The last deglaciation in the SW Iberian margin: changes in the Atlantic surface and Mediterranean bottom waters

Abstract

The transition from the Last Glacial Maximum to the Holocene interglacial period is marked by abrupt global changes in which ocean thermohaline circulation, ice sheets and atmosphere interacted. Mediterranean overturning circulation and thus Mediterranean outflow were strongly influenced by these changes and might even have played a role by exporting heat and salt to the North Atlantic. The gulf of Cádiz Contourite Depositional System is characterized by the presence of two sandy contourite layers, corresponding to periods of reduced Atlantic Overturning Circulation (AMOC) during late Heinrich stadial 1 and Younger Dryas. In this work we present new multiproxy record for last 30ka from a sediment core located in the main branch of Mediterranean overflow. Planktic foraminifera assemblages have been used to reconstruct North Atlantic-influenced sea surface temperatures (SST), and Mg/Ca in benthic foraminifera to reconstruct Mediterranean overflow-influenced seawater bottom temperature (SBT).

Results from planktic foraminifera are well correlated with what is recorded in nearby sites, marked by an abrupt SST drop during Heinrich event 1 and relatively high SST during LGM. Sea bottom temperatures raised gradually from Greenland stadial 3, as observed in Greenland ice temperature records, showing relatively warm values during LGM as noticed in SST. We suggest that this synchronism between Mediterranean deep water and Greenland air temperatures trends can be explained by the atmospheric teleconnection between both regions. Cool air temperatures in Greenland are transferred to the Mediterranean through winter winds that caused surface water cooling and sinking to the deep Mediterranean. This long-term warming trend that reflects the average temperature of Mediterranean deep water was punctuated by by two events of higher temperatures at times of Sandy Contourite layers deposition (Late Heinrich stadial and late Younger Dryas). These pulses of heat and salt export to the North Atlantic just before the onset of AMOC restoration are consistent with the hypothesized Mediterranean Outflow contribution during Terminations.