Rapid deglacial and early Holocene expansion of peatlands in Alaska

Abstract

Northern peatlands represent one of the largest biospheric carbon (C) reservoirs; however, the role of peatlands in the global carbon cycle remains intensely debated, owing in part to the paucity of detailed regional datasets and the complexity of the role of climate, ecosystem processes, and environmental factors in controlling peatland C dynamics. Here we used detailed C accumulation data from four peatlands and a compilation of peatland initiation ages across Alaska to examine Holocene peatland dynamics and climate sensitivity. We find that 75% of dated peatlands in Alaska initiated before 8,600 years ago and that early Holocene C accumulation rates were four times higher than the rest of the Holocene. Similar rapid peatland expansion occurred in West Siberia during the Holocene thermal maximum (HTM). Our results suggest that high summer temperature and strong seasonality during the HTM in Alaska might have played a major role in causing the highest rates of C accumulation and peatland expansion. The rapid peatland expansion and C accumulation in these vast regions contributed significantly to the peak of atmospheric methane concentrations in the early Holocene. Furthermore, we find that Alaskan peatlands began expanding much earlier than peatlands in other regions, indicating an important contribution of these peatlands to the pre-Holocene increase in atmospheric methane concentrations.climate seasonality | Holocene thermal maximum | peatland carbon | Alaska | Siberia O ngoing and future warming at high latitudes has generated significant interest in terrestrial carbon-cycle feedbacks to climate change (1). Of particular concern and considerable debate is the long-term effect of climate warming on soil carbon (C) pools (2-5). Numerous studies have documented that warming negatively impacts soil C storage by increasing respiration and decomposition (2, 4, 6). However, long-term effects of warming on C storage remain controversial (2, 3), in part because these studies only cover relatively short time scales. Furthermore, most of these studies were performed in mineral soils, and few studies consider long-term climate sensitivity of C storage in organic-rich peat soils (5), which represent up to onethird of the global soil C pool (7). In peatlands, climate warming has the potential to increase net C accumulation by stimulating net primary productivity (NPP) but also decrease it through greater ecosystem respiration (including decomposition of old peat C) (8). Peatlands accumulate carbon where productivity is greater than the rate of decay, which occurs when the soil is waterlogged and water tables are relatively stable (8, 9). Saturated soils are necessary for the existence of peatlands, but the role of moisture in peatland C accumulation remains unclear. On relatively short time scales, water table depth manipulations have not produced consistent results (10, 11), and numerous studies have shown stronger responses of C dynamics to temperature than moisture changes (10-13).Most modern peatlands formed during th...

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…This was Guthrie's (1990Guthrie's ( , 2001) basic hypothesis, and it fits with how post-glacial changes in climate affected the biophysical processes that he asserts were important in maintaining the Mammoth Steppe. We know that paludification began on the North Slope ca 16 cal ka BP (Jones and Yu, 2010) and that the present-day tundra vegetation types were in place, at least in the Arctic Foothills, by 9e10.5 cal ka BP (Mann et al, 2002). This chronology is consistent with the estimated extinction dates of horse, bison, and mammoth on the North Slope (Figs.…”

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

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