INCORPORATING SPATIAL AND TEMPORAL VARIABILITY OF SALT-MARSH FORAMINIFERA INTO SEA-LEVEL RECONSTRUCTIONS

Salt-marsh foraminifera have been widely used as proxies to reconstruct sea level because their modern distributions are strongly linked with tidal elevation. Although salt-marsh foraminifera are known to vary spatially at small (meter) scales, and temporally among seasons and years, this variability has not formally been included in the error term of transfer function based sea-level reconstructions.

Here, we present results of a three-year study of salt-marsh foraminifera to quantify spatial and temporal variability. Surface sediment samples were collected four times per year with replicate samples from four monitoring stations in an intertidal zone of southern New Jersey. The four monitoring stations encompass low to high marsh floral environments along a salinity gradient from 40 to 3 psu. Over 30,000 modern foraminifera consisting of 14 species from 144 samples show four distinct site-specific assemblage zones corresponding to the four monitoring stations. Station 1 was dominated by Trochammina inflata; Station 2 by Jadammina macrescens and Balticammina pseudomacrescens; Station 3 contained a mixed assemblage dominated by Tiphotrocha comprimata, B. pseudomacrescens, and Haplophragmoides spp; highest marsh Station 4 was dominated by J. macrescens. While overall species assemblages remained consistent among spatial replicate samples, relative abundances among those species varied up to 30% and standing crop varied up to 150 forams/5cm³ among replicates. Similarly, dominant species for each station remained consistent seasonally and interannually; however, relative abundances varied up to 30% and standing crop ranged from <50 to >400 forams/5cm³. The information gained from this study will be incorporated into a Bayesian transfer function that will adjust species response curves to formally account for spatial and temporal uncertainties when reconstructing elevations.