Publication Date:
2019-07-16
Description:
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 yield monitors equilibrate with dissolved Th in seawater on a time scale of much
less than one day. Samples of filtered seawater acidified to a pH between 1.7 and 1.8
experienced no detectable loss of dissolved Th or Pa during storage for up to three years.
The Bermuda Atlantic Time Series station will serve as a GEOTRACES baseline station
for future intercalibration of 232Th and 230Th concentrations in seawater. Efforts to
improve blanks and standard calibration are ongoing, as is the development of methods to
determine concentrations of particulate nuclides, tests of different filtration methods, and
an increasing awareness of the need to define protocols for reporting uncertainties.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
peerRev
Format:
application/pdf
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