HR: 17:30h
AN: PP44A-07    [Abstracts]
TI: Evidence for Oceanic/Continental Climate Linkages During Freshwater Inputs to the Gulf of Mexico
AU: * Hill, H W
EM: hhill@marine.usf.edu
AF: University of South Florida, College of Marine Science 140 7th Ave South, St. Petersburg, FL 33701 United States
AU: Flower, B P
EM: bflower@marine.usf.edu
AF: University of South Florida, College of Marine Science 140 7th Ave South, St. Petersburg, FL 33701 United States
AU: Hollander, D J
EM: davidh@marine.usf.edu
AF: University of South Florida, College of Marine Science 140 7th Ave South, St. Petersburg, FL 33701 United States
AU: Quinn, T M
EM: tquinn@marine.usf.edu
AF: University of South Florida, College of Marine Science 140 7th Ave South, St. Petersburg, FL 33701 United States
AB: Understanding the linkage between oceanic and continental responses to millennial-scale climate variability can provide insight into the mechanisms controlling abrupt global climate change, however there are few marine depositional systems where these linkages can be studied simultaneously. Here we present new evidence for freshwater input (Laurentide Ice Sheet (LIS) meltwater versus precipitation?) to the northern Gulf of Mexico from 28-45 ka (within Marine Isotope Stage 3), and draw linkages to continental climate using organic geochemical proxies. A 32-m laminated sediment core (MD02-2551) from the anaerobic Orca Basin was collected aboard the R/V Marion Dufresne in July 2002 as part of the IMAGES program. Radiocarbon dates suggest that the average sedimentation rate is $>$50 cm/1000 years during this interval, allowing for 40-year resolution sampling at 2-cm intervals. Paired $\delta$$^{18}$O and Mg/Ca data on the planktic foraminifer Globigerinoides ruber are used to separate changes in Mg-derived sea-surface temperature (SST) and the oxygen isotopic composition of seawater, which can be interpreted in terms of salinity. Three large negative excursions in $\delta$$^{18}$O$_{sw}$ ($<$0.5 \permil), each lasting ~3 ka, exist in the record. Two of these excursions may correlate with Heinrich events 3 and 4, but show no clear relationship to Dansgaard-Oeschger warmings. $\delta$$^{18}$O$_{sw}$ excursions have significant ramifications for Gulf of Mexico salinity, which can be constrained using two freshwater end members: the current Mississippi River (MR) value of -7 \permil and an LIS value of -30 \permil. Use of the MR end-member would require extraordinarily large floods and changes in salinity of 5-6 psu, whereas use of the LIS end-member results in a salinity decrease of 2-3 psu. Preliminary results of analyses of organic biomarkers preserved in the Orca Basin sediments suggest that the freshwater events are dominated by terrigenous organic matter, but are also associated with an increase in marine-derived algal inputs, suggesting that changes in the nutrient flux to the Gulf of Mexico from the North American continent may support marine production. Molecular carbon and hydrogen isotopic components of biomarkers will be used to evaluate shifts in continental climate through analyses of vegetation ($\delta$$^{13}$C; C3 vs C4 plants) and source water ($\delta$D) changes during large salinity excursions observed in the Gulf of Mexico.
DE: 4267 Paleoceanography
DE: 1620 Climate dynamics (3309)
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting