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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q09V10, doi:10.1029/2008GC002043.
    Description: Patterns of overwash deposition observed within back-barrier sediment archives can indicate past changes in tropical cyclone activity; however, it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions. Here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane-overwash reconstruction. To alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site, we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean-atmosphere hurricane model set to simulate modern climatology. Thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes, a prescribed threshold for overwash, and a specified temporal resolution based on sedimentation rates observed at a particular site. As a test case we apply this Monte Carlo technique to a hurricane-induced overwash reconstruction developed from Laguna Playa Grande (LPG), a coastal lagoon located on the island of Vieques, Puerto Rico in the northeastern Caribbean. Apparent overwash rates in the LPG overwash record are observed to be four times lower between 2500 and 1000 years B.P. when compared to apparent overwash rates during the last 300 years. However, probability distributions based on Monte Carlo simulations indicate that as much as 65% of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates. Periods of no apparent overwash activity at LPG between 2500 and 3600 years B.P. and 500–1000 years B.P. are exceptionally long and are unlikely to occur (above 99% confidence) under the current climate conditions. In addition, breaks in activity are difficult to produce even when the hurricane model is forced to a constant El Niño state. Results from this study continue to support the interpretation that the western North Atlantic has exhibited significant changes in hurricane climatology over the last 5500 years.
    Description: Funding for this research was provided by the Earth Systems History Program of the National Science Foundation, Risk Prediction Initiative, National Geographic Society, Coastal Ocean Institute at WHOI, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research.
    Keywords: Tropical cyclones ; Paleotempestology ; Paleoclimate ; Holocene ; Climate change ; Sedimentology
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 2993–3008, doi:10.1002/ggge.20217.
    Description: Recent work suggests that the patterns of intense (≥category 3 on the Saffir-Simpson scale) hurricane strikes over the last few millennia might differ from that of overall hurricane activity during this period. Prior studies typically rely on assigning a threshold storm intensity required to produce a sedimentological overwash signal at a particular coastal site based on historical analogs. Here, we improve on this approach by presenting a new inverse-model technique that constrains the most likely wind speeds required to transport the maximum grain size within resultant storm deposits. As a case study, the technique is applied to event layers observed in sediments collected from a coastal sinkhole in northwestern Florida. We find that (1) simulated wind speeds for modern deposits are consistent with the intensities for historical hurricanes affecting the site, (2) all deposits throughout the ∼2500 year record are capable of being produced by hurricanes, and (3) a period of increased intense hurricane frequency is observed between ∼1700 and ∼600 years B.P. and decreased intense storm frequency is observed from ∼2500 to ∼1700 and ∼600 years B.P. to the present. This is consistent with prior reconstructions from nearby sites. Changes in the frequency of intense hurricane strikes may be related to the degree of penetration of the Loop Current in the Gulf of Mexico.
    Description: This work was supported by the National Science Foundation.
    Description: 2014-02-22
    Keywords: Tropical cyclones ; Paleotempestology ; Paleoclimate ; Holocene ; Inverse-modeling ; Sedimentology
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 3
    Publication Date: 2022-10-26
    Description: Author Posting. © The Author(s), 2020. This is the author's version of the work. It is posted here by permission of Nature Research for personal use, not for redistribution. The definitive version was published in Bramante, J. F., Ford, M. R., Kench, P. S., Ashton, A. D., Toomey, M. R., Sullivan, R. M., Karnauskas, K. B., Ummenhofer, C. C., & Donnelly, J. P. (2020). Increased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes. Nature Geoscience, 13, 806–811. doi:10.1038/s41561-020-00656-2.
    Description: 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.
    Description: This work was supported by the Strategic Environmental Research and Development Program (SERDP RC-2336). C.C.U. acknowledges support from NSF under AGS-1602455. We thank student intern D. Carter for extensive labwork on core LTD3. We acknowledge the WCRP’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. CMIP5 model output was provided by the WHOI CMIP5 Community Storage Server via their website: http://cmip5.whoi.edu/. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.
    Description: 2021-05-16
    Keywords: Tropical cyclones ; Little Ice Age ; Last millennium ; Paleoclimate
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 4
    Publication Date: 2022-10-21
    Description: 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 climate’s influence on tropical cyclone behavior is restricted by the short historical record and sparse prehistorical reconstructions, particularly in the western North Pacific where coastal communities suffer loss of life and livelihood from typhoons annually. Here we reconstruct three millennia of deep tropical North Pacific cyclogenesis and compare with other records to explore past regional typhoon dynamics. These records demonstrate low baseline activity prior to 1350 C.E. followed by a rapid culmination in activity during the Little Ice Age. This pattern is concurrent with hydroclimate proxy variability, suggesting a centennial-scale link between Pacific hydroclimate and tropical cyclone climatology. Using an ensemble of global climate models, we demonstrate that migration of the Pacific Walker circulation and variability in two Pacific climate modes during the Little Ice Age contributed to enhanced tropical cyclone activity in the tropical western North Pacific. Changes to Walker Circulation and expansion of the tropics projected for the next century invert Little Ice Age hydroclimate trends, potentially reducing typhoon activity in the deep tropical Pacific.
    Description: This project was supported by the Strategic Environmental Research and Development Program through award SERDP RC-2336
    Keywords: Tropical cyclones ; Little Ice Age ; Last millennium ; Paleoclimate
    Repository Name: Woods Hole Open Access Server
    Type: Dataset
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