Nitrogen-15 Uptake, F-ratio, Ammonium Concentration, and Low-level Nitrate Concentration Measured during the U.S. JGOFS Arabian Sea Process Study

A component of U.S. Joint Global Ocean Flux Study (JGOFS) is the
Arabian Sea Process Study. Eleven cruises took place aboard the R/V
Thomas G. Thompson for about sixteen months from October 1994 until
January 1996. These cruises provided seasonal coverage of the annual
monsoon and inter-monsoon cycles in the area southeast of Oman - from
where the cruises were staged. The monsoons of the Arabian Sea drive
a uniquely intense carbon cycling system, and it is the goal of JGOFS
to better understand the role of the oceans in global carbon cycling.

Biological uptake of nitrogen was determined by labeling substrates
with nitrogen-15. Water samples were obtained with the trace
metal-clean rosette bottle sampler.

Depth profiles of nitrogen-15 uptake rates are available for nitrite
(NO2) labeled substrate, nitrate (NO3) labeled substrate, and
ammonium (NH4) labeled substrate. N-15 uptake rate units are in nMol
N /kg/h.

Areal summary data reflect corrections to the profile data and a
reassessment of the diel cycle for nitrogen uptake. The profile data
are integrated (1% Io) daily to create the areal summary. Units for
nitrogen-15 uptake areal summaries are in mMol N /m^2/day.

F-ratio data are calculated as follows: pNO3/(pNO2+pNO3+NH4), where p
is the N-15 uptake rate from the indicated substrate.

Depth profiles of ammonium concentration are also available. These
are high sensitivity data of ammonium in the euphotic zone, with a
detection limit of 0.002 micro molar.

Depth profiles of low-level (nanomolar range) nitrate concentrations
are also available.

The data is public domain and can be retrieved on-line at
"http://usjgofs.whoi.edu/jg/dir/jgofs/"

[This information was obtained from U.S. JGOFS website at WHOI.]