Photosynthetic parameters in water masses in the vicinity of the Chatham Rise, South Pacific Ocean, during late summer

The relationship between photosynthesis (P) and light (E) was determined for phytoplankton from the mixed layer and the deep chlorophyll maximum (DCM) at 23 stations off the east coast of New Zealand during February-March 1995. The stations encompassed three water masses, Sub-tropical, Sub-antarctic and the Sub-tropical Convergence Zone. The light-saturated rate of photosynthesis (P-max) and slope of the light-limited portion of the curve (alpha) were determined using a light gradient incubator. The absorption spectra of the phytoplankton assemblages were used to calculate the maximum quantum efficiency of photosynthesis (phi(max)). A higher mixed-layer P-max in Sub-tropical water over Sub-antarctic water (4.26 compared to 5.85 mg C (mg Chl.a)(-1) h-1) was consistent with the temperature difference of 4 degrees C, although there was also a taxonomic composition difference between these waters. The highest variability of P-max and alpha, as well as the highest P-max values, were seen within the STC, but ranges for all water masses overlapped. Physical conditions in the water masses were similar and no correlations between any measured physical or chemical feature of the stations and any P-E parameter could be identified.