The dependence of the stable carbon isotope composition of plankton on water temperature forms the basis of a paleoclimatological tool useful for deep-sea sediments. Detailed work on a 12-m core (E-49-30) taken from a depth of 4,200 m at 59°0.3^primeS, 95°13.8^primeE, shows a trend in ^dgr¹³C_PDB for total organic carbon from approximately -22 parts per thousand at the top to -28 parts per thousand at the bottom. Several systematic excursions to about -18 parts per thousand occur at intermediate depths. The most obvious explanation for the primary trend is a general increase in the amounts of warm-water plankton residues, relative to those of cold water, deposited at this location over the time represented by these sediments (about 1 m.y.). his increase implies a southward migration of the Polar Front.

Two other cores (28-266, 28-272) taken near Antarctica during the Deep Sea Drilling Project show similar trends which, presumably, are due to the same process.

Advantages of this potential tool are that it is directly related to surface water temperatures and is especially useful for carbonate-free sediments. Disadvantages include an incomplete understanding of the factors which determine modern carbon isotope compositions of plankton, kerogen recycling near the Antarctic continent, and obliteration of the paleotemperature signal by terrestrial, plant-derived organic matter deposited contemporaneously with the plankton-derived organic matter.

End_of_Article - Last_Page 519------------