Meridional distribution of molecular hydrogen and its deuterium content in the atmosphere

Abstract

The atmospheric molecular hydrogen concentration and its deuterium abundance were measured in remote air samples collected onboard six Pacific Ocean ship transects between 37°N and 77°S during years 2001 through 2005. The data reveal a year‐round interhemispheric gradient in H2 concentration and isotopic composition with the extratropical Northern Hemisphere lower in H2 concentration by 17 ± 11 ppb and δD of H2 by 16 ± 12‰ than the Southern Hemisphere (95% confidence). On the basis of these snapshots, the interhemispheric gradient in δD was observed to be smallest in September through November, a time that experiences the largest gradient in concentration, and the largest in April, a time that has a small gradient in concentration. A simple hemispheric box model of the atmosphere indicates that, while the hemispheric asymmetry in soil sink of H2 is primarily responsible for the observed interhemispheric gradient in H2 concentration, the hemispheric difference in the δD of the H2 sources and sinks are equally responsible for the observed interhemispheric gradient in δD. Both the inverse correlation between interhemispheric H2 and δD gradients and their seasonal changes point to the importance of the H2 produced by photochemical sources. Comparisons with a three‐dimensional chemical transport model shows reasonable agreement with mean behavior in both variables and provides an accounting for H2 sources and sinks within ±15% without a dramatic change in the H2 budget. Anomalous H2 concentrations and δD in tropics and low‐latitude regions observed during the November–December 2001 meridional H2 and δD snapshot is thought to be a result of H2 emissions from biomass burning, possibly from continental Africa.

The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft

“…Recently, isotope effects in the production processes of H 2 have been studied (Gerst and Quay, 2001;Rahn et al, 2002bRahn et al, , 2003Röckmann et al, 2003;Rhee et al, 2006a;Feilberg et al, 2007;Rhee et al, 2008;Röckmann et al, 2010a,b;Vollmer et al, 2010;Walter et al, 2011;Haumann et al, 2012), as well as the isotope effects in the H 2 uptake by soils (Gerst and Quay, 2001;Rahn et al, 2002a;Rice et al, 2011). Two chemical transport models have been adapted to incorporate the stable isotopic composition of H 2 , namely GEOS-CHEM (Price et al, 2007) and TM5 (Pieterse et al, 2009(Pieterse et al, , 2012, and many more δD data have become available for the validation of such models (Rice et al, 2010;Batenburg et al, 2011). However, for obvious practical reasons, most of these data were collected at ground level, and yield little information about processes higher up in the atmosphere, particularly in the Upper TroposphereLower Stratosphere (UTLS) region.…”

“…Not only are some altitudes underrepresented in the published δD data, also some regions of the world are not well covered. Previously published data were mostly from samples collected at two stations at the west coast of North America and on Pacific Ocean transects (Gerst and Quay, 2000;Rice et al, 2010), or at stations in Europe and the polar regions . Data from other regions, such as South Asia, are scarce.The aim of analyzing data from the CARIBIC program is to close both the altitudinal and the regional gap in the observations.…”

Isotopic signatures of production and uptake of H<sub>2</sub> by soil

“…The δD soil values (−629 to −451 ‰) shown in Table 2 are less depleted than the H 2 in isotopic equilibrium with water (≈ −700 ‰). Previous observations from environmental H 2 production yielded a δD of −628 ‰ for two seawater samples (Rice et al, 2010), −778 ‰ for a termite headspace sample and −690 ‰ for two headspace samples from a eutrophic water pond (Rahn et al, 2002b). Kawagucci et al (2010) proposed that microbiological H 2 consumption and production could destroy the thermal isotopic equilibrium between H 2 and H 2 O in low-temperature hydrothermal fluids.…”

“…The δD values are usually given in per mill (‰). Recent studies showed that the global mean δD value of atmospheric H 2 is about +130 ‰ Quay, 2000, 2001;Rice et al, 2010).…”

The stable isotopic signature of biologically produced molecular hydrogen (H<sub>2</sub>)

“…Tropospheric H 2 is enriched in deuterium with δD ∼ +130 ‰, (Gerst and Quay, 2001;Rhee et al, 2006;Rice et al, 2010;Batenburg et al, 2011) compared to surface emissions from fossil fuel combustion and biomass burning (δD approximately −200 ‰ and −300 ‰, respectively) (Gerst and Quay, 2001;Rahn et al, 2002;Röckmann et al, 2010a;Vollmer et al, 2010). As originally proposed by Gerst and Quay (2001) from budget closure, the photochemical sources of H 2 are also enriched in deuterium with δD between ∼ +100 ‰ and +200 ‰, (Rahn et al, 2003;Röckmann et al, 2003Röckmann et al, , 2010bFeilberg et al, 2007;Nilsson et al, 2007Nilsson et al, , 2010Pieterse et al, 2009 (Novelli et al, 1999;Hauglustaine and Ehhalt, 2002;Ehhalt and Rohrer, 2009;Pieterse et al, 2011) the extreme deuterium depletion relative to ambient atmospheric H 2 makes it a quite important contributor to the isotope budget (Price et al 2007;Pieterse et al 2011).…”