T. M. Mighall

Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa hill, Cwmystwyth, mid-Wales. UK

This paper presents geochemical data from a blanket peat located close to a Bronze Age copper mine on the northern slopes of the Ystwyth valley, Ceredigion, mid-Wales, UK. The research objective was to explore the possibility that the peat contained a geochemical record of the pollution generateD by mining activity. Four peat monoliths were extracted from the blanket peat to reconstruct the pollution history of the prehistoric mine. Three different geochemical measurement techniques were employed and four copper profiles have been reconstructed, two of which are radiocarbon-dated. The radiocarbon dates at one profile located close to the mine confirm that copper enrichment occurs in the peat during the known period of prehistoric mining. Similar enrichment of copper concentrations is shown in one adjacent profile and a profile within 30 m away. In contrast, copper was not enriched in the other radiocarbon-dated monolith, collected approximately 1.35 km to the north of the mine. Whilst other possible explanations to explain the copper concentrations are discussed, it is argued that the high copper concentrations represent evidence of localised atmospheric pollution caused by Bronze Age copper mining in the British Isles. The results of this study suggest that copper may be immobile in blanket peat and such deposits can usefully be used to reconstruct atmospheric pollution histories in former copper mining areas.

Linking changes in atmospheric dust deposition, vegetation change and human activities in northwest Spain during the last 5300 years:

A high-resolution, 5300-yr record of pollen and lithogenic elements (K, Ca, Ti, Rb, Sr, Y, Zr) from an ombrotrophic peat bog located in northwest Spain, reveals that the variations in the fluxes of lithogenic elements supplied to the bog by atmospheric deposition were coupled to the evolution of the vegetation of the area. A strong negative correlation exists between the percentage of tree pollen and the concentration of lithogenic elements. For example, the correlation between total tree pollen and Sr concentrations is - 0.94. The main phases of decline of the deciduous forest occurred during known cultural periods (late Neolithic, the Metal Ages, the Roman Period, the Middle Ages and the Industrial period) suggesting a close link between human activities (fires and forest clearances), changes in the vegetation and soil erosion. The flux of lithogenic elements seems to have increased before a significant variation in pollen is detected, which may indicate that changes in soil erosion are reflected earlier than the changes in vegetation in the bog record. Variations in the composition of the deposited dust reflect impacts that occurred at different spatial scales, with local sources dominant in the late Neolithic, the Metal Ages and the Middle Ages, whilst regional sources are more important in the Roman period and the Industrial Revolution. During the prehistoric period, arboreal pollen percentages recovered to their former levels, suggesting that woodland regenerated following a disturbance phase, but for the last 1400 years no significant recovery took place until afforestation with pines was introduced 200 years ago. While this must be the result of continuous clearances to convert forest into arable land, a cumulative effect on soil degradation must also be implied.

Sedimentology, palaeoecology and geochronology of Last Interglacial deposits from Deeping St James, Lincolnshire, England

Pollen, plant macrofossil, molluscan and coleopteran data from organic muds below the low terrace of the River Welland at Deeping St James, Lincolnshire indicate deposition in the mixed oak forest phase of a Late Pleistocene interglacial. Coleopteran and molluscan data suggest summer temperatures up to 4°C warmer than at present in eastern England, and plant macrofossil material suggests a climate more continental than that of Britain in the Holocene. No direct analogue of this biota, however, exists currently in Europe. Biostratigraphical indications from the pollen coleoptera and Mollusca suggest an age in the Ipswichian Interglacial. Thermoluminescence dates between 120 ka and 75 ka and amino-acid ratios with a mean of 0.11 show that deposition of the sediments took place during Oxygen Isotope Stage 5. This accurate dating of a partial Ipswichian succession allows discussion of the ages of a number of other interglacial sites in eastern England of assumed Ipswichian age. Copyright

An atmospheric pollution history for lead-zinc mining from the Ystwyth Valley, Dyfed, mid-Wales, UK as recorded by an upland blanket peat

This paper presents records of the atmospheric deposition of lead and zinc close to a former metal mining area as recorded by an upland blanket peat that has accumulated on the northern slopes of the Ystwyth valley, Dyfed, mid-Wales, UK. The research objective was to explore the possibility that the peat contained a geochemical record of the pollution generated by mining activity during the last four millennia. Four monoliths were extracted from the blanket peat to reconstruct the pollution history of lead and zinc mining. Three different geochemical measurement techniques were employed, and five lead and zinc profiles have been reconstructed, two of which are radiocarbon-dated. In the radiocarbon-dated monoliths lead enrichment occurs in the peat during the Roman occupation whilst both lead and zinc concentrations increase from the Mediaeval period until the early part of the 20th century. Similar enrichment of lead and zinc is shown in the remaining profiles. Whilst other possible explanations are discussed, it is argued that the high lead concentrations represent evidence of atmospheric pollution caused by mining. Zinc, however, may have suffered from post-depositional mobility. The results of this suggest that lead is largely rendered immobile in blanket peat and can be used to reconstruct atmospheric pollution histories in former lead mining areas.

