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Modern and past processes of ocean-atmosphere-climate interactions in the low-latitude western Pacific and Indian Ocean
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Effect of changes in the Indian/African monsoon on the circulation, oxygen content and P cycling of Sapropel Intermediate Water (500-1800m) in Eastern Mediterranean
P-G2-06-S
Dongdong Zhu* , University of Haifa
Michael D. Krom, University of Haifa
Eleen Zirks, University of Haifa
Gerhard Schmiedl, University of Hamburg
Beverly N. Goodman-Tchernov, University of Haifa
Presenter Email: zdd2dd@163.com |
| Sapropels are the sedimentological record of recurring anoxic events in the Eastern Mediterranean Sea (EMS) caused by global changes in the Indian/African monsoon pattern. The most recent of those events, S1, occurred in the early Holocene (~6-10.4 ka BP) and the 8.2 ka BP global cooling event can be identified within the sediment records. Recent modelling and field studies have suggested that natural climate change during S1 caused the water column to be divided into 4 layers. Below the surface thermohaline circulation there was a Sapropel Intermediate Water mass (SIW; 500-1800m) and a deeper fully stagnant water mass. This SIW acted as an OMZ with anoxia first in the upper layers and progressively occurring in deeper water. In this study, we examined S1 from a sediment core collected from 1250m offshore from Israel. The extent of sapropel was defined by Ba/Al and TOC and the oxygen status of the overlying water determined from benthic foraminifera abundance and species distribution and V/Al as a redox sensitive trace metal. Our results show that the beginning of S1a was gradual over 400-500 years. The system became anoxic for ~1400 years. The 8.2 ka BP event was visible as an interruption in the sapropel in Ba/Al and TOC. As in other locations across the EMS, S1b was suboxic i.e. somewhat less intense than S1a. The P speciation in the sediment as determined by SEDEX measurements showed that changes in P content were controlled both by the redox state of the overlying water and the input from the nearby major river, the Nile. Our results show the effects of natural climate change on the oxygen status of deeper waters of the EMS. It is important to understand past hypoxic/anoxic events since oxygen minimum zones are spreading in the oceans nowadays which may cause major environmental problems.
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