Sea surface temperature variations in the western Mediterranean Sea over the last 20kyr: A dualorganic proxy (UK37 and LDI) approach

A high-resolution sea surface temperature (SST) reconstruction of the western Mediterranean was accomplished using two independent, algae-based molecular organic proxies, i.e., the U37 index based on long-chain unsaturated ketones and the novel long-chain diol index (LDI) based on the relative abundances of C28 and C30 1,13and 1,15-diols. Twomarine records, from the western and eastern Alboran Sea basin, spanning the last 14 and 20 kyr, respectively, were studied. Results from the surface sediments suggest that the two proxies presently reflect seasons with similar SST or simply annual mean SST. Both proxy records reveal the transition from the Last Glacial Maximum to the Holocene in the eastern Alboran Sea with an SST increase of approximately 7°C for U37 and 9°C for LDI. Minimum SSTs (10–12°C) are reached at the end of the Last Glacial Maximum and during the last Heinrich event with a subsequent rapid SST increase in LDI-SST toward the beginning of the Bölling period (20°C), while U37-SST remains constantly low (~12°C). The Bölling-Alleröd period is characterized by a rapid increase and subsequent decrease in U37-SST, while the LDI-SST decrease continuously. Short-term fluctuations in U37-SST are probably related to the availability of nutrients and seasonal changes. The Younger Dryas is recorded as a short cold interval followed by progressively warmer temperatures. During the Holocene, the general lower U37-derived temperature values in the eastern Alboran (by approximately 1.5–2°C) suggest a southeastward cold water migration by the western Alboran gyre and divergence in the haptophyte blooming season between both basins.