While most of our colleagues are searching for brightly colored corals and mysterious microscopic bacteria, we (Brendan Roark -Texas A&M and Nancy Prouty-USGS) seem to be the only ones to jump to our feet when the remotely operated vehicle (ROV) stumbles upon a dead-looking skeleton peaking out from the fine silt-sediment.
Yep, we are akin to a hagfish, scavenging the sea bottom and ROV quivers for dead corals and accepting the discarded skeletons from the biologists. But we are all smiles!
Why the smiles? Why the jubilation? Basically, every skeleton we collect on this cruise provides a window into the past. Like a puzzle piece, each coral specimen contributes to our understanding of how climate and the environment have varied in different parts of the world and at different times.
To study past variations in climate, we will look at the biological, geological, and chemical characteristics of the skeletons of deep-sea corals recovered from Baltimore and Norfolk Canyons in the mid-Atlantic. In general, studies utilizing these organisms have been based on samples recovered in dredges and hauls. However, using remotely operated vehicles, such as the Kraken II and Jason II, allows us to do selective sampling as well know exactly what kind of environment the coral lived in in order to gain a better understanding of their living environment.
One reason deep-sea corals may be excellent recorders of past climate changes is that they fill a gap between tropical corals (surface water from the tropics) and the foraminiferan records from ocean sediment cores (surface and bottom water) in that they record both surface and intermediate water variability on different time scales.
Deep-sea corals occur in all the world's oceans, at depths ranging from nearshore to 6,200 meters and in water temperatures ranging from 4 to 29°C. The highest population density of deep-sea corals occurs between 500 and 2,000 meters (e.g. intermediate waters), including a large and diverse distribution along the canyon walls of the mid-Atlantic region.
A secondary objective of our study is to document the longevity of these deep-sea macrofauna. Gigantism and longevity (“big and old”) are common biological adaptations in deep-sea fauna. Our own research on deep-sea macrofauna, including stony corals and proteinaceous zooanthids, indicates that some individuals live for centuries to millennia – they are the "old-growth redwoods" of the deep ocean. The fact that these individuals live for such a long time means that we can use them to reconstruct past variations in ocean circulation and surface ocean productivity, in the same fashion that we can reconstruct climate variability from tree rings.
These large, deep-sea fauna have even more in common with old-growth redwoods: They provide habitat for what would otherwise be a much less diverse group of deep-ocean organisms (biota). Deep-sea corals take a long time to grow large and are threatened by indiscriminate human activities such as trawling and dredging.
We wonder, what will happen to these organisms and the deep-sea ecosystems they support as people grapple with climate change, how to curb carbon-dioxide emissions the world over, as well as how to manage and protect our marine resources in areas where human activities also occur?