HIGH-RESOLUTION COMPOUND-SPECIFIC HYDROGEN ISOTOPE RECORD OF LATE PLEISTOCENE - HOLOCENE CLIMATE TRANSITION FROM SOUTHERN NEW ENGLAND

Extensive paleoecological studies indicate that northeastern North America experienced major climate shifts during the Late Pleistocene - Early Holocene transition (LPEH). However, the uncertainties inherent to the modern analog technique increase the difficulty of using pollen and chironomidae data to assess abrupt (less than centennial-scale) climate variability. Compound-specific hydrogen isotope analyses of aquatic lipids in lake sediments offer a new, alternative way to quantify past climate variations. The technique is especially promising for regions like New England where the dominance of granitic bedrock fosters acidic natural waters, precluding the formation of the carbonate deposits in lake sediments. Here we present the first high-resolution record of climate change during LPEH based on compound-specific hydrogen isotope ratios of behenic acid (C22 n-acid) from a sediment core in Blood Pond, Massachusetts. Surface calibrations from modern lake systems in eastern North America show that hydrogen isotopes of behenic acid quantitatively track temperature variations (4.3 permil per degree). This is consistent with the isotopic-temperature gradient for precipitation in eastern North America (5.2 permil per degree) if the biosynthetic isotopic fraction of behenic acid (0.8681) is taken into consideration. The abrupt climate events observed in downcore records at Blood Pond show remarkable similarity with Greenland ice core oxygen isotope during the late Pleistocene (warm Bolling and Allerod period, cold Younger Dryas). This implies that climate change in both Greenland and New England during this time was related to a common cause, namely the changes in thermohaline circulation in North Atlantic Ocean due to freshwater outbursts. During the early Holocene, climate in New England showed greater variability than in Greenland, possibly reflecting multiple climate forcing factors in New England versus a more uniform control by solar insolation on top of the Greenland ice sheet. Multiple episodes of fresh water outbursts from Lake Agassiz may have induced a number of abrupt climate cooling events in New England during the early Holocene, each lasting several decades.