Thorium-234 Activity in Particulate and Dissolved Components 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.

Thorium-234 can be used as a tracer to estimate particle and carbon
fluxes and cycling rates. Water samples were collected by in situ
pump, the Slurper. At every station, samples were collected at the
surface. At long stations, samples were collected at discrete depth
levels. At intermediate and long stations, 0-100m composite samples
were collected.

In addition to gamma and beta counting to determine thorium
activities, CHN analysis was performed to determine particulate
organic carbon (POC) and particulate organic nitrogen (PON)
concentrations. Particulate thorium, POC and PON are fractionated into
2 size fractions: greater than 53 microns, and 1-53 microns.

Thorium-234 activities are measured in decays per minute per liter
(dpm/l). POC and PON are measured in micromoles per liter (umol/l).

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

[This information was obtained from the U.S. JGOFS website and from the
Cafe Thorium website at WHOI.]