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 .

Over the past 50 years the most enigmatic feature of pollen diagrams from northwest Europe has been the mid-Holocene ‘elm decline’, and there has been much speculation as to the origin(s) and cause(s) of this event. A total of 150 radiocarbon dates from 139 sites spanning the elm decline in Britain and Ireland have been collated and scrutinized. Statistical analyses on 138 dates show that the event has a mean date of 5036 14C yr BP with a standard deviation of ± 247. Calibration of the dates and combining the sum probabilities yielded a range spanning 6347-5281 cal yr BP (1s), covering 1066 years. The start of the elm decline event lies between 6343 and 6307 cal yr BP (1s), a period of 36 years, indicating that the onset was rapid. The end of the event lies between 5290 and 5420 cal yr BP (1s), a period of 130 years. The probability distribution indicates that the elm decline was a uniform phased event across the British Isles. It appears that the elm decline can be explained to a large extent by the outbreak of disease. However, recent research on palaeoclimatic change and the nature of the transition from the Mesolithic to Neolithic in the British Isles suggests that both climatic change and human activities were implicated. It was probably the interplay between these factors, rather than any in isolation, that catalyzed the widespread, catastrophic decline of elm populations during the mid-Holocene.

Palaeohydrological and palaeoecological investigations from five locations in northern Scotland reveal a distinct and large-scale shift to wetter climatic conditions which may reflect a major transition in climate from the mid-to late Holocene. Radiocarbon age estimates place this transition between about 3900 and 3500 cal. BP, although the transition appears to have occurred abruptly, possibly over a decadal to century timescale. This event appears to be synchronous with changes inferred for other regions, suggesting that it reflects a continental-scale, or possibly even global-scale, change in climate. Broad correlation with deepsea sediment records suggests that the transition may reflect colder sea-surface temperatures in the North Atlantic Ocean.

Farming can be shown to have spread very rapidly across the British Isles and southern Scandinavia around 6000 years ago, following a long period of stasis when the agricultural ‘frontier’ lay further south on the North European Plain between northern France and northern Poland. The reasons for the delay in the adoption of agriculture on the north-west fringe of Europe have been debated by archaeologists for decades. Here, we present fresh evidence that this renewed phase of agricultural expansion was triggered by a significant change in climate. This finding may also have implications for understanding the timing of the expansion of farming into some upland areas of southern and mid-latitude Europe.