# Pan‐Arctic Peatlands Have Expanded During Recent Warming

## TL;DR

Arctic peatlands have expanded rapidly in recent decades due to warming, which could impact carbon storage in the region.

## Contribution

The study provides the first large-scale evidence of pan-Arctic peatland expansion in response to recent warming.

## Key findings

- Peatlands have expanded laterally at rates exceeding ~1 meter per year since 1950 AD in some regions.
- New peat formation has occurred at two-thirds of the studied sites since ~1990 AD.
- Peatland expansion is likely a widespread phenomenon across the Arctic despite regional constraints.

## Abstract

The fate of carbon stored in Arctic peatlands remains uncertain because of the complex nature of the effects of climate change on permafrost and peatland carbon cycling. Expansion and/or shrinkage of Arctic peatlands under climate change also remain unknown due to lack of ground data and difficulties detecting changes in the extent of these ecosystems, meaning that land surface model predictions currently inadequately quantify Arctic terrestrial carbon storage changes. Pan‐Arctic shifts in peatland extent would profoundly change the fate of carbon in the terrestrial Arctic. Here, we tackle this knowledge gap by answering three main questions: (a) has lateral expansion occurred in Arctic peatlands as a response to recent warming? (b) if so, how fast has this occurred? (c) how does the response vary regionally? To answer these, we collected a dataset (12 peatland sites, 91 peat cores) combining peat cores collected across two latitudinal (north–south) transects: one in the European Arctic and one in the Canadian Arctic. In each region, we selected three peatland sites, with cores collected from transects spanning the peat‐edge to the peat‐centre. Our large‐scale dataset shows that peatlands have expanded, often rapidly, with some rates exceeding ~1 m per year since 1950 AD. This rapid expansion has occurred during a period of widespread Arctic warming and is still ongoing: two thirds (8/12) of our peatland sites evidence new peat formation after ~1990 AD based on age‐depth models constrained by 14C and 210Pb dating. Given that our sites comprise a broad range of Arctic conditions, we expect peatland expansion to be a pan‐Arctic phenomenon. Within specific regions, there are constraints on peat expansion including topographical limits, but we present the basis for future work to estimate pan‐Arctic peatland expansion, plus the associated carbon cycle implications under future climate change.

Arctic peatland carbon is important because it represents a large carbon stock that may be vulnerable to climate change. This work explores the expansion and/or shrinkage of Arctic peatlands using observations in two north–south transects in Canada and in Europe. We find that lateral expansion has occurred in Arctic peatlands as a response to recent warming, often rapidly, with some rates exceeding ~1 m per year since 1950 AD. Given the differing conditions of our selected sites, we expect peatland expansion to be a pan‐Arctic phenomenon.