Peat Accumulation Rates Research Articles

Carbon accumulation rates in two poor fens with different water regimes: Influence of anthropogenic impact and environmental change

Fens are underestimated carbon sinks. Knowledge about their role in the sequestration of CO2 in the past is limited. The research reported here focused on identifying long-term carbon accumulation rates (CARs) in a drained fen (Bagno Bruch) and a waterlogged fen (Bagno Mikołeska) in southern Poland. On the basis of 210Pb and AMS 14C dates and age–depth modeling, 7000- and 2000-year records of changes in bulk composition and carbon and sulfur content are presented and discussed. Strong human impact is detected, especially in Bagno Bruch. However, minor climatic signals linked to the ‘Little Ice Age’ and to the influence of wind-blown sands are also evident. The sand may have influenced the plant composition, peat accumulation rates (PARs), and CARs, in addition to the bulk composition at Bagno Mikołeska. The mean value of the CAR in the youngest peat layers spanning the last 200 years is generally lower in two cores from Bagno Bruch ( c. 85 and 86 g/m2/yr) than in two cores from Bagno Mikołeska ( c. 140 and 142 g/m2/yr). The fens are characterized by higher CARs compared with boreal peatlands. The reproducibility of the CAR values is the most promising result, suggesting the low mobility of 210Pb and the reliability of this method in assessing the chronology of fens.

Incorporation of radiometric tracers in peat and implications for estimating accumulation rates

Accurate dating of peat accumulation is essential for quantitatively reconstructing past changes in atmospheric metal deposition and carbon burial. By analyzing fallout radionuclides 210Pb, 137Cs, 241Am, and 7Be, and total Pb and Hg in 5 cores from two Swedish peatlands we addressed the consequence of estimating accumulation rates due to downwashing of atmospherically supplied elements within peat. The detection of 7Be down to 18–20cm for some cores, and the broad vertical distribution of 241Am without a well-defined peak, suggest some downward transport by percolating rainwater and smearing of atmospherically deposited elements in the uppermost peat layers. Application of the CRS age–depth model leads to unrealistic peat mass accumulation rates (400–600gm−2yr−1), and inaccurate estimates of past Pb and Hg deposition rates and trends, based on comparisons to deposition monitoring data (forest moss biomonitoring and wet deposition). After applying a newly proposed IP-CRS model that assumes a potential downward transport of 210Pb through the uppermost peat layers, recent peat accumulation rates (200–300gm−2yr−1) comparable to published values were obtained. Furthermore, the rates and temporal trends in Pb and Hg accumulation correspond more closely to monitoring data, although some off-set is still evident. We suggest that downwashing can be successfully traced using 7Be, and if this information is incorporated into age–depth models, better calibration of peat records with monitoring data and better quantitative estimates of peat accumulation and past deposition are possible, although more work is needed to characterize how downwashing may vary between seasons or years.

The carbon stock of alpine peatlands on the Qinghai–Tibetan Plateau during the Holocene and their future fate

Most studies about carbon dynamics of peatlands have been focused on boreal, subarctic and tropical peatlands. However, there is limited data about carbon dynamics of alpine peatlands, like Zoige peatlands on the Qinghai–Tibetan Plateau (QTP), which are sensitive to climate change and human disturbance. We studied the role of these peat deposits on the Zoige as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 7 sites. The peat depths of the sample sites ranged from 0.20 to 6.0 m; the basal age on the plateau varied from 1635 to 14095 cal yr BP; the peat accumulation rates ranged from 0.12 to 0.85 mm yr−1, and the C accumulation rates from 5 to 48 g m−2 yr−1. Based on data of field studies and remote sensing, we regarded that with 3179 km2 of intact peatlands, about 1426 km2 of degraded peatlands, and the total area of Zoige peatlands was 4605 km2. The current peat C stock of Zoige peatlands was0.477 Pg (ranging from 0.206 to 0.672 Pg). We also estimated that peatlands covered an area of about 5091 km2on the QTP and sequestered 0.543 Pg C, 88% in Zoige and the rest in other parts of the plateau. Human activities, together with the ubiquitous warming on the plateau (temperature increased by 0.2 °C per decade over the past 50 years) not only shrank the area of intact peatlands, but also caused substantial carbon releasing from peatlands.

