Carbonate dissolution and temporal abundances of Foraminifera in Long Island Sound sediments

Abstract

The dynamics of benthic Foraminifera assemblages can be used to examine carbonate dissolution processes in nearshore sediments and as a general assay of physical‐chemical factors affecting survival of juvenile benthos. Abundances of total Foraminifera (live and dead) fluctuate regularly throughout the year in Long Island Sound (LIS) mud deposits, with highest numbers in spring‐summer and lowest in winter. Essentially all forams disappear each year. Pore‐water undersaturation with respect to carbonate minerals coincides with periods of rapid disappearance of forams and suggests that these fluctuations reflect a balance between the rate of production‐recruitment and the rates of death and dissolution of the calcareous tests of the animals. Reworking by macrofauna in LIS central basin sediments inhibits accumulation or depletion of pore‐water solutes and is responsible for minimizing pore‐water carbonate saturation states. Quantitative estimates of seasonal patterns of foram dissolution with a simple mass balance model give a minimum average annual flux of Ca2+ in LIS sediments of ∼6 mmol Ca2+ m−2 d−1 (due solely to Foraminifera dissolution). Abandoned tests have a maximum mean residence time of ∼86±13 d. Dissolution‐precipitation of forams may significantly affect benthic ∑CO2 fluxes and likely accounts for a large proportion (>30%) during some seasons or at some locales. Other organisms with carbonate tests of similar size, particularly juvenile bivalves, may also be affected by periods of undersaturated pore waters. Conditions promoting dissolution of tests may represent an important source of mortality for calcareous meiofauna.