A 5000-year lacustrine sediment oxygen isotope record of late Holocene climate change in Newfoundland, Canada. (15th February 2022) - Finkenbinder, Matthew S.
Abstract: The spatiotemporal patterns and underlying causes of climate variations spanning the mid-to late-Holocene in the North Atlantic region are largely unsettled. Here, we present a decadally resolved carbonate oxygen isotope (δ 18 O) record spanning the last ∼5000 calibrated years before present (cal yr BP) from Norman's Pond, a small, hydrologically open lake located in west-central Newfoundland, Canada. Stable isotope data from regional lakes, rivers, and precipitation samples indicate the δ 18 O record primarily reflects changes in the integrated, annual δ 18 O of precipitation, which is largely controlled by local atmospheric temperature and to a lesser extent, changes in the seasonality of precipitation. The record exhibits a general trend of decreasing δ 18 O values over the last ∼5000 cal yr BP that is consistent with gradually declining Boreal summer insolation and long-term cooling. Large decadal to centennial timescale fluctuations in δ 18 O values occurred during the last millennium, with persistent low δ 18 O values during the early Medieval Climate Anomaly (MCA, 950 to 1250 CE) and more variable and low values across the Little Ice Age (LIA, 1450 to 1850 CE). Relatively low δ 18 O values during the early MCA at ∼950 cal yr BP (∼1000 CE) suggest colder temperatures in Newfoundland and/or an increase in cold-season or decrease in warm-season precipitation across the island. MCA δ 18 O values are lower than those of the LIA, revealing that climate conditions in Newfoundland were variable and differed from the broader North Atlantic region. For example, the shift to very low δ 18 O during the early MCA is coincident with a transition to colder sea surface temperatures (SSTs) in the Labrador Sea region, which was potentially triggered by melting of the Greenland Ice Sheet and alpine glaciers and ice caps in/around Baffin Bay, and subsequent delivery of cold waters further south via the Labrador Current. The early MCA interval of inferred cooling is coincident with Norse settlement at L'Anse aux Meadows in northern Newfoundland at ∼929 cal yr BP (∼1021 CE). Subsequent low and variable δ 18 O during the LIA suggests regional shifts in the seasonality of precipitation and/or cooling, consistent with other terrestrial climate records from the region. Proxy evidence from Norman's Pond therefore reinforces the idea of substantial spatiotemporal variability in climatic change in the broader North Atlantic region since at least the mid-Holocene, and in particular during the MCA, when cooler conditions prevailed in Newfoundland as a result of lower offshore sea surface temperatures that were likely driven by greater meltwater delivery via the Labrador current. Highlights: Newfoundland lake sediments reveal hydroclimate variability over the last 5000 years. Carbonate oxygen isotope record reveals cooling trend and/or shift in precipitation seasonality. Climate sensitive to Labrador Sea temperatures and sea ice pack on decadal to centennial timescales. Inferred cold conditions during Norse settlement at L'Anse Aux Meadows ∼1021 CE.