Record of climate and late quaternary paleoclimate from stable isotopes in lakes and lake sediments, eastern Canadian Arctic.

摘要

High latitude regions comprise a critical component of the Earth's climatic system. Studies of climate records and the geologic evidence for paleoclimate change show that hemispheric or global climate anomalies are often amplified in the Arctic. This study uses stable isotopes preserved in lake sediments to construct continuous paleoclimate records from continental regions in the eastern Canadian Arctic. Because stable isotope ratios of oxygen and hydrogen in precipitation strongly correlate with mean annual temperature in cold parts of the world, they provide a tool for monitoring climate variability, both spatially and temporally.; To infer past climate from isotope records derived from lake sediments, two conditions must be met: (1) that lake water stable isotope ratios reflect precipitation, and (2) that a suitable material can be identified which records the lakewater isotopic composition. The first question was answered by analyzing water samples from a transect of 209 sites across strong climate gradients, and time series of water samples collected over several summers at 7 sites. These samples determine where temperature is the dominant control on lakewater isotope ratios and under what conditions evaporation and other hydrologic processes may interfere with the expected isotope-temperature relationship. Cellulose of aquatic organic material was analyzed as a proxy for lakewater oxygen isotopic composition. Cellulose extracted from submerged aquatic plants is shown to record water isotope ratios.; Records of stable isotope ratios of fossil aquatic moss cellulose from 5 sediment show Holocene climate variability along Labrador and eastern Baffin Island. These records show a pattern of early Holocene warmth followed by Neoglacial cooling in the past 4 ka, presumably forced by changes in Milankovitch forcing. Warming is delayed in the northern sites after the summer insolation maximum in the early Holocene. These interpretations are supported by correlation with other indicators of warmth such as thermophilous pollen in lake sediments (Betula and Alnus) and molluscs in raised marine deposits. A dramatic cooling is indicated at 2.2 ka in sites north of 66{dollar}spcirc{dollar}N, possibly due to southward migration of the oceanic polar front. Temperature has increased measurably in the past few hundred years, although not to the levels of the early Holocene.