LATE-HOLOCENE SEDIMENTATION IN CONE POND, NH

Lake core sediments can offer an exciting glimpse into the climate and events of the past. In the summer of 2021 and winter of 2022, two ~40 cm long 3” diameter surface cores and a 3 meter long, 2” diameter Livingstone piston core was taken from Cone Pond, Thornton, NH. Cone Pond has been heavily studied since the 1950’s, primarily to gain deeper understanding of occurrences of natural ecosystem disturbances, human-impacted environments and nutrient cycling. The purpose of this new core collection is to determine if the sediments are annually laminated and to reconstruct late-Holocene climate changes affecting lower elevation regions of the White Mountains. Here we report initial findings from the upper 2 meters of this composite core. Based on prior studies with radiocarbon dating, this is expected to be a 3000-year record.

The 33.4 ha Cone Pond watershed is primarily mixed conifer forest, with some stands of northern hardwood. Elevations range from 476 m at the pond to 650 m at Cone Mt. The soils are primarily acidic spodosols developed in thin (< 2 m) glacial till. We use sediment and macrofossil analysis, in conjunction with radioisotope dating with lead-10, cesium-137 and carbon-14, to assess changes in sediment characteristics (carbon content, bulk density, particle-size, geochemistry and magnetic susceptibility) and rates of sediment loading.

Our preliminary results indicate that the uppermost meter (T1) is composed of 45-60% organic material with fine laminations, especially below 62 cm sediment depth. In contrast, the second meter (T2) has a looser, less organized soil construction with small gas cavities found throughout this core section, and no clear lamination or color changes. Multi-sensor core scans of a 1978 core from Cone Pond, completed on archival core materials in 2019, indicate that core laminations do persist to at least 5 meters sediment depth, but vary notably in thickness and color. We hope to better understand the nature of these variations as a preliminary step towards more detailed analyses of this core and two additional (7 m long) cores collected in 2022.