A MULTIPROXY ANALYSIS OF ENVIRONMENTAL CHANGE FROM PINEO POND, DEBLOIS, ME SINCE THE LATE PLEISTOCENE

The post-glacial stratigraphy of Pineo Pond, associated with the Pineo Ridge moraine system in Downeast Maine, was studied to reconstruct environmental conditions over the Late Pleistocene and Holocene Epochs. Pineo Pond is a small (2.8 ha), hydrologically closed kettle pond with a maximum depth of 15.7 m and elevation of 62 m. A 3 m long sediment core was taken from the deep hole of Pineo Pond, split, and analyzed for multiple proxies, including loss on ignition (LOI), magnetic susceptibility (MS), image analysis, two AMS radiocarbon dates, and organic matter stable isotope analysis (CNS). Four distinct lithofacies are observed. The base of the core consists of an organic-poor gray massive clay facies with minor sand laminae and elevated MS values (ca. 9.9 to 46.1 x 10^-5 SI units), interpreted as the glaciomarine Presumpscot Formation. Overlaying this basal unit is a black and dark brown laminated mud facies with lower MS values (ca. 0.8 to 6.8 x 10^-5 SI units) and higher organic matter (9.1 to 17.2‰ OC). An AMS radiocarbon age of a terrestrial macrofossil (11,680 ± 120 ¹⁴C years; ca. 13,691 ± 269 cal BP) constrains this as a post isostatic rebound lacustrine unit, associated with deposition during the Bølling-Allerød interstadial. The next overlying facies consists of two distinct units: a lower light gray and brown laminated mud that grades into an upper light brown sandy mud. This facies has elevated MS values (8.0 to 28.0 x 10^-5 SI units), low organic matter (1.3 to 4.0‰ OC), and our age model constrains the age between 11.0 and 12.9 cal BP, coeval with the Younger Dryas stadial. The upper 2.5 m consists of an organic-rich black laminated gyttja with lower MS values (-0.7 to 2.0 x 10^-5 SI units) and increasing organic matter (14.0 to 55.1% OC). The gyttja represents Holocene lacustrine deposition, and a general trend of increasing organic matter is observed, with average values of ca. 50% over the past three millennia. δ¹³C (-35.5‰ to -21.3‰) and C/N (10 to 20) data suggest there has been a mixed source of algal and terrestrial C3 organic matter, and that variability in productivity, source, and/or preservation of organic matter has occurred over the length of the record. Lower C/N ratios in the Late Pleistocene suggest that algal sources may have been more dominant during that time.