Recent amplified climate warming in the Arctic has caused profound changes in terrestrial ecosystems, with the potential for strong feedback on climate change. Arctic tundra landscapes have developed patchy and thin organic soil (peat) layers at the surface that may continue to grow into mature peatlands and become a larger carbon sink under future warming. Here we use paleoecological analyses of multiple soil and peat cores collected from the North Slope of Alaska to document and understand the formation and development histories of tundra peat patches and permafrost peatlands. We find a consistent peat development sequence for peat patches, first from mineral soils to sedge peat during the Little Ice Age, and then to Sphagnum peat during the recent warming with high carbon accumulation rates. These findings suggest that climate cooling is likely critical for the initial peat buildup on tundra soils due to reduced decomposition, whereas climate warming triggers the regime shift into an increased abundance of Sphagnum mosses that are likely central to enhancing their carbon sink capacity. Additionally, peat patches become similar to permafrost peatlands in the vicinity in terms of ecosystem processes and carbon dynamics, and therefore may have developed the same ecohydrological feedback system to maintain their long-term stability. This study implies that the potential future expansion of peat patches into peatlands may strongly alter the carbon balance of Arctic tundra, supporting the new United Nations Environment Programme's report that calls for incorporating widespread shallow peat into understanding the peatland–carbon–climate nexus.
PLAIN LANGUAGE SUMMARY
The ongoing trend of global warming has the fastest rate in the Arctic and has caused rapid and widespread environmental changes in the Arctic tundra. A major concern is the warming-induced permafrost thaw that may destabilize the rich soil-carbon pools underground, providing positive feedback to further accelerate warming. However, warming may also induce northward expansion of northern peatlands that function as persistent carbon sinks over millennia, just like how northern peatlands colonized boreal and sub-Arctic landscapes during and after deglacial warming 14,000∼8,000 years ago. If true, new peatland formation may provide negative feedback to mitigate warming. This study focuses on patchy and thin peat layers found on Alaska's tundra and uses paleoecological analyses to understand their histories on the landscape. We find that these peat patches were formed during the cold Little Ice Age, but recent climate warming triggered a shift into dominance of Sphagnum mosses, the major peat-forming species for northern peatlands. By comparing with permafrost peatlands nearby, we present multiple lines of evidence to argue that tundra peat patches may be transformed into new Arctic peatlands with important carbon-cycle consequences and recommend future research to further understand such processes with new observational data, laboratory experiments, and model simulations.
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