Hydrology-mediated differential response of carbon accumulation to late Holocene climate change at two peatlands in Southcentral Alaska Eric S. Klein a, * , Robert K. Booth a , Zicheng Yu a , Bryan G. Mark b , Nathan D. Stansell b a Department of Earth and Environmental Sciences, Lehigh University,1 West Packer Avenue, Bethlehem, PA 18015, USA b Byrd Polar Research Center, The Ohio State University, 108 Scott Hall, 1090 Carmack Road, Columbus, OH 43210, USA article info Article history: Received 31 August 2012 Received in revised form 28 November 2012 Accepted 21 December 2012 Available online 30 January 2013 Keywords: Peatland hydrology Peatland carbon accumulation Late Holocene paleoclimate Surficial geology Paleohydrology Peatland response to climate change Testate amoebae Southcentral Alaska abstract Peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere. Under- standing how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks. Peatland carbon accumulation rates (PCAR) are controlled by the difference between pro- duction and decomposition, which is affected by local and climatic factors including hydrology and temperature. To better understand how local controls can influence the response of PCAR to climate change, we investigated modern hydrology, paleohydrology, and PCAR at two nearby Sphagnum-domi- nated peatlands with different surficial geology (lowland and moraine settings) in Southcentral Alaska. Modern hydrological data indicated a higher rate of subsurface drainage at the lowland site, suggesting greater hydrologic sensitivity to prolonged dry periods of the past. We investigated past responses of these peatlands to well-documented climatic changes, like the Medieval Climate Anomaly (MCA) at w1000e600 cal yr BP and Little Ice Age (LIA) at w600e200 cal yr BP, using water-table depth (WTD) inferred from testate amoebae and PCAR calculated from loss-on-ignition and 14 C-dating analyses. Our results indicate that WTD and PCAR remained relatively stable at the moraine site throughout the last 1100 years, including the MCA and LIA. However, the lowland site experienced relatively stable WTD and higher PCAR during the MCA, but highly variable WTD and lower PCAR during the LIA. These differences suggest that hydrology and likely decomposition were the primary control on PCAR at these peatlands. Our results highlight the importance of local-scale controls, like surficial geology, in mediating the response of peatland hydrology and carbon accumulation to climate change. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Peatlands are wetlands where the long-term rate of biological production exceeds that of decomposition, resulting in the accu- mulation and storage of carbon-rich organic matter (Clymo, 1984). High latitude northern peatlands cover about 4 million km 2 and store up to 550 Pg (1 Pg ¼ 10 15 g) of carbon (C) (e.g., Gorham, 1991; Turunen et al., 2002; Yu et al., 2010), equivalent to about 1/3 of the world’s soil C (Jobbagy and Jackson, 2000) and more than 1/2 to- day’s atmospheric CO 2 (Battle et al., 2000). The response of this globally important C reservoir to global climate change and the potential for climate feedbacks is currently an area of much active debate and research (Davidson and Janssens, 2006; McGuire et al., 2010; Grosse et al., 2011; Turetsky et al., 2011). Although there have been broad-scale syntheses looking at the influence of climate changes on carbon-rich peatlands (MacDonald et al., 2006; Jones and Yu, 2010; Yu et al., 2011), the influence of hydrogeologic set- ting on the response of peatland C accumulation to climate change remains largely unstudied. Given the importance of peatland hy- drology in controlling C accumulation rates, and the potentially complex hydrogeologic setting of peatlands in topographically and geologically variable landscapes, the responses of peatland C accumulation rates to climatic change might be expected to vary among peatlands in geologically heterogeneous settings. Rates of production and decomposition in peatlands are sensi- tive to changes in climate, although understanding relative changes in the rates of these processes is not always straightforward. For example, decreased precipitation may lead to a lower peatland water-table, a thicker aerobic zone at the peat surface, and a faster decomposition rate (McGuire et al., 2009). However, temperature changes could potentially increase or decrease peat accumulation rates by affecting both production and decomposition. Increased temperatures could lengthen the growing season and lead to greater production (Gorham, 1991), but could also increase * Corresponding author. E-mail address: esk209@lehigh.edu (E.S. Klein). Contents lists available at SciVerse ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 0277-3791/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.quascirev.2012.12.013 Quaternary Science Reviews 64 (2013) 61e75