W. J. Jenkins et al.: A comprehensive global oceanic dataset of helium isotope and tritium measurements 
0 
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Figure 5. Four meridional tritium sections along roughly 52° W in 
the North Atlantic taken in 1982, 1997, 2003, and 2012. The tri- 
tium concentrations have been decay-corrected to a common time 
(1 January 1997) for comparison. Contour intervals are 0.2 TU97, 
and measurement uncertainties are of order 0.01 TUg97 or better. 
Due to differences in cruise tracks, the topography for the 1982 oc- 
cupation differs from the others. 
mal °He, which center around 550 mol yr7! (Bianchi et al., 
2010; Holzer et al., 2017; Schlitzer, 2016). This estimate can 
be usefully compared to the expected global flux of tritiu- 
genic He. The global tritium production by atmospheric nu- 
clear weapons tests has been estimated to be of order 3 GCi 
(Weiss and Roether, 1980, corrected from 1972 to 1963) to 
5 GCi (Michel, 1976). Given that the bulk of the tritium “im- 
pulse” entered the hydrologic system and subsequently the 
oceans within a decade or so, one can argue that the pro- 
duction rate of tritiugenic °He was of order 3000 mol yr”' 
in the mid-1970s. By the mid-1990s, this would be of or- 
der 1000 mol yr”!. Separating the two “types” of °He (tri- 
Augenic vs. primordial) in the Northern Hemisphere, where 
‘he bulk of the tritium delivery occurred (Doney et al., 1992; 
Weiss and Roether, 1980), is relatively simple in that the 
former appears largely at the sea surface, and the latter is 
concentrated in older, deeper waters. The separation in the 
Southern Hemisphere is not so simple. 
41 Data availabilitv 
[nformation about the underlying dataset can be found in 
Seect. 2.5. 
zarth Syst. Sci. Data. 11. 441-454. 2014 
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Figure 6. Four meridional 8°He sections along roughly 52° W in 
the North Atlantic taken in 1982, 1997, 2003, and 2012. Contour 
intervals are 1 %, and measurement uncertainties are 0.15 %. Due to 
differences in cruise tracks, the topography for the 1982 occupation 
differs from the others. 
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Figure 7. A time series of tritium (upper) and helium isotope mea- 
surements in the vicinity of Bermuda (North Atlantic). Tritium val- 
ves have been decay-corrected to a common time (1 January 1997). 
White dots indicate sampling depths and times. 
www.earth-svst-sci-data.net/11/441/2019