26 Feb 2021

26 Feb 2021

Review status: a revised version of this preprint is currently under review for the journal CP.

Eddy permitting simulations of freshwater injection from major Northern Hemisphere outlets during the last deglacial

Ryan Love1, Heather Andres1, Alan Condron2, and Lev Tarasov1 Ryan Love et al.
  • 1Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada
  • 2Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

Abstract. Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial to millennial scale climate variability such as the Younger Dryas and Dansgaard-Oeschger Events. Indeed, freshwater injection/hosing experiments with climate models have long shown that freshwater has the capability of generating such abrupt climate transitions. However, the relationship between freshwater and abrupt climate transitions is not straightforward. Large-scale glacial runoff events, such as Meltwater Pulse 1A, are not always temporally proximal to subsequent large-scale cooling. As well, the typical design of hosing experiments tends to artificially amplify the climate response. This study explores the impact that limitations in the representation of runoff in conventional hosing simulations has on our understanding of this relationship and addresses the more fundamental question of where coastally released freshwater is transported when it reaches the ocean. We focus particularly on the prior use of excessive freshwater volumes (often by a factor of 5) and present-day (rather than paleo) ocean gateways, as well as the injection of freshwater directly over sites of deep-water formation (DWF) rather than at runoff locations.

We track the routing of glaciologically-constrained freshwater volumes from four different plausible injection locations in a suite of eddy-permitting glacial ocean simulations using MITGCM under both open and closed Bering Strait conditions. Restricting freshwater forcing values to realistic ranges results in less spreading of freshwater across the North Atlantic and indicates that the response of DWF depends strongly on the geographical location of meltwater input. In particular, freshwater released into the Gulf of Mexico has little impact on DWF regions as a result of turbulent mixing by the Gulf Stream. In contrast, freshwater released from the Eurasian Ice sheet or initially into the Arctic is found to have the largest impact on DWF in the North Atlantic and GIN seas. Additional experiments show that when the Bering Strait is open, much like present-day, the Mackenzie River source exhibits twice as much freshening of the Labrador sea as a closed Bering Strait. Finally, our results illustrate that applying a freshwater hosing directly into the North Atlantic with even realistic freshwater amounts still over-estimates the effect of terrestrial runoff on ocean circulation.

Ryan Love et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'RC: caveats not sufficiently discussed', Anonymous Referee #1, 01 Apr 2021
  • CC1: 'Comment on cp-2021-15', Pearse Buchanan, 19 Apr 2021
  • RC2: 'Comment on cp-2021-15', Anonymous Referee #2, 27 Apr 2021

Ryan Love et al.

Ryan Love et al.


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Short summary
Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial to millennial scale climate variability and climate transitions. We track the routing of glaciologically-constrained freshwater volumes in glacial ocean simulations. Our simulations capture important small scale features (boundary currents & eddies) not generally well represented. We show that the dilution of freshwater as it is transported to key climate regions reduces the freshening to 20 %–60 %.