Entrainment of meltwaters in hyperpycnal flows during deglaciation superfloods in the Gulf of Mexico

Northern Gulf of Mexico is a key archival site of the Laurentide Ice Sheet melting history and the only margins containing evidence of meltwater outflows contemporaneous with global meltwater pulse mwp-1A. Inconsistencies between these meltwater floods and the absence of strong climate responses to large freshwater fluxes predicted by climate models raised questions concerning the validity of planktonic foraminiferal δ¹⁸O record in the Gulf of Mexico as a reliable index of freshwater fluxes. Isotope records of depth-stratified foraminifera document unusual trends compatible with entrainment of ¹⁸O-depleted freshwaters in hyperpycnal flows reaching the seafloor and rising to the surface as buoyant plumes. These exceptionally large outbursts of floodwaters, coeval with a prominent erosion intensity peak in continental paleohydrology, were catastrophically released in a rapid succession over a period of ca. 500 yr (14.7–14.2 kyr). Correspondence in time and magnitude between the torrential floods and the mwp-1A event supports the view that LIS was likely a substantial freshwater source. Drainage of meltwaters through torrential hyperpycnal flows that underwent substantial mixing with seawater may resolve the problem with ocean modeling results that predict a much stronger climate response to large freshwater hypopycnal fluxes into the ocean.