Julie Loisel

A Database and Synthesis of Northern Peatland Soil Properties and Holocene Carbon and Nitrogen Accumulation

Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

Effects of permafrost aggradation on peat properties as determined from a pan-Arctic synthesis of plant macrofossils

Permafrost dynamics play an important role in high-latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, and thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, and C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost-free fens, while boreal permafrost peatlands more closely resembled permafrost-free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost-free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long-term C accumulation rates were higher in fens (23g C m(-2)yr(-1)) than in permafrost-free bogs (18g C m(-2)yr(-1)) and were lowest in boreal permafrost peatlands (14g C m(-2)yr(-1)). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and reaggradation. Using data synthesis, we have identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation.

Holocene peatland carbon dynamics in the circum-Arctic region: An introduction

Peatlands represent the largest and most concentrated carbon pool in the terrestrial biosphere, and their dynamics during the Holocene have had significant impacts on the global carbon cycle. In this Introduction paper, we provide an overview of the contributions presented in this Special Issue on Holocene peatland carbon dynamics. We also provide a brief history and current status of peat-core-based research on peatland carbon dynamics. Finally, we identify and discuss some challenges and opportunities that would guide peatland carbon research in the near future. These challenges and opportunities include the need to fill data gaps and increase geographic representations of peat carbon accumulation records, a better understanding of peatland lateral expansion process and improved estimate of peatland area change over time, developing regional carbon accumulation histories and carbon pool estimates, and projecting and quantifying overall peatland net carbon balance in a changing world.

Networking our science to characterize the state, vulnerabilities, and management opportunities of soil organic matter

Soil organic matter (SOM) supports the Earths ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.

Transformations of landscape and peat‐forming ecosystems in response to late Holocene climate change in the western Antarctic Peninsula

We used subfossil mosses and peats to document changes in regional climate, cryosphere, and terrestrial ecosystems in the western Antarctic Peninsula at ~65°S latitude. We find that most peat forming ecosystems have initiated since 2800 cal B.P., in response to warmer summers and increasing summer insolation. The period at 900–600 cal B.P. was coldest as indicated by ice advance, abundance of kill ages from ice-entombed mosses exposed recently from retreating glacial ice, and apparent gap in peatbank initiation. Furthermore, the discovery of a novel Antarctic hairgrass (Deschampsia antarctica) peatland at 2300–1200 cal B.P. from the mainland Antarctic Peninsula suggests a much warmer climate than the present. A warming and wetting climate in the 1980s caused very high carbon accumulation in a Polytrichum strictum moss peatbank. Our results document dramatic transformations of landscape and ecosystems in response to past warmer climate, providing a telltale sign for what may come in the future.

Latitudinal limits to the predicted increase of the peatland carbon sink with warming

The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around ad 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.Analysis of peatland carbon accumulation over the last millennium and its association with global-scale climate space indicates an ongoing carbon sink into the future, but with decreasing strength as conditions warm.

Peatland Ecosystem Processes in the Maritime Antarctic During Warm Climates

We discovered a 50-cm-thick peat deposit near Cape Rasmussen (65.2°S), in the maritime Antarctic. To our knowledge, while aerobic ‘moss banks’ have often been examined, waterlogged ‘peatlands’ have never been described in this region before. The waterlogged system is approximately 100 m2, with a shallow water table. Surface vegetation is dominated by Warnstorfia fontinaliopsis, a wet-adapted moss commonly found in the Antarctic Peninsula. Peat inception was dated at 2750 cal. BP and was followed by relatively rapid peat accumulation (~0.1 cm/year) until 2150 cal. BP. Our multi-proxy analysis then shows a 2000-year-long stratigraphic hiatus as well as the recent resurgence of peat accumulation, sometime after 1950 AD. The existence of a thriving peatland at 2700–2150 cal. BP implies regionally warm summer conditions extending beyond the mid-Holocene; this finding is corroborated by many regional records showing moss bank initiation and decreased sea ice extent during this time period. Recent peatland recovery at the study site (<50 years ago) might have been triggered by ongoing rapid warming, as the area is experiencing climatic conditions approaching those found on milder, peatland-rich sub-Antarctic islands (50–60°S). Assuming that colonization opportunities and stabilization mechanisms would allow peat to persist in Antarctica, our results suggest that longer and warmer growing seasons in the maritime Antarctic region may promote a more peatland-rich landscape in the future.

Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest

The American Southwest has experienced a series of severe droughts interspersed with strong wet episodes over the past decades, prompting questions about future climate patterns and potential intensification of weather disruptions under warming conditions. Here we show that interannual hydroclimatic variability in this region has displayed a significant level of non-stationarity over the past millennium. Our tree ring-based analysis of past drought indicates that the Little Ice Age (LIA) experienced high interannual hydroclimatic variability, similar to projections for the 21st century. This is contrary to the Medieval Climate Anomaly (MCA), which had reduced variability and therefore may be misleading as an analog for 21st century warming, notwithstanding its warm (and arid) conditions. Given past non-stationarity, and particularly erratic LIA, a ‘warm LIA’ climate scenario for the coming century that combines high precipitation variability (similar to LIA conditions) with warm and dry conditions (similar to MCA conditions) represents a plausible situation that is supported by recent climate simulations. Our comparison of tree ring-based drought analysis and records from the tropical Pacific Ocean suggests that changing variability in El Niño Southern Oscillation (ENSO) explains much of the contrasting variances between the MCA and LIA conditions across the American Southwest. Greater ENSO variability for the 21st century could be induced by a decrease in meridional sea surface temperature gradient caused by increased greenhouse gas concentration, as shown by several recent climate modeling experiments. Overall, these results coupled with the paleo-record suggests that using the erratic LIA conditions as benchmarks for past hydroclimatic variability can be useful for developing future water-resource management and drought and flood hazard mitigation strategies in the Southwest.

Widespread global peatland establishment and persistence for the last 130,000 years

Claire C. Treat, Thomas Kleinen, Nils Broothaerts, April S. Dalton, René Dommain, Thomas A. Douglas, Judith Drexler, Sarah A. Finkelstein, Guido Grosse, Geoff Hope, Jack Hutchings, Miriam C. Jones, Peter Kuhry, Terri Lacourse, Outi Lähteenoja, Julie Loisel, Bastiaan Notebaert, Richard Payne, Dorothy Peteet, A. Britta K. Sannel, Jonathan M. Stelling, Jens Strauss, Graeme T. Swindles, Julie Talbot, Charles Tarnocai, Gert Verstraeten, Christopher J. Williams, Zhengyu Xia, Zicheng Yu, Minna Väliranta, Martina Hättestrand, Helena Alexanderson, Victor Brovkin

Holocene circum-Arctic peatland carbon dynamics

Northern peatlands represent the largest biosphere carbon (C) pool in the Earth system, containing about 500 GtC (Gorham 1991; Yu 2012); however, how this large C pool responds to climate change is still poorly understood. The overarching goal of this workshop was to understand climate and other controls on Holocene C accumulation through a community-wide collaborative and coordinated effort. This Holocene-scale synthesis aims at extending the effort on the peat C synthesis of northern peatlands for the last millennium as reported in Charman et al. (2013).