The Pleistocene Cooling Built Challenger Mound, a Deep-water Coral Mound in the NE Atlantic: Synthesis from IODP Expedition 307

Abstract

IODP Expedition 307 revealed the interior of a deep-water coral mound in NE Atlantic for the first time and improved our understanding of these intriguing structures. From the summit of our drilling target, Challenger Mound at ~800 m deep in the Porcupine Seabight, south west of Ireland, we recovered the entire mound section of 155 m long, which almost entirely consists of coral-bearing sediments and rests on the Miocene siliciclastics. The mound initiation is temporally correlated to the global cooling at the beginning of Pleistocene, when modern circulation was established in Atlantic.A key oceanographic feature of the mound provinces is the density gradient that developed above the saline Mediterranean Outflow Water where organic particles persist for a longer time and fuel the coral communities. Growth of the deep-water mounds reflected the glacial/interglacial change. Our age model recognized two growth stages separated by a substantial hiatus; the depositionally continuous lower mound (2.61.7 Ma) accumulated under the low-amplitude relative sea-level change, and the discontinuous upper mound (1.0 Ma to midHolocene) developed under the high-amplitude relative sea-level change. Low cellular abundances in the geochemical features of the mound sediments did not support the hypothesis that hydrocarbon seepage and associated microbial activity significantly enhanced mound initiation and development.