RECONSTRUCTING PAST CLIMATE VARIABILITY AFTER THE LAURENTIDE ICE SHEET RETREAT IN NORTHERN NEW JERSEY USING A LAKE SEDIMENT CORE

We present a lacustrine record from Lower Blauvelt Lake, Franklin Lakes, New Jersey, which records past regional climate variability since the last deglaciation. The six-meter sediment core is constrained in absolute time by ten radiocarbon dates on seeds and wood fragments, and reveals a complete paleolimnology record back to ~15,000 years BP. The core was divided into ten-centimeter sections, and one-gram samples were extracted at 3-4 cm intervals for analysis. Particle size analysis, which can be an indicator of lake recharge related to rainfall and/or glacial meltwater, was performed on sediments using a Shimadzu particle size analyzer. Total organic carbon (TOC) and total nitrogen (TN) was analyzed on the same subsamples. Paleomagnetic analyses including magnetic susceptibility and anhysteretic remanant magnetization (ARM) was also conducted.

These proxies reveal similar patterns of variability, whereby periods of larger-grained sediment input into the lake occur with higher TOC and TN values and vice versa, indicating that both proxies likely reflect changes in lake recharge. Higher values of TOC and a higher C:N ratio suggest the organic material came from land sources brought to the lake by flowing water thus reflecting lake recharge. Together, these data indicate that the Younger Dryas epoch (~12.8-11.5 kyr) was characterized by generally dry conditions, which culminated with a rapid transition to wet conditions during the early Holocene. This transition marked the wettest period of the last fifteen thousand years and occurs in parallel with peak summer insolation and high atmospheric CH₄ values. Results of the ARM analyses reveal a strong coherence with the C:N ratios, with higher C:N values corresponding with lower ARM values and vice versa. Both records exhibit patterns that are coherent with local sea surface temperatures and Aug insolation (40^o N), suggesting that shifts in the C:N and ARM values may reflect changes in the source of organic matter (e.g. algal versus vascular dominated) and/or other environmental factors related to climate.