Fluctuations of Mediterranean outflow water circulation in the Gulf of Cadiz during MIS 5 to 7: Evidence from benthic foraminiferal assemblage and stable isotope records

Abstract

We studied variations in benthic foraminiferal assemblages and δ¹³C for the last 225 kyr at IODP site U1387 which is currently bathed by upper core of the Mediterranean Outflow Water (MOW). The MOW paleocirculation and sea-floor environment (oxygen level, trophic condition, bottom current strength) have been inferred from faunal composition; species diversity, abundances of selected index species/groups, microhabitat preferences combined with δ¹³C record of the epifaunal Cibicidoides pachyderma. The faunal and isotope records indicate relatively better ventilation at sea-floor and low trophic condition during MIS 1, 5 and 7 possibly due to increased influence of upper MOW in the Gulf of Cadiz. Our multi-proxy record reflects significant and rapid changes during cold (stadial) and warm (interstadial) phases within the interglacials MIS 5 and 7 and at Termination II. The faunal and isotope records reveal strong MOW flow and better ventilated, oligotrophic bottom-water conditions during stadials MIS 5b, 5d, 7b and 7d. The study further demonstrates weakened MOW intensity associated with poor ventilation and increased trophic level at sea-floor during interstadials MIS 5a, 5e, 7a and 7c. MOW flow was relatively sluggish at Termination II, followed by its strengthening at the end of MIS 5e. The chronology of these events suggests that periods of weakened MOW correlate with sapropel layers of the Mediterranean Sea, implying strong coupling between glacial–interglacial climate and MOW circulation in the Gulf of Cadiz