Sclerosponges: Potential High-Resolution Recorders of Marine Paleotemperatures
Gary B. Hughes, Charles W. Thayer, 2001. "Sclerosponges: Potential High-Resolution Recorders of Marine Paleotemperatures", Geological Perspectives of Global Climate Change, Lee C. Gerhard, William E. Harrison, Bernold M. Hanson
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Sclerosponges have great potential as seawater temperature recorders. These animals precipitate their skeletons in carbon and oxygen isotopic equilibrium with the surrounding seawater (Druffel and Benavides, 1986). Their skeletons also display chemical properties that vary directly with changes in environmental conditions. Lack of photosynthetic symbionts allows sclerosponges to live below the photic zone, providing the potential to investigate past marine conditions beyond the range of corals. Individual sponges live for several centuries, preserving archives of pre- and postindustrial seawater variations within single specimens (Hartman and Reiswig, 1980). Crosscorrelation of successively older specimens could yield up to 2000 years of marine history. Extracting environmental information can be accomplished by determining elemental characteristics preserved in skeletal growth bands. A method is presented here that utilizes energy dispersive spectroscopy (EDS) to provide inexpensive assessment of magnesium (Mg): calcium (Ca) and chlorine (Cl): calcium (Ca) ratios at high spatial resolution, yielding environmental data with correspondingly high temporal resolution. The relationship between environmental conditions and skeletal characteristics is defined by a spectral transfer function, which can then be applied to skeletal carbonate data from ancient sponges to reconstruct past environmental conditions. Accurate reconstruction of seawater temperature and salinity variations is demonstrated here at submonthly resolution. The technique’s efficiency is ideal for documenting long, high-resolution records of marine paleoenvironments.
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Access A Broad Range of Paleoclimatic Studies. Current debates regarding potential man-induced modification of climate make this volume especially timely. Introductory sections address the major and minor physical controls, or drivers, that affect Earth's climate. Several chapters describe the naturally occurring range of variation of climatic conditions and illustrate past changes in global temperatures. Case studies show how ancient temperature conditions are determined, as well as new techniques that have significant potential as proxies for assessing paleoclimates. Several chapters demonstrate the magnitude and length of duration of numerous temperature variations, which occurred during geologic time periods.