The late-Holocene history of Gormire Lake (NE England) and its catchment: a multiproxy reconstruction of past human impact

Abstract

Sedimentary evidence spanning the last 3500 years from cores taken from the centre of Gormire Lake, Cleveland, northeast England, points to two periods of deforestation and catchment erosion. The first, mainly late Iron Age/Romano-British phase, began c. 200 BC and ended c. AD 600. The second began c. AD 1200, the time of early Monastic activity, and continued into the nineteenth century. The chronology for the core rests on ¹³⁷Cs, ²¹⁰Pb and ¹⁴C measurements and on the history of lead accumulation in the sediments. The majority of the AMS ¹⁴C dates are shown to be too old to varying degrees, depending on the source of the organic matter in the sediments. The record of vegetation change is derived from pollen analysis. Evidence for changes in sediment composition and source and for catchment erosion comes from magnetic measurements, element analyses using XRF, and organic biogeochemical analyses. There is a high degree of coherence between all these lines of evidence. Interpretation of the magnetic record is complicated as a result of the formation of biogenic magnetite by magnetotactic bacteria, especially during periods of minimal erosion, by the presence of the authigenic magnetic sulphide greigite and by probable magnetite dissolution. Despite these modifications to the magnetic mineral assemblage in the sediments, magnetic indications of catchment erosion are clearly distinguishable, especially in the record of the antiferromagnetic minerals haematite and goethite. Partial estimates of catchment erosion rates are presented, based on the evidence from the sediments from the deepest part of the lake.