Tracing Past Northern Hemisphere Meltwater Events: Source Dynamics, Oceanic Transport, and Atmospheric Impacts in Proxy Records

The large-scale release of meltwater from continental ice sheets to the North Atlantic during past deglaciations at times played a pivotal role in the reorganization of atmospheric patterns, climate, and ocean circulation. However, reconstructing these events and their impact on the earth system in proxy records is not trivial due to several uncertainties in ice sheet geometries and derived meltwater histories.

Firstly, meltwater might originate from different sectors of an ice sheet, carrying unique isotopic signatures, and secondly, changes in ice sheet geometry associated with the meltwater release directly affects large-scale atmospheric conditions. Deriving the meltwater fluxes directly from an ice sheet reconstruction propagates the underlying uncertainties about ice sheet extent while adding additional uncertainty related to the timing and exact location of the discharge to the ocean. Moreover, direct evidence of melt events is limited because the relevant Arctic regions were often covered with sea ice during a glacial period, and most proxy locations capture localized signals. Most model studies of freshwater “hosing” simplify the discharge region to a relatively uniform distribution and apply meltwater to a large portion of the North Atlantic basin. However, to reconstruct the surface meltwater signal in the North Atlantic, a more detailed study with specific meltwater outlet locations is needed.

We perform a set of glacial period HadCM3 simulations with conservative dye tracers to examine the probable pathways and associated uncertainties in relating a surface Atlantic meltwater anomaly to proxy archives such as speleothems or sediment cores. Our results suggest a direct dependency of the archives’ signal on meltwater source region, and we are able to determine which of the source regions undergo more or less efficient meltwater dispersal by the surface and/or deep North Atlantic. Additionally, melt events from different origins produce different spatial fingerprints of melting, which may be used to reconstruct plausible melt histories from proxy record compilations. Further analysis points to the crucial role of the strength of Atlantic deep convection in mediating the re-distribution of meltwater throughout the ocean. The disruption of Atlantic deep convection impacts atmospheric conditions, and we demonstrate the effect of changes in pressure, winds, precipitation and evaporation on our ability to detect Arctic-Atlantic meltwater in terrestrial records.