Temperature control of cold-water coral (Lophelia) mound growth by climate-cycle forcing, Northeast Gulf of Mexico

Abstract

Chronostratigraphy, of a northern Gulf of Mexico Lophelia pertusa (cold-water coral) mound (Roberts Reef), indicated that mound development included periods of growth and non-growth that are closely tied to Late Pleistocene climate cycles. U/Th and 14C dating of coral fragments in two ~ 16 m cores (mound crest and mound flank) and foraminiferal biostratigraphy provided a stratigraphic framework that identified five mound-growth sequences separated by four hiatuses, a total of ~ 300 ka. Mound growth occurred during interglacials while non-growth and unconformity formation correlates to glacial periods. In each cycle, growth on the mound flank persisted after growth at the crest ceased. Results of our study suggest warming bottom-water as the most probable environmental condition for limiting L. pertusa growth and mound accretion as sea level fell toward a glacial maximum. At highstands of sea level, the mound resided in the Oxygen Minimum Layer with a present temperature range of ~ 9.0–12.8 °C. During falling-to-lowstands of sea level, isotherms of warm, Subtropical Underwater (~ 12.8–21 °C) progressively exposed the mound to water above the thermal range for L. pertusa. A comparison of non-growth periods in the mound cores indicates that coral mortality and suppression of mound growth started at the crest and moved down the flank, a trend that supports progressive immersion of the mound in warm Subtropical Underwater. Multiday episodes of vertical down-mixing may have also transported warm ocean water, above the tolerance level of Lophelia, to the mound. Present average bottom-water temperatures at the mound crest range between 9 and 10.5 °C, ideal for L. pertusa growth in the Gulf of Mexico. Experimental work indicates that relatively short periods (weeks) of L. pertusa exposure to water of ~ 12–14 °C results in mortality. At periods of lowered sea level, the mound is projected to have been immersed in ocean water of ~ 12–14 °C for millennial scale time periods.