History of Laurentide meltwater flow to the Gulf of Mexico during the last deglaciation, as revealed by reworked calcareous nannofossils

Abstract

The history of meltwater flow from the Laurentide Ice Sheet to the Gulf of Mexico during the last deglaciation, which holds possible implications for the cause of the Younger Dryas cold episode, is not well understood. We propose a new chronology based on using the percentage of reworked calcareous nannofossils in Orca Basin sediments as a proxy for erosion. The period of greatest meltwater flow to the gulf was between 12.7 and 12.1 ka (during the Bølling warm interval), and flow remained high until the beginning of the Younger Dryas cold episode at 11.3 ka; this corresponds to meltwater pulse IA. A sharp meltwater decrease at 12.2 ka may represent the Older Dryas glacial readvance. Little or no meltwater is inferred to have flowed to the gulf from ϳ10 to 9 ka, which is the time of the second major meltwater pulse, IB. Therefore, meltwater must have been permanently diverted away from the Gulf of Mexico at the beginning of the Younger Dryas.

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…All support the variable influence of LIS meltwater in the Gulf of Mexico during the last deglaciation (Flower et al, 2011). In addition to an isotopic signature from LIS meltwater, evidence from proxies of continental erosion (Brown and Kennett, 1998;Marchitto and Wei, 1995;Meckler et al, 2008) indicates that a large volume of freshwater runoff from the LIS was directed into the Gulf of Mexico during the last deglaciation, with a dynamic melting history and periods of high meltwater discharge (Brown and Kennett, 1998). Gulf of Mexico in the past also presents challenges.…”

Marine Molluscs as Indicators of Environmental Change in Glaciated North America and Greenland During the Last 18 000 Years

“…It had been thought that flow returned to the Gulf of Mexico after blockage of eastern outlets about 9.9 ka BP. However, it now appears that Lake Agassiz discharged northward at that time into the Arctic Ocean via glacial Lake McConnell (Fisher and Smith, 1995), that this flow continued until re-establishment of eastward drainage about 9.5 ka BP, and that meltwaterflow never resumed down the Mississippi River (Marchitto and Wei, 1995).…”

A revised Holocene geochronology for the Lower Mississippi Valley

“…17) (Flower and Kennett, 1990;Marchitto and Wei, 1995;Aharon, 2003). During this period, the Mississippi River discharge and the size and amount of sediment load was were significantly reduced.…”

“…17) from 11,000 to 10,000 cal yr B.P., was marked by at least four meltwater flood periods (Aharon, 2003). Increased meltwater flow to the Gulf of Mexico has been shown to have greatly enhanced the erosion of stored sediments in the Mississippi Alluvial Valley (Marchitto and Wei, 1995). It is suggested that these meltwater episodes caused erosion of the upstream channel.…”