Ice core evidence for decoupling between midlatitude atmospheric water cycle and Greenland temperature during the last deglaciation

Abstract

Abstract. The last deglaciation represents the most recent example of natural global warming associated with large-scale climate changes. In addition to the long-term global temperature increase, the last deglaciation onset is punctuated by a sequence of abrupt changes in the Northern Hemisphere. Such interplay between orbital- and millennial-scale variability is widely documented in paleoclimatic records but the underlying mechanisms are not fully understood. Limitations arise from the difficulty in constraining the sequence of events between external forcing, high- and low- latitude climate, and environmental changes. Greenland ice cores provide sub-decadal-scale records across the last deglaciation and contain fingerprints of climate variations occurring in different regions of the Northern Hemisphere. Here, we combine new ice d-excess and 17O-excess records, tracing changes in the midlatitudes, with ice δ18O records of polar climate. Within Heinrich Stadial 1, we demonstrate a decoupling between climatic conditions in Greenland and those of the lower latitudes. While Greenland temperature remains mostly stable from 17.5 to 14.7 ka, significant change in the midlatitudes of the northern Atlantic takes place at ∼16.2 ka, associated with warmer and wetter conditions of Greenland moisture sources. We show that this climate modification is coincident with abrupt changes in atmospheric CO2 and CH4 concentrations recorded in an Antarctic ice core. Our coherent ice core chronological framework and comparison with other paleoclimate records suggests a mechanism involving two-step freshwater fluxes in the North Atlantic associated with a southward shift of the Intertropical Convergence Zone.

Baffin Bay sea ice extent and synoptic moisture transport drive water vapor isotope (<i>δ</i><sup>18</sup>O, <i>δ</i><sup>2</sup>H, and deuterium excess) variability in coastal northwest Greenland

“…As a result, this record is the first reported for Greenland that continuously spans over 2 years, permitting comparative multiyear analysis of isotopic patterns and anomalies. Thule Air Base has been a focus of high Arctic research for many years (e.g., Schytt, 1955;Mastenbrook, 1968;Sullivan et al, 2008;Rogers et al, 2011;Leffler and Welker, 2013;Schaeffer et al, 2013), and our observing station on northern Baffin Bay allows a focus on how changing seasonal and interannual sea ice coverage affect the local climate and water vapor isotopes.…”

The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice‐Sheet—AMOC Interactions and Climate Instability

“…Taken together, these results suggest an early reinvigoration in AMOC strength well before the Bølling warming but restricted to the upper ocean (≤2,000 m). This AMOC recovery, and the subsequent northward shift in the polar front in Europe (Cowling et al., 2020), likely explains the climate reorganization and hydroclimate shift observed in the North Atlantic region during HS1(Broecker & Putnam, 2012; Landais et al., 2018; Lincoln et al., 2020; Naughton et al., 2009). During this time, the upper branch of the AMOC also “pushed” northwards the subsurface warming (Figures 6d and 6e) initially caused by the preceding (∼18–16 ka) strong ice‐sheet—ocean interactions (i.e., EIS melting and the HE1; Alvarez‐Solas et al., 2011; Hodell et al., 2017; Ivanovic et al., 2018; Ng et al., 2018; Toucanne et al., 2015; Zaragosi et al., 2001).…”

Baffin Bay sea ice extent and synoptic moisture transport drive water vapor isotope (<i>δ</i><sup>18</sup>O, <i>δ</i>D, <i>d</i>-<i>excess</i>) variability in coastal northwest Greenland

“…More recently, additional consideration has been given to secondary isotopic variables like dxs and other environmental drivers such as moisture source, sea ice extent, and atmospheric circulation (e.g., Grumet et al, 2001;Vinther et al, 2003;Steffensen et al, 2008;Landais et al, 2018;Kopec et al, 2019). While our two-year Thule record is too short to statistically determine the strongest drivers of interannual isotopic variability, changes in the duration of sea ice coverage and mean NAO phase appear most likely to control year-to-year differences in mean isotopic composition.…”