Sensitivity of Northern Peatland Carbon Dynamics to Holocene Climate Change

Abstract

In this paper, we evaluate the long-term climate sensitivity and global carbon (C) cycle implications of northern peatland C dynamics by synthesizing available data and providing a conceptual framework for understanding the dominant controls, processes, and interactions of peatland initiation and C accumulation. Northern peatlands are distributed throughout the climate domain of the boreal forest/taiga biome, but important differences between peatland regions are evident in annual temperature vs. precipitation (T-P) space, suggesting complex hydroclimatic controls through various seasonal thermal-moisture associations. Of 2380 available basal peat dates from northern peatlands, nearly half show initiation before 8000 calendar years (cal years) B.P. Peat-core data from sites spanning peatland T-P space show large variations in apparent C accumulation rates during the Holocene, ranging from 8.4 in the Arctic to 38.0 g C m-2 a-1 in west Siberia, with an overall time-weighted average rate of 18.6 g C m-2 a-1. Sites with multiple age determinations show millennial-scale variations, with the highest C accumulation generally at 11,000-8000 cal years B.P. The early Holocene was likely a period of rapid peatland expansion and C accumulation. For example, maximum peat expansion and accumulation in Alaska occurred at this time when climate was warmest and possibly driest, suggesting the dominant role of productivity over decomposition processes or a difference in precipitation seasonality. Northern peatland C dynamics contributed to the peak in atmospheric CH 4 and the decrease in CO 2 concentrations in the early Holocene. This synthesis of data, processes, and ideas provides baselines for understanding the sensitivity of these C-rich ecosystems in a changing climate.

Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century

“…4 we highlight a comparison of simulated versus reconstructed apparent C accumulation rates for two sites in Scotland and one site in Canada (as compiled in Yu et al, 2009;Anderson, 2002;Gorham et al, 2003). The apparent accumulation rates at the Scottish sites, both located in the same model grid cell, show an early Holocene increase and a linear decrease towards the present.…”

“…Each region itself represents an average of 3 or more records with basal ages between 5.5 and 14.2 kyr BP. Measured apparent C accumulation rates range between 8.4 and 38.0 g C m −2 yr −1 for these regions over the Holocene, with an overall time-weighted average rate of 18.6 g C m −2 yr −1 for all 33 sites (Yu et al, 2009). The locations of the 33 reconstructed apparent peat accumulation rate sites fall into 24 grid cells of the LPX model grid.…”

“…We thus use simulated changes in catotelm gross C accumulation (mainly acrotelm-to-catotelm C transfer, F AC ) summed over 1000 yr intervals, and let this accumulated C decompose until present with the time dependent catotelm decomposition rate as calculated by LPX, averaged over the same intervals. In this way we derive an apparent accumulation rate history, which can be compared to the peatcore data in Yu et al (2009). As the metric for evaluating the comparison we use the root-mean-square deviation (RMSD) of simulated versus reconstructed apparent C accumulation rates.…”

“…As a tuning target, we use reconstructed Holocene apparent peat accumulation rates from a compilation of 33 peatland sites in the northern high-latitudes (Yu et al, 2009). The data include fens and bogs as well as permafrost peatlands from the following major peatland regions: Alaska, Canada, Scotland, Finland and Siberia.…”

Stratigraphic and Paleoenvironmental Reconstruction of a Mid-Pliocene Fossil Site in the High Arctic (Ellesmere Island, Nunavut): Evidence of an Ancient Peatland with Beaver Activity + Online Appendix Figures S1 and S2 (See Article Tools)

“…Fens are peatlands that receive water supply from groundwater rich in dissolved minerals, often from association with calcareous rocks, with vegetation dominated by graminoids, sedges, and brown mosses (Mitsch et al, 2009;Keddy, 2010). We estimated the duration of the peat layer at the Beaver Pond site using published, timeweighted carbon accumulation averages from five Holocene analogue forest fen sites (Alaska, n = 3; and Finland, n = 2) (Mäkilä et al, 2001;Mäkilä and Moisanen, 2007;Yu et al, 2009). These fens are all more than 10 000 years old and were selected because they are similar to the Beaver Pond fossil site, in that they are currently located near the tree line, but not within the zone of continuous permafrost, and (Table 2).…”