Dwyer Gary S.

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Dwyer
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Gary S.
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  • Article
    Western Arctic Ocean temperature variability during the last 8000 years
    (American Geophysical Union, 2011-12-17) Farmer, Jesse R. ; Cronin, Thomas M. ; de Vernal, Anne ; Dwyer, Gary S. ; Keigwin, Lloyd D. ; Thunell, Robert C.
    We reconstructed subsurface (∼200–400 m) ocean temperature and sea-ice cover in the Canada Basin, western Arctic Ocean from foraminiferal δ18O, ostracode Mg/Ca ratios, and dinocyst assemblages from two sediment core records covering the last 8000 years. Results show mean temperature varied from −1 to 0.5°C and −0.5 to 1.5°C at 203 and 369 m water depths, respectively. Centennial-scale warm periods in subsurface temperature records correspond to reductions in summer sea-ice cover inferred from dinocyst assemblages around 6.5 ka, 3.5 ka, 1.8 ka and during the 15th century Common Era. These changes may reflect centennial changes in the temperature and/or strength of inflowing Atlantic Layer water originating in the eastern Arctic Ocean. By comparison, the 0.5 to 0.7°C warm temperature anomaly identified in oceanographic records from the Atlantic Layer of the Canada Basin exceeded reconstructed Atlantic Layer temperatures for the last 1200 years by about 0.5°C.
  • Article
    The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean
    (Elsevier B.V., 2010-08-22) Cronin, Thomas M. ; Hayo, K. ; Thunell, Robert C. ; Dwyer, Gary S. ; Saenger, Casey P. ; Willard, Debra. A.
    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.