Holocene development of maritime ombrotrophic peatlands of the St. Lawrence North Shore in eastern Canada

Macrofossil analyses were used to reconstruct long-term vegetation successions within ombrotrophic peatlands (bogs) from the northern shorelines of the St. Lawrence Estuary (Baie-Comeau) and the Gulf of St. Lawrence (Havre-St-Pierre). Over the Holocene, the timing and the ecological context of peatland inception were similar in both regions and were mainly influenced by fluctuations in relative sea level. Peat accumulation started over deltaic sands after the withdrawal of the Goldthwait Sea from 7500calyr BP and above silt–clay deposits left by the Laurentian marine transgression after 4200calyr BP. In each region, the early vegetation communities were similar within these two edaphic contexts where poor fens with Cyperaceae and eastern larch (Larix laricina) established after land emergence. The rapid transitions to ombrotrophy in the peatlands of Baie-Comeau are associated with particularly high rates of peat accumulation during the early developmental stage. The results suggest that climate was more propitious to Sphagnum growth after land emergence in the Baie-Comeau area. Macrofossil data show that treeless Sphagnum-dominated bogs have persisted over millennia and that fires had few impacts on the vegetation dynamics. This study provides insight into peatland vegetation responses to climate in a poorly documented region of northeastern America.

Differential Development of Two Palsa Fields in a Peatland Located Near Whapmagoostui-Kuujjuarapik, Northern Québec, Canada

Macrofossil analysis of the peat and topographic surveys of two palsa fields (Fields 3 and 4) within a permafrost peatland located in subarctic Québec was conducted to trace the factors that contributed to their differential development. The two palsa fields are visibly different in terms of their geomorphology, ecology, and hydrology. According to our results, the evolution of the two fields was largely synchronous in terms of the respective trophic conditions. Moreover, the climate certainly played a significant role in the evolution of this ecosystem. For example, the cooling of the Neoglacial period would have favored the ombrotrophication of both sites, whereas the Little Ice Age conditions would have contributed to palsa formation. Despite the synchronous changes within the two fields, significant differences were also noted. These include the rate of peat accumulation, the number of species found in the peat monoliths, and the presence or absence of forest cover during the ombrotrophic phase. The topography of the underlying substrate would also have influenced the hydrological conditions. For example, a light slope toward the northwest engendered a faster trophic impoverishment in Field 4. In addition, streaming water in Field 3 favored the preservation of wet and rich conditions that triggered the following changes: more diverse vegetation, the significant accumulation of peat, and the formation of higher palsas.

High-Resolution Age-Depth Model of a Peat Bog in Poland as an Important Basis for Paleoenvironmental Studies

This article focuses on constructing a high-resolution age-depth model for the Puścizna Mała peat bog located in Orawa-Nowy Targ Basin (S Poland). The chronology was established on the basis of both210Pb and14C measurements, and further confirmed by pollen diagrams and the peat bulk composition (density, ash content, and measurements of C, N, S). The137Cs profile revealed significant downward migration of this radionuclide and was not suitable for geochronological interpretation. The peat profile in southern Poland records almost 2000 yr of paleoecological and geochemical changes. Major historical events linked to anthropogenic and climatic changes are recorded in the investigated proxies, which confirm the reliability of the age-depth model. Specifically, the Roman period, Migration period, Medieval times, as well as the Industrial Revolution are reflected in the palynology and bulk composition of the peat. However, dating results obtained for the core segment between 22–45 cm are problematic when confronted with other analyses. The highest peat accumulation rate of 2 mm yr-1(AD 1300–1400 according to the age-depth model) is not compatible with the section of the highest peat decomposition revealed by lithological description. Moreover, the onset of a drastic decline of forests reflected in the palynological data and dated to AD 1280–1340 (40 cm) is difficult to explain in the light of historical data. Therefore, the lithology, bulk density, and pollen were used to validate the obtained age-depth model. External forcing factors on the peat formation process may be indicated, including agricultural activity, water-level fluctuations, and natural climatic factors, which paradoxically caused doubling of the obtained peat accumulation rate.

