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Coupled climate-carbon cycle simulation of the Last Glacial Maximum atmospheric CO2 decrease using a large ensemble of modern plausible parameter sets

Published version
Peer-reviewed

Type

Article

Change log

Authors

Kemppinen, KMS 
Holden, PB 
Edwards, NR 
Ridgwell, A 
Friend, AD 

Abstract

During the Last Glacial Maximum (LGM), atmospheric <span classCombining double low line"inline-formula">CO2 was around 90 ppmv lower than during the pre-industrial period. The reasons for this decrease are most often elucidated through factorial experiments testing the impact of individual mechanisms. Due to uncertainty in our understanding of the real system, however, the different models used to conduct the experiments inevitably take on different parameter values and different structures. In this paper, the objective is therefore to take an uncertainty-based approach to investigating the LGM <span classCombining double low line"inline-formula">CO2 drop by simulating it with a large ensemble of parameter sets, designed to allow for a wide range of large-scale feedback response strengths. Our aim is not to definitely explain the causes of the <span classCombining double low line"inline-formula">CO2 drop but rather explore the range of possible responses. We find that the LGM <span classCombining double low line"inline-formula">CO2 decrease tends to predominantly be associated with decreasing sea surface temperatures (SSTs), increasing sea ice area, a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a strengthening of the Antarctic Bottom Water (AABW) cell in the Atlantic Ocean, a decreasing ocean biological productivity, an increasing <span classCombining double low line"inline-formula">CaCO3 weathering flux and an increasing deep-sea <span classCombining double low line"inline-formula">CaCO3 burial flux. The majority of our simulations also predict an increase in terrestrial carbon, coupled with a decrease in ocean and increase in lithospheric carbon. We attribute the increase in terrestrial carbon to a slower soil respiration rate, as well as the preservation rather than destruction of carbon by the LGM ice sheets. An initial comparison of these dominant changes with observations and paleoproxies other than carbon isotope and oxygen data (not evaluated directly in this study) suggests broad agreement. However, we advise more detailed comparisons in the future, and also note that, conceptually at least, our results can only be reconciled with carbon isotope and oxygen data if additional processes not included in our model are brought into play.

Description

Keywords

37 Earth Sciences, 3708 Oceanography, 3709 Physical Geography and Environmental Geoscience, 3702 Climate Change Science, 13 Climate Action

Journal Title

Climate of the Past

Conference Name

Journal ISSN

1814-9324
1814-9332

Volume Title

15

Publisher

EGU
Sponsorship
European Commission (238366)
This research has been supported by the UK Natural Environment Research Council (NERC) through funding for the project DESIRE (grant no. NE/E007554/1).