Multi-proxy analysis of a late holocene sediment core from Swanpool, Falmouth, Cornwall

DN Henon, NM Matthews, PE O'Sullivan, L Slater, TSC Williams, MJ Nicholson, A Morris

Research output: Contribution to journalConference proceedings published in a journalpeer-review

Abstract

Microfossil (diatoms, palynomorphs), inorganic chemical and mineral magnetic analysis of a 4.5 m sediment core from the deepest part of Swanpool, Falmouth indicates that a sharp contact between oxidised brown laminated clays, and overlying black, anoxic laminated muds, records the change in lake physics, chemistry and ecology which followed lowering of lake level and connection to the sea in 1826. At the contact, marked changes in the subfossil diatom flora, in favour of taxa more tolerant of increased salinity, and an increase above the contact in authigenic phosphorus concentration, and a corresponding decrease in biogenic silica, occur. Changes in pollen stratigraphy indicate a decline in both frequency and concentration of arboreal taxa and grasses, and an increase in species of open, maritime habitat. Impact of mining upon Swanpool may be seen in peaks in sedimentary IRM/χ and heavy metal concentrations which occur mainly above the clay/mud contact. Although Swanpool mine was operational for about a century, its most active phase took place during the 1850s. In the deeper parts of the core, there are indications of other events, in the form of changes in the subfossil diatom flora and in frequencies of Myriophyllum pollen, which may be associated with marine influence on what was then essentially a body of fresh water. In the topmost sediments, concentrations of sedimentary authigenic phosphorus increase, as a result of remobilisation of the element owing to deoxygenation of the sediment water interface (SWI) after connection of the pool to the sea. Further variations in the diatom flora take place, and the curve for Pinus pollen expands, perhaps owing to planting of ornamental trees in nearby Falmouth.
Original languageEnglish
Pages (from-to)318-324
Number of pages0
JournalGeoscience in South-West England
Volume9
Issue number4
Publication statusPublished - 1 Dec 1999

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