Glacier retreat in New Zealand during the Younger Dryas stadial

Abstract

Millennial-scale cold reversals in the high latitudes of both hemispheres interrupted the last transition from full glacial to interglacial climate conditions. The presence of the Younger Dryas stadial (approximately 12.9 to approximately 11.7 kyr ago) is established throughout much of the Northern Hemisphere, but the global timing, nature and extent of the event are not well established. Evidence in mid to low latitudes of the Southern Hemisphere, in particular, has remained perplexing. The debate has in part focused on the behaviour of mountain glaciers in New Zealand, where previous research has found equivocal evidence for the precise timing of increased or reduced ice extent. The interhemispheric behaviour of the climate system during the Younger Dryas thus remains an open question, fundamentally limiting our ability to formulate realistic models of global climate dynamics for this time period. Here we show that New Zealand's glaciers retreated after approximately 13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent approximately 1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision (10)Be chronology and reconstruction of former ice extents and snow lines from well-preserved cirque moraines. Our late-glacial glacier chronology matches climatic trends in Antarctica, Southern Ocean behaviour and variations in atmospheric CO(2). The evidence points to a distinct warming of the southern mid-latitude atmosphere during the Younger Dryas and a close coupling between New Zealand's cryosphere and southern high-latitude climate. These findings support the hypothesis that extensive winter sea ice and curtailed meridional ocean overturning in the North Atlantic led to a strong interhemispheric thermal gradient during late-glacial times, in turn leading to increased upwelling and CO(2) release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

The last deglaciation: timing the bipolar seesaw

“…According to the current concept of north-south climate coupling, the resumption of southern warming at the end of the ACR was triggered by the onset of the YD stadial in the north (at 12.85 ka BP) (e.g. Denton et al, 2010;Kaplan et al, 2010). Our results, within dating uncertainties, remain consistent with this view but offer new detail.…”

“…Previous studies confirm opposing climate trends on millennial timescales between the northern and southern mid to high-latitudes during this interval (e.g. Sowers and Bender, 1995;Blunier et al, 1998;Blunier and Brook, 2001;Shakun and Carlson, 2010;Kaplan et al, 2010). Antarctica first warmed during the glacial conditions of Greenland stadial 2 (GS-2), then cooled during the Antarctic Cold Reversal (ACR), as Greenland experienced the warmth of the Bølling-Allerød interstadial (B-A or GI-1a-e).…”

The Last Glacial Maximum in the central North Island, New Zealand: palaeoclimate inferences from glacier modelling

“…This good agreement between model and manual reconstruction of glacier ELAs echoes previous similar findings (e.g. Kaplan et al, 2010;Doughty et al, 2013), demonstrating the utility of simple ELA reconstructions for efficient extraction of palaeoclimate data from moraine records.…”

Spatial and temporal variability of annual glacier equilibrium line altitudes in the Southern Alps, New Zealand

“…This is important because some of the glaciers of New Zealand demonstrate asynchronous behaviour both regionally and also with northern hemisphere examples. For example, Schaefer et al (2009) found disparities between the timing of maximum Holocene ice extent around Mount Cook, New Zealand, and Kaplan et al (2010) describe glacier retreat in New Zealand during the Younger Dryas stadial. Furthermore, New Zealand presently only has one glacier, Brewster Glacier, in the World Glacier Monitoring Service (WGMS 2009;Zemp et al 2009).…”