The chlorine stable
isotope analyses presented in this paper were measured using methyl-chloride gas
mass spectrometry. Aqueous chloride samples were diluted with chlorine-free
distilled water to a concentration of ~100 mg/L and acidified with ultrapure HNO3
acid to a pH of 2. Four-molar potassium nitrate solution equivalent to 10% of
the sample volume was added as buffer, and the solution was warmed to 85șC. The
samples were then treated with AgNO3 to precipitate chlorine as AgCl.
The precipitate was rinsed with 5% HNO3 and then dried carefully to
avoid photo degradation from light sources. Between 5 and 7 mg of dried AgCl
were transferred to a reaction vessel. An excess of CH3I was
introduced and reacted with the AgCl for 48 hr at 80șC to form CH3Cl.
The excess CH3I was separated and the CH3Cl purified using
a gas chromatograph. It was analyzed on a gas mass spectrometer (Sira 9) to
determine the isotopic ratio 37Cl/35Cl. Laboratory
precision for 
37Cl
is ±0.15
(1
standard deviation [STD], unless otherwise specified; Table
1). All samples were corrected to standard mean ocean chloride (SMOC),
the standard being run after every 8-10 samples. An internal standard labeled
EIL 90 is run monthly. Inter-lab comparisons of this standard and SMOCs at
Utrecht and Arizona provided acceptable results.
Deuterium analyses were
performed using a Micromass 602 mass spectrometer. Ten microlitres of water were
heated at 505șC for 3 hr on manganese metal in a Pyrex reaction vessel. The
reduced water liberates hydrogen/deuterium that was analyzed for isotopic ratio.
Laboratory precision for D
(1 STD) is ±2
(worst case); the average precision for this study was ±0.90
(1 STD, Table 1). Deuterium
results were corrected to a regression line drawn from standards run daily.
These standards are in-house laboratory waters whose values are based on the
International Atomic Energy Agency (IAEA) international standards standard mean
ocean water (SMOW), Standard Light Antarctic Precipitation (SLAP),
and Greenland Ice Sheet Precipitation (GISP) and are monitored yearly for
change. Like the IAEA standards the EIL waters cover a wide range (from EIL-14
[+10.4] to
EIL-15 [-492]).
The analytical work for Cl and D/H was carried out at the University of
Waterloo, Ontario, Canada. Samples for oxygen isotope analysis were prepared
from 1 to 2 mL aliquots by the standard carbon dioxide equilibration method
(Epstein and Mayeda, 1953). Results (Table
1) are expressed in delta notation ()
relative to the SMOW standard. Laboratory precision for 18O
is ± 0.1.
The standard used for oxygen is Vienna standard mean ocean water (V-SMOW).
Oxygen isotope analyses were run at the Geology Department of the University of
Tokyo; additional analyses were provided by the GMS-Laboratory, Department of
Geology, University of Bergen. Of the two data sets, the Tokyo values were used,
except for those sample depths for which no analyses were available from Tokyo.
The analyses from the Bergen lab showed a systematic difference of +1.16
compared to the Tokyo analyses, for which no explanation exists. The Bergen
values (Table 1; values in
italics) were corrected by this amount. All pore-water samples were stored in
glass ampoules.
The shipboard chlorinity determinations (Paull, Matsumoto, Wallace, et al., 1996) have been corrected for bromide and iodide concentrations measured after the cruise and possible seawater contamination estimated from sulfate content (Egeberg and Dickens, 1999). Only a subset of the shipboard Cl- analyses is included, mostly those for which also isotopic analyses are available.
