Holocene climate trend, variability, and shift documented by lacustrine stable-isotope record in the northeastern United States

Earlier studies indicated that the general pattern of the Holocene climate in the northeastern United States changed from cool and dry (11.6-8.2 ka; 1 ka = 1000 cal yr BP) to warm and wet (8.2-5.4 ka) to warm and dry (5.4-3 ka) to cool and wet (after 3 ka). A new similar to 35-year resolution stable isotope record of endogenic calcite from a sediment core for Lake Grinnell in northern New Jersey provided a chance to examine the Holocene climate variations of the region in a finer detail. After the Younger Dryas cold climate reversal, the delta O-18 fluctuated around a constant value of 7.4 parts per thousand until 5.8 ka, thereafter shifted to a steadily decreasing trend to the most recent value of -8.2 parts per thousand. Responding to this shift, the widely observed hemlock decline in the northeastern USA occurred about similar to 350-500 (+/- 143.5) years later. Detrended delta O-18 and delta C-13 records show a clear covariance at 910-year periodicity. The amplitudes of centennial-scale 6180 variations became much smaller after 4.7 ka. At the same time, the dominant frequency of these variations changed from 330 to 500 years. We suggest that a non-linear response of atmospheric circulation to the gradual decrease in insolation is responsible for the shift in the climate trend at 5.8 ka as indicated by the deceasing delta O-18 values. A dominant frequency shift in solar forcing and the decreased seasonal contrast of insolation might have caused the change in climate variability at 4.7 ka through modulating ocean and atmosphere circulations. (C) 2010 Elsevier Ltd. All rights reserved.