Spatial and temporal distribution of scleractinian coral ecosystems from the Drake Passage over the last 35,000 years

Scleractinian coral populations exist in every ocean basin from shallow reefs in the tropics to the depths of the Southern Ocean. These corals have aragonite skeletons and when they die their skeletons can be preserved for hundreds of thousands of years forming a long-term record of their biogeography. Dating these corals has the potential to allow us to test hypotheses that link climate change to major changes in the coral populations. We have a collection of more than 20,000 solitary deep-sea coral fossils collected on three cruises from locations that cross the Drake Passage (Southern Ocean) with a depth range of 120-2941 m. In order to examine the long-term ecosystem regime shifts we have radiocarbon dated more than 500 solitary scleractinian corals at depths between 120 and 1922 m from four distinct locations crossing the major polar frontal zones; Burdwood Bank on the South American continental shelf, Sars Seamount in the Antarctic Circumpolar Current, and two sites south of the Polar Front, Interim Seamount and Shackleton Fracture Zone. We focused on four species of coral D. dianthus, G. antarctica (a species that has never been sampled before in this region), B. malouinesis, and F. curvatum. D. dianthus was found at all sites, whereas G. antarctica was only found at one location south of the Polar Front. By contrast B. malouinesis and F. curvatum were only found on the shelf regions, so we dated specimens from Burdwood Bank. The calendar ages of the corals range from modern to >35,000 years before present (radiocarbon-dead). Within this age range there are clear changes in the distributions of the corals, both by location, and by depth. For example, at intermediate water depths from Burdwood Bank there are no corals older than 17,000 years, with most having ages from 15,000 years ago to modern times with two distinct non-synchronous population peaks observed in B. malouinesis and D. dianthus. At Interim Seamount more than 66 percent of the D. dianthus population existed >35,000 years ago, in contrast G. antarctica population peaked between 30,000 and 35,000 years ago. Neither species are represented during the Holocene. The differences and similarities in the coral-based ecosystems are explored in this study with references to the changes in climate and oceanography that occurred in the Southern Ocean during the major transition from glacial to interglacial conditions.