Jeffrey J. Blackford

Proxy climate record for the last 1000 years from Irish blanket peat and a possible link to solar variability

Recent research has shown that ombrotrophic mires can yield a proxy climate signal based on changes in the degree of peat humification [1,2], and that oceanic margin sites show the most sensitive record [3]. We compare humification records for the last 1000 yr from two radiocarbon-dated blanket peat profiles from western Ireland, and show several corresponding periods of climatic fluctuations. Periods favouring reduced peat decomposition, suggestive of wetter and/or cooler climatic conditions, seem to coincide with periods of reduced sunspot activity and atmospheric14C anomalies. Whilst climatologists have continued to debate a link between solar variability on a century timescale and climate change, the exact nature of that link remains elusive [4–7]. The results from Ireland demonstrate that data derived from mires could be relevant to the debate as to the extent of solar forcing in natural climatic variability, and the curves shown provide a continuous record to add to previous evidence for the so-called ‘Medieval Optimum’ and ‘Little Ice Age’ [8]. The record may imply that, during the past millennium, climatic change at the oceanic margin of the northeast Atlantic largely corresponded to inferred variations in solar output.

Charcoal fragments in surface samples following a fire and the implications for interpretation of subfossil charcoal data

Abstract Following an uncontrolled fire in an area of heathland in SW England, surface samples were taken from selected positions. Charcoal concentrations, charcoal/pollen ratio and size-class frequencies were measured and the data from burned, unburned and forest areas are compared. Charcoal concentrations show distinct variability between closely-spaced samples, but despite this differences are shown between the burned and unburned areas. Selected size-classes are suggested as being appropriate for distinguishing between burned and unburned areas in palaeoecological studies. While in need of replication, these data should provide a basis for further studies of this type.

Palaeoenvironmental evidence for solar forcing of Holocene climate: linkages to solar science

Current concern over ‘greenhouse’ warming and possible human influence upon global climate has been countered by claims that recent advances in solar theory demonstrate a greater role than previously thought for solar forcing in recent climate change. This is still disputed for this century, but new evidence from a range of palaeoenvironmental indicators lends strong support to the notion that not only the long-term (105 to 103 years) climate changes of the Pleistocene but also short-term (101 to 102 years) climate changes in the Holocene may derive in large or small part from solar variability. Evidence from recent research into proxy climate records is reviewed and set in the context of recent advances elsewhere in studies of late Quaternary palaeoenvironments and in solar science.

Testing peatland testate amoeba transfer functions: Appropriate methods for clustered training-sets

Transfer functions are widely used in palaeoecology to infer past environmental conditions from fossil remains of many groups of organisms. In contrast to traditional training-set design with one observation per site, some training-sets, including those for peatland testate amoeba-hydrology transfer functions, have a clustered structure with many observations from each site. Here we show that this clustered design causes standard performance statistics to be overly optimistic. Model performance when applied to independent data sets is considerably weaker than suggested by statistical cross-validation. We discuss the reasons for these problems and describe leave-one-site-out cross-validation and the cluster bootstrap as appropriate methods for clustered training-sets. Using these methods we show that the performance of most testate amoeba-hydrology transfer functions is worse than previously assumed and reconstructions are more uncertain.

Volcanic impacts on the Holocene vegetation history of Britain and Ireland? A review and meta-analysis of the pollen evidence

Volcanic ash layers show that the products of Icelandic volcanism reached Britain and Ireland many times during the Holocene. Historical records suggest that at least one eruption, that of Laki in a.d. 1783, was associated with impacts on vegetation. These results raise the question: did Icelandic volcanism affect the Holocene vegetation history of Britain and Ireland? Several studies have used pollen data to address this issue but no clear consensus has been reached. We re-analyse the palynological data using constrained ordination with various representations of potential volcanic impacts. We find that the palynological evidence for volcanic impacts on vegetation is weak but suggest that this is a case of absence of evidence and is not necessarily evidence of absence of impact. To increase the chances of identifying volcanic impacts, future studies need to maximise temporal resolution, replicate results, and investigate a greater number of tephras in a broader range of locations, including more studies from lake sediments.

Holocene comment and reply Hekla-4 ash, the pine decline in Northern Ireland and the effective use of tephra isochrones: a comment on Hall, Pilcher and McCormac

In response to a paper by Blackford et al. (1992) which showed a coincidence between the deposition of Hekla-4 tephra and a decline of Pinus pollen in two northern Scottish sites, Hall et al. (1994) investigated the tephra/pine pollen relationship at two sites in Northern Ireland. We argue that their sites are inappropriate for such comparison because pine was effectively absent from Co. Antrim long before the deposition of Hekla-4. The opportunity is taken to make some additional points concerning the Irish data and the wider use of tephra isochrones.

Mesolithic Environments at Star Carr, the Eastern Vale of Pickering and Environs: Local and Regional Contexts

Abstract Star Carr in the eastern Vale of Pickering is an emblematic site for the British Early Mesolithic and for the development of wetland archaeology, being one of the first studies where scientific techniques of environmental reconstruction were integrated within an archaeological research strategy, allowing detailed understanding of site conditions and the environmental context of human activities. Pollen diagrams from Star Carr and around palaeo-Lake Flixton record natural woodland development in the early Holocene and a mosaic of productive wetland environments as the lake progressively filled with sediment. High resolution pollen and microscopic charcoal data show that the lake-edge reedswamp was regularly burned during the Mesolithic occupation. Deciduous forest spread across the Yorkshire region, but fire was an important diversifying factor during the whole of the Mesolithic period in most areas, particularly in the later Mesolithic in the Pennine and North York Moors uplands where concentration of fire-disturbance episodes at higher altitudes may have prevented woodland extending to the summit plateaux. In places repeated disturbance led to environmental degeneration. Detailed reconstruction of the environmental history of the Vale and the Yorkshire region allows Star Carr to be considered within conceptual models of Mesolithic economic strategies, land-use and settlement patterns.