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 estu ary (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 t he relationship between flooding duration and taxa was strongest for diatom s and testate amoebae and weakest for foraminifera. The vertical range of t estate amoebae in saltmarshes is small. Their lower tolerance limit in pres ent-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 in dicators because information for sea-level reconstruction is best derived f rom sediments that originate in the highest part of the intertidal zone. Di atoms span the entire sampled range in intertidal and supratidal areas, whe reas the upper limit of foraminifera is found very close to the highest ast ronomical tide level. Local training sets provide reconstructions with high er accuracy and precision than combined training sets, but their use is lim ited if they do not represent adequate modern analogues for fossil assembla ges. Although analyses are time consuming, a regional training set of all t hree groups of micro-organisms yields highly accurate (r(2) = 0.80) and pre cise (low value of root mean square error) predictions of tidal level. This approach therefore could improve the accuracy and precision of Holocene se a-level reconstructions. Copyright (C) 2001 John Wiley & Sons, Ltd.