Millennial‐Scale Climate Oscillations Triggered by Deglacial Meltwater Discharge in Last Glacial Maximum Simulations

Abstract

Our limited understanding of millennial‐scale variability in the context of the last glacial period can be explained by the lack of a reliable modeling framework to study abrupt climate changes under realistic glacial backgrounds. In this article, we describe a new set of long‐run Last Glacial Maximum experiments where such climate shifts were triggered by different snapshots of ice‐sheet meltwater derived from the early stages of the last deglaciation. Depending on the location and the magnitude of the forcing, we observe three distinct dynamical regimes and highlight a subtle window of opportunity where the climate can sustain oscillations between cold and warm modes. We identify the Eurasian Arctic and Nordic Seas regions as being most sensitive to meltwater discharge in the context of switching to a cold mode, compared to freshwater fluxes from the Laurentide ice sheets. These cold climates follow a consistent pattern in temperature, sea ice, and convection, and are largely independent from freshwater release as a result of effective AMOC collapse. Warm modes, on the other hand, show more complexity in their response to the regional pattern of the meltwater input, and within them, we observe significant differences linked to the reorganization of deep water formation sites and the subpolar gyre. Broadly, the main characteristics of the oscillations, obtained under full‐glacial conditions with ice‐sheet reconstruction derived meltwater patterns, share similar characteristics with δ18O records of the last glacial period, although our experiment design prevents detailed conclusions from being drawn on whether these represent actual Dansgaard‐Oeschger events.

High-latitude precipitation as a driver of multicentennial variability of the AMOC in a climate model of intermediate complexity

“…Therefore, there has been considerable interest in understanding the variability of the AMOC across timescales, from interannual to multidecadal (Buckley and Marshall, 2016) and millennial scales (Lynch-Stieglitz, 2017). For example, recently, several studies using comprehensive climate models found unforced millennial-scale AMOC oscillations under glacial boundary conditions (Vettoretti et al, 2022;Klockmann et al, 2020;Kuniyoshi et al, 2022;Romé et al, 2022), which resemble the Dansgaard-Oeschger events found in paleoclimate records. However, at intermediate, (multi-)centennial timescales, the variability of the AMOC has been studied less extensively, and we will focus on these timescales in the remainder of this study.…”

A multicentennial mode of North Atlantic climate variability throughout the Last Glacial Maximum

“…The different spatiotemporal patterns and amplitudes of AMOC variation point to different modes of operation, although the millennial-scale DO mode may also rely on a meridional salt oscillation as suggested previously (41,(44)(45)(46). A key characteristic of a DO-type cycle is the formation of a strong halocline in the North Atlantic covered by a winter sea-ice lid extending southward to the Bay of Biscay during the cold stadial phase (28,44,(47)(48)(49). This suppresses surface heat loss from the subpolar ocean and prevents convection and deep-water formation.…”

“…A key characteristic of a DO-type cycle is the formation of a strong halocline in the North Atlantic covered by a winter sea-ice lid extending southward to the Bay of Biscay during the cold stadial phase ( 28 , 44 , 47 – 49 ). This suppresses surface heat loss from the subpolar ocean and prevents convection and deep-water formation.…”

High-latitude precipitation as a driver of multicentennial variability of the AMOC in a climate model of intermediate complexity

“…Therefore, there has been considerable interest in understanding the variability of the AMOC across timescales, from interannual to multidecadal (Buckley and Marshall 2016) and millennial scales (Lynch-Stieglitz 2017). For example, recently, several studies using comprehensive climate models found unforced millennial-scale AMOC oscillations under glacial boundary conditions (Vettoretti et al 2022;Klockmann et al 2020;Kuniyoshi et al 2022;Romé et al 2022), which resemble the Dansgaard-Oeschger events found in paleoclimate records.…”