T86 Shallow Lakes and Wetlands: Sedimentary Records and Modern Dynamics of Small Systems That Pack a Big Punch in the Carbon Cycle

Monday, 10 October 2011
8:00 AM - 12:00 PM
Room M100DE

HYDROCLIMATIC VARIABILITY DRIVES PULSES OF PEAT FORMATION AND CARBON STORAGE IN GLACIAL KETTLEHOLES

Paper number: T86-13
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

Abundant small, closed-basin kettlehole lakes and peatlands characterize the Great Lakes Region of the United States. At regional scales, kettlehole systems rarely occupy > 30% of the landscape, but recent work has demonstrated that peat deposits and lake sediments stored in these systems represent ~80% of the total fixed-carbon (C) pool. However, historic patterns of C accumulation in these systems and their linkages to climate are poorly understood. Because peat deposits generally have higher C densities and faster vertical accumulation rates than lake sediments, understanding the rates and mechanisms of peatland invasion of kettlehole lakes is particularly important for reconstructing past or modeling future regional carbon fluxes. Contrary to widely-accepted models of autogenic peatland development in kettlehole basins, we hypothesize that water level fluctuations control spatiotemporal patterns of peatland development in kettlehole basins and that most of these systems have experienced episodic peat accumulation histories during the Holocene.

Here, we present results from a paleoecological study aimed at testing our hypothesis in a small northern Wisconsin kettle lake – peatland complex (Fallison Bog). We collected a sediment core from the centrally-located remnant pond, determined the spatiotemporal pattern of peatland establishment along coring transects from the center to the margin of the peat mat, and performed both loss-on-ignition and plant macrofossil analyses along the lengths of peatland cores. Aboveground plant macrofossils were radiocarbon dated from the lake-peat contact in each peatland core and used to estimate the timing of peatland establishment at each coring location. Data suggest that peatland expanded episodically and that large areas of similar basin depth were synchronously invaded by peatland around 5000, 3000, 2000 and 1000 calendar years before present. The timing of these expansion episodes corresponds with times of rapid climate change documented in regional paleoclimate records. Our results suggest that kettleholes may be vulnerable to abrupt peatland invasion resulting from anticipated changes in mid-latitude hydroclimatic variability, with major implications for long-term carbon cycling in glaciated regions.