Last Interglacial sea surface warming during the sea-level highstand in the Canary Islands: Implications for the Canary Current and the upwelling off African coast
Résumé
The Canary Islands, east of the North Atlantic Ocean (27°N-29°N), are under the influence of the Canary Current, the descending branch of the North Atlantic Gyre, which is modulated by coastal upwelling off NorthWest Africa. They constitute strategic sites for palaeoclimatic reconstructions, especially for the Last Interglacial (LIG, 129 to 116 ky BP) estimated to be warmer than present. Seventy-four carbon and oxygen isotope bulk analyses and time series measurements were performed on 32 aragonitic mollusc shells from the LIG marine deposits on Lanzarote and Fuerteventura islands during a period of sea-level highstand that we estimated to occur between 125 and 119-116 ky BP. Our SST calculations, inferred from shell 18 O values using available isotopic fractionation equations, provide a seasonal SST amplitude ranging from 3.5°C to 6.0°C, in agreement with the modern seasonal amplitude, along with a mean SST comprised between 20.41.3°C and 22.21.2°C. With respect to the pre-industrial times, we deduce a positive SST anomaly in the range of +1.01.4°C to +2.81.3°C, consistent with the presence of the species Persististrombus latus, typical of warm SSTs. Although this finding does not match with the zonal negative anomaly of a reconstructed SST at low latitudes of the North Atlantic, it is nevertheless corroborated by other climate reconstructions in the northeastern tropical Atlantic region. We attribute this trend to an excess of summer insolation during the LIG which warmed the Canary Current, enhanced by a weakening of the North African upwelling. The entire North Atlantic Gyre was probably warmer during the LIG.
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