Late Holocene ecohydrological and carbon dynamics of a UK raised bog: impact of human activity and climate change

Understanding the ecohydrological responses of peatlands to climate change is particularly challenging over the late Holocene owing to the confounding influence of anthropogenic activity. To address this, a core spanning the last ∼2400 years from a raised bog in northern England was analysed using a comprehensive suite of proxy methods in an attempt to elucidate the drivers of change. A testate amoebae-based transfer function was used to quantitatively reconstruct changes in water table depth, supported by humification analysis and a plant macrofossil-derived hydroclimatic index. Pollen and plant macrofossil data were used to examine regional and local vegetation change, and human impacts were inferred from charcoal and geochemistry. Chronological control was achieved through a Bayesian age-depth model based on AMS radiocarbon dates and spheroidal carbonaceous particles, from which peat and carbon accumulation rates were calculated. Phases of both increased and decreased bog surface wetness (inferred effective precipitation) are present, with dry phases at c. AD 320–830, AD 920–1190 and AD 1850–present, and a marked period of increased effective precipitation at c. AD 1460–1850. Coherence with other records from across Northern Europe suggests that these episodes are primarily driven by allogenic climatic change. Periods of high bog surface wetness correspond to the Wolf, Spörer and Maunder sunspot activity minima, suggesting solar forcing was a significant driver of climate change over the last ∼1000 years. Following the intensification of agriculture and industry over the last two centuries, the combined climatic and anthropogenic forcing effects become increasingly difficult to separate due to increases in atmospheric deposition of anthropogenically derived pollutants, fertilising compounds, and additions of wind-blown soil dust. We illustrate the need for multiproxy approaches based on high-resolution palaeoecology and geochemistry to examine the recent trajectories of peatlands.

Surface vegetation patterning controls carbon accumulation in peatlands

AbstractLocalized ecohydrological feedbacks have been proposed as important internal drivers of patterns and processes in terrestrial ecosystems. However, there is a significant gap between the prominence of theoretical models and the paucity of observations describing linkages between ecosystem structure and functioning. Here we report empirical evidence for strong interactions between surface vegetation patterning and long‐term carbon sequestration rates in four peat bogs in Patagonia on the basis of high‐resolution stratigraphic analyses. Peatland development across the study region was characterized by repeated switches between wet‐ and dry‐adapted plant communities, depicting changes between hollows (wet assemblages) and lawns (dry assemblages) that could represent past surface patterning. We found a site‐specific relationship between the frequency of the wet‐to‐dry cycles and carbon accumulation rates that followed a power function, with rapid vegetation shifts causing high peat accumulation rates. Our results show strong evidence for internal regulation of vegetation dynamics and peatland growth, implying that understanding peatland processes is a prerequisite for peat‐based paleoclimate reconstructions.

Deposition, floral composition and sequence stratigraphy of uppermost Triassic (Rhaetian) coastal coals, southern Sweden

