Intra-Allerød Cold Period (IACP) likely not triggered by deglacial outburst floods from the Hudson River, New York City, USA

Abstract:

It has long been hypothesized that periodic meltwater input from a retreating Laurentide Ice Sheet (LIS) inhibited North Atlantic deep water (NADW) formation, weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC), and triggered several cold periods in the North Atlantic region during the last deglaciation (21-8ka yrs BP). Since the establishment of this hypothesis more than thirty years ago, geomorphic and chronologic evidence of meltwater flows from the LIS have been shown to roughly coincide with centennial-to-millennial scale cool periods (e.g., Younger Dryas, the 8.2 ka event). The complexity of LIS meltwater routing during deglaciation, a lack of tight spatial and temporal constraint on meltwater events and volumes, and insights from models have however made it difficult to point to a specific meltwater event as the trigger for a particular cold period. Here, we use a numerical model to investigate the possibility of meltwater discharge from the Hudson River, New York City, USA ~13,350 yrs BP as a potential trigger of the Inter-Allerød Cold Period (IACP). Using flood volumes estimated from paleoshorelines, we assess the sensitivity of AMOC to both short duration (1 month), and long duration (1 year) flood events. We also assess the impact of successive flood events on AMOC to determine if sequential floods impact AMOC differently than a single flood event. We find that in all of our experiments (regardless of flood magnitude, duration, or reoccurrence interval) there is no significant weakening of the AMOC. This limited impact suggests that although the Hudson Valley floods likely occur close to the beginning of the IACP, it is unlikely the trigger. Further observations to constrain the timing of the Hudson Valley Floods and additional modeling experiments exploring different and/or multiple meltwater inputs are needed to determine if meltwater inputs from the LIS could have been a trigger and/or contributor of the IACP. Our results have significant implications for determining whether other deglacial flood events triggered periods of climatic cooling: for example, the millennial-length Younger Dryas cooling is thought to have been triggered by a flood only 3-times larger than the one from the Hudson River, which again questions the role meltwater played in triggering climate cooling.