Suitability of salt-marsh foraminifera as proxy indicators of sea level in Tasmania

This paper aims to establish whether contemporary salt-marsh foraminifera from eastern Tasmania are suitably related to elevation and can therefore be used to reconstruct past sea levels. A proxy reconstruction of recent sea-level change in Tasmania is potentially useful because in New Zealand a prominent early 20th century acceleration of sea-level rise has been documented which requires regional confirmation. Forty-three surface samples were collected from two salt marshes in the Little Swanport Estuary. Common species are: Trochammina inflata, Jadammina macrescens, Miliammina fusca, Trochamminita irregularis and Trochamminita salsa. The latter two species have been previously grouped together as T. salsa, but are distinguished here because they occupy distinct vertical niches. We performed regression analyses on the agglutinated foraminifera and their surface elevations using the software package C2 and tested the accuracy of various regression models by comparing predicted heights of the two transects with surveyed heights. We found that the surveyed heights are closely matched by elevations predicted by Weighted-Average Partial-Least-Squares (WA-PLS) models. These models predict sea level to within ± 0.10 m. PLS models showed favourable statistical parameters but were unreliable when used for predictions. Applications of PLS regression models in sea-level reconstructions therefore require caution. We compare our results with other studies from around the world and conclude that microtidal coastlines provide the most advantageous conditions for precise sea-level reconstructions.