Two uppermost Triassic (Rhaetian) coal beds (A- and B-bed; Bjuv Member, southern Sweden) deposited at the margin of the Danish Basin were investigated in order to interpret the peat-forming environments in a sequence stratigraphic context and to establish the peat-forming vegetations of the precursor mires. Peat formed close to the coastline and was governed by base-level (watertable) rise linked to relative sea-level rise, which is emphasized by rare occurrences of marine phytoplankton, Micrhystridium, Lunnomidinium scaniense and Rhaetogonyaulax rhaetica, in the B-bed. A maximum flooding surface (MFS7) between the coal beds A and B shows that peat accumulation occurred as a coastal response to the continued transgression of the Danish Basin that culminated with deposition of the coal-bearing Bjuv Member. The lower B-bed accumulated in a transgressive systems tract (TST) and the upper A-bed in a highstand systems tract (HST). The B-bed consists of coal and coaly mudstone intervals showing that peat formation repeatedly was outpaced by relative watertable rise. The huminite-rich coal intervals indicate peat formation under oxygen-deficient stagnant water conditions, where the peat accumulation rate balanced the watertable rise. Overall low TS values indicate a freshwater mire. The base of coal bed B marks the start of a relative decrease in creation of accommodation space, and the surface between the sediments and coal bed B represents a Terrestrialisation Surface (TeS). The palynofloral composition suggests that the initial mire was characterised by dipterid/dicksoniacean tree ferns and marattialean ground ferns, and few canopy trees dominated by cupressacean/taxodiacean wet-loving conifers with subordinate bennettitalean and caytonialean trees. The coal intervals in the B-bed represent Terrestrialisation situations characterised by a reduced ratio of accommodation rate/peat accumulation rate. The palynology of these intervals indicates establishment of canopy trees, primarily cupressacean/taxodiacean conifers accompanied by bennettitaleans and caytonialeans, with an understory of marattialean ground ferns and rarer tree ferns. Flooding Surfaces (FS) and Accommodation Reversal Surfaces (ARS) in the B-bed reflect changes in the rate of watertable rise. The coaly mudstone intervals represent Paludification situations with an upward increasing ratio of accommodation rate/peat accumulation rate. In general the palynology of the B-bed suggests a coal floral composition that was dominated by mid and upper canopy plants consisting of cupcressaceaen/taxodiaceaen trees, probably occupying areas with standing water, while ginkgos, cycads, Bennettiales, and Caytoniales and other seed ferns grew in less wet areas. Understory plants were less abundant, whereas a ground cover of ferns, mainly of the families Marattiales and Osmundales, as well as lycophytes may have been pronounced. The upper surface of the B-bed is a Give-up Transgressive Surface (GUTS) above which peat accumulation was replaced by siliciclastic deposition. The palynofloral composition suggests an open-mire dominated by ground ferns and probable tree ferns, with minor bennettitalean and caytonialean mid canopy trees, and with hardly any upper canopy trees. The A-bed is considerably richer in inertinite compared to the B-bed. The palynofloral and petrographic change correlates with an increase in fire activity across the Triassic–Jurassic boundary and deforestation of the Early Jurassic mires.

Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century

Abstract. The development of northern high-latitude peatlands played an important role in the carbon (C) balance of the land biosphere since the Last Glacial Maximum (LGM). At present, carbon storage in northern peatlands is substantial and estimated to be 500 ± 100 Pg C (1 Pg C = 1015 g C). Here, we develop and apply a peatland module embedded in a dynamic global vegetation and land surface process model (LPX-Bern 1.0). The peatland module features a dynamic nitrogen cycle, a dynamic C transfer between peatland acrotelm (upper oxic layer) and catotelm (deep anoxic layer), hydrology- and temperature-dependent respiration rates, and peatland specific plant functional types. Nitrogen limitation down-regulates average modern net primary productivity over peatlands by about half. Decadal acrotelm-to-catotelm C fluxes vary between −20 and +50 g C m−2 yr−1 over the Holocene. Key model parameters are calibrated with reconstructed peat accumulation rates from peat-core data. The model reproduces the major features of the peat core data and of the observation-based modern circumpolar soil carbon distribution. Results from a set of simulations for possible evolutions of northern peat development and areal extent show that soil C stocks in modern peatlands increased by 365–550 Pg C since the LGM, of which 175–272 Pg C accumulated between 11 and 5 kyr BP. Furthermore, our simulations suggest a persistent C sequestration rate of 35–50 Pg C per 1000 yr in present-day peatlands under current climate conditions, and that this C sink could either sustain or turn towards a source by 2100 AD depending on climate trajectories as projected for different representative greenhouse gas concentration pathways.

