Reconstructing sea-level change in the Falkland Islands (Islas Malvinas) using salt-marsh foraminifera, diatoms and testate amoebae

Proxy records of past sea-level change provide a means of extending sea-level histories from tide gauges into the pre-industrial period. This is especially valuable in the South Atlantic region where sea-level data are limited to only a few tide-gauge records. Multi-proxy approaches to sea-level reconstruction are relatively rare but have distinct benefits when groups of micro-organisms are sparse or under-represented in modern or fossil sediments. Here, we address this challenge by utilising surface foraminifera, testate amoebae and diatoms from a salt marsh at Swan Inlet, East Falkland. All three micro-organism groups occupied distinct vertical niches in the contemporary salt-marsh. We investigated the relative performance of each group of micro-organisms in providing a sea-level reconstruction using individual (group-specific) regression models and with a multi-proxy regression model that combined all three groups. Foraminifera alone were not a suitable proxy. Surveyed sample elevations were closely matched by estimated elevations using Weighted-Average (WA) and Weighted-Average PartialLeast-Squares (WA- PLS) regressions. Relative sea-level reconstructions were derived by applying each model to microfossil assemblages recovered from a core (SI-2) from the same site. The combined transfer function yielded reconstructive precision (+/- 0.08 m) comparable to our best single-proxy transfer function (+/- 0.06 m) but only 18% of palaeo-samples were identified as having close or good analogues in the combined training data set. We highlight the benefit of a pragmatic approach to sea-level reconstructions whereby additional proxies should be employed if the use of only one proxy performs poorly across the width of the elevation gradient.

Automated summary

Proxy records of past sea-level change provide valuable information for extending sea-level histories into the pre-industrial period, especially in regions with limited sea-level data. The use of multi-proxy approaches, combining different micro-organisms, can improve the accuracy of sea-level reconstructions. In this study, surface foraminifera, testate amoebae, and diatoms from a salt marsh in East Falkland were utilized to reconstruct sea-level changes, with the combined multi-proxy regression model showing comparable reconstructive precision to the best single-proxy model.