Primary productivity in the Eastern Great Australian Bight during the summer/autumn upwelling season.

Data presented here form part of a study designed to examine the influence of seasonal coastal upwelling 
on primary and secondary productivity in the Eastern Great Australian Bight (EGAB), an area that supports 
an economically important sardine fishery. Results relate to research cruises conducted during the 
upwelling seasons of 2004 and 2005. The euphotic depth ranged from 31m to 90m and the surface mixed 
layer from 30m to 65m with a deep-water chlorophyll maxima associated with the thermocline. Surface 
chlorophyll concentrations ranged from 0-2.2 µg L-1. Maximum rates of photosynthesis saturated between 
69-99 umol m-2 s-1 but both Pb
max (0.178-0.237 mg C (mg chl)-1 hr-1) and photosynthetic efficiencies (α, 
0.0024-0.0026 mg C (mg chl)-1 hr-1 (umol m-2 s-1)-1) measured via 14C uptake were low compared with global 
estimates. Zooplankton grazing pressure was also generally low, suggesting something other than grazing was causing the low chlorophyll concentrations. Upwelling areas of the EGAB were rich in nitrogen and phosphorus (4-85 µg N L-1, 1-50 µg P L-1), and the addition of N and P did not stimulate the algal growth potential suggesting that something other than N and P may be limiting phytoplankton productivity in 
the area. Silica concentrations in the EGAB were well below levels that would be expected to limit phytoplankton growth (<1mg Si L-1), and it appears that an inadequate supply of silica is the most likely cause of low diatom productivity in the region