Examining the role of allogenous and autogenous factors in the long-term dynamics of a temperate headwater peatland (southern Québec, Canada)

Plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwater peatland located near the summit of a hill at the northern extension of the Adirondack Mountains (Québec, Canada). The aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autogenous factors associated with its long-term dynamics. Results were compared with a quantitative paleoclimatic reconstruction based on the modern analog technique using pollen data from the same core. The long-term development of the peatland (pond—rich fen—intermediate fen—poor fen—bog) mainly reflects an autogenous hydroseral succession. Active peat accumulation under the relatively dry climate of the Early Holocene suggests that summer temperature was a critical factor in peat accumulation through enhanced biomass production. A major long-term decrease in net peat accumulation rates and a progressive decline of mean water-table depth occurred during the Mid- to Late-Holocene (7900–500calyr BP), even though annual precipitation was abundant at the time. The high summer temperature associated to the highest evapotranspiration rates maintained a low water table which in turn led to strong humification of the peat. A similar, synchronous pattern in vertical peat accumulation dynamics characterized another nearby peatland. Based on these results, we suggest that small peatlands situated atop a watershed and/or within a small watershed are ecosystems sensitive to changes in precipitation and/or evapotranspiration, due to their limited water supply.

Quantifying landscape morphology influence on peatland lateral expansion using ground‐penetrating radar (GPR) and peat core analysis

AbstractNorthern peatlands contain vast amounts of organic carbon. Large‐scale datasets have documented spatial patterns of peatland initiation as well as vertical peat accumulation rates. However, the rate, pattern, and timing of lateral expansion across the northern landscape remain largely unknown. As peatland lateral extent is a key boundary condition constraining the dynamics of peatland systems, understanding this process is essential. Here we use ground penetrating radar (GPR) and peat core analysis to study the effect of local slope and topography on peatland development at a site in south‐central Alaska. The study site is unique in that a thick tephra (volcanic ash) layer, visible in the GPR data, interrupted the peatland development for about one thousand years during the mid Holocene. In our analysis, this tephra layer serves as a re‐initiation point for peatland development. By comparing the initial mineral basin vs. the post‐tephra surfaces, the influence of topography and slope on peatland expansion rate and peat‐carbon sequestration was analyzed. Our results show that (1) peatland surface slope becomes progressively shallower over the Holocene, (2) slope affects peatland lateral expansion nonlinearly, (3) the relationship between lateral expansion rate and slope follows a power‐law behavior, and (4) peatland expansion becomes slope‐limited above a threshold (0.5°). Furthermore, we propose a conceptual model linking slope to peatland lateral expansion where slope gradient and basin topography exert deterministic controls on peatland lateral expansion directly or through hydrology and vertical accumulation rates.

The impact of sea-level rise on organic matter decay rates in Chesapeake Bay brackish tidal marshes

Abstract. The balance between organic matter production and decay determines how fast coastal wetlands accumulate soil organic matter. Despite the importance of soil organic matter accumulation rates in influencing marsh elevation and resistance to sea-level rise, relatively little is known about how decomposition rates will respond to sea-level rise. Here, we estimate the sensitivity of decomposition to flooding by measuring rates of decay in 87 bags filled with milled sedge peat, including soil organic matter, roots and rhizomes. Experiments were located in field-based mesocosms along 3 mesohaline tributaries of the Chesapeake Bay. Mesocosm elevations were manipulated to influence the duration of tidal inundation. Although we found no significant influence of inundation on decay rate when bags from all study sites were analyzed together, decay rates at two of the sites increased with greater flooding. These findings suggest that flooding may enhance organic matter decay rates even in water-logged soils, but that the overall influence of flooding is minor. Our experiments suggest that sea-level rise will not accelerate rates of peat accumulation by slowing the rate of soil organic matter decay. Consequently, marshes will require enhanced organic matter productivity or mineral sediment deposition to survive accelerating sea-level rise.

