Foraminifera, testate amoebae and diatoms as sea-level indicators in UK saltmarshes: a quantitative multiproxy approach

The vertical distribution of foraminifera, testate amoebae and diatoms was investigated in saltmarshes in the Taf estuary (south Wales), the Erme estuary (south Devon) and the Brancaster marshes (north Norfolk), to assess the use of multiproxy indicators in sea-level reconstructions, A total of 116 samples were subjected to regression analyses, using the program CALIBRATE, With duration of tidal flooding as the dependent variable. We found that the relationship between flooding duration and taxa was strongest for diatoms and testate amoebae and weakest for foraminifera. The vertical range of testate amoebae in saltmarshes is small. Their lower tolerance limit in present-day saltmarshes occurs where tides cover the marsh less than a combined total of 7 days (1.9%) in a year. However, they are important sea-level indicators because information for sea-level reconstruction is best derived from sediments that originate in the highest part of the intertidal zone. Diatoms span the entire sampled range in intertidal and supratidal areas, whereas the upper limit of foraminifera is found very close to the highest astronomical tide level. Local training sets provide reconstructions with higher accuracy and precision than combined training sets, but their use is limited if they do not represent adequate modern analogues for fossil assemblages. Although analyses are time consuming, a regional training set of all three groups of micro-organisms yields highly accurate (r(2) = 0.80) and precise (low value of root mean square error) predictions of tidal level. This approach therefore could improve the accuracy and precision of Holocene sea-level reconstructions. Copyright (C) 2001 John Wiley & Sons, Ltd.