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Circulation changes and nutrient concentrations in the late Quaternary Aegean Sea: a nonsteady state concept for sapropel formation

Circulation changes and nutrient concentrations in the late Quaternary Aegean Sea: a nonsteady state concept for sapropel formation
Circulation changes and nutrient concentrations in the late Quaternary Aegean Sea: a nonsteady state concept for sapropel formation
The modern Aegean Sea is an important source of deep water for the eastern Mediterranean. Its contribution to deep water ventilation is known to fluctuate in response to climatic variation on a decadal timescale. This study uses marine micropalaeontological and stable isotope data to investigate longer-term variability during the late glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions, we identify the start of “seasonal” stratification and highlight a lag in 18O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the 18O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in a stagnant basin for 1–1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its “stratified” sapropel mode, which is of the order of 450 years.
sapropel, Mediterranean, Holocene, foraminifera, climate variability
0883-8305
1024
Casford, J.S.L.
ab6215ef-d18d-4b90-bb9c-31468744826e
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Abu-Zied, R.
bd449980-1df2-43f4-bb04-4888e518b683
Cooke, S.
d5031b11-137c-4b03-8115-5a1d334bfa62
Fontanier, C.
8cd62729-bb6f-4b48-a244-6d9ec43a46dd
Leng, M.
d19fe835-d2c9-44d3-be83-bbf0b258e4d2
Lykousis, V.
ce29036d-416f-4cea-b717-9bd09863b7b7
Casford, J.S.L.
ab6215ef-d18d-4b90-bb9c-31468744826e
Rohling, E.J.
a2a27ef2-fcce-4c71-907b-e692b5ecc685
Abu-Zied, R.
bd449980-1df2-43f4-bb04-4888e518b683
Cooke, S.
d5031b11-137c-4b03-8115-5a1d334bfa62
Fontanier, C.
8cd62729-bb6f-4b48-a244-6d9ec43a46dd
Leng, M.
d19fe835-d2c9-44d3-be83-bbf0b258e4d2
Lykousis, V.
ce29036d-416f-4cea-b717-9bd09863b7b7

Casford, J.S.L., Rohling, E.J., Abu-Zied, R., Cooke, S., Fontanier, C., Leng, M. and Lykousis, V. (2002) Circulation changes and nutrient concentrations in the late Quaternary Aegean Sea: a nonsteady state concept for sapropel formation. Paleoceanography, 17 (2), 1024. (doi:10.1029/2000PA000601).

Record type: Article

Abstract

The modern Aegean Sea is an important source of deep water for the eastern Mediterranean. Its contribution to deep water ventilation is known to fluctuate in response to climatic variation on a decadal timescale. This study uses marine micropalaeontological and stable isotope data to investigate longer-term variability during the late glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions, we identify the start of “seasonal” stratification and highlight a lag in 18O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the 18O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in a stagnant basin for 1–1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its “stratified” sapropel mode, which is of the order of 450 years.

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More information

Published date: 2002
Additional Information: Actual pagination: 14.1-14.12
Keywords: sapropel, Mediterranean, Holocene, foraminifera, climate variability

Identifiers

Local EPrints ID: 26786
URI: http://eprints.soton.ac.uk/id/eprint/26786
ISSN: 0883-8305
PURE UUID: 0c358c99-bc09-4d67-8723-d9f7b4be55c4
ORCID for E.J. Rohling: ORCID iD orcid.org/0000-0001-5349-2158

Catalogue record

Date deposited: 12 Apr 2006
Last modified: 19 Nov 2019 01:59

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