Gibraltar Outflow and Mediterranean overturning circulation during the last 500 ky

20th Congress of the International Union for Quaternary Research (INQUA). Dublin, 25th and 31st July 2019, AbstractsIn order to explore past changes in the Mediterranean Outflow Water (MOW) we analyzed the fine sand content in the sediments together with some geochemical proxies and planktic and benthic stable isotopes at IODP site U1389. This site was recovered in the vicinity of the Strait of Gibraltar along the path of the main core of the MOW. The content of fine sand together with Zr/Al ratios were used to investigate the MOW speed variability along the past 500 ky. The MOW speed variability at this site was mainly driven by changes in the density contrast between the Inflow and Outflow, which was, in turn, governed by changes in the Mediterranean heat and freshwater budgets. Events of enhanced freshwater input to the Mediterranean associated to northward shifts of the Intertropical convergence Zone reduced the density contrast at Gibraltar and weakened the MOW at Gibraltar. Weak MOW events were recorded at times of sapropel deposition in the eastern Mediterranean. At millennial scale, the MOW intensified at times of Greenland stadials and weakened during interstadials. However, during Heinrich stadials typical three-phase events were observed, with a sandy contourite layer at the bottom and top and a phase of weak MOW in the middle of the stadial, coinciding with the arrival of icebergs to the Gulf of Cadiz. For Heinrich stadial 1 this weak MOW event occurred at the time of the massive release of icebergs from the Laurentian ice sheets. However, the inflow of less saline water to the Mediterranean should have increased not decreased the density contrast between the Inflow and Outflow, especially because freshwater discharge to the Mediterranean from the African monsoons was extremely low. We propose different scenarios to explain these weak MOW events in the middle of Heinrich stadials that were certainly triggered by prominent changes in the Mediterranean heat and freshwater budget.Universidad de Salamanca, EspañaUniversity of Cambridge, Reino UnidoLeibniz-Laboratory for Radiometric Dating and Isotope Research, AlemaniaJapan Agency for Marine-Earth Science and Technology, JapónInstitute of Earth Sciences, Heidelberg University, AlemaniaRoyal Holloway, University of London, Reino UnidoSchool of Environmental Sciences, University of Hull, Reino UnidoInstituto Geológico y Minero de España, Españ

Meltwater flux from northern ice-sheets to the mediterranean during MIS 12

Planktonic foraminifer oxygen isotopes through MIS 12 were analysed from Ocean Drilling Program Site 977 in the Alboran Sea. After the correction of the sea surface temperature (SST) effect on the δ18O composition of foraminiferal calcite, the resulting seawater δ18O (δ18Ow) was used to reconstruct variations in the δ18Ow of the Atlantic inflow into the Mediterranean. A synchronous record from the KC01B core, in the Ionian Sea, was used to evaluate changes in the oxygen isotope gradient within the Mediterranean due to hydrological variations during MIS 12. Instead of the glacial δ18Ow enrichment expected for the Mediterranean, lower values than today have been observed both in the Alboran and the Ionian seas, especially between 455 ka and the end of MIS 12 (424 ka). These negative oxygen isotope anomalies must have been caused by a flux of freshwater to the Mediterranean during MIS 12. Although the largest fraction of the freshwater anomalies entered the Mediterranean through the Atlantic inflow, especially during Heinrich stadials, the Mediterranean δ18Ow gradient allowed us to identify other sources of freshwater to the eastern basin. One of these sources was probably the meltwater generated at the southern margin of the Fennoscandian ice-sheet that entered via the Caspian and Black seas. However, the proximity of core KC01B to the Adriatic Sea points to meltwater delivered from the Alpine ice-sheet and transported through the Po river into the Mediterranean as the main cause of the Ionian Sea 18O depletions

A new perspective of the Alboran Upwelling System reconstruction during the Marine Isotope Stage 11: a high-resolution coccolithophore record

A high-resolution study of the MIS 12/MIS 11 transition and the MIS 11 (430-376 kyr) coccolithophore assemblages at Ocean Drilling Program Site 977 was conducted to reconstruct the palaeoceanographic and climatic changes in the Alboran Sea from the variability in surface water conditions. The nannofossil record was integrated with the planktonic oxygen and carbon stable isotopes, as well as the U-37(k') Sea Surface Temperature (SST) at the studied site during the investigated interval. The coccolithophore primary productivity, reconstructed from the PPP (primary productivity proxy = absolute values of Gephyrocapsa caribbeanica + small Gephyrocapsa group) revealed pronounced fluctuations, that were strongly associated with variations in the intensity of the regional Alboran Upwelling System. The comparison of the nannoplankton record with opal phytolith content for the studied site and the already available pollen record at the nearby Integrated Ocean Drilling Program Site U1385, suggests an association of the upwelling dynamics with the variability of the North Atlantic Oscillation-like (NAO-like) phase. High PPP during positive (+) NAO-like phases is the result of intensified upwelling, owing to the complete development of the surface hydrological structures at the Alboran Sea. This scenario was identified during the MIS 12/MIS 11 transition (428-422 kyr), the late MIS 11c (405-397 kyr), and MIS11 b to MIS 11a (397-376 kyr). Two short-term minima in the PPP and SST were observed during MIS 11 b and were coeval with the North Atlantic Heinrich-type (Ht) events Ht3 (similar to 390 kyr) and Ht2 (similar to 384 kyr). Increased abundance of the subpolar Coccolithus pelagicus subsp. pelagicus and Gephyrocapsa muellerae was consistent with the inflow of cold surface waters into the Mediterranean Sea during the Ht events. Lowered PPP during negative (-) NAO-like phases is the result of moderate upwelling by the incomplete development of surface hydrological structures at the Alboran Sea. This scenario is expressed during the early MIS 11c (422-405 kyr). Overall, the results of our study provide evidence of the important role of atmospheric circulation patterns in the North Atlantic region for controlling phytoplankton primary production and oceanographic circulation dynamics in the Western Mediterranean during MIS 11.UIDB/04326/2020, CEECIND/02208/2017info:eu-repo/semantics/publishedVersio