DURATION AND MAGNITUDE OF FRESHWATER FLOODS DURING THE 13.0 KA AND 11.4 KA BP EVENTS IN THE CHAMPLAIN SEA

Volumetric flow magnitude and duration of proglacial flood events in the Champlain Sea around 13.0 ka and 11.4 ka BP are estimated using a one-dimensional hydrodynamic flow model that simulates water height, flow, and salinity in estuarine environments. Proxy data of salinity levels from several cores within the present-day Lake Champlain watershed, along with reconstructions of paleo-bathymetry, are used to initialize the model. Freshwater floods are then simulated in order to diagnose the flood volumes and durations required to match observed salinity changes from the Champlain Sea for the 13.0 ka and 11.4 ka BP events. The model is first tested on a well studied estuary, the Delaware Bay, during a year in which few major weather events were observed.

The Bathymetric parameters and instrumental water data for the test year are compiled for 34 stations down the Delaware with starting values of salinity, flow, and water height used at each site to initialize the simulation. Instrumental freshwater flow magnitudes at the head of the bay are then used to force the model in order to re-create the observed annual salinity distribution. After a successful simulation, the bathymetric parameters for the Champlain Sea for 13.0 ka and 11.4 ka BP are ascribed to the model with a number of stations depending on the complexity of the bathymetry. Salinity values for the head and mouth of the Champlain Sea are used to start the model which is run forward until convergence to a steady state of salinity is achieved. Freshwater flow is then increased to varying levels over a range of timescales in order to obtain combinations of flood magnitude and duration that best fit the empirical salinity record as recovered from the sediment core proxy data; keeping total flood volume during each run constant using values reported in the literature. These flood magnitude and duration estimates are then applied to the most probable water source, Lake Agassiz, in order to better constrain the timing, magnitude, and routing of flood events associated with the draining of the proglacial lake. Better understanding of these flood events has utility among modelers and climate scientists as large fluxes of freshwater have strong implications for global ocean circulation.