COMPARISON OF PROXY PRECIPITATION RECORDS FOR THE GULF OF MEXICO

Four proxy precipitation records from around the Gulf of Mexico with decadal resolution are compared to ascertain an overall picture of changes in atmospheric circulation during the last 1200 years. The four records used in this study are from: 1) lacustrine sediments (Lake Tulane, FL), 2) tree ring index (Choctawhatchee River, FL), 3) speleothem isotopes (Brooksville Ridge Cave, FL) and 4) marine sediments (Cariaco Basin, Southern Gulf of Mexico). The types of records are quite disparate in the environmental measure used to derive climatic information: lacustrine sediments - äD of terrestrial organic matter, tree ring index - standardized ring widths, speleothem record - oxygen isotopes, and the marine basin - titanium levels. There is good agreement between all of the four records’ interpretation of how precipitation changes over this period. The proposed reason for these changes in rainfall is the latitudinal movement of the intertropical convergence zone (ITCZ) across this region. The Medieval Warm Period from 1000 to 700 yrBP was a wetter period, with the ITCZ being further north, bringing more humid air from equatorial latitudes. This period is then followed by the Little Ice Age which has a drier climate, caused by the movement of the ITCZ to the south.