Nineteen labs representing nine nations participated in the
GEOTRACES intercalibration initiative that determined
concentrations of 232Th, 230Th, 231Pa or 10Be in seawater,
suspended particles or sediments. Results generally demonstrated
good agreement among labs that analyzed marine sediments. Two
sets of seawater samples, aliquots of particulate material
filtered in situ, and/or aliquots of biogenic sediments were
distributed to participating labs. Internal consistency among
participating labs improved substantially between the first and
second set of seawater samples. Contamination was a serious
problem for 232Th. Standard Niskin™ bottles introduced no
detectable contamination, whereas sample containers, reagents
and labware were implicated as sources of contamination. No
detectable differences in concentrations of dissolved 232Th,
230Th or 231Pa were observed among samples of seawater filtered
through Nuclepore ™, Supor ™ or QMA™ (quartz) filters with pore
diameters ranging between 0.4 and 1.0 μm. Isotope