A POLLEN-BASED CLIMATE RECONSTRUCTION OF THE PAST 10,000 YEARS OF CONE POND, NH

Pollen-based climate reconstructions use pollen assemblages and abundances as proxies for climatic variables by calibrating a modern-pollen set with current climate data. By understanding how vegetation has interacted and responded to climate trends previously, hypotheses of how vegetation may response in the future to our changing climate can be made.

Cone Pond, Thornton, NH (43.9037° N, 71.6046° W), is a 3.1 ha, closed pond with a maximum depth of 9 meters. In the winter of 2022, two 7.5 m-long sediment records were collected. These records extend from Late-Holocene into glacial clays, and may also contain evidence of the Bølling-Allerød warm period. The cores were split and logged for XRF chemistry and magnetic susceptibility in 2023. To add to these analyses, we sampled for loss-on-ignition (LOI) and pollen. The core appears to be laminated at a high resolution, possibly annual.

Pollen preparation followed a modified Fægri & Iversen (1989) with processing limited to HCl, KOH, addition of a Lycopodium clavatum spike, and coarse sieving. Using total pine pollen percentages, we assess the historic trends of annual precipitation, mean July, and mean January temperatures (Webb III et al. 1993).

Our 2023 results supplement and extend the previous work of Ford (1990) on a 1978 core for this pond. The chronology is established by wiggle-matching of LOI and pollen data with Ford’s. Starting at the oldest point of CP-B, the total pine percentage (10.65%) indicates a warm, wet climate that interrupts the glacial clays. This event is possibly the Bølling-Allerød warm period, 14,700-12,700 cal yr BP (Broeker, 1992). Further evidence of this hypothesis is provided by the peak of total pine percentage (44.77%) following this period, indicating a cool, dry climate associated with the Younger Dryas interval. A radiocarbon date has been submitted for the possible Bølling-Allerød warm period to confirm this hypothesis. If confirmed, this could be one of the longest lacustrine records for the White Mountain region of NH.