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

Abstract

Abstract. We present the neodymium isotopic composition (εNd) of mixed planktonic foraminifera species from a sediment core collected at 622 m water depth in the Balearic Sea, as well as εNd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442 m water depth in the Alboran Sea and at 414 m 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 (δ 18 O) and carbon (δ 13 C) isotopes. The foraminiferal and coral εNd values from the Balearic and Alboran seas are comparable over the last ∼ 13 kyr, with mean values of −8.94 ± 0.26 (1σ ; n = 24) and −8.91 ± 0.18 (1σ ; n = 25), respectively. Before 13 ka BP, the foraminiferal εNd 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 εNd values. The slight εNd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal δ 13 C composition between intermediate and deeper depths, which started at ∼ 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of εNd 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 εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n = 3 at ∼ 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 WaPublished by Copernicus Publications on behalf of the European Geosciences Union. ter (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel (∼ 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.

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

“…This implies that the circulation during S1 was confined to each basin, leading to the situation that both WMS and EMS had their own circulation. For instance, reconstructed intermediate water ε Nd values in the South of Sardinia (Dubois-Dauphin et al, 2017) are close to the values in the Alboran and Balearic Seas (Dubois-Dauphin et al, 2017;Jiménez-Espejo et al, 2015) during S1, whereas they matched with the values obtained for core MD04-2797CQ before and after the S1 period ( Figure 4a). This spatial trend suggests a drastic decrease in the LIW flow from the EMS toward the WMS during S1 and the possible existence of WMS intermediate water for this period.…”

“…The different symbols correspond to the benthic foraminiferal species used (filled circles = composite or multispecies record; half‐filled circles = C. pachyderma ; cross‐circles = C. wuellerstorfi ; open circles = C. kullenbergi ). Cores are colored according to their longitude (EMS: reddish colors; ODP967 = 2550 m, Scrivner et al, ; SL123 = 728 m, Kuhnt et al, ; ODP968 = 1961 m, Ziegler et al, ; SL78 = 450 m, Grimm et al, ; MD04‐2722 = 1780 m, Cornuault et al, , this study); central Mediterranean Sea = greenish colors (RECORD23 = 441 m, Dubois‐Dauphin et al, ; MD04‐2797CQ = 771 m, this study); WMS = purplish colors (302G/304G = 1,989 m/2,382 m, Jiménez‐Espejo et al, ; SU92‐33 = 622 m, Dubois‐Dauphin et al, ). Refer to Figure for cores location.…”

“…10.1002/2017PA003227 Scrivner et al (2004) argued that radiogenic foraminiferal ε Nd values during S1 in the Levantine Sea were a consequence of higher input from the Nile. In addition, the difference in reconstructed seawater ε Nd values at intermediate and deep water depths between the EMS (mean ε Nd = À4.1 ± 0.7, 1 SD, n = 34; Scrivner et al, 2004; this study) and the WMS (mean ε Nd = À9.0 ± 0.4, 1 SD, n = 7; Dubois-Dauphin et al, 2017;Jiménez-Espejo et al, 2015) suggests distinct behavior of the two basins during S1 (Figure 4a). Sluggish circulation of intermediate and bottom waters at the Strait of Sicily (MD04-2797CQ and SL78) is inferred from low carbon isotope values (Figure 4c).…”

“…The period from LGM until HE1 was also characterized by well‐ventilated intermediate and deep waters in the eastern basin as indicated by δ 13 C values higher than those of the Late Holocene (Figure c), which cannot be explained by general glacial/interglacial changes (Curry et al, ; Duplessy et al, ; Shackleton, ). Since elevated δ 13 C values are recorded in the WMS at the end of the LGM (Figure c, Dubois‐Dauphin et al, ), they highlight active intermediate and deep water formation in both EMS and WMS.…”

The large-scale evolution of neodymium isotopic composition in the global modern and Holocene ocean revealed from seawater and archive data

“…9 Horikawa et al, 2011;Asahara et al, 2012;Carter et al, 2012;Chen et al, 2012;López Correa et al, 2012;Piotrowski et al, 2012;Wilson et al, 2012;Xie et al, 2012;Haley and Polyak, 2013;Jang et al, 2013;Kraft et al, 2013;Maccali et al, 2013;Montero-Serrano et al, 2013;Noble et al, 2013;Pena et al, 2013;Skinner et al, 2013;Achyuthan et al, 2014;Huang et al, 2014;Molina-Kescher et al, 2014;Werner et al, 2014;Jiménez-Amat and Zahn, 2015;Jonkers et al, 2015 ;Roberts and Piotrowski, 2015;Abbott et al, 2016;Du et al, 2016;Dubois-Dauphin et al, 2016b ;Howe et al, 2016a;Hu et al, 2016 ;Lang et al, 2016;Lippold et al, 2016;Meinhardt et al, 2016 ;Wei et al, 2016) (Figure 1).…”