# Subsurface/intermediate and deep-water oxygenation states in Mediterranean Sea during the Holocene sapropel deposition inferred from planktonic foraminiferal I/Ca and U/Ca ratios.

Vincent Guarinos, Marie Revel, Kazuyo Tachikawa, Laurence Vidal, Marta Garcia, Nathan Minon, Corinne Sonzogni, Hartmut Schulz, Francisco J Sierro

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Vincent Guarinos, Marie Revel, Kazuyo Tachikawa, Laurence Vidal, Marta Garcia, et al. Subsurface/intermediate and deep-water oxygenation states in Mediterranean Sea during the Holocene sapropel deposition inferred from planktonic foraminiferal I/Ca and U/Ca ratios. Goldschmidt2023, Jul 2023, Lyon, France. 10.7185/gold2023.16677. hal-05248868

HAL Id: hal-05248868

https://hal.science/hal-05248868v1

Submitted on 10 Sep 2025

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# Subsurface/intermediate and deep-water oxygenation states in Mediterranean Sea during the Holocene sapropel deposition inferred from planktonic foraminiferal $I/Ca$ and $U/Ca$ ratios.

VINCENT GUARINOS<fnref n="1" />, KAZUYO TACHIKAWA<fnref n="1" />, LAURENCE VIDAL<fnref n="1" />, MARTA GARCIA<fnref n="1" />, NATHAN MINON<fnref n="1" />, CORINNE SONZOGNI<fnref n="1" />, MARIE REVEL<fnref n="2" />, HARTMUT SCHULZ<fnref n="3" /> AND FRANCISCO J. SIERRO<fnref n="4" />

Presenting Author: guarinos@cerege.fr

Mediterranean Sea is a climate change hotspot threatened by a possible reduction of thermohaline circulation. Its sensitivity is exemplified by rhythmic occurrences of organic-rich layers called sapropels in the eastern basin, indicative of reduced oxygenation state. The deep-water hypoxia has been studied using geochemical and micropaleontological approaches whereas the reconstruction of subsurface/intermediate oxygenation states has been hampered by scarce of appropriate proxy.

We applied planktonic foraminiferal $I/Ca$ ratio as an indicator of minimum dissolved $O_2$ concentration of the first 500m in the water column and $U/Ca$ ratio of the same planktonic foraminifera as deep-water oxygenation proxy for the past 12,000 (12 ka) by focusing on Holocene sapropel S1 (10.5-6.1 ka BP). Four cores along a zonal transect were studied: MD04-2724 in the Levantine Sea and SL95 in the Gulf of Sirte, both are currently occupied by Eastern Mediterranean Deep Water. MD04-2797 at the Sicily strait is bathed essentially in Levantine Intermediate Water and ODP977 from the Alboran Sea is occupied by Western Mediterranean Deep Water.

As $I/Ca$ is a fairly new proxy, we examined the influence of foraminifera cleaning, size fraction and species on $I/Ca$ variability. The results confirmed negligible influence of these parameters. The $I/Ca$ ratio varied between 0 and 7 µmol/mol for the study period with the highest ratio in the core-top, being consistent with well oxygenated present-day Mediterranean Sea. The most striking feature is a sharp decrease of foraminiferal $I/Ca$ in the Levantine Sea and Gulf of Sirte at the beginning of S1, which is accompanied by enhanced foraminiferal $U/Ca$ up to 120 nm/mol. These results suggest $O_2$-depletion in both intermediate and deep waters during S1 in the eastern basin. In contrast, only moderate $U/Ca$ increase of around 50 nmol/mol is observed at the Sicily Strait and the ratio is stable and as low as 20 nmol/mol in Alboran Sea. We will compare our new results with planktonic foraminiferal $d^{13}C$ and $d^{18}O$ to study the relationship between oxygen consumption, hydrological

<footnote n="1">¹Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE</footnote>

<footnote n="2">²University Cote d'AZUR</footnote>

<footnote n="3">³University of Tubingen</footnote>

<footnote n="4">⁴Univ. de Salamanca</footnote>