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Abstract

Cold-water corals are common throughout the Alboran Sea (AS; western Mediterranean Sea), however large coral mound provinces have only been discovered along the Moroccan margin. During research cruise MSM36 "MoccoMeBo", the Bremen drill rig MeBo successfully drilled 70 m long coral bearing cores from the East Melilla Coral Province (EMCP) presented here. Using high precision U-series dating method, the two cores presented here provide a unique insight into the mound evolution over 550 ka. For the second time ever, a CWC mound has been fully penetrated and thus the timing of the onset of coral growth in this location could be determined. The other mound, potentially drilled to only half its height (70 m), may provide a first estimate of the basin-wide onset of coral growth in the AS. However, the discontinous temporal evolution of both mounds revealed unprecedented complex age-depth profiles and thus two different mound evolution models over several full glacial-interglacial cycles are proposed. The predominantly interglacial evolution of CWC occurrence in the AS provided close contraints of the climate conditions during interglacial periods facilitating vigorous coral growth. Changes in climate conditions during interglacial periods determined the decline of flourishing coral growth, leading to a glacial demise of CWC in the AS. Based on the Li/Mg proxy, the past temperature variability of the near Bottom Water Temperature (nBWT) was closely regarded. For the first time, a high-resolution nBWT record in the AS was conducted and compared with published Sea surface Temperatures (SST). The observed variability in temperature suggests a common global driver of SST variability and coral occurrence in the AS. MSM36 "MoccoMeBo" was motivated by the hypotheses of a "Gibraltar seesaw pattern", describing the long-term development of predominantly glacial CWC growth in the Gulf of Cádiz (GoC) and predominantly interglacial CWC growth in the AS. Combined U-series records from both sides of the Strait if Gibraltar, may have revealed a common global driver of the observed seesaw pattern and thus, may have unveiled a most possible onset of CWC growth in the Mediterranean Region during the Mid-Pleistocene Transition. Lastly, the evolution of seawater ẟ234U, an indicator of the global weathering rate and crucial for the high precision U-series dating method, was closely investigated. Contrary to the general assumption of global ẟ234U, a Mediterranean Sea offset, compared to the Atlantic ẟ234U, is presented. Furthermore, the combined Atlantic and MEditerranean records comprised of over 1500 published and unpublished data provide unique insights into the ẟ234U evolution over several full glacial-interglacial cycles.