Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals

• Published in: Climate of the Past
• Main Authors: Dubois-dauphin, Quentin, Montagna, Paolo, Siani, Giuseppe, Douville, Eric, Wienberg, Claudia, Hebbeln, Dierk, Liu, Zhifei, Kallel, Nejib, Dapoigny, Arnaud, Revel, Marie, Pons-branchu, Edwige, Taviani, Marco, Colin, Christophe
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Gesellschaft Mbh 2017
• Subjects: Western Basin; Lophelia pertusa; Planktonic foraminifera
• Online Access: https://archimer.ifremer.fr/doc/00420/53193/55001.pdf; https://doi.org/10.5194/cp-13-17-2017; https://archimer.ifremer.fr/doc/00420/53193/

We present the neodymium isotopic composition (epsilon Nd) of mixed planktonic foraminifera species from a sediment core collected at 622m water depth in the Balearic Sea, as well as epsilon Nd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442m water depth in the Alboran Sea and at 414m depth in the southern Sardinian continental margin. The aim is to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 kyr. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera from the Balearic Sea were also analyzed for stable oxygen (delta O-18) and carbon (delta C-13) isotopes. The foraminiferal and coral epsilon Nd values from the Balearic and Alboran seas are comparable over the last similar to 13 kyr, with mean values of -8.94 +/- 0.26 (1 sigma; n = 24) and -8.91 +/- 0.18 (1 sigma; n = 25), respectively. Before 13 ka BP, the foraminiferal epsilon Nd values are slightly lower (-9.28 +/- 0.15) and tend to reflect higher mixing between intermediate and deep waters, which are characterized by more unradiogenic epsilon Nd values. The slight epsilon Nd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal delta C-13 composition between intermediate and deeper depths, which started at similar to 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic epsilon Nd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of epsilon Nd values, from 8.66 +/- 0.30 to 5.99 +/- 0.50, and a lower average (7.31 +/- 0.73; n = 19) compared to the CWC and foraminifera from the Alboran and Balearic seas, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the epsilon Nd values of the Sardinian CWC become more unradiogenic (8.38 +/- 0.47; n = 3 at similar to 8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. We propose that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel (similar to 8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigation to be confirmed.