Staggered cold-water coral mound build-up on an Alboran ridge during the last deglacial (East Melilla Mound Field, western Mediterranean)

The start-up, build-up and demise of cold-water coral mounds are governed by environmental changes at global, regional and local scales. Whilst the formation of cold-water coral mounds across the globe is widely documented to follow interglacial-glacial cycles, less is known about their response to local environmental fluctuations during short time intervals. This study investigates the local variations in coral mound build-up along Brittlestar Ridge I (East Melilla Coral Province, Southeast Alboran Sea) by comparing three on-mound gravity cores collected -1 km apart, together with five previously described on-mound records, along a longitudinal transect on the ridge crest. Radiocarbon foraminiferal dating associated to U-series coral dating allowed to correlate the different records and to estimate mound aggradation rates, whilst grain-size analysis provided information on bottom current velocities. Prior to a rapid period of coral mound build-up initiated at -14.75 ka BP, the three cores present an occurrence of cm-thick bryozoan-dominated intervals nearly entirely consisting of the erect cheleistome Buskea dichotoma. Offsets between benthic foraminiferal and coral ages suggest that older dead allochtonous benthic foraminifera are possibly eroded from neighbouring settings, transported and deposited within the coral framework. In contrast, younger benthic foraminifera would develop on dead coral framework during periods of reef stagnation. The comparison of all cores indicates that mound build-up along the ridge did not follow the same timing during the last -16 kyr and that mound aggradation was marked by a staggered dynamic. Both local differences in bottom current velocities and patchiness of other key environmental actors (e.g. substrate availability) are suspected to drive the observed staggered mound build-up. Cold-water coral mound buildup shows important differences during Greenland Interstadial 1 (i.e. the Bolling-Allerod) and the Holocene, hence examplifying how local environmental variability may overprint global and regional climate variability over short time periods.