Reply to ‘Challenging the hypothesis of an arctic ocean lake during recent glacial episodes’ by Hillaire‐Marcel, et al

Abstract

Hillaire-Marcel et al. bring forward several physical and geochemical arguments against our finding of an Arctic glaciolacustrine system in the past. In brief, we find that a physical approach to further test our hypothesis should additionally consider the actual bathymetry of the Greenland-Scotland Ridge (GSR), the density maximum of freshwater at 3-4°C, the sensible heat flux from rivers, and the actual volumes that are being mixed and advected. Their geochemical considerations acknowledge our original argument, but they also add a number of assumptions that are neither required to explain the observations, nor do they correspond to the lithology of the sediments. Rather than being additive in nature, their arguments of high particle flux, low particle flux, export of 230 Th and accumulation of 230 Th, are mutually exclusive. We first address the arguments above, before commenting on some misunderstandings of our original claim in their contribution, especially regarding our dating approach.

A 600-kyr reconstruction of deep Arctic seawater δ18O from benthic foraminiferal δ18O and ostracode Mg/Ca paleothermometry

“…In addition, ostracodes inhabit both fresh and marine environments and experience large faunal transitions in many locations, yet no fresh water ostracodes have been observed from Arctic Ocean sediments (Cronin et al 1995, Poirier et al 2012. Instead, terrigenous material dilution provides an explanation consistent with all observations, including low excess 230 Th, low-to-absent 10 Be, and limited microfossil abundance (e.g., Hillaire-Marcel, 2022; but see rebuttal by Geibert et al, 2022a).…”

“…The "Fresh Arctic" hypothesis (Geibert et al, 2021) has generated significant discussion about both the interpretation of excess 230 Th and cosmogenic 10 Be in Arctic sediments (Hillaire-Marcel, 2022;Geibert et al, 2022a) and the evidence supporting or refuting this hypothesis from outside the Arctic Ocean (Spielhagen et al, 2022;Geibert et al, 2022b).…”

A resilient ice cover over the southernmost Mendeleev Ridge during the late Quaternary

“…Note that Geibert et al . (2022) associated the high 230 Th xs values of samples in the MIS 3 interval with continuous but low sedimentary fluxes, considering that ‘even a short particle pulse would be enough to remove 230 Th from the water column’.…”