A Saltier Glacial Mediterranean Outflow

Abstract

The state of Atlantic Meridional Overturning Circulation (AMOC) is influenced by both the strength and the location of the Mediterranean Outflow Water (MOW) plume in the Gulf of Cadiz. To evaluate the influence of MOW on AMOC over deglaciations, precise and accurate salinity and temperature reconstructions are needed. For this purpose, we measured Mg/Ca and clumped isotopes of several benthic foraminiferal species at Integrated Ocean Drilling Program Site U1390 in the Gulf of Cadiz. The clumped isotope results of Cibicidoides pachyderma, Uvigerina mediterranea, and Pyrgo spp. are consistent between species and record no significant difference in Last Glacial Maximum to Holocene deep water temperature. Over the deglaciation, the Mg/Ca‐based temperatures derived from U. mediterranea indicate three periods of MOW absence at Site U1390. Mg/Ca‐based temperatures of Hoeglundina elegans and C. pachyderma are on average 6°C too cold when compared to the present core‐top temperature, which we explain by a carbonate ion effect on these epibenthic species related to the high alkalinity of the MOW. Combining deep water temperature estimates with the benthic oxygen isotope data and considering different relationships between seawater oxygen isotopes and salinity, we infer a salinity decrease of MOW by three to eight units over the deglaciation and four units during Sapropel 1, accounting for the global δ18O depletion due to the decrease in ice volume. Our findings confirm that the Mediterranean Sea accumulates excess salt during a glacial low stand and suggest that this salt surged into the Atlantic over the deglaciation, presumably during Heinrich Stadial 1.

Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations

“…4), which is deeper than its modern main flow core depth between 500 and 800 m water along the continental slope of the Gulf of Cadiz 28,30 . Notably, the simulated model depth is in line with MOW flow core settling depth reconstructions from the Last Glacial Maximum when a MOW with higher-than-modern salinity (<40 PSU) settled at water depths of roughly 800-1200 m 56 . Hence, the simulated heat transport already does take into account the deeper MOW flow path as a consequence of the increased salinity.…”

Source-to-sink pathways of clay minerals in the cadiz contourite system over the last 25 kyrs: The segregational role of mediterranean outflow water

“…However, recent studies which investigated the sedimentary records of IODP Sites U1386, U1389 and U1390 over the last 25 kyrs cal. BP, have not observed any evidences of turbidity current effects on sedimentation at these IODP sites (Bahr et al, 2015;Kaboth et al, 2017;Dijk et al, 2018).…”

“…However, IODP Site U1390 located under the path of the MOW L , is characterized by sedimentation rates between two and ten times higher than MOW U influenced IODP Site U1386 (Fig. 8; Dijk et al, 2018) . Huelva Drift sedimentation rates (IODP Site U1389; MOW PROX ) are similar to those observed at Faro Drift during MIS1 (0.23-0.69 m kyrs -1 ) with a significant increase (>1 m kyrs -1 ) during the MIS2 (Bahr et al, 2015;Fig.…”

“…Chronology of IODP Site U1389 is based on a combination of AMS 14 C dating and visual correlations of planktonic δ 18 O records with North Greenland Ice Core Project (NGRIP) and the Iberian margin core MD01-2444 (Bahr et al, 2015). The age model of IODP Site U1390 combines AMS 14 C dates and tie points based on visual correlation between planktonic δ 18 O records and J o u r n a l P r e -p r o o f NGRIP (Dijk et al, 2018). The sedimentation rates obtained in this study at IODP sites U1386, U1389 and U1390 range between 0.16 m kyrs -1 (Site U1386) and 3.46 m kyrs -1 (Site U1390) for the last 25 kyrs.…”