Patterns in cumulative increase in live and dead species from foraminiferal time-series of Cowpen Marsh, Tees Estuary, UK: implications for sea-level studies

We have collected live and dead foraminiferal times-series data at 2-weekly intervals for a 12-month period from the intertidal zone of Cowpen Marsh, Tees Estuary, UK. The data from the 689 samples show profound differences between live and dead assemblages, although assemblages are dominated by just three species, Haynesina germanica, Jadammina macrescens and Trochammina inflata, which represent over 70% of the assemblage. The cumulative increase in species of most environments approximates to a lognormal or log series. None of the datasets show a broken stick pattern. The cumulative maximum number of species, which represents the species carrying capacity of the environment, is recorded earlier in the life assemblages than the dead counterparts. The dead assemblage of Cowpen Marsh is found to have a higher abundance (435 compared to 163 individuals/10 cm3) and number of species (52 compared to 28) than its live counterpart because the dead assemblage represents many generations added over a long period of time. In contrast, some species are recorded in the live dataset that were not found in the dead assemblage, indicating the dead record is either incomplete (e.g. taphonomic change) or inadequately sampled.

We investigated the influence of patterns in cumulative increase on dead assemblages for sea-level reconstructions through the development of foraminiferal-based transfer functions. The cumulative transfer functions suggest that the performance improves during the first six sample intervals of the time-series dataset with reconstruction differing by 1.2 m and remains constant thereafter.