Circulation Changes in the Eastern Mediterranean Sea Over the Past 23,000 Years Inferred From Authigenic Nd Isotopic Ratios

Abstract

The Eastern Mediterranean Sea (EMS) is a key region to study circulation change because of its own thermohaline circulation. In this study, we focused on intermediate/deep water circulation since the Last Glacial Maximum (LGM) including the sapropel S1 period. Two cores from the Levantine Sea and the Strait of Sicily, respectively, collected at 1,780 m and 771 m water depth, were studied using 143Nd/144Nd (εNd) of foraminiferal tests and leachates as well as benthic foraminiferal stable isotopes (δ13C, δ18O). This approach allowed the determination of variations in (1) the North Atlantic water contribution to the Mediterranean basin, (2) water exchanges at the Strait of Sicily, and (3) the influence of the Nile River over the last 23,000 years. During the LGM, high benthic foraminiferal δ13C values indicate well‐ventilated intermediate and deep waters in the EMS. The εNd values were more radiogenic than at present, reflecting a smaller contribution of unradiogenic North Atlantic waters to the EMS due to reduced exchange at the Strait of Sicily. The sluggish circulation in the EMS initiated during deglaciation was further enhanced by increased Nile River freshwater inputs between 15 ka BP and the S1 period. Partial dissolution of Nile River particles contributed to an increase in EMS εNd. The large εNd gradient between the EMS and the Western Mediterranean Sea observed during LGM and S1 suggests that each basin had a distinct circulation mode. Decreasing εNd values at the Strait of Sicily after S1 reflected improved water exchange between both basins, leading to the modern circulation pattern.

Eastern Mediterranean Deep Water Formation During Sapropel S1: A Reconstruction Using Geochemical Records Along a Bathymetric Transect in the Adriatic Outflow Region

“…(Bosmans et al, ; Emeis et al, , ; Grant et al, ; Marino et al, ; Rohling et al, ; Tzedakis, ). Furthermore, deglaciation may have triggered the initial stratification of the water column thus facilitating the onset of sapropel formation (Cornuault et al, ; Grimm et al, ; Rohling et al, ). It seems likely that stagnation and thus conditions facilitating preservation initiated at greater depths, whereas biological activity in the surface waters must have been uniform in the study area.…”

Suborbital Hydrological Variability Inferred From Coupled Benthic and Planktic Foraminiferal‐Based Proxies in the Southeastern Mediterranean During the Last 19 ka

“…Although these authors do not give an explanation for the first benthic δ 13 C increase, we here hypothesize an active production of intermediate water masses (glacial analog of LIW) enriching benthic environments in 13 C. For the following decreasing trend in benthic δ 13 C from late H1, these authors suggested a progressively sluggish ventilation of the deep sea. The study of Cornuault et al () use neodymium isotopes in core MD04‐2722 further to hypothesize that enhanced EM stratification is associated to a higher contribution of the Modified Atlantic Water. That said, the overall negative Δ 13 Cp‐b (benthic δ 13 C > planktic δ 13 C) during the second part of H1 (~16.5–15 ka) is complex and may be the result of both the benthic signature and relatively low values of planktic δ 13 C due to either low productivity or inflow of Nile water with low riverine δ 13 C‐DIC values characterizing this period (Figure ).…”

“…At a water depth of 552 m, our studied core is, today, mainly located at the transition between LIW and the Eastern Mediterranean Deep Water (Mojtahid et al, 2019). However, it may have been bathed by different water masses during the LGM that is characterized by a lower sea level or during the S1 period characterized by a reduced LIW formation (Cornuault et al, 2018;Freydier et al, 2001;Scrivner et al, 2004;Tachikawa et al, 2015;Wu et al, 2019).…”

“…The study of Cornuault et al (2018) use neodymium isotopes in core MD04-2722 further to hypothesize that enhanced EM stratification is associated to a higher contribution of the Modified Atlantic Water. That said, the overall negative Δ 13 Cp-b (benthic δ 13 C > planktic δ 13 C) during the second part of H1 (~16.5-15 ka) is complex and may be the result of both the benthic signature and relatively low values of planktic δ 13 C due to either low productivity or inflow of Nile water with low riverine δ 13 C-DIC values characterizing this period ( Figure 5).…”

“…Geographical location of core PS009PC. Locations of the cores used in the text for discussion are indicated on the map: core PS009PC (32°07.7′N, 34°24.4′E; 552‐m water depth), MD04‐2722 (33°06′N, 33°30′E; 1,780‐m water depth; Cornuault et al, , ), SL112 (32°44.5′N, 34°39′E; 892‐m water depth; Kuhnt et al, ), GA‐110 (31°56.61′N, 34°19.79′E, 670‐m water depth; Schilman, Bar‐Matthews, et al, ), GA‐112 (31°56.41′N, 34°22.13′E, 470‐m water depth; Schilman et al, ), and GeoB 7702‐3 (31°39.1′N, 34°04.4′E, 592‐m water depth; Castañeda et al, ). White arrows indicate the surface water current (MSW) and green arrows the intermediate water mass (LIW).…”