Modelling Holocene carbon accumulation and methane emissions of boreal wetlands – an Earth system model approach

Abstract. Since the Last Glacial Maximum, boreal wetlands have accumulated substantial amounts of peat, estimated at 180–621 Pg of carbon. Wetlands have significantly affected the atmospheric greenhouse gas composition in the past and will play a significant role in future changes of atmospheric CO2 and CH4 concentrations. In order to investigate those changes with an Earth system model, biogeochemical processes in boreal wetlands need to be accounted for. Thus, a model of peat accumulation and decay was developed and included in the land surface model JSBACH of the Max Planck Institute Earth System Model (MPI-ESM). Here we present the evaluation of model results from 6000 yr BP to the pre-industrial period. Over this period of time, 240 Pg of peat carbon accumulated in the model in the areas north of 40° N. Simulated peat accumulation rates agree well with those reported for boreal wetlands. The model simulates CH4 emissions of 49.3 Tg CH4 yr−1 for 6000 yr BP and 51.5 Tg CH4 yr−1 for pre-industrial times. This is within the range of estimates in the literature, which range from 32 to 112 Tg CH4 yr−1 for boreal wetlands. The modelled methane emission for the West Siberian Lowlands and Hudson Bay Lowlands agree well with observations. The rising trend of methane emissions over the last 6000 yr is in agreement with measurements of Antarctic and Greenland ice cores.

Improving the 210Pb-chronology of Pb deposition in peat cores from Chao de Lamoso (NW Spain)

The natural radionuclide 210Pb is commonly used to establish accurate and precise chronologies for the recent (past 100–150years) layers of peat deposits. The most widely used 210Pb-dating model, Constant Rate of Supply (CRS), was applied using data from three peat cores from Chao de Lamoso, an ombrotrophic mire in Galicia (NW Spain). On the basis of the CRS-chronologies, maximum Pb concentrations and enrichment factors (EFs) occurred in the 1960s and late 1970s, consistent with the historical use of Pb. However, maximum Pb fluxes were dated in the 1940s and the late 1960s, 10 to 20 years earlier. Principal component analysis (PCA) showed that, although the 210Pb distribution was mainly (74%) controlled by radioactive decay, about 20% of the 210Pb flux variability was associated with atmospheric metal pollution, suggesting an extra 210Pb supply source and thus invalidating the main assumption of the CRS model. When the CRS-ages were recalculated after correcting for the extra input from the 210Pb inventory of the uppermost peat layers of each core, Pb flux variations were consistent with the historical atmospheric Pb deposition. Our results not only show the robustness of the CRS model to establish accurate chronologies of recent peat deposits but also provide evidence that there are confounding factors that might influence the calculation of reliable peat accumulation rates (and thus also element accumulation rates/fluxes). This study emphasizes the need to verify the hypotheses of 210Pb-dating models and the usefulness of a full geochemical interpretation of peat bog records.

A high resolution Holocene pollen record from Braamhoek, eastern Free State, South Africa

