New Production and Nitrogen-15 Uptake Rates Measured during the JGOFS Equatorial Pacific Process Study

The Equatorial Pacific Process Study (EQPAC) was conducted along 140 deg W longitude during 1992. Four cruises took place: February 3 - March 9, March 19 - April 15, August 5 - September 18, and September 24 - October 21. A fifth benthic cruise and sediment trap legs were added. During the first cruise (TT007), 15 stations were occupied along 140 deg W longitude from 12 deg N latitude to 12 deg S latitude. During the second cruise (TT008), data were collected at 8 stations along 140 deg W longitude from 9 deg S latitude to 9 deg N latitude. During the third cruise (TT011), data were collected at 15 stations along 140 deg W from 12 deg N latitude to 12 deg S latitude. During the fourth cruise (TT012), data were collected at 5 stations along 140 deg W longitude from 17 deg S latitude to the equator. During the first and third cruises, 6-8 depths were sampled per station with the cable/rosette system for nitrogen-uptake measurements. Standard autoanalyzer techniques were used to determine nitrogen concentrations of each sample. Nitrogen-15 tracer was added to each sample at 10% of the ambient substrate concentration. The samples were incubated for 3-4 hours in simulated in situ conditions: subsurface light was approximated with a combination of neutral density and colored filters, and temperature was maintained +/- a few degrees C of the depth from which the sample was collected. Rates of nitrogen uptake were determined for labeled substrate of nitrate, nitrite and ammonium. In addition, F-ratios were calculated as follows: f = pNO3/(pNO3+pNO2+pNH4), where pNO2 is the N-15 uptake rate from nitrite labeled substrate, pNO3 is the N-15 uptake rate from nitrate labeled substrate, and pNH4 is the N-15 uptake rate from ammonium labeled substrate. The data is public domain and can be retrieved on-line at "http://usjgofs.whoi.edu/jg/dir/jgofs/" [The information in this summary was taken from the JGOFS World Wide Web pages.]