METEORIC 10BE FLUX RECORDS POTENTIALLY SYNCHRONIZE NORTH AMERICAN VARVED SEDIMENTS WITH GREENLAND ICE

We investigate the time relationship between the North American Varve Chronology (NAVC) and Greenland ice cores using atmospherically-produced (meteoric) ¹⁰Be. The NAVC is a 5700-year sequence of lake varves deposited in a proglacial lake that occupied the Connecticut River Valley (northeastern North America) ~18,000-12,500 years ago. This annually resolved record includes details of regional climate and ice-marginal processes at 40-45° N latitude, both near to and distant from the margin of the retreating Laurentide Ice Sheet (LIS).

Age calibration for the NAVC based on radiocarbon-dated plant macrofossils in individual varves implies several relationships between climate events in North America and Greenland, such as an increase in the retreat rate of the LIS during the Bolling warming in Greenland and a re-advance of the LIS margin during the Older Dryas cold period. However, the uncertainty in the radiocarbon calibration is ~± 200 years, so testing these relationships at finer resolution requires a more robust metric for synchronization. We explore the use of meteoric ¹⁰Be flux records for this purpose. Meteoric ¹⁰Be production and delivery rates in any given year are directly related to solar variability, which is globally synchronous. Thus, a ¹⁰Be flux record for NAVC varves can, in principle, be used to align the NAVC with existing ¹⁰Be flux records from Greenland ice cores that exhibit solar variability on a range of time scales.

We test this potential by generating ¹⁰Be flux records at two different timescales. First, we use 2-year, amalgamated varves to determine the existence of short-period variability (11-year Schwabe cycle) in two 80-year sequences. We analyze flux estimates using multi-taper spectral analysis, and complimentary analyses including grain size and seasonality help discriminate the effects of climate from these high-resolution records. Second, we test a 1700-year record of ¹⁰Be flux at decadal resolution (15-year amalgamated samples) for comparison with Greenland ice core records at centennial timescales. No definitive correlation is discernible from preliminary data, but results show promise to that end.