HR: 0830h
AN: PP31B-0250    [PDF]
TI: Integrated Study of Ice-Rafted Debris, Temperaturess, and Stable Isotopes on a Spliced Record (piston cores and ODP Site 177-1090) From the South Atlantic
AU: * Warnke, D A
EM: dwarnke@csuhayward.edu
AF: California State University, Hayward, 25800 Carlos Bee Blvd., Hayward, CA 94542
AU: Teitler, L
EM: lteitler@csuhayward.edu
AF: California State University, Hayward, 25800 Carlos Bee Blvd., Hayward, CA 94542
AU: Becquey, S
EM: sbecquey@awi-bremerhaven.de
AF: A.W.I., Columbusstrasse, Bremerhaven, 27515 Germany
AU: Gersonde, R
EM: rgersonde@awi-bremerhaven.de
AF: A.W.I., Columbusstrasse, Bremerhaven, 27515 Germany
AU: Venz, K
EM: venz@ufl.edu
AF: University of Florida, 241 Williamson Hall, Gainesville, FL 32611 United States
AU: Hodell, D A
EM: dhodell@geology.ufl.edu
AF: University of Florida, 241 Williamson Hall, Gainesville, FL 32611 United States
AB: We have conducted an integrated study of ice-rafted debris (IRD) and stable isotopes on a spliced record (TN057-6-PC4/ODP Site 177-1090, about $43\deg$ S, $9\deg$ E) raised on the Agulhas Ridge, in the South Atlantic. The site is just north of the northern boundary of the present-day Polar-Front Zone (PFZ), and is in a very sensitive location to record both ice-rafting and stable-isotopic-ratio changes. Our combined record reveals a pattern of ice-rafting episodes that may be characteristic for the subantarctic South Atlantic, at least for locations N of the PFZ. Ice rafting occurs during the waxing stages of each glaciation, and ends at, or before, the peak of each glaciation. IRD peaks are also associated with strong stadials during "cold" interglacials, e.g. MIS 7. A little IRD shows up during the entire interval studied here, from the Holocene to mid-MIS 14. We suggest that the IRD record at this site is essentially a temperature record on glacial-interglacial timescales. If the temperature is low enough, enough icebergs survive to melt at this location. If the temperature is too warm, only an occasional iceberg survives to deliver debris. A peculiar aspect of the combined record is the fact that during Ice-rafting events (IREs), the planktic oxygen-isotopic ratios are higher at the end of an IRE compared to the beginning. Further, by comparing our records with the Summer Sea Surface Temperature record of Becquey and Gersonde (2002) for a nearby (respectedly the same) site (PS2489-2/ODP177-1090), we see that the temperature is generally very similar at the beginning and the end of an IRE. The same age model provided by Venz and Hodell (2002) was used for both sites, allowing such direct comparisons of the data. Assuming as a working hypothesis that the IRD record is a pure temperature record, and ignoring the salinity effect for the present, then this difference in oxygen-isotopic ratios must be the ice volume effect. For MIS 12, the difference in planktic oxygen-isotopic ratios at the beginning and the end of the IRE is about 1.3 permil, which translates to 130 m sea level equivalent. The present-day temperature at the site is about $10\deg$ C (Levitus and Boyer, 1998). To attain a temperature of about $4\deg$ C (presently located at about $47\deg$ S in this area), as indicated by the SSST record of Becquey and Gersonde (2002) for the IRE during MIS 12, the Polar Front Zone (the zone of major iceberg melting) had to move north by about $4\deg$ latitude (about 240 nautical miles), a not unreasonable assumption.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 9310 Antarctica
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting