A combination of particulate carbon analysis and a baking procedure to remove organic matter is proposed for separating total particulate carbon into inorganic and organic components. Changes in weight and carbonate‐carbon content were tested on powdered, anhydrous CaCO3 at 500° and 550°C and baking durations up to 7 h; the method was applied to field samples of particulate matter in seawater and microplankton net samples. The method is potentially useful for separating the carbon components, especially in coral reef environments or in calcium carbonate enriched sediments.

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Phytoplanktonconditions were examined at two stations off the leeward coast of Oahu, Hawaii. Significant temporal variability was observed in the chlorophyll and pheopigment data. Significant temporal and spatial variability was observed in the ATP and productivity data. Most (60-80%) of the microbial biomass occurred in the <3-pm fraction. Pigment profiles showed distinct subsurface maxima at 90 m. Annual primary production was estimated at 60.4 g C.m-2.yr-1, and low nutrient levels and P:B ratios indicated persistent nutrient limitation.Dissimilar inflection depths for nitrate, phosphate, and silicate indicated nitrate availability and phosphate limitation in the lower photic zone. Production between January and May was 11 x that between May and November; productivity below 44 m accounted for most of this variation. Biological and physical analyses indicate that variations in vertical nutrient supply, related to differences in current shear, caused this temporal variation.

Planktonic community respiration rates were assessed every 30 min through two 48-h periods in near-surface water taken automatically from a fertilized carthen pond and incubated in a plastic chamber for 2 1 min of each sampling cycle. Parallel records of water temperature, air temperature, windspccd, and solar irradiance permitted calculation of gross and net primary production and photosynthesis-irradiance relationships. Nighttime respiration rates generally matched oxygen depletion rates in pond water, indicating that incubation-based rates were representative of a quickly darkened pond community throughout the day. Daytime rates averaged nearly 2 times the mean night rate and 58% higher than the mean day rate determined by a typical interpolation used in free-water production calculations. Daily gross production ranged from 0.7 to 1.2 mmol 0, liter-l d I; respiration constituted 65-75% of gross rates. Gross oxygen production per unit Chl a during sampling intervals was light saturated at irradiance values >600 PEinst m-2 s-l, with an asymptotic value of 1.58 pmol 0, (kg Chl a) -I h I. This system and method were capable ofresolving respiration and gross and net production when chlorophyll concentrations were near 40 pg liter-l.