A HIGH RESOLUTION SEDIMENT RECORD OF THE LAST ~11,240 14C YR FROM A LAMINATED LAKE CORE FROM BALLSTON LAKE, EASTERN NEW YORK STATE

Ballston Lake, located in eastern New York State (~42°55’N; 73°52’W), is long (~5 km), narrow (<0.5 km) and eutrophic, and occupies an avulsed reach of the Mohawk River. The Lake formed at the onset of the Younger Dryas (~11,000 ¹⁴C yr BP) when the Mohawk River abandoned ~ 25 km of channel downstream from Schenectady, New York. Most of the lake is <15 m deep, however, the southernmost end of the lake reaches depths of >30 m. This southern basin is meromictic and permanently anoxic at depth; all other parts of the lake are dimictic and are only anoxic for part of the year. Cores from northern and central parts of the lake reveal a monotonous Holocene section of massive gyttja with ~30% organic carbon that overlies a thin inorganic section of varved silt and clay. All cores bottom in a sandy gravel, which presumably was deposited by the Mohawk River prior to avulsion.

In February 2002, we retrieved an ~15.5 meter-long core from the deep southern basin. The anoxic state of this basin has enabled the preservation of abundant organic matter and millimeter-thick couplets of organic and inorganic laminae throughout the Holocene section of the core. The varved sections of Holocene mud are sporadically interspersed with massive sediment ~10-20 cm thick, which may reflect intervals during which the southern basin was actively overturning. Eight AMS radiocarbon analyses have been performed on macrovegetal material in the core. The base of the core dates to ~11,240 ± 40 ¹⁴C yr BP. Bulk sedimentation rates appear to be driven by organic productivity in the water column and sediment focusing to the coring locality. Lowest sedimentation rates (~0.3 mm yr^-1) occurred during the late glacial, and sedimentation accelerated steadily to ~0.9 mm yr^-1 in the early Holocene and ~1.9 mm yr^-1 during the late Holocene. High-resolution measurement of organic carbon content reveals a first order trend of increasing organic carbon levels from the late glacial (<6%) to the early Holocene (17%), a near constant early to mid-Holocene organic carbon level of ~14-18%, and a sharp decline in organic carbon over the last two centuries to ~10%. Superimposed on these first order changes are millennial-century scale oscillations in carbon content that may be driven by high frequency oscillations in nutrient flux and/or meromixsis, which may ultimately be driven by regional climate.