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. 2018 Aug 9;8(1):11307.
doi: 10.1038/s41598-018-29226-8.

Greenland ice mass loss during the Younger Dryas driven by Atlantic Meridional Overturning Circulation feedbacks

Eleanor Rainsley  1 , Laurie Menviel  2 , Christopher J Fogwill  3   2 , Chris S M Turney  2 , Anna L C Hughes  4 , Dylan H Rood  5   6
Affiliations

Greenland ice mass loss during the Younger Dryas driven by Atlantic Meridional Overturning Circulation feedbacks

Eleanor Rainsley et al. Sci Rep. .

Abstract

Understanding feedbacks between the Greenland Ice Sheet (GrIS) and the Atlantic Meridional Overturning Circulation (AMOC) is crucial for reducing uncertainties over future sea level and ocean circulation change. Reconstructing past GrIS dynamics can extend the observational record and elucidate mechanisms that operate on multi-decadal timescales. We report a highly-constrained last glacial vertical profile of cosmogenic isotope exposure ages from Sermilik Fjord, a marine-terminating ice stream in the southeast sector of the GrIS. Our reconstruction reveals substantial ice-mass loss throughout the Younger Dryas (12.9-11.7 ka), a period of marked atmospheric and sea-surface cooling. Earth-system modelling reveals that southern GrIS marginal melt was likely driven by strengthening of the Irminger Current at depth due to a weakening of the AMOC during the Younger Dryas. This change in North Atlantic circulation appears to have drawn warm subsurface waters to southeast Greenland despite markedly cooler sea surface temperatures, enhancing thermal erosion at the grounding lines of palaeo ice-streams, supporting interpretation of regional marine-sediment cores. Given current rates of GrIS meltwater input into the North Atlantic and the vulnerability of major ice streams to water temperature changes at the grounding line, this mechanism has important implications for future AMOC changes and northern hemisphere heat transport.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Location map. (A) Northeast Atlantic region with ocean currents in solid lines (IC: Irminger Current; NAC: Norwegian Atlantic Current; EGC: East Greenland Current; WGC: West Greenland Current) and return flow of NADW in dashed lines. Red and blue lines indicate warm and cold currents respectively. JI: Jakobshavn Isbrae; KL: Kangerlussuaq; SS: Scoresby Sund; SF: Sermilik Fjord. Box shows location of (B). Black star shows location of ocean cores referenced in text,. Triangle shows location (just south of this image) of ocean cores from. Bathymetry of ocean shown in inset scale in m b.s.l. Base map and bathymetry from https://www.ngdc.noaa.gov/mgg/bathymetry/arctic/ (Version 3.0 ref.. (B) Locations and altitudes of in situ cosmogenic exposure ages in Sermilik Fjord. Location and altitudinal range of the Island (samples SF0915-30) and East wall (samples SF0936-55) vertical transects shown by red brackets. Discrete sample locations (West wall and Mouth) and altitudes shown by red dots. Red star shows location of basal radiocarbon dates from lakes. Base Landsat image downloaded from Earth Explorer *(https://earthexplorer.usgs.gov/ USGS/NASA Landsat Program). Figure generated in Adobe Illustrator 2015 1.0 release (19.1.0).
Figure 2
Figure 2
Sermilik Fjord thinning trajectory. (A) Age-modelled thinning trajectory of Sermilik Fjord from in situ cosmogenic exposure ages (SF numbers, brackets denote 10Be exposure ages combined into a single event by C_Combine) and two radiocarbon ages from basal lake sediments (AAR-1542 and K-0638). Dark blue envelope to 1 s.d., pale blue to 2.s.d. Light grey cumulative probability functions show raw 10Be exposure ages after outliers were omitted by C_Combine function (Table S2). Dark grey probability density functions show Bayesian modelled ages (Table S4). Plotted against δ18O curve from Renland Ice Core (black line). (B) Stable isotope data showing freshwater spikes from SE Greenland ocean cores JM96-1216/2-GC (green line), JM96-1215/2-GC (blue line) and JM96-1213/1-GC (orange). (C) Timeseries showing AMOC strength (Sv, grey line) and ocean temperature at 484- 694 m water depth off SE Greenland (62.5°N-67°N,40°W-36°W) (red line) as simulated in the LOVECLIM transient deglacial experiment. YD (12.9-11.7 ka) marked with grey box. Constructed with OxCal 4.1 (ref.) and Figure generated in Adobe Illustrator 2015 1.0 release (19.1.0).
Figure 3
Figure 3
Modelled ocean dynamics. Simulated ocean temperature (shaded, °C) and currents (m/s) averaged over 484–693 m water depth immediately prior to the YD (top, 13.05-13 ka), at the onset of the event (middle, 13-12.95 ka), and during the early YD (bottom, 12.85-12.8 ka). (constructed using ferret http://ferret.pmel.noaa.gov/Ferret).
See this image and copyright information in PMC

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