Karnauskas
Kristopher B.
Karnauskas
Kristopher B.
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PreprintIncreased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes(Nature Research, 2020-11-16) Bramante, James F. ; Ford, Murray R. ; Kench, Paul S. ; Ashton, Andrew D. ; Toomey, Michael R. ; Sullivan, Richard M. ; Karnauskas, Kristopher B. ; Ummenhofer, Caroline C. ; Donnelly, Jeffrey P.The instrumental record reveals that tropical cyclone activity is sensitive to oceanic and atmospheric variability on inter-annual and decadal scales. However, our understanding of the influence of climate on tropical cyclone behaviour is restricted by the short historical record and the sparseness of prehistorical reconstructions, particularly in the western North Pacific, where coastal communities suffer loss of life and livelihood from typhoons annually. Here, to explore past regional typhoon dynamics, we reconstruct three millennia of deep tropical North Pacific cyclogenesis. Combined with existing records, our reconstruction demonstrates that low-baseline typhoon activity prior to 1350 ce was followed by an interval of frequent storms during the Little Ice Age. This pattern, concurrent with hydroclimate proxy variability, suggests a centennial-scale link between Pacific hydroclimate and tropical cyclone climatology. An ensemble of global climate models demonstrates a migration of the Pacific Walker circulation and variability in two Pacific climate modes during the Little Ice Age, which probably contributed to enhanced tropical cyclone activity in the tropical western North Pacific. In the next century, projected changes to the Pacific Walker circulation and expansion of the tropics will invert these Little Ice Age hydroclimate trends, potentially reducing typhoon activity in the deep tropical Pacific.
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PreprintOceanography : oxygen and climate dynamics(Nature Publishing Group, 2014-09) Doney, Scott C. ; Karnauskas, Kristopher B.Low oxygen levels in tropical oceans shape marine ecosystems and biogeochemistry with climate change expected to expand these regions. Now, a study indicates that regional dynamics control tropical oxygen trends, bucking projected global reductions in ocean oxygen.
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PreprintEquatorial refuge amid tropical warming( 2012-03-16) Karnauskas, Kristopher B. ; Cohen, Anne L.Upwelling across the tropical Pacific Ocean is projected to weaken in accordance with a reduction of the atmospheric overturning circulation, enhancing the sea surface temperature (SST) increase relative to other regions in response to greenhouse forcing. In the central Pacific, home to one of the largest Marine Protected Areas (MPAs) and fishery regions in the global tropics, SSTs are projected to increase by 2.8°C by the end of this century. Of critical concern is that MPAs may not provide refuge from the anticipated rate of large–scale warming, which could exceed the evolutionary capacity of coral and their symbionts to adapt. Combining high–resolution satellite measurements, an ensemble of global climate models, and an eddy–resolving regional ocean circulation model, we show that warming and productivity decline around select Pacific islands will be mitigated by enhanced upwelling associated with a strengthening of the equatorial undercurrent (EUC). Enhanced topographic upwelling will act as a negative feedback, locally mitigating the surface warming. At the Gilbert Islands, the rate of warming will be reduced by 0.7 ± 0.3°C or 25 ± 9% per century, or an overall cooling effect comparable to the local anomaly for a typical El Niño by the end of this century. Since the EUC is dynamically constrained to the equator, only a handful of coral reefs stand to benefit from this equatorial island effect. Nevertheless, those that do face a lower rate of warming, conferring a significant advantage over neighboring reef systems. If realized, these predictions help to identify potential refuges for coral reef communities from anticipated climate changes of the 21st century.