The last 3000 years in the Ría de Vigo (NW Iberian Margin): climatic and hydrographic signals

Abstract

The hydrographic evolution of the Ria de Vigo (NW Spain) during the last 3000 years has been reconstructed using benthic foraminiferal assemblages, stable oxygen isotopes, molecular biomarkers and seasurface temperatures (SST) reconstructed from the U^K ₃₇ index. Benthic oxygen isotopes and SST records provide evidence of episodic salinity contrasts between surface and bottom waters. The comparison of SSTs with other climate records for the Northern Hemisphere has allowed the inference of oceanographic and climatic signals, which describe the changes in hydrographic conditions of the ría. In general, two different periods can be recognized. From 975 cal. BC to cal. AD 1000, the organic carbon is mainly of continental origin, benthic foraminiferal assemblages are typical of environments that are poorly oxygenated, rich in organic matter and dominated by eurihaline taxa. Percentages of planktonic foraminifera are low and SSTs are warmer than today. These data suggest a restricted environment where the exchange with open ocean waters was diminished. At cal. AD 1000, an important hydrographic change in the ría circulation involved an intensification of coastal upwelling processes as reflected in colder SSTs and increases in the contribution of marine organic carbon and planktonic and opportunistic benthic foraminifera. In these conditions, the sediments of the ría recorded not only local factors but also several well-known Northern Hemisphere climate signals.