Submerged forests : a dendrochronological and palynological investigation
The distribution and nature of submerged forest beds are described, in particular those on the coasts of N.W. England, Wales, and the Bristol Channel. Present-day analogues of submerged forest vegetation are identified, and the relationship of coastal woodlands to tidal levels is discussed, as a necessary preliminary to the deduction of past sea levels, from the evidence provided by submerged forests. Experiments were carried out to determine the effect on seedling oaks of various tidal regimes of immersion in salt water. They proved to be little-affected, confirming observations of mature oaks in coastal woodlands, and suggesting that submerged forest trees grew at a lower relative level than has previously been assumed. The results of pollen analysis and radiocarbon dating of peat and wood (c3500-6000 B.P.) are given, for sites at Stolford (Bridgwater Bay, Somerset) and Clarach Bay and Borth (Cardigan Bay). Other sites are more briefly discussed, and evidence of human settlement is described. The relative dates of death of trees were determined by dendrochronological techniques, and the very precise chronology thus established is used to deduce the course of events. The extensive use of the trees in the calibration of radiocarbon dates is also described. Rapid increases in the organic content of sediments are shown to be possible when sea level rise slows to a critical rate: no fall in relative sea level need be invoked. Estimates are made of the past frequency of abnormally-high tides, and the “effective sea-level” resulting from these and other tidal effects is discussed, but the uncertainties involved are shown to be such that no great increase in the precision of determinations of past sea levels can be expected.