ABSTRACT
On 14 November 2016, northeastern South Island of New Zealand was struck by a major moment magnitude (Mw) 7.8 earthquake. Field observations, in conjunction with interferometric synthetic aperture radar, Global Positioning System, and seismology data, reveal this to be one of the most complex earthquakes ever recorded. The rupture propagated northward for more than 170 kilometers along both mapped and unmapped faults before continuing offshore at the island's northeastern extent. Geodetic and field observations reveal surface ruptures along at least 12 major faults, including possible slip along the southern Hikurangi subduction interface; extensive uplift along much of the coastline; and widespread anelastic deformation, including the ~8-meter uplift of a fault-bounded block. This complex earthquake defies many conventional assumptions about the degree to which earthquake ruptures are controlled by fault segmentation and should motivate reevaluation of these issues in seismic hazard models.
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.
ABSTRACT
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.
ABSTRACT
Isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation. However, 10Be exposure dates show that large-scale retreat of mid-latitude Last Glacial Maximum glaciers commenced at about the same time in both hemispheres. The timing of retreat is consistent with the onset of temperature and atmospheric CO2 increases in Antarctic ice cores. We suggest that a global trend of rising summer temperatures at the end of the Last Glacial Maximum was obscured in North Atlantic regions by hypercold winters associated with unusually extensive winter sea ice.
