THE TWENTIETH CENTURY’S LAMINATED SEDIMENTS OF SLUICE POND, LYNN, MA

Sluice Pond in Lynn, MA has been the subject of several previous studies, which have observed but not investigated a change in the most recently deposited sediment from a brown, massive mud to a black, laminated mud. It has been hypothesized that these laminations could be varves, annual layers that can form at the bottom of lakes which experience seasonal changes in deposition and have anoxic bottom conditions that prevent the bioturbation of fine laminations. Sluice Pond experienced a change from oxic to anoxic bottom conditions in the late 19th century, likely due to cultural eutrophication, and this change may have allowed the preservation of varves. This study seeks to establish whether the laminations in the most recently deposited sediment of Sluice Pond are varves.

A freeze core was taken in 2015 to examine these sediments with as little deformation as possible. The core was dated by correlating with an age model from a previous study by Monecke et al. (2018), which used a core from the same part of the deep basin. Thin sections were produced by removing water and impregnating the sediment with resin. The thin sections were scanned to a computer and laminations were counted and compared to the age model. Preliminary lamination counting results do not show enough laminations for the transition between them to be seasonal. Assuming two laminations to represent one year’s deposition produces a ten year difference in age between the laminations and the age model at 18 cm, more than can be accounted for by error at the transitions between the thin sections.

Carbon and nitrogen stable isotope analysis was also conducted at a 2 mm resolution to explore the possibility that there might be a correlation between the isotopic composition of the sediment and climatic variables. This high-resolution isotopic record shows the same general trends as previous lower-resolution records. Preliminary correlations between isotopic and elemental composition and a number of climatic variables, including precipitation, temperature, and Southern Oscillation Index, show no significant correlation, indicating that forcings by non-climate variables dominate. Further research into isotope proxies, possible forcings, and lamination counts is ongoing.