Geological archives record multiple reversals of Earth’s magnetic poles, but
the global impacts of these events, if any, remain unclear. Uncertain radiocarbon
calibration has limited investigation of the potential effects of the last major
magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago
(ka)]. We use ancient New Zealand kauri trees (Agathis
australis) to develop a detailed record of atmospheric
radiocarbon levels across the Laschamps Excursion. We precisely characterize the
geomagnetic reversal and perform global chemistry-climate modeling and detailed
radiocarbon dating of paleoenvironmental records to investigate impacts. We find
that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima,
caused substantial changes in atmospheric ozone concentration and circulation,
driving synchronous global climate shifts that caused major environmental changes,
extinction events, and transformations in the archaeological record.
Occupying about 14 % of the world's surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54° S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes
Determining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here highresolution ice sheet modelling was combined with new terrestrial geological constraints (in situ 14 C and 10 Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.
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