Carolin Petry
Institute for Baltic Research, Seestr. 15, D-18119 Warnemünde, Germany
Particulate organic matter (POM) sinking from the surface water to the deep sea bottom is subjected to changing environmental conditions. Decreasing temperature and increasing pressure are factors that influence bacterial degradation processes associated with the particles. During cruise M33/1 in the Arabian Sea in autumn 1995 experiments were conducted to investigate how and how fast POM is degraded under these varying conditions. Fresh POM from surface water was incubated in the dark in plastic bags at 28, 17, 7 and 0-2°C under atmospheric pressure. Additionally, samples were incubated at 7°C and 300 atm to check for pressure effects. Bacterial secondary production (BSP, via 3H-thymidine incorporation) and potential enzyme activity (EEA, via fluorigenic model substrates at saturation concentrations) tended to decline with decreasing temperature. Pressure effects were not very strong with BSP and EEA except for peptidase activity which was reduced substantially at 300 atm. Changes of C/N ratios and concentrations of organic carbon and nitrogen were minor, especially in the cold water treatments. Another experiment was set up with fresh POM from surface waters (0-150 m), POM from an unpoisened sediment trap (500 m above the bottom) and "fluff" from sediment cores (4020 m). This experiment was designed to test whether the aging process during sedimentation affects enzyme activity on the particles, since POM collected in the deep water column and on the sediment has probably already been degraded to a certain extent. The proportions of potential enzyme activities of three different enzymes changed. The activities of b-glucosidase and chitobiase decreased with depth, while peptidase activity was higher in the deeper water.
