Climatic significance of the marginalization of Scots pine (Pinus sylvestris L.) c. 2500 BC at White Moss, south Cheshire, UK

Subfossil wood from White Moss, south Cheshire, has become the focus of palaeoenvironmental research employing not only conventional coring, pollen analysis, radiocarbon dating and dendrochronology on pine and oak, but also the exhumation of in situ peat areas and dendroecology of the pine ring-width records. Initial dendrochronological research at the site yielded five pine chronologies dating from 3520 to 2462 cal. BC. These and other data indicate three episodes of pine colonization of the mire in the period between 3643 and 1740 cal. BC. Comparison of the pollen and spore records suggest that pine became marginalized at the site c. 2500 cal. BC after successive episodes of increased wetness, and this may represent a staged response to climatic deterioration. Two oak chronologies were dated by reference to the Belfast and to English oak master chronologies to 3228-2898 BC and 2190-1891 BC, respectively, showing the possible co-existence of pine and oak on the mire for part of the time. Further dendrochronological work on subfossil pine at the site resulted in a chronology (WM4) that was cross-matched with pine from elsewhere in England, and subsequently dated absolutely to 2881-2559 BC. Detailed dendroecological information, such as fire episodes and periods of environmental stress indicated in the tree-ring records, have been assigned, precisely and accurately, to calendar years in prehistory. The detailed data show the potential for both dendroecological and wider palaeoclimatic and palaeoenvironmental information that may become available from prehistoric bog-pine chronologies, which might then permit precise correlation and comparisons of proxy-climate data between sites

Mineral deficiency and the presence of Pinus sylvestris on mires during the mid- to late Holocene: Palaeoecological data from Cadogan's Bog, Mizen Peninsula, Co. Cork, southwest Ireland

Pollen records across parts of Ireland, England and northern Scotland show a dramatic collapse in Pinus pollen percentages at approximately 4000 radiocarbon years BP. This phenomenon has attracted much palaeoecological interest and several hypotheses have been put forward to account for this often synchronous and rapid reduction in pine from mid-Holocene woodland. Explanations for the 'pine decline' include prehistoric human activity, climatic change, in particular a substantial increase in precipitation resulting in increased mire wetness, and airborne pollution associated with the deposition of tephra. Hitherto, one largely untested hypothesis is that mineral deficiency could adversely affect pine growth and regeneration on mire surfaces. The discovery of pine-tree remains (wood pieces, stumps and trunks) within a peat located at Cadogan's Bog on the Mizen Peninsula, southwest Ireland, provided an opportunity to investigate the history of Pinus sylvestris and also to assess the importance of mineral nutrition in maintaining pine growth on mires. Pollen, plant macrofossils, microscopic charcoal and geochemical data are presented from a radiocarbon dated monolith extracted from this peat together with tree ring-width data and radiocarbon dated age estimates from subfossil wood. Analyses of these data suggest that peat accumulation commenced at the site around 6000 years BP when pine was the dominant local tree. Thereafter Pinus pollen percentages diminish in two stages, with the second decline taking place around 4160 ± 50 years BP. Concomitant with this decline in Pinus pollen, there is a noticeable, short-lived increase in wet-loving mire taxa and a decrease in the concentration of phosphorus, potassium, magnesium, calcium, sodium, iron and zinc. These results suggest that increased mire surface wetness, possibly the result of a change in climate, created conditions unsuitable for pine growth c. 4000 years BP. Mire surface wetness, coupled with a period of associated nutrient deficiency, appears to be a possible explanation for a lack of subsequent pine-seedling establishment for most of the later Holocene

