The influence of Atlantic climate variability on the long-term development of Mediterranean cold-water coral mounds (Alboran Sea, Melilla Mound Field)

Abstract

Abstract. This study provides a detailed reconstruction of climatic events affecting a cold-water coral mound located within the East Melilla Coral Province (Southeast Alboran Sea) over the last 300 ky. Based on benthic foraminiferal assemblages, macrofaunal quantification, grain size analysis, sediment geochemistry, and foraminiferal stable isotope compositions, a reconstruction of environmental conditions prevailing in the region is proposed. The variations in planktonic and benthic δ18O values indicate that cold-water coral mound formation follows global climatic variability. Cold-water corals develop during both interglacial and glacial periods, although interglacial conditions would have allowed better proliferation. Environmental conditions during glacial periods, particularly during the Last Glacial Maximum, appear to better suit the ecological requirements of the erect cheilostome bryozoan Buskea dichotoma. Benthic foraminiferal assemblages suggest that high organic carbon flux characterized interglacial periods. Results from this study imply that increased influence of warm and moist Atlantic air masses during interglacial periods led to increased fluvial discharge, providing nutrients for cold-water corals. Important interglacial Atlantic Water mass inflow further promoted strong Alboran Gyres, and thus mixing between surface and intermediate water masses. Increased turbulence and nutrient supply would have hence provided suitable conditions for coral development. In contrast, benthic foraminiferal assemblages and grain size distributions suggest that the benthic environment received less organic matter during glacial periods, whilst bottom flow velocity was reduced in comparison to interglacial periods. During glacial periods, arid continental conditions combined to more stratified water masses caused a dwindling of coral communities in the southeastern Alboran Sea, although aeolian dust input may have allowed these to survive. In contrast to Northeast Atlantic counterparts, coral mound build-up in the southeastern Alboran Sea occurs during glacial as well as during interglacial periods and at very low aggradation rates (between 1 and 9 cm ky−1). We propose that Buskea dichotoma plays an important role in long-term mound formation at the East Melilla Coral Province, noticeably during glacial periods.