Title

Using modern oxygen and carbon isotopic calibrations to characterize 14,600 calendar years of atmospheric circulation and precipitation in the NE United States of America

Date of Award

2001

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Henry T. Mullins

Keywords

Oxygen, Carbon, Isotopic calibrations, Atmospheric circulation, Precipitation

Subject Categories

Earth Sciences | Environmental Sciences | Physical Sciences and Mathematics

Abstract

Paleoclimate proxy data from the NE USA covering the late glacial through Holocene are rare. Here, we present two sediment core records from Fayetteville Green Lake, New York (i.e., NE USA), a basin core and a wetland core. Using a 63 cm varved sediment core from the neck region of Green Lake, we calibrate historic period (i.e., 20 th century) oxygen and carbon isotope values to measured meteorological indices such as the latitude of the winter vortex over the NE USA and early summer precipitation. These historically-derived isotope-meteorological calibrations are extended back into the pre-historic record (to 14,600 cal yr BP) at ∼10 to ∼50 year resolution using isotope values from a 11.2 m wetland core.

Our results indicate that the winter vortex is characterized by a strong multi-decadal-to-centennial component of variability fluctuating between expanded and contracted geometries. When the winter vortex is expanded, storms track more frequently from the southeast and southwest carrying precipitation with relatively high δ 18 O values. Conversely, when the winter vortex is contracted, storms track more frequently from the west (cross-continental) carrying precipitation with relatively low δ 18 O values. As the position of the winter vortex changes, dominant storm tracks are modified producing isotopically distinct precipitation that is ultimately recorded by the δ 18 O calcite in Green Lake.

Over long time scales (i.e., millennia), the NE USA winter vortex moves in response to precession-forced changes in insolation and the gradual retreat of the Laurentide ice sheet. Over shorter time scales, the winter vortex is likely responding to ocean-atmosphere linkages related to thermohaline circulation in the North Atlantic region.

The historic correlation between δ 13 C calcite and early summer (May-July) precipitation show that greater early summer precipitation results in calcite with relatively low δ 13 C values, and vice versa. In other words, primary productivity in Green Lake is reduced during periods of greater precipitation due to increased cloud cover and reduced light availability. Using this relationship, we show that the late glacial/Holocene is characterized by multi-decadal-to-centennial scale paleo-precipitation/cloud variability that fluctuates about a mean value.

Together, these results provide the first late glacial/Holocene record of winter vortex variability and early summer precipitation for the NE USA at ∼10-50 year resolution.

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