Land-sea climatic variability in the eastern North Atlantic subtropical region over the last 14,200 years: Atmospheric and oceanic processes at different timescales

摘要

High-temporal resolution analysis of different climatic tracers (pollen, foraminiferal-based winter sea surface temperature (SST), benthic foraminiferal δ~(18)O) from marine core MD95-2042, retrieved off SW Iberia, allows us to directly compare, without any chronological ambiguity, Mediterranean vegetation and eastern North Atlantic winter SST changes for the last 14.2 kyr. We identify on land and in the ocean several climatic phases such as the end of the warm and humid Boiling-Allerod, the cold and dry Younger Dryas, and the warm and humid Holocene with the Mediterranean forest (MF) optimum between 9.6 and 8.1 kyr. This record shows that, at multi-centennial timescale (～800 years), declines in forest cover generally related to dry and cool periods in southern Iberia are synchronous with cold SST in the eastern part of the North Atlantic subtropical gyre. At multi-centennial timescale, changes in thermohaline circulation, via freshwater content fluctuations, appear to be responsible for the coupling between dryness in Iberia and SST cooling in eastern North Atlantic subtropical gyre. In contrast, some Holocene events include centennial-scale oscillations (～100 years) marked by MF declines in southern Iberia concomitant with SST warming in the eastern North Atlantic subtropical gyre. This climatic pattern is similar to that observed at decadal timescale under the influence of the positive mode of the North Atlantic Oscillation (NAO). We suggest, therefore, that synchronous SW Iberian dryness and SST warming at centennial timescale could be explained by atmospheric fluctuations related to NAO changes.