MELTWATER STORAGE IN LAKE AGASSIZ; VOLUME, DELIVERY, AND TIMING

The delivery of meltwater from glacial Lake Agassiz to ocean basins adjacent to North America has been implicated in numerous abrupt climate change events during the last deglacial cycle. Robust chronologic control is necessary before teleconnections between Greenland ice core stratigraphy, receiving basin sediment cores and Lake Agassiz event stratigraphy can be made. Here, we focus on recent chronology results from the Lake Agassiz basin; a necessary first step before evaluating abrupt climate changes triggered by meltwater delivery variability from glacial Lake Agassiz.

Shorelines represent static water planes. Their extension around glacial lake margins establishes time-synchronous lake levels and their ice-proximal extent records the location and age of ice margins. More than 25 OSL ages from littoral deposits permit age assignment to beaches. The laterally extensive Herman beach in the southern basin records rapid retreat of an ice margin during a stable lake level with an average age of 14.1 ± 0.3 ka. Episodic incision of the southern outlet is recorded by flights of strandlines below the Herman Beach with ages between 13.6 ± 0.2 and 13.4 ± 0.3 ka. These incision events overlap in time with the last of three meltwater events recorded in the Gulf of Mexico at 13.7–13.0 ka. Increased meltwater from the Laurentide Ice Sheet discharging through Lake Agassiz may have driven outlet incision with the effect of releasing minor volumes of stored lake meltwater. Shoreline mapping and radiocarbon dated ice margin data from the eastern and northwestern outlet areas limit earliest meltwater delivery to the Atlantic or Arctic, respectively, to 10.5 ± 0.3 ka or ~9400 ¹⁴C yrs BP, the age of the Campbell strandline. Strandlines dating to the start of the Younger Dryas are missing from the Lake Agassiz data set. With OSL dating of strandlines in the Lake Agassiz basin, a more robust history of Mississippi valley evolution and meltwater delivery to the Gulf of Mexico becomes available.