|
Titel |
Isotopic evidence for biogenic molecular hydrogen production in the Atlantic
Ocean |
VerfasserIn |
Sylvia Walter, Annette Kock, Tobias Steinhoff, Björn Fiedler, Peer Fietzek, Jan Kaiser, Maarten Krol, Elena Popa, Qianjie Chen, Toste Tanhua, Thomas Röckmann |
Konferenz |
EGU General Assembly 2017
|
Medientyp |
Artikel
|
Sprache |
en
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250152175
|
Publikation (Nr.) |
EGU/EGU2017-16983.pdf |
|
|
|
Zusammenfassung |
Oceans are a net source of molecular hydrogen (H2) to the atmosphere. The production of
marine H2 is assumed to be mainly biological by N2 fixation, but photochemical pathways
are also discussed. We present measurements of mole fraction and isotopic composition of
dissolved and atmospheric H2 from the southern and northern Atlantic between 2008 and
2010. In total almost 400 samples were taken during five cruises along a transect
between Punta Arenas (Chile) and Bremerhaven (Germany), as well as at the coast of
Mauritania.
The isotopic source signatures of dissolved H2 extracted from surface water are highly
deuterium-depleted and correlate negatively with temperature, showing δD values of
(-629±54) ‰ for water temperatures at (27±3) ˚ C and (-249±88) ‰ below (19±1) ˚ C.
The results for warmer water masses are consistent with biological production of H2. This is
the first time that marine H2 excess has been directly attributed to biological production by
isotope measurements. However, the isotope values obtained in the colder water masses
indicate that beside possible biological production a significant different source should be
considered.
The atmospheric measurements show distinct differences between both hemispheres as
well as between seasons. Results from the global chemistry transport model TM5 reproduce
the measured H2 mole fractions and isotopic composition well. The climatological
global oceanic emissions from the GEMS database are in line with our data and
previously published flux calculations. The good agreement between measurements and
model results demonstrates that both the magnitude and the isotopic signature of the
main components of the marine H2 cycle are in general adequately represented in
current atmospheric models despite a proposed source different from biological
production or a substantial underestimation of nitrogen fixation by several authors. |
|
|
|
|
|