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Silicate weathering and carbon cycle controls on the Oligocene-Miocene transition glaciation

Silicate weathering and carbon cycle controls on the Oligocene-Miocene transition glaciation
Silicate weathering and carbon cycle controls on the Oligocene-Miocene transition glaciation
Changes in both silicate weathering rates and organic carbon burial have been proposed as drivers of the transient “Mi-1” glaciation event at the Oligocene-Miocene transition (OMT; ~23 Ma). However detailed geochemical proxy data are required to test these hypotheses. Here we present records of Li/Ca, Mg/Ca, Cd/Ca, U/Ca, δ18O, δ13C, and shell weight in planktonic foraminifera from marine sediments spanning the OMT in the equatorial Atlantic Ocean. Li/Ca values increase by 1 μmol/mol across this interval. We interpret this to indicate a ~20% increase in silicate weathering rates, which would have lowered atmospheric CO2, potentially forcing the Antarctic glaciation circa 23 Ma. δ13C of thermocline dwelling planktonic foraminifera track the global increase in seawater δ13C across the OMT and during the Mi-1 event, hence supporting a hypothesized global increase in organic carbon burial rates. High δ13C previously measured in epipelagic planktonic foraminifera and high Cd/Ca ratios during Mi-1 are interpreted to represent locally enhanced primary productivity, stimulated by increased nutrients supply to surface waters. The fingerprint of high export production and associated organic carbon burial at this site is found in reduced bottom water oxygenation (inferred from high foraminiferal U/Ca), and enhanced respiratory dissolution of carbonates, characterised by reduced foraminiferal shell weight. Replication of our results elsewhere would strengthen the case that weathering-induced CO2 sequestration preconditioned climate for Antarctic ice sheet growth across the OMT and increased burial of organic carbon acted as a feedback that intensified cooling at this time.
Stewart, Joseph A.
3d7f8398-d59b-458b-a3c9-e6a54d87e9b1
James, Rachael H.
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Anand, Pallavi
25ea12f3-4a91-4587-83a0-568f6d0ece4f
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Stewart, Joseph A.
3d7f8398-d59b-458b-a3c9-e6a54d87e9b1
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Anand, Pallavi
25ea12f3-4a91-4587-83a0-568f6d0ece4f
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Stewart, Joseph A., James, Rachael H., Anand, Pallavi and Wilson, Paul A. (2017) Silicate weathering and carbon cycle controls on the Oligocene-Miocene transition glaciation. Palaeoceanography. (doi:10.1002/2017PA003115).

Record type: Article

Abstract

Changes in both silicate weathering rates and organic carbon burial have been proposed as drivers of the transient “Mi-1” glaciation event at the Oligocene-Miocene transition (OMT; ~23 Ma). However detailed geochemical proxy data are required to test these hypotheses. Here we present records of Li/Ca, Mg/Ca, Cd/Ca, U/Ca, δ18O, δ13C, and shell weight in planktonic foraminifera from marine sediments spanning the OMT in the equatorial Atlantic Ocean. Li/Ca values increase by 1 μmol/mol across this interval. We interpret this to indicate a ~20% increase in silicate weathering rates, which would have lowered atmospheric CO2, potentially forcing the Antarctic glaciation circa 23 Ma. δ13C of thermocline dwelling planktonic foraminifera track the global increase in seawater δ13C across the OMT and during the Mi-1 event, hence supporting a hypothesized global increase in organic carbon burial rates. High δ13C previously measured in epipelagic planktonic foraminifera and high Cd/Ca ratios during Mi-1 are interpreted to represent locally enhanced primary productivity, stimulated by increased nutrients supply to surface waters. The fingerprint of high export production and associated organic carbon burial at this site is found in reduced bottom water oxygenation (inferred from high foraminiferal U/Ca), and enhanced respiratory dissolution of carbonates, characterised by reduced foraminiferal shell weight. Replication of our results elsewhere would strengthen the case that weathering-induced CO2 sequestration preconditioned climate for Antarctic ice sheet growth across the OMT and increased burial of organic carbon acted as a feedback that intensified cooling at this time.

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Accepted/In Press date: 3 October 2017
e-pub ahead of print date: 10 October 2017

Identifiers

Local EPrints ID: 414777
URI: http://eprints.soton.ac.uk/id/eprint/414777
PURE UUID: de2152f0-34f4-4e10-9a1b-fe1f4e4a6d64
ORCID for Rachael H. James: ORCID iD orcid.org/0000-0001-7402-2315

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Date deposited: 11 Oct 2017 16:31
Last modified: 07 Oct 2020 01:54

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