Variability of the North Atlantic Current over the Common Era
Abstract:Over the last 2000 years, the climate of the North Atlantic region was punctuated by centennial oscillations, which despite their small magnitude had important societal impacts, particularly in NW Europe. The most favoured explanations for this climate variability invoke changes in external forcings (such as solar activity and explosive volcanism) amplified by ocean and atmosphere feedbacks, mainly involving the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Oscillation. However, the scarcity of highly resolved archives has hampered our understanding of the involvement of the ocean-atmosphere interactions in these climatic oscillations.
We present a subdecadally resolved temperature and salinity record derived from paired Mg/Ca-δ18O measurements on planktonic foraminifera from a marine sediment core located in the pathway of the North Atlantic Current. Our findings show a strong centennial co-variability of the temperature and salinity of the surface limb of the AMOC with solar irradiance (Moffa-Sánchez et al. 2014- NGS). Climate model results from this study show a similar correlation over the last millennium and we infer that the hydrographic changes were linked to the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic, also known as blocking event, modifies the flow of the westerly winds. To further explore the response of the upper limb of the AMOC to solar forcing found in Moffa-Sánchez et al. 14, we synthesize new and available proxy-data from the North Atlantic Current in combination with analysis from CMIP5 simulations of the last millennium.