An abrupt, century-scale cooling ~8200 years ago, known as the "8.2 ka event," is believed to have been caused by the catastrophic release of freshwater from a giant ice-dammed lake (Lake Agassiz) into the North Atlantic Ocean. However, a comprehensive understanding of this prominent climate change is hampered by uncertainty about the magnitude, nature, and timing of this meltwater pulse. Current estimates of the freshwater volume associated with the 8.2 ka event correspond to an equivalent sea-level rise of ~0.3 to ~1.4 m. In the Mississippi Delta region, basal peat (brackish water derived) encroaches on a consolidated Pleistocene basement and the microtidal regime in the Gulf of Mexico enables the reconstruction of sea-level change with exceptionally high resolution. In this project, the PI's will 14C date basal-peat samples that track sea-level change during this critical time interval. Sampling resolution will be on the order of 10 cm. Stable carbon isotope data will provide data to estimate the salinity of the peat-forming ecosystem so as to establish the relationship with sea level. The combined data will be used to estimate the total amount of sea-level rise as well as determining the timing of this event. These data will also permit the PI's to provide an estimate of the amount of freshwater delivered directly by the Laurentide Ice Sheet, as well as providing input data to explore the climatic effects of different mechanisms and locations of freshwater release using a coupled ocean-atmosphere model. These results will provide new insights about the sensitivity of ocean circulation to various scenarios of freshwater forcing, which could help to better understand the consequences of continued freshening of the North Atlantic Ocean in the greenhouse world. The project will provide training for one PhD student, as well as four undergraduate field assistants.