Late Devensian and Holocene relative sea level and environmental changes from an isolation basin in southern Skye

Synopsis Detailed lithostratigraphical and biostratigraphical studies from an isolation basin at Inver Aulavaig on the Sleat Peninsula, Isle of Skye, Scotland, disclose changing environmental conditions during the Late Devensian and Holocene. In particular, they reveal three marine transgressions at the site since the Late Devensian, when the sea crossed the rock threshold at +5.10 mod. The radiocarbon dates obtained may incorporate hard water errors, but are considered broadly indicative of the ages of these events. The earliest event recorded at Inver Aulavaig, took place prior to c. 12600 14C bp and probably occurred soon after deglaciation as relative sea levels rose while the area was isostatically depressed. The second, which occurred between 8850±170 and 5440+50 14C bp, is correlated with the Main Postglacial Transgression. The third, which briefly took place between the statistically indistinguishable dates of 3160±40 and 3070±60 14C bp is believed to correlate with a widespread transgression recorded at several sites around the periphery of the Scottish glacio-isostatic uplift centre. The results would also appear to indicate that relative sea level in this area during the Younger Dryas did not exceed +5.10 mod.

Holocene relative sea levels and coastal changes in the lower Cree valley and estuary, SW Scotland, U.K.

Changes in Holocene (Flandrian) relative sea levels and coastal geomorphology in the lower Cree valley and estuary, SW Scotland, are inferred from detailed morphological and stratigraphical investigations. A graph of relative sea level changes is proposed for the area. Rising relative sea levels during the early Holocene were interrupted at c . 8300–8600 14 C years B.P.( c . 9400–9900 calibrated years B.P.), when an extensive estuarine surface was reached at c . −1 m O.D., after which a fluctuating rise culminated at c . 6100–6500 14 C B.P. ( c . 7000–7500 calibrated years B.P.) in a prominent shoreline and associated estuarine surface measured at 7·7–10·3 m O.D. A subsequent fall in relative sea level was followed by a rise to a shoreline at 7·8–10·1 m O.D., exceeding or reoccupying the earlier shoreline over much of the area after c . 5000 14 C B.P. ( c . 5,800 calibrated years B.P.), before relative sea level fell to a later shoreline, reached after c . 2900 14 C B.P. ( c . 3100 calibrated years B.P.) at 5·5–8·0 m O.D., following which relative sea levels fell, ultimately reaching present levels. During these changes, a particular feature of the coastline was the development of a number of barrier systems. The relative sea level changes identified are compared with changes elsewhere in SW Scotland and their wider context is briefly considered.

Holocene relative sea-level change in the lower Nith valley and estuary

Synopsis Detailed morphological, lithostratigraphical and biostratigraphical studies in the lower Nith valley and estuary, Scotland, disclose evidence for changing relative sea levels during the Holocene. The Main Postglacial Transgression was in progress in the area around c. 7500 14C years bp (8350 cal. years bp) to c. 7800 14C years bp (c. 8600 cal. years bp), perhaps by c. 7675 14C years bp (c. 8490 cal. years bp); relative sea levels fell briefly after c. 7200 14C years bp (c. 8020 cal. years bp); then resumed their rise after c. 7000 14C years bp (c. 7800 cal. years bp) and culminated by c. 590014C years bp (c. 6720 cal. years bp) reaching the Main Postglacial Shoreline, the evidence for which is widespread in the lower Nith valley. Subsequently, relative sea levels may have fluctuated, modifying or exceeding Main Postglacial Shoreline features along the estuary coastline before falling to a lower shoreline and then falling farther to reach present levels at c. 1760 14C years bp (c. 1800 cal. years bp), after which there is no evidence for relative sea-level change in the area. This sequence is considered broadly comparable with sequences recorded at other sites along the northern shore of the Solway Firth, in particular confirming evidence for a fluctuation in the Main Postglacial Transgression and for the age of the Main Postglacial Shoreline.

Early Holocene pollen and molluscan records from Enfield Lock, Middlesex, UK

Pollen, molluscan data, and sediment analyses, are presented from Enfield Lock, Middlesex, UK. The pollen data, from organic muds, show similarities with Pre-boreal and Boreal pollen spectra at other sites in the Thames basin; an overlying non-polleniferous marl yielded a diverse molluscan fauna. Radiocarbon dates on organic sediments at the site confirm the pollen records are from the early Holocene, but the shelly marl is less easily dated; there are affinities with molluscan records of the early to mid Holocene from sites elsewhere in southeast England. The biological and sedimentological data chronicle the changing depositional environments of the floodplain of the River Lea during four millennia of the early to mid Holocene. Charcoal records imply that fire was, at times, a significant influence on early Holocene vegetation, but a lack of local human artefacts contrasts with evidence for Mesolithic sites elsewhere, and has implications for the interpretation of early Holocene pollen assemblages from charcoal-rich sediments.

Intertidal peat deposits and early Holocene relative sea-level changes, Traigh Eileraig, Isle of Coll, Scottish Hebrides

Synopsis An intertidal organic deposit is described for Traigh Eileraig, Isle of Coll, Scottish Inner Hebrides. The organic sediments are overlain by sands containing marine diatoms. Radiocarbon dating and diatom analysis indicate that a relative marine transgression took place in Coll at c. 8000 14C years bp, an interpretation consistent with the results of pollen analysis of the organic material. The age and biostratigraphical interpretation of this relative marine transgression is in agreement with the results of sea-level research undertaken in recent years at Arisaig, western Scotland. However, the altitude at which the early-Holocene relative marine transgression is recorded in Coll is significantly lower than Arisaig, this difference reflecting the influence of differential glacio-isostatic uplift across the Inner Hebrides.