Increased decomposition of subsurface peat in Swedish raised bogs:are temperate peatlands still net sinks of carbon?

An increased rate of decomposition has been observed in a large number of raised bogs in southern Sweden and elsewhere since the 1970s. The effect is manifest as a discoloured and mucous subsurface peat layer, and there is associated subsidence of mire surfaces. This paper reports the results of a systematic investigation of the phenomenon in 14 raised bogs in southern Sweden, which was carried out between 1997 and 2005. Degree of decomposition, bulk density and ash content were measured and evidence of surface subsidence over recent decades was collected. Shallow peat layers of ‘normal’ appearance could not be found anywhere within the study sites, and all showed the same signs of secondary decomposition. In particular, the ombrotrophic parts of the Komosse Bog Complex appeared to have subsided by at least 150 mm over the last 35 years, i.e. at a rate of approximately 4.3 mm per annum, which is more than four times the average rate of peat formation in circumboreal raised bogs. The changes observed could have been caused by change in any one of a number of factors, e.g. climate, hydrology and rate of nutrient supply; or by a combination of such factors. However it seems most likely that they are attributable to the heavy modern nutrient load, e.g. of dust from anthropogenic sources. There is cause for concern that many high-latitude peatlands may consequently have switched over from being net sinks, to net sources, of atmospheric carbon

Microscopic charcoal and tar (CHAT) particles in peat: a 6500-year record of palaeo-fires in southern Sweden

Peat stratigraphies of eleven raised bogs in southern Sweden were investigated. Measurements included the occurrence of charcoal and various tar particles. Most of the particles found were microscopic, i.e. 5–100 µm in diameter. Two distinctly different groups of particles were distinguished: (A) charred fragments of plant tissue and (B) objects formed from tar, which were classified into five sub-groups on the basis of morphology. Both charcoal and tar are indicative of mire and forest fires. We suggest that it is possible to use the different groups of particles as fire regime indicators. Hence, the high frequency of charcoal and tar (CHAT) in the lower parts of the stratigraphies, i.e. in the lower strongly decomposed fen and carr peats that were formed before ca. 4000 cal 14C BP, could be indicative of intense and frequent local fires. The decreasing abundance of CHAT and the lower relative share of Type A particles within the lower strongly decomposed Sphagnum peat ca. 4000–2500 cal 14C BP signify a transition from local to regional fires. With a few exceptions, the uppermost weakly decomposed ombrotrophic peats formed after ca. 2500 cal 14C BP, in which both charcoal and tar are rare, indicate a period of low fire frequency at both local and regional scales. There is no regional variation in the lower material, and it seems that wildfires were common phenomena throughout southern Sweden during the first few thousand years after peat formation began 6–8000 years ago. From a climatological point of view, the mass occurrence of CHAT in the lower parts of the profiles indicates a warm and dry Mid Holocene with frequent and widespread wildfires, and a moist and cool Late Holocene with more sporadic fires. Spectral analysis of the entire dataset shows significant periodicities of 610, 70, 30, 21, 17 and 14 years, the two most significant being 14 and 70 years

The potential peatland extent and carbon sink in Sweden, as related to the Peatland / Ice Age Hypothesis

Peatlands cover approximately 65,600 km2 (16 %) of the Swedish land area. The available areas suitable for peatland expansion are far from occupied after ca. 12,000 years of the present interglacial. We estimate the potential extent of peatland in Sweden, based on slope properties of possible areas excluding lakes and glaciofluvial deposits. We assume no human presence or anthropic effects, so the calculation is speculative. It may have been relevant for previous interglacials.We calculate the potential final area of peatlands in three scenarios where they cover all available land with different maximum slope angles (1−3 º) using a Digital Elevation Model (DEM). The three scenarios yield potential peatland areas of 95,663 km2 (21 % of total available area), 168,287 km2 (38 %) and 222,141 km2 (50 %). The relative increases from the present 65,600 km2 are 46, 157 and 239 % respectively.The slope scenarios give CO2 uptake rates of 8.9−10.8, 18.1−22.4 and 24.6−30.5 Mt yr−1. Under global warming conditions with isotherms moved northwards and to higher altitudes, following an increase of raised bog area, the CO2 uptake rates might increase to 12.2−13.8, 24.4−27.7 and 33.5−37.9 Mt yr−1; i.e. up to 4.3−4.9 vpb of atmospheric CO2. If we make the speculative extrapolation from Sweden to all high latitude peatlands, and assume that all suitable areas with slope angle ≤ 3 ° become occupied, the global peatland CO2 sink might approach 3.7 Gt yr−1 (about 2 vpm yr−1) and potentially cause a net radiative cooling approaching 5 W m−2

Carvalheiro2019Ecography_data

Dataset to run TREND function This file contains richness change values per cell obtained after running Multilevel.RAR_EXTR.r (https://github.com/lgcarvalheiro/richness.change/blob/master/Multilevel.RAR_EXTR.r) which were later used to run Trend.extractorV3 (https://github.com/lgcarvalheiro/richness.change/blob/master/Trend.extractorV3) and generate Figures published in Carvalheiro et al. 2019 (doi: 10.1111/ecog.04656) Note that bias due to differences in sampling effort is checked and corrected after running Trend.extractorV3, so this database is just an intermediate file and should not be used in other analyses or for plotting richness change values. For access to the original files (spatially and temporally explicit list of records) that were used to run Multilevel.RAR_EXTR.r please contact the authors. Dataset after running TREND function This file provides the corrected richness change values per cell for different time periods comparisons. This file was used to generate Fig 2 and Fig 3 of Carvalheiro et al. 2019 (doi: 10.1111/ecog.04656) and was used to run the analyses which generated Fig 4 of the same publication

Crinoids from the Silurian of Western Estonia

The Silurian crinoids of Estonia are re-evaluated based on new collections and museum holdings. Nineteen species-level crinoid taxa are now recognized. All crinoid names applied to Estonian Silurian crinoids during the middle 19th century are disregarded. Especially significant is the fauna reported herein from the Pridoli because coeval crinoids are very poorly known from the Baltic region and elsewhere. One new genus and four new species are described from Estonia, namely Calceocrinus balticensis sp. nov., Desmidocrinus laevigatus sp. nov., Eucalyptocrinites tumidus sp. nov., and Saaremaacrinus estoniensis gen. et sp. nov