2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 41-13
Presentation Time: 9:00 AM-5:30 PM


VERLAAK, Zoe R.F.1, COLLINS, Laurel S.1 and ALLEN, Joshua2, (1)Department of Earth and Environment, Florida International University, Miami, FL 33199, (2)Department of Earth and Environment, Florida International University, 11200 SW 8th St, Miami, FL 33199, zverl001@fiu.edu

This study quantifies the influence of deep-dwelling benthic foraminifera on down-core foraminiferal samples for their use in reconstructing paleoenvironments of the Everglades, a habitat threatened by sea-level rise and saltwater intrusion. Inferring environmental preferences of subfossil foraminiferal assemblages entails making the assumption of similarity to modern distributions. Studying modern distributions commonly involves sampling the upper 1 cm of sediment. However, infaunal species can live at greater depths, which can form issues when abundances are large or when different species assemblages occur at these depths compared to the surface sediment. Deeper infaunal individuals will eventually also end up in the subfossil record, but will be overlooked when collecting recent samples that contain only the upper 1 cm of sediment. Therefore, one needs to have a thorough understanding of the vertical distribution and abundances of living (stained) benthic foraminifera before making interpretations based on modern foraminiferal surface assemblages. To study the vertical distribution, we collected eight 30-cm-long surface cores using a 5-cm-in-diameter Russian corer from four sites along the Shark River (west coast) and a 13-cm-long core at Garfield Bight (south coast). The Garfield Bight core was sampled every 1 cm, the other cores were sampled every 1 cm down to 10 cm, then with intervals of 2, 4, or 5 cm, and preserved in an 85% buffered alcohol solution. Each sample was stained overnight with rose Bengal, rinsed over nested screens of 2.80 mm and 63 µm, and split into subsamples using a wet splitter. Live (stained) individuals were picked and sorted onto slides for identification, while dead individuals were counted according to wall type. Preliminary results show that for Garfield Bight, the top 1 cm of sediment contains 0.94% of live foraminifera. Deep infaunal live foraminifera occur sparsely at greater depths, e.g., at 12-13 cm and 11-12 cm, where they make up <0.2% of the total (live + dead) assemblage. The final results will determine if large abundances of live individuals occur at greater depths, as well as which species occur alive at different depths, to improve accuracy in interpreting Everglades paleoenvironments.