Deep-dwelling Creatures Hold Clues to Climate Change
Thomas P. Guilderson
Department of Ocean Sciences,
Univ. of California, Santa Cruz,
Center for Accelerator Mass Spectrometry, LLNL
Robert B. Dunbar
B. Lynn Ingram
Univ. of California, Berkeley
This expedition includes a research study to increase our understanding of climate and ecosystem variability in the Gulf of Alaska. We will focus on the natural variability of the dominant atmospheric pressure cell (the Aleutian Low) as it relates to the Pacific Decadal Oscillation (a change in climate that occurs approximately every every few decades) and air circulation over the Pacific Ocean. Observational evidence indicates that regional-scale disturbances of the Aleutian Low generate far-field temperature anomalies in the central and eastern North Pacific. The size and intensity of the Aleutian Low, in conjunction with North Pacific sea-surface temperature patterns, initiate prominent and persistent anomalies that have profound consequences on the climate of the Pacific and North America.
These changes in atmospheric circulation can, for example, reposition the jet stream, among other things. These anomalies are known to have certain rhthyms, lasting from a year to a decade, with distinct shifts in temperature. We do not know, however, what triggers them, or whether warmer or colder temperatures will be favored as atmospheric concentrations of carbon dioxide continue to increase.
To study past variations in climate, we will look at the biological, geological, and chemical characteristics of the skeletons of microscopic animals, such as foraminifera, and macrofauna, such as deep-sea corals (Azooxanthellate) and related organisms (e.g., sclerosponges, proteinaceous zooanthids). In general, studies utilizing these organisms have been based on individuals recovered in dredges and hauls. Only recently has there been a more concerted effort to understand the biogeochemistry of these species and their novel applications in reconstructing surface and subsurface conditions.
One reason deep-sea corals may be an excellent source of clues to the distant past is that they occur in all the world's oceans, at depths ranging from 0 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 m, including a large and diverse distribution along the Alaskan continental margin and the Gulf of Alaska.
A secondary objective of our study is to document the longevity of these deep-sea macrofauna. Gigantia and longevity (big and old) is a common biological adaptation in species. 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 "greenhouse warming" and if they do not strive to reduce carbon-dioxide emissions the world over?
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