Contrasting sea-surface responses between the western Mediterranean Sea and eastern subtropical latitudes of the North Atlantic during abrupt climatic events of MIS 3

Abstract

Dinoflagellate cyst (dinocyst) analysis was conducted on two cores from the SW Iberian margin and central Alboran Sea from which high quality records of Marine Isotope Stage 3 have been previously derived. Our aim in this study is to compare the dinocyst signature between 50 and 25 ka BP with existing datasets of foraminiferal and geochemical proxies related to hydrological parameters. Quantitative reconstructions of sea-surface temperatures (SSTs) and salinities (SSS) based on dinocysts are performed for the first time in this area. The results are compared to SSTs derived from planktonic foraminifera and alkenone measurements, and to SSS calculated from planktonic δ18O and foraminiferal SST. Significant oscillations related to Dansgaard–Oeschger cycles are recorded in both cores. Dinocyst-derived hydrological parameters exhibit synchronous fluctuations and similar values to those derived from the other methods, in particular when considering quantitative reconstructions for February based on foraminifera and dinocysts. Our study shows that the influence of subpolar waters was felt during each Greenland Stadial (GS) off Portugal, and that the amplification of the Heinrich Stadial cooling in the Alboran Sea was related to the penetration of subpolar waters through the Strait of Gibraltar. During Greenland Interstadials (GI), we provide evidence for the occurrence of warm and nutrient-rich sea-surface waters in the Alboran Sea, probably due to gyre-induced upwelling. Finally, the difference between August and February dinocyst SST estimates suggests higher seasonal contrasts during GS compared to GI at the two core sites. Additionally, precession appears to have an imprint on dinocyst-derived long-term seasonality record. However, this observation needs to be confirmed by longer records.