism, Earth System models require many independent physical and biological processes to explain the full observed CO2 signal. Here we show that biologically sequestered carbon in the ocean can explain an atmospheric CO2 change of 75 ± 40 ppmv, based on a mass balance calculation using published carbon isotopic measurements. An analysis of the carbon isotopic signatures of different water masses indicates similar regenerated carbon inventories at the Last Glacial Maximum and during the Holocene, requiring that the change in carbon storage was dominated by disequilibrium. We attribute the inferred change in carbon disequilibrium to expansion of sea-ice or change in the overturning circulation. Atmospheric CO2 was ~ 90 ppmv lower at the Last Glacial Maximum (LGM) than during the Holocene. Based on a carbon isotope budget, this study infers that at the LGM biological production pumped carbon into the deep ocean and sea ice kept it there. [ABSTRACT FROM AUTHOR]

Published
2024
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8. Inherent characteristics of sawtooth cycles can explain different glacial periodicities

Author

Michael J. Follows, Rosalind E. M. Rickaby, G.A.K. van Voorn, Bob W. Kooi, Anne Willem Omta, Theoretical Life Sciences, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Omta, Anne Willem, and Follows, Michael J.

Subjects
Physics, Atmospheric Science, Emergent phenomena, 010504 meteorology & atmospheric sciences, Forcing (mathematics), Sawtooth wave, 15. Life on land, PE&RC, 010502 geochemistry & geophysics, 01 natural sciences, Mid-Pleistocene Transition, Biometris, Glacial-interglacial, 13. Climate action, Climatology, Bifurcation, 14. Life underwater, Glacial period, Sawtooth cycle, 0105 earth and related environmental sciences
Abstract

At the Mid-Pleistocene Transition about 1 Ma, the dominant periodicity of the glacial-interglacial cycles shifted from ~40 to ~100 kyr. Here, we use a previously developed mathematical model to investigate the possible dynamical origin of these different periodicities. The model has two variables, one of which exhibits sawtooth oscillations, resembling the glacial-interglacial cycles, whereas the other variable exhibits spikes at the rapid transitions. When applying a sinusoidal forcing with a fixed period, there emerges a rich variety of cycles with different periodicities, each being a multiple of the forcing period. Furthermore, the dominant periodicity of the system can change, while the forcing periodicity remains fixed, due to either random variations or different frequency components of the orbital forcing. Two key relationships stand out as predictions to be tested against observations: (1) the amplitude and the periodicity of the cycles are approximately linearly proportional to each other, a relationship that is also found in the δ[superscript 18]O temperature proxy. (2) The magnitude of the spikes increases with increasing periodicity and amplitude of the sawtooth. This prediction could be used to identify one or more currently hidden spiking variables driving the glacial-interglacial transitions. Essentially, the quest would be for any proxy record, concurrent with a dynamical model prediction, that exhibits deglacial spikes which increase at times when the amplitude/periodicity of the glacial cycles increases. In the specific context of our calcifier-alkalinity mechanism, the records of interest would be calcifier productivity and calcite accumulation. We believe that such a falsifiable hypothesis should provide a strong motivation for the collection of further records., National Science Foundation (U.S.) (NSF Grant OCE-1155295), European Research Council (ERC) (Grant SP2-GA-2008-200915), National Science Foundation (U.S.) (NSF Grant OCE-1259388), Netherlands. Ministry of Economic Affairs (Knowledge Base IV (KBIV) ‘sustainable spatial development of ecosystems, landscapes, seas and regions’)

Published
2015

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