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The 405 kyr and 2.4 Myr eccentricity components in Cenozoic carbon isotope records

The 405 kyr and 2.4 Myr eccentricity components in Cenozoic carbon isotope records
The 405 kyr and 2.4 Myr eccentricity components in Cenozoic carbon isotope records
Cenozoic stable carbon (δ13C) and oxygen (δ18O) isotope ratios of deep-sea foraminiferal calcite co-vary with the 405kyr eccentricity cycle, suggesting a link between orbital forcing, the climate system, and the carbon cycle. Variations in δ18O are partly forced by ice-volume changes that have mostly occurred since the Oligocene. The cyclic δ13C–δ18O co-variations are found in both ice-free and glaciated climate states, however. Consequently, there should be a mechanism that forces the δ13C cycles independently of ice-dynamics. In search of this mechanism, we simulate the response of several key components of the carbon cycle to orbital forcing in the Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir model (LOSCAR). We force the model by changing the burial of organic carbon in the ocean with various astronomical solutions and noise, and study the response of the main carbon cycle tracers. Consistent with previous work, the simulations reveal that low frequency oscillations in the forcing are preferentially amplified relative to higher frequencies. However, while oceanic δ13C mainly varies with a 405kyr period in the model, the dynamics of dissolved inorganic carbon in the oceans and of atmospheric CO2 are dominated by the 2.4Myr cycle of eccentricity. This implies that the total ocean and atmosphere carbon inventory is strongly influenced by carbon cycle variability that exceeds the time scale of the 405kyr period (such as silicate weathering). To test the applicability of the model results, we assemble a long (~22Myr) δ13C and δ18O composite record spanning the Eocene to Miocene (34 to 12Ma) and perform spectral analysis to assess the presence of the 2.4Myr cycle. We find that, while the 2.4Myr cycle appears to be overshadowed by long-term changes in the composite record, it is is present as an amplitude modulator of the 405 and 100kyr eccentricity cycles.
1814-9324
91-104
Kocken, I.J.
9a15c736-f27f-4467-96e0-71fcf837ff29
Cramwinckel, M.J.
e467976c-be0c-47a5-a7eb-ecfe93048373
Zeebe, R.
486455f0-45ce-415d-9f14-a9a5e95aa5a8
Middelburg, J.B.M.
11840a96-97ca-479e-aa86-6976464fff87
Sluijs, A.
4f68782c-15c3-4d42-ae22-8ffb13887dc6
Kocken, I.J.
9a15c736-f27f-4467-96e0-71fcf837ff29
Cramwinckel, M.J.
e467976c-be0c-47a5-a7eb-ecfe93048373
Zeebe, R.
486455f0-45ce-415d-9f14-a9a5e95aa5a8
Middelburg, J.B.M.
11840a96-97ca-479e-aa86-6976464fff87
Sluijs, A.
4f68782c-15c3-4d42-ae22-8ffb13887dc6

Kocken, I.J., Cramwinckel, M.J., Zeebe, R., Middelburg, J.B.M. and Sluijs, A. (2019) The 405 kyr and 2.4 Myr eccentricity components in Cenozoic carbon isotope records. Climate of the Past, 15 (1), 91-104. (doi:10.5194/cp-15-91-2019).

Record type: Article

Abstract

Cenozoic stable carbon (δ13C) and oxygen (δ18O) isotope ratios of deep-sea foraminiferal calcite co-vary with the 405kyr eccentricity cycle, suggesting a link between orbital forcing, the climate system, and the carbon cycle. Variations in δ18O are partly forced by ice-volume changes that have mostly occurred since the Oligocene. The cyclic δ13C–δ18O co-variations are found in both ice-free and glaciated climate states, however. Consequently, there should be a mechanism that forces the δ13C cycles independently of ice-dynamics. In search of this mechanism, we simulate the response of several key components of the carbon cycle to orbital forcing in the Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir model (LOSCAR). We force the model by changing the burial of organic carbon in the ocean with various astronomical solutions and noise, and study the response of the main carbon cycle tracers. Consistent with previous work, the simulations reveal that low frequency oscillations in the forcing are preferentially amplified relative to higher frequencies. However, while oceanic δ13C mainly varies with a 405kyr period in the model, the dynamics of dissolved inorganic carbon in the oceans and of atmospheric CO2 are dominated by the 2.4Myr cycle of eccentricity. This implies that the total ocean and atmosphere carbon inventory is strongly influenced by carbon cycle variability that exceeds the time scale of the 405kyr period (such as silicate weathering). To test the applicability of the model results, we assemble a long (~22Myr) δ13C and δ18O composite record spanning the Eocene to Miocene (34 to 12Ma) and perform spectral analysis to assess the presence of the 2.4Myr cycle. We find that, while the 2.4Myr cycle appears to be overshadowed by long-term changes in the composite record, it is is present as an amplitude modulator of the 405 and 100kyr eccentricity cycles.

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Accepted/In Press date: 11 December 2018
e-pub ahead of print date: 16 January 2019
Published date: 2019

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Local EPrints ID: 443367
URI: http://eprints.soton.ac.uk/id/eprint/443367
ISSN: 1814-9324
PURE UUID: f77bd90a-b9b9-4c0b-9171-f66ae5b3d3a5
ORCID for M.J. Cramwinckel: ORCID iD orcid.org/0000-0002-6063-836X

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Date deposited: 21 Aug 2020 16:31
Last modified: 16 Mar 2024 09:01

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Contributors

Author: I.J. Kocken
Author: M.J. Cramwinckel ORCID iD
Author: R. Zeebe
Author: J.B.M. Middelburg
Author: A. Sluijs

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