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The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes

The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes
The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes
The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or ‘sapropels’ throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation–sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model–data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation–sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for sapropel S1, whereas monsoon forcing was more important for sapropels S3, S4, and S5.
Eastern Mediterranean, Sapropels, African monsoon, Sea level, Ice sheets, Insolation, Precession, Meltwater pulses
0277-3791
125-141
Grant, K.M.
4258644a-ecaa-48cc-baad-739ced4bd945
Grimm, R.
b3be5c4f-d20c-4f0f-836a-791f33fb8f4e
Mikolajewicz, U.
4f8e5906-1caa-4f80-8fdc-ae095b0116b4
Marino, G.
d2f4dc29-b2e7-4cf0-8abd-6fd855bfab81
Ziegler, M.
803ba330-20ad-426a-9f0d-c3164f927812
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Grant, K.M.
4258644a-ecaa-48cc-baad-739ced4bd945
Grimm, R.
b3be5c4f-d20c-4f0f-836a-791f33fb8f4e
Mikolajewicz, U.
4f8e5906-1caa-4f80-8fdc-ae095b0116b4
Marino, G.
d2f4dc29-b2e7-4cf0-8abd-6fd855bfab81
Ziegler, M.
803ba330-20ad-426a-9f0d-c3164f927812
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685

Grant, K.M., Grimm, R., Mikolajewicz, U., Marino, G., Ziegler, M. and Rohling, E.J. (2016) The timing of Mediterranean sapropel deposition relative to insolation, sea-level and African monsoon changes. Quaternary Science Reviews, 140, 125-141. (doi:10.1016/j.quascirev.2016.03.026).

Record type: Article

Abstract

The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or ‘sapropels’ throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation–sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model–data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation–sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for sapropel S1, whereas monsoon forcing was more important for sapropels S3, S4, and S5.

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Grant et al 2016_JQSR-D-15-00402R1.pdf - Accepted Manuscript
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More information

Accepted/In Press date: 22 March 2016
e-pub ahead of print date: 4 April 2016
Published date: 15 May 2016
Keywords: Eastern Mediterranean, Sapropels, African monsoon, Sea level, Ice sheets, Insolation, Precession, Meltwater pulses
Organisations: Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 394375
URI: http://eprints.soton.ac.uk/id/eprint/394375
ISSN: 0277-3791
PURE UUID: c89f25cc-6d8d-460c-ae25-e90101a069f4
ORCID for E.J. Rohling: ORCID iD orcid.org/0000-0001-5349-2158

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Date deposited: 13 May 2016 13:37
Last modified: 15 Mar 2024 05:34

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Contributors

Author: K.M. Grant
Author: R. Grimm
Author: U. Mikolajewicz
Author: G. Marino
Author: M. Ziegler
Author: E.J. Rohling ORCID iD

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