Freeze-drying partially affects dead benthic foraminiferal shells in estuarine sediments

Abstract

Foraminiferal proxies are often used to understand both pollution and past climatic changes. The freeze-drying is a viable alternative to commonly used method of oven-drying to process marine sediments for foraminiferal studies. The freeze-drying has, however, not yet been tested to process estuarine sediments to study living benthic foraminifera. Here, we assess the difference, if any, in benthic foraminiferal population after processing the estuarine sediments by both direct wet sieving, and freeze-drying followed by wet sieving. The surface sediments were collected from the Zuari estuary, Goa, India. Both the living and dead benthic foraminifera were picked. The sediments contain a large number of reworked foraminifera. The absolute abundance of both the calcareous and agglutinated dead benthic foraminifera was consistently lower in the sediments that were freeze-dried before wet sieving, as compared to the samples that were directly sieved, without any pre-treatment. Interestingly, the absolute abundance of living benthic foraminifera, as well as that of calcareous and agglutinated foraminifera was similar in both the freeze-dried and directly processed samples. The lower dead benthic foraminiferal abundance in the freeze-dried sediments suggests, breakage of comparatively fragile, thin-walled foraminifera tests. Therefore, estuarine sediments can be freeze-dried before wet-sieving to study living benthic foraminifera. The freeze-drying may, however, reduce the dead benthic foraminiferal count in the estuarine sediments