Testate Amoebae as Sea-level Indicators in Northwestern Norway: Developments in Sample Preparation and Analysis

Proxy based sea-level reconstructions are an important tool for defining past patterns of sea-level change and salt-marsh testate amoebae are a newly emerging proxy with high potential as sea-level indicators. This study develops existing analytical techniques concerned with the preparation and counting of testate amoebae for sea-level studies and demonstrates the predictive power of this group of micro-organisms. Two salt marshes in northwestern Norway were sampled for testate amoebae and multiple sub-samples were prepared using different procedures and count totals. Analytical efficiency can be improved upon by using a mild alkali, chemical disaggregant (5% KOH) to break up fibrous, salt-marsh peat and concentrate tests prior to counting. A count total of 100 individuals, rather than 150, can be used to make time gains with little or no loss of taxon information. The Norwegian salt-marsh testate amoebae showed strong zonation relative to tidal elevation. Key indicator taxa from the high marsh included Centropyxis cassis type, Cyclopyxis arcelloides type and Euglypha spp. Those from the low marsh included Difflugia pristis type and a distinctive morphotype of Centropyxis platystoma type. Combined, the two surface data sets from Norway were capable of predicting marsh surface elevations to within ± 0.09 m.