This research uses single celled marine organisms called foraminifera, or ‘forams’, to understand how sea levels have changed through time. These organisms are about the size of a grain of sand, and produce shells called ‘tests’ that preserve in sedimentary environments like coastal salt marshes. In the salt marsh environment, forams are found in a clearly zoned pattern with certain species occurring in different parts of the intertidal zone, e.g., some species are restricted to the high marsh, on the other extreme some only occur down on the mudflats, and others inbetween. When sea levels rise and fall through time, the forams respond by adjusting their distribution, and when those forams die, they preserve in the sediments. Through the use of a mathematical model known as a transfer function, we are able to use this relationship to build a sea level curve. Salt marsh forams are widely used as reliable sea-level indicators, and when combined with sedimentological and geochemical data provide a powerful tool to understand the palaeoenvironmental evolution of these coastal environments. 

Of course, we already have data from tide gauges that tells us how sea levels have fluctuated through time. But these records are limited to the very recent past, so they don’t tell us anything meaningful about natural sea-level variability, or what sea levels were doing before humans began altering climatic patterns through industrialisation. 

Strachan, K.L., Hill, T.R., Finch, J.M., Barnett, R.L., Frenzel, P. (2017). Distribution of Salt-Marsh Foraminifera in Two South African Estuaries and Application. Journal of Coastal Research 33, 619-631. 

Strachan, K.L., Finch, J.M., Hill, T.R., Barnett, R.L., Morris, C.D. (2016). Environmental controls on the distribution of saltmarsh foraminifera from the southern coastline of South Africa. Journal of Biogeography 43, 887-898. 

Strachan, K.L., Hill, T.R., Finch, J.M., Barnett, R.L. (2015). Vertical zonation of foraminifera assemblages in Galpins salt marsh, South Africa. The Journal of Foraminiferal Research 45: 29-41. 

Strachan, K.L., Finch, J.M., Hill, T.R., Barnett, R.L. 2014. A late Holocene sea-level curve for the east coast of South Africa. South African Journal of Science 110: 74-82.