Freeze coring soft sediments in tropical lakes

A new freeze corer is described that is specifically designed for operation in warm tropical lakes. It combines the standard wedge-shaped freeze-on container with a 20-liter thermos from which pellets of solid CO₂ descend into the wedge to replace those that have sublimated. This extends the duration of effective freezing from ~20 to ~45 min, sufficient to form an adequate thickness of frozen crust in warm (> 22 °C) lakes and prevent its premature melting during retrieval through the water column. The instrument contains no electrical components, which simplifies construction, operation, and maintenance. The front and back surfaces of the freeze wedge are fitted length-wise with serrated ridges to facilitate removal of the crust as four rectangular sediment slabs. The feasibility of freeze coring studies in tropical regions is mainly determined by the local availability of a large-volume dry ice producer.