Trevor Chinn

High-frequency Holocene glacier fluctuations in New Zealand differ from the northern signature.

Vive La Différence How closely do climate changes in the Northern and Southern Hemispheres resemble each other? Much discussion has concentrated on the Holocene, the warm period of the past 11,500 years in which we now live, which represents a baseline to which contemporary climate change can be compared. Schaefer et al. (p. 622; see the Perspective by Balco) present a chronology of glacial movement over the last 7000 years in New Zealand, which they compare to similar records from the Northern Hemisphere. Clear differences are observed between the histories of glaciers in the opposing hemispheres, which may be owing to regional controls. Thus, neither of two popular arguments—that the hemispheres change in-phase or that they change in an anti-phased manner—appear to be correct. The patterns of glacial advances and retreats in New Zealand during the Holocene contrast markedly with those of the Northern Hemisphere. Understanding the timings of interhemispheric climate changes during the Holocene, along with their causes, remains a major problem of climate science. Here, we present a high-resolution 10Be chronology of glacier fluctuations in New Zealand’s Southern Alps over the past 7000 years, including at least five events during the last millennium. The extents of glacier advances decreased from the middle to the late Holocene, in contrast with the Northern Hemisphere pattern. Several glacier advances occurred in New Zealand during classic northern warm periods. These findings point to the importance of regional driving and/or amplifying mechanisms. We suggest that atmospheric circulation changes in the southwest Pacific were one important factor in forcing high-frequency Holocene glacier fluctuations in New Zealand.

Glacier retreat in New Zealand during the Younger Dryas stadial

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 (∼12.9 to ∼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 ∼13 kyr bp, at the onset of the Younger Dryas, and in general over the subsequent ∼1.5-kyr period. Our evidence is based on detailed landform mapping, a high-precision 10Be 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 CO2. 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 CO2 release from the Southern Ocean, thereby triggering Southern Hemisphere warming during the northern Younger Dryas.

Holocene glacier variations in New Zealand: A review

Abstract In the central Southern Alps of New Zealand, ice-surface lowering has exposed extensive sections of lateral moraines, allowing investigation of moraine stratigraphy and genesis. The presence of multiple superposed palaeosurfaces within moraine sequences allows recognition of any disturbances, displacements or contamination of till layers and interbedded organic material. Radiocarbon dating of buried wood and soils allows comparison between the Holocene glacial history of the Eastern Ranges and that of the Westland region. The periodicity of glacier response has been similar to both areas, although the precise timing of events has differed due to local climatic and environmental factors. In general, glaciers in New Zealand expanded about 5000, 4500-4200, 3700, 3500-3000, 2700-2200, 1800-1700, 1500, 1100, 900, 700-600 and 400-100 BP.

RECENT GLACIER ADVANCES IN NORWAY AND NEW ZEALAND: A COMPARISON OF THEIR GLACIOLOGICAL AND METEOROLOGICAL CAUSES

ABSTRACT. Norway and New Zealand both experienced recent glacial advances, commencing in the early 1980s and ceasing around 2000, which were more extensive than any other since the end of the Little Ice Age. Common to both countries, the positive glacier balances are associated with an increase in the strength of westerly atmospheric circulation which brought increased precipitation. In Norway, the changes are also associated with lower ablation season temperatures. In New Zealand, where the positive balances were distributed uniformly throughout the Southern Alps, the period of increased mass balance was coincident with a change in the Interdecadal Pacific Oscillation and an associated increase in El Niño/Southern Oscillation events. In Norway, the positive balances occurred across a strong west‐east gradient with no balance increases to the continental glaciers of Scandinavia. The Norwegian advances are linked to strongly positive North Atlantic Oscillation events which caused an overall increase of precipitation in the winter accumulation season and a general shift of maximum precipitation from autumn towards winter. These cases both show the influence of atmospheric circulation on maritime glaciers.

The Impact Of Extreme Summer Melt on Net Accumulation of an Avalanche Fed Glacier, as Determined by Ground‐Penetrating Radar

Abstract Glacier mass balance is more sensitive to warming than cooling, but feedbacks related to the exposure of previously buried firn and ice in very warm years is not generally considered in sensitivity studies. A ground‐penetrating radar survey in the accumulation area of Rolleston Glacier, New Zealand shows that five years of previous net accumulation was removed by melt from parts of the glacier above the long‐term equilibrium line altitude during a single negative mass balance year. Rolleston Glacier receives a large amount of accumulation from snow avalanches, which may temporarily buffer it from climate warming by providing additional mass that has accumulated at higher elevations, effectively increasing the elevation range of the glacier. However, glaciers reliant on avalanche input may have high sensitivity to climatic variations because the extra mass is concentrated on a small part of the glacier, and small variations in avalanche input could have a large impact on overall glacier accumulation. Further research is needed to better estimate the amount and spatial distribution of accumulation by avalanche in order to quantify the climate sensitivity of small avalanche‐fed glaciers.