Location-dependent differences in the C-14 content of wood

The long C-14 chronologies currently used as calibration curves combine results from wood that grew in the western United States, the British Isles and Germany. Although these results show few significant differences in the C-14 content of contemporaneous wood when averaged over the length of the chronology (i.e, the means of overlapping sections of chronology are the same), closer examination shows considerable variability. Separating the sections of chronology according to the provenance of the wood used for calibration reveals patterns that suggest small but finite differences in the C-14 content of wood from different locations. We conclude that there is some evidence that German and American wood give dates older by between 20 and 40 yr from those of Irish oak for some periods. Additionally we suggest that the shift of the Belfast 1986 calibration data by ca. 18yr toward older dates may not be valid and that the resultant offset between the Belfast 1986 and Seattle 1993 data shows a small but real difference in the C-14 content of contemporaneous American, German and Irish wood. Intralaboratory measurements made in Belfast on contemporaneous German and Irish oak, and bristlecone pine and Irish oak, give offsets of 39 and 41 yr, respectively, with the Irish oak dating younger. Previous studies, in which sample pairs of American and English and French wood were processed in the same laboratory, also showed American wood to be slightly depleted in C-14. None of the findings of this study would significantly alter calibrated C-14 dates

Subfossil European bog oaks: population dynamics and long-term growth depressions as indicators of changes in the Holocene hydro-regime and climate

Some 2600 bog oaks have been dated from German, Dutch and Irish bogs covering the period 6000 bc to ad 1000. The ring patterns of these ‘bog oaks’ are characterized by recurrent, long-term growth depressions. In addition, obvious changes in the temporal distribution of the bog-oak trunks throughout the Holocene are found. Both features were probably caused by unfavourable growth conditions, which are most likely linked to changes in site hydrology.We use a new variable, ‘annual mean age’, as a tool to analyse the population dynamics of bog oaks in more detail, enabling the detection of synchronous intersite and interregional changes. It is calculated as the arithmetic mean of the age of all trees in each calendar year. We performed the calculation on regional (Germany, The Netherlands, Ireland) subsets of the bog-oak series. Abrupt changes in annual mean age are taken to indicate periods of generation change. We Ž find good agreement for the interval from 5000 bc to 2000 bc between the continental (combined German and Dutch) and the Irish mean-age chronologies. Most changes in population dynamics correspond with contemporary changes in the associated regional tree-ring chronologies. It is concluded that the observed changes in population dynamics and growth activity are responses to common environmental forcing, most likely related to climate

Calibration of the Radiocarbon Time Scale for the Southern Hemisphere: AD 1850-950

We have conducted a series of radiocarbon measurements on decadal samples of dendrochronologically dated wood from both hemispheres, spanning 1000 years (McCormac et al. 1998; Hogg et al. this issue). Using the data presented in Hogg et al., we show that during the period AD 950–1850 the 14C offset between the hemispheres is not constant, but varies periodically (~130 yr periodicity) with amplitudes varying between 1 and 10‰ (i.e. 8–80 yr), with a consequent effect on the ¹⁴C calibration of material from the Southern Hemisphere. A large increase in the offset occurs between AD 1245 and 1355. In this paper, we present a Southern Hemisphere high-precision calibration data set (SHCal02) that comprises measurements from New Zealand, Chile, and South Africa. This data, and a new value of 41 ± 14 yr for correction of the IntCal98 data for the period outside the range given here, is proposed for use in calibrating Southern Hemisphere ¹⁴C dates

ADVANCE-10K: a European contribution towards a hemispheric dendroclimatology for the Holocene

This editorial introduces a special issue of The Holocene containing 12 papers which represent highlights from a European Commission research project: ‘Analysis of Dendrochronological Variability and Associated Natural Climates in Eurasia – the last 10000 years’ (ADVANCE-10K). The focus is on the climatic implications of dendrochronology and especially on developing an integrated, dendrochronological approach to high-resolution climatic reconstruction in the Holocene, with the ultimate aim of extending this to the global scale. Emphasis is given to: (1) long chronologies from northern Fennoscandia (pine), temperate central and western Europe (oak) and Siberia (larch); (2) the precise climatic signals reflected in these chronologies and possible links to atmospheric circulation patterns; (3) complementary methodologies for extracting climatic information from subfossil trees in a variety of different environmental settings; and (4) the use of a large (subhemispheric) network of tree-ring density data to examine detailed, geographical patterns in climatic varia bility at a high temporal resolution. These studies are placed in their wider context and future directions for research in this field are also highlighted