Primary production, biomass, size structure and nitrogen nutrition of phytoplankton in the Coral Sea (RV Franklin Cruise 05/85)

Brief description

Subsamples of water for chlorophyll analyses were taken from water samples collected in the upper 150 meters at most first leg stations. In addition to unfractionated subsamples (total population), portions of the subsamples were size-fractionated through 10 and 22μm screens to estimate the contributions of net- (>10μm), nano- (10-2μm) and pico-phytop1ankton <2μm) to total community biomass. These samples were frozen for analysis at a later time. Twenty-seven primary production experiments were carried out with size-fractionated phytoplankton populations using 14-C tracer methods. Experiments carried out on Leg 1 (n=21) focussed on estimating the magnitude of water column productivity and the relative contributions of net-, nano- and picoplankton to that productivity in the various areas covered by the hydrographic survey. Experiments carried out on Leg 2 (n=6) were designed to investigate the 1ight-dependent photosynthetic characteristics of near-surface and deep living populations of phytoplankton in the >2 and <2μm size classes. All chlorophyll analyses relevant to the first 21 experiments were analysed at sea and radioactivity levels for the first 24 experiments were counted at sea on the shipboard scintillation counter. The final three experiments were not counted due to exhaustion of scintillation cocktail supplies and were be counted ashore. The scintillation counter performed well throughout the cruise and a standard quench curve has been established for 14-C counted in AOUASOLII with a glass fibre filter and 100μl of 1N HCL in .glass mini-vials. The quench curve is stored in program AI. In conjunction with the productivity experiments, twenty submarine light penetration profiles were taken with a Biospherical Instruments 4m underwater light profiler. Subsurface light penetration values Here used to select sampling depths for primary production experiments. With the exception of more turbid inshore waters along the PNG coast, euphotic zone (> 0.5% surface irradiance) depths generally exceed 120 m. On one occasion, a secchi disk depth of 47 meters was recorded. Under normal good viewing conditions, secchi depths were generally between 35 and 40 m. Duplicate vertical zooplankton tows (60μm mesh) were made daily at each productivity station to obtain an estimate of zooplankton biomass and community structure in the euphotic zone. A limited number of tows were made at night to give comparative day/night changes. This research was undertaken during legs 1 and 2 of the RV Franklin Cruise 5/85. Leg 1 - 1/10/85 to 21/10/85 Leg 2 - 23/10/85 to 5/11/85

Lineage

Maintenance and Update Frequency: notPlanned

Notes

Credit
Furnas, Miles J, Dr (Principal Investigator)