Extracellular enzyme activity in the Arctic Northeast Water polynya

Abstract

We studied extracellular enzyme activity (EEA) in samples of the water column and sediments of the Northeast Water polynya (77 to 81 N, 6 to 17' W) during July-August 1992 in order to determine controls on bacterial hydrolytic activity and possible roles of EEA in the fates of particulate organic matter (POM) on an arctic continental shelf. Samples were taken by Niskin bottle, floating sediment trap and box corer from the USCGC 'Polar Sea' at stations throughout the polynya and icecovered surroundings. Fluorogenic substrate analogs were used to estimate potential maximal rates of peptidase, chitobiase and lipase EEA in time course experiments over incubation periods of 1.3 to 14 h at -1, 2 , 5 , 10, and 16OC. Increasing incubation temperature typically increased EEA, but psychrophilic rates (little to no increase upon warming) were detected in several samples, usually for peptidase activity. Rates adjusted to in situ temperature (EEAIS) and normalized to bacterial abundance were compared to similarly determined rates reported previously for other (including temperate) environments and to each other. In general, EEAls rates in polynya waters were lower than in other pelagic environments, while rates in polynya sediments were comparable to those in other sediments. The whole polynya data set, which allows the first comparison between pelagic and benthic rates within a given environment, revealed that EEA, rates (usually peptidase activity), whether normalized to bacterial abundance or to sample dry weight, were generally higher in pelagic samples, particularly in samples from sediment traps deployed in the subzero Polar Surface Water mass. Although relationships between EEAls and temperature or several other environmental parameters (measured by other researchers on the Polar Sea) could not be identified, chitobiase and lipase EEA, did correlate positively, and peptidase activity negatively, with indicators of POM supply to the benthos (pigment concentrations). Observed differences in the effects of incubation temperature and environmental POM supply between enzymes may be explained by differences in location and regulation of peptidase and other EEA.