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Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal re-cords from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (similar to 9e6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Peatlands are valuable archives of information about past environmental conditions and represent a globally-important carbon store. Robust proxy methods are required to reconstruct past ecohydrological dynamics in high-latitude peatlands to improve our understanding of change in these carbon-rich ecosystems. The High Arctic peatlands in Svalbard are at the northern limit of current peatland distribution and have experienced rapidly rising temperatures of 0.81 °C per decade since 1958. We examine the ecology of peatland testate amoebae in surface vegetation samples from permafrost peatlands on Spitsbergen, the largest island of the Svalbard archipelago, and develop new transfer functions to reconstruct water-table depth (WTD) and pH that can be applied to understand past peatland ecosystem dynamics in response to climate change. These transfer functions are the first of their kind for peatlands in Svalbard and the northernmost developed to date. Multivariate statistical analysis shows that WTD and pore water pH are the dominant controls on testate amoeba species distribution. This finding is consistent with results from peatlands in lower latitudes with regard to WTD and supports work showing that when samples are taken across a long enough trophic gradient, peatland trophic status is an important control on the distribution of testate amoebae. No differences were found between transfer functions including and excluding the taxa with weak idiosomic tests (WISTs) that are most susceptible to decay. The final models for application to fossil samples therefore excluded these taxa. The WTD transfer function demonstrates the best performance (R2LOO = 0.719, RMSEPLOO = 3.2 cm), but the pH transfer function also performs well (R2LOO = 0.690, RMSEPLOO = 0.320). The transfer functions were applied to a core from western Spitsbergen and suggest drying conditions ~1750 CE, followed by a trend of recent wetting and increasing pH from ~1920 CE. These new transfer functions allow the reconstruction of past peatland WTD and pH in Svalbard, thereby enabling a greater understanding of long-term ecohydrological dynamics in these rapidly changing ecosystems.

Permafrost peatlands are found in high-latitude regions and store globally-important amounts of soil organic carbon. These regions are warming at over twice the global average rate, causing permafrost thaw, and exposing previously inert carbon to decomposition and emission to the atmosphere as greenhouse gases. However, it is unclear how peatland hydrological behaviour, vegetation structure and carbon balance, and the linkages between them, will respond to permafrost thaw in a warming climate. Here we show that permafrost peatlands follow divergent ecohydrological trajectories in response to recent climate change within the same rapidly warming region (northern Sweden). Whether a site becomes wetter or drier depends on local factors and the autogenic response of individual peatlands. We find that bryophyte-dominated vegetation demonstrates resistance, and in some cases resilience, to climatic and hydrological shifts. Drying at four sites is clearly associated with reduced carbon sequestration, while no clear relationship at wetting sites is observed. We highlight the complex dynamics of permafrost peatlands and warn against an overly-simple approach when considering their ecohydrological trajectories and role as C sinks under a warming climate.

Climate warming and human impacts are thought to be causing peatlands to dry,\ud potentially converting them from sinks to sources of carbon. However, it is unclear\ud whether the hydrological status of peatlands has moved beyond their natural envelope.\ud Here we show that European peatlands have undergone substantial, widespread drying\ud during the last ~300 years. We analyse testate amoeba-derived hydrological\ud reconstructions from 31 peatlands across Britain, Ireland, Scandinavia and continental\ud Europe to examine changes in peatland surface wetness during the last 2000 years.\ud 60% of our study sites were drier during the period CE 1800-2000 than they have been\ud for the last 600 years; 40% of sites were drier than they have been for 1000 years; and\ud 24% of sites were drier than they have been for 2000 years. This marked recent\ud transition in the hydrology of European peatlands is concurrent with compound\ud pressures including climatic drying, warming and direct human impacts on peatlands,\ud although these factors vary between regions and individual sites. Our results suggest\ud that the wetness of many European peatlands may now be moving away from natural\ud baselines. Our findings highlight the need for effective management and restoration of\ud European peatlands.

The response of Arctic wetland ecosystems and their associated organic carbon stores to future warming is uncertain. For the first time in the Canadian High Arctic I use a multi-proxy palaeoecological approach to test how organic-rich wetlands have responded to pronounced warming since the mid-twentieth century. This approach enables ecological analysis on a timescale beyond that of contemporary studies. An ice-wedge polygon mire was a dual-state system with the raised centre mound showing no response to recent warming, but ~AD 2000 the surrounding trough exhibited a shift to wetter conditions and a transition from sedge and herb-dominated to brown moss-dominated vegetation. The accumulation of this vegetation layer may have the effect of insulating ice-wedges and provide a negative ecological feedback to permafrost degradation, mitigating potential carbon losses. In a valley fen, an increase in growing degree days above 0°C (GDD0) since ~AD 1950 is linked to greater inundation from increased snow and ice melt early in the growing season, coupled with increased drying towards the end of the growing season from elevated evapotranspiration. This may have initiated a pathway to wetland desiccation – although wetland persistence is likely to be determined by future Arctic precipitation patterns. In a coastal fen, greater GDD0 combined with isostatic uplift induced shrubification ~AD 1950 and led to rapid carbon accumulation. After this, increasing bird grazing pressures from ~AD 2000 may have affected vegetation and carbon accumulation. My results illustrate a variety of pathways for change in High Arctic wetlands in response to rapid warming. The results of this study suggest that predictions of the future extent and carbon accumulation rates of northern peatlands should consider the marked, yet complex response of High Arctic wetlands to warming alongside external non-climatic factors such as increased bird grazing pressures.

Understanding the chronology of Norse settlement is crucial for deciphering the archaeology of many sites across the North Atlantic region and developing a timeline of human-environment interactions. There is ambiguity in the chronology of settlements in areas such as the Northern Isles of Scotland, arising from the lack of published sites that have been scientifically dated, the presence of plateaus in the radiocarbon calibration curve, and the use of inappropriate samples for dating. This novel study uses four absolute dating techniques (AMS radiocarbon, tephrochronology, spheroidal carbonaceous particles and archaeomagnetism) to date a Norse house (the “Upper House”), Underhoull, Unst, Shetland Isles and to interpret the chronology of settlement and peat which envelops the site. Dates were produced from hearths, activity surfaces within the structure, and peat accumulations adjacent to and above the structure. Stratigraphic evidence was used to assess sequences of dates within a Bayesian framework, constraining the chronology for the site as well as providing modelled estimates for key events in its life, namely the use, modification and abandonment of the settlement. The majority of the absolute dating methods produced consistent and coherent datasets. The overall results show that occupation at the site was not a short, single phase, as suggested initially from the excavated remains, but instead a settlement that continued throughout the Norse period. The occupants of the site built the longhouse in a location adjacent to an active peatland, and continued to live there despite the encroachment of peat onto its margins. We estimate that the Underhoull longhouse was constructed in the period cal. AD 805–1050 (95% probability), and most probably in cal. AD 880–1000 (68% probability). Activity within the house ceased in the period cal. AD 1230–1495 (95% probability), and most probably in cal. AD 1260–1380 (68% probability). The Upper House at Underhoull provides important context to the expansion and abandonment of Norse settlement across the wider North Atlantic region.