Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera

Jiawang Wu; Katharina Pahnke; Philipp Böning; Li Wu; Annie Michard; Gert J. de Lange

doi:10.1016/j.epsl.2019.01.036

Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera

Jiawang Wu^*
, Katharina Pahnke
, Philipp Böning
, Li Wu
, Annie Michard
, Gert J. de Lange

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition (ε _Nd ) as paleo-seawater tracer. Our ε _Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional ε _Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed ε _Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

Original language	English
Pages (from-to)	141-153
Number of pages	13
Journal	Earth and Planetary Science Letters
Volume	511
DOIs	https://doi.org/10.1016/j.epsl.2019.01.036
Publication status	Published - 1 Apr 2019

Funding

Many thanks are given to Martina Schulz for sample preparation and chromatography at ICBM. Amalia Filippidi is thanked for laboratory assistance at Utrecht. Qiong Wu and Meng Wang are thanked for the helpful discussion on Nd extraction and box modeling at Tongji, respectively. We thank the captain & crew, scientists, and technicians on board the RVs' cruises for core collection: Tyro 1987 & 1993, Bannock 1988, Marion Dufresne 1991 & 1994/5, Urania 1998, Logachev 1999, and Pelagia 2001 & 2011. Financial supports from the National Natural Science Foundation of China ( 41806064 ), China Postdoctoral Science Foundation ( 2018M640418 ), and from the EU-projects MARFLUX ( MAST1- 90022C ), PALEOFLUX (MAS2-CT93-0051) & SAP ( MAS3-CT97-0137 ) are acknowledged. We also appreciate the shiptime and logistics granted by CNR and NWO. We are grateful for the critical but constructive comments given by four anonymous reviewers and the editor, that all were very useful to improve our initial manuscripts. This study is part of JW's PhD project, funded by the CSC–UU PhD Program ( CSC No. 201206260116 ; USES contribution 146). Appendix A

Keywords

fish debris/teeth
Mediterranean thermohaline circulation
Nd isotopes
sapropel S1
ε modeling

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Divergent MediterraneanFinal published version, 2.9 MBLicence: Taverne

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@article{d18614aad495485ca00398b8f5990b9c,

title = "Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera",

abstract = " The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition (ε Nd ) as paleo-seawater tracer. Our ε Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional ε Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed ε Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50\% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation. ",

keywords = "fish debris/teeth, Mediterranean thermohaline circulation, Nd isotopes, sapropel S1, ε modeling",

author = "Jiawang Wu and Katharina Pahnke and Philipp B{\"o}ning and Li Wu and Annie Michard and \{de Lange\}, \{Gert J.\}",

year = "2019",

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doi = "10.1016/j.epsl.2019.01.036",

language = "English",

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journal = "Earth and Planetary Science Letters",

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T1 - Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera

AU - Wu, Jiawang

AU - Pahnke, Katharina

AU - Böning, Philipp

AU - Wu, Li

AU - Michard, Annie

AU - de Lange, Gert J.

PY - 2019/4/1

Y1 - 2019/4/1

N2 - The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition (ε Nd ) as paleo-seawater tracer. Our ε Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional ε Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed ε Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

AB - The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition (ε Nd ) as paleo-seawater tracer. Our ε Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional ε Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed ε Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

KW - fish debris/teeth

KW - Mediterranean thermohaline circulation

KW - Nd isotopes

KW - sapropel S1

KW - ε modeling

UR - https://www.scopus.com/pages/publications/85061033190

U2 - 10.1016/j.epsl.2019.01.036

DO - 10.1016/j.epsl.2019.01.036

M3 - Article

AN - SCOPUS:85061033190

SN - 0012-821X

VL - 511

SP - 141

EP - 153

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

ER -

Divergent Mediterranean seawater circulation during Holocene sapropel formation – Reconstructed using Nd isotopes in fish debris and foraminifera

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Keywords

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