Reconstructing relative sea-level change using UK salt-marsh foraminifera

The position of past sea levels can be reconstructed using a series of sea-level index points that possess information on age, location, altitude, and a quantified vertical relationship with a former tidal frame (the “indicative meaning”). Whilst these points fix the altitude of relative sea-level at one instant in time, they provide no information on its variation between them. Here, a foraminiferal transfer function is used to reconstruct changes in water depth from fossil assemblages preserved within salt-marsh sediments. The transfer function performs reliably in the high marsh zone, where agglutinated foraminiferal species are dominant. In lower marsh environments where calcareous species are prevalent, postmortem test dissolution alters the fossil assemblages and leaves them without modern analogues. To circumvent this problem, a new transfer function based on agglutinated foraminifera and utilising preserved test linings is developed. This new transfer function significantly reduces the number of samples without modern analogues, but at the expense of diminished sensitivity in the low marsh environment. Additionally, the transfer function is used to establish a series of sea-level index points that place observed lateral shifts in depositional environment into a vertical and temporal context. The combination of age-altitude and high-resolution water-level reconstructions offers the potential to obtain more detailed and reliable records of relative sea-level change from salt-marsh sediments.