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Middle Miocene climate instability associated with high-amplitude CO2 variability

Middle Miocene climate instability associated with high-amplitude CO2 variability
Middle Miocene climate instability associated with high-amplitude CO2 variability
The amplitude of climatic change, as recorded in the benthic oxygen isotope record, has varied throughout geological time. During the late Pleistocene, changes in the atmospheric concentration of carbon dioxide (CO2) are an important control on this amplitude of variability. The contribution of CO2 to climate variability during the pre-Quaternary however is unknown. Here we present a new boron isotope-based CO2 record for the transition into the middle Miocene Climatic Optimum (MCO) between 15.5 and 17?Myr that shows pronounced variability between 300?ppm and 500?ppm on a roughly 100?kyr time scale during the MCO. The CO2 changes reconstructed for the Miocene are ~2 times larger in absolute terms (300 to 500?ppm compared to 180 to 280?ppm) than those associated with the late Pleistocene and ~15% larger in terms of climate forcing. In contrast, however, variability in the contemporaneous benthic oxygen isotope record (at ~1‰) is approximately two thirds the amplitude of that seen during the late Pleistocene. These observations indicate a lower overall sensitivity to CO2 forcing for Miocene (Antarctic only) ice sheets than their late Pleistocene (Antarctic plus lower latitude northern hemisphere) counterparts. When our Miocene CO2 record is compared to the estimated changes in contemporaneous ?18Osw (ice volume), they point to the existence of two reservoirs of ice on Antarctica. One of these reservoirs appears stable, while a second reservoir shows a level of dynamism that contradicts the results of coupled climate-ice sheet model experiments given the CO2 concentrations that we reconstruct.
boron isotopes, middle Miocene, CO2, climate change
0883-8305
845-853
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Lear, Caroline H.
c0caf74d-ed6c-4b04-b5c8-de8fc794943c
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Lear, Caroline H.
c0caf74d-ed6c-4b04-b5c8-de8fc794943c

Greenop, Rosanna, Foster, Gavin L., Wilson, Paul A. and Lear, Caroline H. (2014) Middle Miocene climate instability associated with high-amplitude CO2 variability. Paleoceanography, 29 (6), 845-853. (doi:10.1002/2014PA002653).

Record type: Article

Abstract

The amplitude of climatic change, as recorded in the benthic oxygen isotope record, has varied throughout geological time. During the late Pleistocene, changes in the atmospheric concentration of carbon dioxide (CO2) are an important control on this amplitude of variability. The contribution of CO2 to climate variability during the pre-Quaternary however is unknown. Here we present a new boron isotope-based CO2 record for the transition into the middle Miocene Climatic Optimum (MCO) between 15.5 and 17?Myr that shows pronounced variability between 300?ppm and 500?ppm on a roughly 100?kyr time scale during the MCO. The CO2 changes reconstructed for the Miocene are ~2 times larger in absolute terms (300 to 500?ppm compared to 180 to 280?ppm) than those associated with the late Pleistocene and ~15% larger in terms of climate forcing. In contrast, however, variability in the contemporaneous benthic oxygen isotope record (at ~1‰) is approximately two thirds the amplitude of that seen during the late Pleistocene. These observations indicate a lower overall sensitivity to CO2 forcing for Miocene (Antarctic only) ice sheets than their late Pleistocene (Antarctic plus lower latitude northern hemisphere) counterparts. When our Miocene CO2 record is compared to the estimated changes in contemporaneous ?18Osw (ice volume), they point to the existence of two reservoirs of ice on Antarctica. One of these reservoirs appears stable, while a second reservoir shows a level of dynamism that contradicts the results of coupled climate-ice sheet model experiments given the CO2 concentrations that we reconstruct.

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More information

e-pub ahead of print date: 2014
Published date: September 2014
Keywords: boron isotopes, middle Miocene, CO2, climate change
Organisations: Geochemistry, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 368650
URI: https://eprints.soton.ac.uk/id/eprint/368650
ISSN: 0883-8305
PURE UUID: 94306bac-c37d-44d0-94a6-c63fec97a726

Catalogue record

Date deposited: 05 Sep 2014 13:14
Last modified: 18 Jul 2017 01:45

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