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  • ITCZ  (1)
  • Last millennium climate  (1)
  • Medieval Climate Anomaly  (1)
  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L11703, doi:10.1029/2009GL038677.
    Description: Proxy reconstructions and model simulations suggest that steeper interhemispheric sea surface temperature (SST) gradients lead to southerly Intertropical Convergence Zone (ITCZ) migrations during periods of North Atlantic cooling, the most recent of which was the Little Ice Age (LIA; ∼100–450 yBP). Evidence suggesting low-latitude Atlantic cooling during the LIA was relatively small (〈1°C) raises the possibility that the ITCZ may have responded to a hemispheric SST gradient originating in the extratropics. We use an atmospheric general circulation model (AGCM) to investigate the relative influence of low-latitude and extratropical SSTs on the meridional position of the ITCZ. Our results suggest that the ITCZ responds primarily to local, low-latitude SST anomalies and that small cool anomalies (〈0.5°C) can reproduce the LIA precipitation pattern suggested by paleoclimate proxies. Conversely, even large extratropical cooling does not significantly impact low-latitude hydrology in the absence of ocean-atmosphere interaction.
    Description: This work was supported by NSF grants OCE 0623364 and ATM 033746 as well as the student research fund of MIT’s Department of Earth, Atmospheric and Planetary Science.
    Keywords: Climate ; ITCZ ; Little Ice Age
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 2
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Paleoceanography 30 (2015): 226–252, doi:10.1002/2014PA002717.
    Description: Most annually resolved climate reconstructions of the Common Era are based on terrestrial data, making it a challenge to independently assess how recent climate changes have affected the oceans. Here as part of the Past Global Changes Ocean2K project, we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics, based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives. Validation exercises suggest that our reconstructions are interpretable for much of the past 400 years, depending on the availability of paleoclimate data within, and the reconstruction validation statistics for, each target region. Analysis of the trends in the data suggests that the Indian, western Pacific, and western Atlantic Ocean regions were cooling until modern warming began around the 1830s. The early 1800s were an exceptionally cool period in the Indo-Pacific region, likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century. Decadal-scale variability is a quasi-persistent feature of all basins. Twentieth century warming associated with greenhouse gas emissions is apparent in the Indian, West Pacific, and western Atlantic Oceans, but we find no evidence that either natural or anthropogenic forcings have altered El Niño–Southern Oscillation-related variance in tropical sea surface temperatures. Our marine-based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change.
    Description: J.E.T. and K.J.A. acknowledge Woods Hole Oceanographic Institution for internal support. K.J.A. acknowledges the Frank and Lisina Hoch Endowed Fund at the Woods Hole Oceanographic Institution for support. N.J.A. is supported by an Australian Research Council QEII fellowship (DP110101161), and this research contributes to ARC Discovery Grant DP140102059. M.N.E. is supported by NSF/ATM0902794 and NSF/ATM0902715. J.Z. was supported by an Indian Ocean Marine Research Centre fellowship and an Honorary Research Fellowship by the University of the Witwatersrand. H.C.W. is supported by the Deutsche Forschungsgemeinschaft through DFG-Research Center/Cluster of Excellence “The Ocean in the Earth System” at the University of Bremen (MARUM Fellowship). C.G. acknowledges MARUM–Center for Marine Environmental Sciences for internal support. K.H.K. is supported by NOAA grant NA11OAR4310171.
    Keywords: Climate reconstruction ; Corals ; Paleoceanography ; Last millennium climate
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/msword
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  • 3
    Publication Date: 2022-05-26
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 297 (2010): 299-310, doi:10.1016/j.palaeo.2010.08.009.
    Description: A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16–17 °C between 600 and 950 CE (Common Era), centuries before the classic European Medieval Warm Period (950–1100 CE) and peak warming in the Nordic Seas (1000–1400 CE). A series of centennial warm/cool cycles began about 1000 CE with temperature minima of ~ 8 to 9 °C about 1150, 1350, and 1650–1800 CE, and intervening warm periods (14–15 °C) centered at 1200, 1400, 1500 and 1600 CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200 CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800 CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean–atmosphere processes.
    Keywords: Medieval Climate Anomaly ; Little Ice Age ; Chesapeake Bay ; Holocene climate
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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