Low-Latitude Western North Atlantic Climate Variability During the Past Millennium: Insights from Proxies and Models
Casey P. Saenger, Ph.D., 2009
Delia Oppo, Co-Advisor; Anne Cohen, Co-Advisor
Estimates of natural climate variability provide a frame of reference in which to interpret recent changes. This thesis presents research that improves the present understanding of western North Atlantic climate variability. A new strontium/calcium- sea surface temperature (SST) calibration derived for Atlantic Montastrea corals shows that Sr/Ca is a promising SST proxy if coral growth is considered. Computed Axial Tomography (CAT) imaging indicates growth in Siderastrea corals varies inversely with SST on interannual timescales. A 440-year reconstruction of low-latitude North Atlantic SST based on this relationship suggests the largest cooling of the last few centuries occurred from ~1650-1730 A.D., and was ~1ºC cooler than today. Sporadic multidecadal variability in this record is inconsistent with a persistent 65-80 year North Atlantic SST oscillation. Volcanic and anthropogenic radiative forcing are detected, with the latter accounting for most of the 20th century warming. An 1800-year reconstruction of SST and hydrography near the Gulf Stream also suggests SSTs remained within ~1ºC of modern values, which is small relative to other regional proxy records, possibly reflecting the influence of internal oceanic and atmospheric circulation. Simulations with an atmospheric general circulation model indicate that the magnitude of proxy-based cooling is consistent with tropical hydrologic reconstructions.