N. J. Jenkins et al.: A comprehensive global oceanic dataset of helium isotope and tritium measurements 
A 
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Figure 4. Global ocean surface water (depth < 50 m) tritium concentrations (in TU) for selected latitude bands. 
congues emanating from mid-ocean ridges and other vol- 
canic edifices on the sea floor (see the map of the helium 
ısotope ratio anomaly at 2500 m depth in Fig. 8), driven by 
‘he roughly order-of-magnitude higher °He/*He ratio in the 
earth’s mantle compared to the atmosphere (Clarke et al., 
1969; Kurz and Jenkins, 1981; Kurz et al., 1982; Lupton 
and Craig, 1975). It was in fact the initial discovery (Clarke 
et al., 1969) that sparked continued interest in the oceanic 
distribution of helium isotopes. In contrast, one sees a dif- 
Wwww.earth-syst-sci-data.net/11/441/20 (4 
ferent pattern deeper down (4000 m, in Fig. 9), where one 
sees the relatively *He-impoverished bottom waters flowing 
northward into the abyssal Pacific. The ongoing survey of 
deep helium features on both basin and regional scales con- 
tinues today, particularly in support of “flux gauge” studies 
of other trace elements and metals influenced by seafloor 
hydrothermal processes (e.g., Jenkins et al., 2018a; Resing 
et al., 2015; Roshan et al., 2016). These are based on re- 
cent model-based estimates of the global flux of hydrother- 
Earth Syst. Sci. Data, 11, 441-454, 2019