Surface coagulation and microbial respiration at a tidal front on Georges Bank

Abstract

In seawater taken from a depth of 10 m at a tidal front on the northeast quadrant of Georges Bank, the coagulation of organic material in the 1–10 μm size range onto bubble surfaces resulted in aggregates that were hundreds of μm across. This aggregation of larger colloidal material by surface coagulation resulted in a rapid increase of microbial respiration in the bubbled seawaters. In unbubbled controls mean respiration over 32 h increased along a transect of four stations, from the mixed layer of a stratified water column in the Northeast Channel through a tidal front at the edge of the bank to well-mixed, particle-rich water on the bank itself. Respiration was enhanced by surface coagulation to approximately the same absolute value at all stations but, when compared to the controls, enhancement decreased by over an order of magnitude from the Northeast Channel to well-mixed water on the bank. This reduced effect of surface coagulation in well-mixed water with high chlorophyll concentrations was probably related to increased respiration of labile organics associated with higher numbers of suspended particles. As a result, the effects of bubbling and surface coagulation may be of greater biological significance in seawater with lower numbers of suspended particles, such as those found in the Northeast Channel.