A report is given of a palaeoecological study based on the analysis of pollen and a variety of micro- and macrofossils and of the pollen density/influx of a section of peat deposits on marine clay from the Assendelver Polder (The Netherlands). The section, representing the time interval of approximately 4500—800 B.P., was studied at five-cm and one-cm intervals. A detailed reconstruction of the vegetational succession is given. The main phases of which the pertaining syntaxonomy is discussed comprise: (a) a Phragmites—Carex swamp formed under eutrophic conditions on top of marine sediments deposited during the Calais IVa transgression, ca. 4500—4200 B.P.; (b) a Thelypteris dominated swamp that prevailed during somewhat drier conditions; (c) a Phragmites–Carex swamp; (d) a Phragmites swamp accompanied by many herbaceous species during drier and less eutrophic conditions (total duration of phases a—d: from ca. 4200—ca. 2500 B.P.); (e) a Molinia fen developed under mesotrophic conditions (ca. 2500—2300 B.P.); and (f) an Ericaceae—Sphagnum and Eriophorum bog, developed during oligotrophic conditions (ca. 2300—1200 B.P.).Using 14C data, the absolute numbers of pollen grains and the bulk density of the subsamples of the upper meter of the deposit, the pollen influx, the approximate age, the net organic production (NOP) and the rate of peat accumulation was calculated. The mean NOP over the interval 2.68-1.97 m below NAP was 145.8 g m −2 yr −1, the highest NOP was found in Calluna—Myrica peat (311 g m −2 yr −1 and the lowest in Eriophorum peat (41.85 g m−2 yr−1) Peat accumulation was also calculated over the same interval. The calculated peat accumulation rate (CPAR) had a mean value of 0.0767 cm yr−1. The highest CPAR of 0.195 cm yr−1 was found in Calluna—Myrica ppeat and the lowest in Eriophorum peat: 0.017 cm yr−1. The mean duration in years of each subsample over the interval 2.62-1.97 m below NAP was 20.2 yr cm−1.Two layers of local human habitation were present. The one, consisting of a charcoal layer at a depth of 2.25 m below NAP, is of Roman Iron Age (ca. 1800 B.P.) and the other, consisting of a clayey layer on top of the peat deposit, from mediaeval time (ca. 12th century). Although the earliest direct evidence of human habitation at the site itself dates from about 1800 B.P., habitation close to the sampling site probably occured from about 2150 B.P. onward. From then on Man may have influenced the vegetation, mainly by the grazing of domestic animals resulting in a greater supply of nutrients. This could be related with the invasion of Myrica gale into the bog.

Do peatland microforms move through time? Examining the developmental history of a patterned peatland using ground‐penetrating radar

Using ground‐penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso‐scale surface patterning of microforms within a raised bog. Common offset GPR measurements were obtained along a 45‐m transect, at frequencies ranging from 100 to 900 MHz. We found that low‐frequency (central frequency < 240 MHz) GPR could not adequately represent the subsurface structures of the peatland because individual peat layers were too thin. However, more detailed high‐frequency measurements (central frequency ≥ 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9° between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.

Carbon isotope evidence for recent climate-related enhancement of CO 2 assimilation and peat accumulation rates in Antarctica.

Signy Island, maritime Antarctic, lies within the region of the Southern Hemisphere that is currently experiencing the most rapid rates of environmental change. In this study, peat cores up to 2m in depth from four moss banks on Signy Island were used to reconstruct changes in moss growth and climatic characteristics over the late Holocene. Measurements included radiocarbon dating (to determine peat accumulation rates) and stable carbon isotope composition of moss cellulose (to estimate photosynthetic limitation by CO 2 supply and model CO 2 assimilation rate). For at least one intensively 14 C-dated Chorisodontium aciphyllum moss peat bank, the vertical accumulation rate of peat was 3.9mmyr-1 over the last 30years. Before the industrial revolution, rates of peat accumulation in all cores were much lower, at around 0.6-1mmyr-1 . Carbon-13 discrimination (Δ), corrected for background and anthropogenic source inputs, was used to develop a predictive model for CO 2 assimilation. Between 1680 and 1900, there had been a gradual increase in Δ, and hence assimilation rate. Since 1800, assimilation has also been stimulated by the changes in atmospheric CO 2 concentration, but a recent decline in Δ (over the past 50-100years) can perhaps be attributed to documented changes in temperature and/or precipitation. The overall increase in CO 2 assimilation rate (13 C proxy) and enhanced C accumulation (14 C proxy) are consistent with warmer and wetter conditions currently generating higher growth rates than at any time in the past three millennia, with the decline in Δ perhaps compensated by a longer growing season.

