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New constraints on climate forcing and variability in the circum-Mediterranean region from magnetic and geochemical observations of sapropels S1, S5 and S6

New constraints on climate forcing and variability in the circum-Mediterranean region from magnetic and geochemical observations of sapropels S1, S5 and S6
New constraints on climate forcing and variability in the circum-Mediterranean region from magnetic and geochemical observations of sapropels S1, S5 and S6
Eastern Mediterranean sapropels are organic-rich layers whose formation was triggered during boreal summer insolation maxima (precession minima). Sapropel formation is associated with increased precipitation and runoff from Europe and North Africa, although the relative influence of high- and low-latitude climate mechanisms is not fully resolved. Likewise, it remains uncertain how centennial-scale interruptions in conditions that give rise to sapropels may reflect atmospheric circulation changes in low latitudes. We present magnetic, geochemical, and diffuse reflectance spectroscopy data from three sapropels that are representative of glacial (S6) and interglacial (S1, S5) conditions in the eastern Mediterranean Sea to assess environmental changes associated with sapropel formation. The extent of diagenetic magnetite dissolution and authigenic formation of fine-grained greigite in these sapropels and their underlying dissolution intervals are linked to enhanced sulphidic conditions during sapropel formation. Aeolian hematite and goethite are largely unaffected by this reductive dissolution except within the interglacial sapropel S5 and its underlying dissolution interval, which formed under relatively stronger sulphidic conditions. Nevertheless, low hematite contents indicate that the three studied sapropels accumulated under reduced aeolian dust inputs in response to an intensified African monsoon, which resulted in expansion of savannah landscapes into NE Saharan dust source areas. Small variations in goethite contents across sapropels indicate additional aeolian entrainment of goethite that formed under previous wet phases in the NE Sahara or in subtropical savannahs located further south. We link short-lived dust abundance peaks within sapropels S1 and S6 to centennial-scale periods of enhanced bottom-water circulation reported previously for these sapropels. Although these sapropel interruptions are driven by high-latitude cooling events, our results indicate that such centennial-scale episodes of atmospheric reorganization affected not only the eastern Mediterranean northern borderlands, but also subtropical North Africa. Overall, our results point to a dominant low-latitude forcing on sapropel formation via boreal summer insolation maxima and intensification of the African monsoon.
Sapropels, Circum-Mediterranean region, Environmental change, Savannah landscapes
0031-0182
1-12
Liu, Qingsong
fbaf8851-e943-4ece-91f5-c5f30306dff1
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c
Torrent, José
d17aec84-5d69-4011-b1c4-bee91761a8bb
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Rohling, Eelco J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Liu, Zhifeng
1579ae8e-e7ad-4464-a79d-7ec1b067de0b
Jiang, Zhaoxia
34e4135c-e7af-48b4-b77a-bf2a2d825fc9
Liu, Qingsong
fbaf8851-e943-4ece-91f5-c5f30306dff1
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c
Torrent, José
d17aec84-5d69-4011-b1c4-bee91761a8bb
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Rohling, Eelco J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Liu, Zhifeng
1579ae8e-e7ad-4464-a79d-7ec1b067de0b
Jiang, Zhaoxia
34e4135c-e7af-48b4-b77a-bf2a2d825fc9

Liu, Qingsong, Larrasoaña, Juan C., Torrent, José, Roberts, Andrew P., Rohling, Eelco J., Liu, Zhifeng and Jiang, Zhaoxia (2012) New constraints on climate forcing and variability in the circum-Mediterranean region from magnetic and geochemical observations of sapropels S1, S5 and S6. Palaeogeography Palaeoclimatology Palaeoecology, 333-334, 1-12. (doi:10.1016/j.palaeo.2012.02.036).

Record type: Article

Abstract

Eastern Mediterranean sapropels are organic-rich layers whose formation was triggered during boreal summer insolation maxima (precession minima). Sapropel formation is associated with increased precipitation and runoff from Europe and North Africa, although the relative influence of high- and low-latitude climate mechanisms is not fully resolved. Likewise, it remains uncertain how centennial-scale interruptions in conditions that give rise to sapropels may reflect atmospheric circulation changes in low latitudes. We present magnetic, geochemical, and diffuse reflectance spectroscopy data from three sapropels that are representative of glacial (S6) and interglacial (S1, S5) conditions in the eastern Mediterranean Sea to assess environmental changes associated with sapropel formation. The extent of diagenetic magnetite dissolution and authigenic formation of fine-grained greigite in these sapropels and their underlying dissolution intervals are linked to enhanced sulphidic conditions during sapropel formation. Aeolian hematite and goethite are largely unaffected by this reductive dissolution except within the interglacial sapropel S5 and its underlying dissolution interval, which formed under relatively stronger sulphidic conditions. Nevertheless, low hematite contents indicate that the three studied sapropels accumulated under reduced aeolian dust inputs in response to an intensified African monsoon, which resulted in expansion of savannah landscapes into NE Saharan dust source areas. Small variations in goethite contents across sapropels indicate additional aeolian entrainment of goethite that formed under previous wet phases in the NE Sahara or in subtropical savannahs located further south. We link short-lived dust abundance peaks within sapropels S1 and S6 to centennial-scale periods of enhanced bottom-water circulation reported previously for these sapropels. Although these sapropel interruptions are driven by high-latitude cooling events, our results indicate that such centennial-scale episodes of atmospheric reorganization affected not only the eastern Mediterranean northern borderlands, but also subtropical North Africa. Overall, our results point to a dominant low-latitude forcing on sapropel formation via boreal summer insolation maxima and intensification of the African monsoon.

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More information

Published date: 2012
Keywords: Sapropels, Circum-Mediterranean region, Environmental change, Savannah landscapes
Organisations: Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 339660
URI: http://eprints.soton.ac.uk/id/eprint/339660
ISSN: 0031-0182
PURE UUID: eee0fb79-1615-4b19-9934-463a5822b714
ORCID for Eelco J. Rohling: ORCID iD orcid.org/0000-0001-5349-2158

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Date deposited: 28 May 2012 12:31
Last modified: 15 Mar 2024 02:47

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Contributors

Author: Qingsong Liu
Author: Juan C. Larrasoaña
Author: José Torrent
Author: Andrew P. Roberts
Author: Zhifeng Liu
Author: Zhaoxia Jiang

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