Peat accumulation in drained thermokarst lake basins in continuous, ice‐rich permafrost, northern Seward Peninsula, Alaska

Thermokarst lakes and peat‐accumulating drained lake basins cover a substantial portion of Arctic lowland landscapes, yet the role of thermokarst lake drainage and ensuing peat formation in landscape‐scale carbon (C) budgets remains understudied. Here we use measurements of terrestrial peat thickness, bulk density, organic matter content, and basal radiocarbon age from permafrost cores, soil pits, and exposures in vegetated, drained lake basins to characterize regional lake drainage chronology, C accumulation rates, and the role of thermokarst‐lake cycling in carbon dynamics throughout the Holocene on the northern Seward Peninsula, Alaska. Most detectable lake drainage events occurred within the last 4,000 years with the highest drainage frequency during the medieval climate anomaly. Peat accumulation rates were highest in young (50–500 years) drained lake basins (35.2 g C m−2 yr−1) and decreased exponentially with time since drainage to 9 g C m−2 yr−1 in the oldest basins. Spatial analyses of terrestrial peat depth, basal peat radiocarbon ages, basin geomorphology, and satellite‐derived land surface properties (Normalized Difference Vegetation Index (NDVI); Minimum Noise Fraction (MNF)) from Landsat satellite data revealed significant relationships between peat thickness and mean basin NDVI or MNF. By upscaling observed relationships, we infer that drained thermokarst lake basins, covering 391 km2 (76%) of the 515 km2 study region, store 6.4–6.6 Tg organic C in drained lake basin terrestrial peat. Peat accumulation in drained lake basins likely serves to offset greenhouse gas release from thermokarst‐impacted landscapes and should be incorporated in landscape‐scale C budgets.

A dynamic model of wetland extent and peat accumulation: results for the Holocene

Abstract. Substantial deposits of peat have accumulated since the last glacial. Since peat accumulation rates are rather low, this process was previously neglected in carbon cycle models. For assessments of the global carbon cycle on millennial or even longer timescales, though, the carbon storage in peat cannot be neglected any more. We have therefore developed a dynamic model of wetland extent and peat accumulation in order to assess the influence of peat accumulation on the global carbon cycle. The model is based on the dynamic global vegetation model LPJ and consists of a wetland module and routines describing the accumulation and decay of peat. The wetland module, based on the TOPMODEL approach, dynamically determines inundated area and water table, which change depending on climate. Not all temporarily inundated areas accumulate peat, though, but peat accumulates in permanently inundated areas with rather stable water table position. Peatland area therefore is highly uncertain, and we perform sensitivity experiments to cover the uncertainty range for peatland extent. The peat module describes oxic and anoxic decomposition of organic matter in the acrotelm, i.e., the part of the peat column above the permanent water table, as well as anoxic decomposition in the catotelm, the peat below the summer minimum water table. We apply the model to the period of the last 8000 years, during which the model accumulates 330 PgC as catotelm peat in the peatland areas north of 40° N, with an uncertainty range from 240 PgC to 490 PgC. This falls well within the range of published estimates for the total peat storage in high northern latitudes, considering the fact that these usually cover the total carbon accumulated, not just the last 8000 years we considered in our model experiments. In the model, peat primarily accumulates in Scandinavia and eastern Canada, though eastern Europe and north-western Russia also show substantial accumulation. Modelled wetland distribution is biased towards Eurasia, where inundated area is overestimated, while it is underestimated in North America. Latitudinal sums compare favourably to measurements, though, implying that total areas, as well as climatic conditions in these areas, are captured reasonably, though the exact positions of peatlands are not modelled well. Since modelling the initiation of peatland growth requires a knowledge of topography below peat deposits, the temporal development of peatlands is not modelled explicitly, therefore overestimating peatland extent during the earlier part of our experiments. Overall our results highlight the substantial amounts of carbon taken up by peatlands during the last 8000 years. This uptake would have substantial impacts on the global carbon cycle and therefore cannot be neglected.