Diurnal variability of dissolved molecular hydrogen in the tropical South Atlantic Ocean
Abstract
In oligotrophic surface waters between 800 and 1600 km off Salvador, Brazil, molecular hydrogen concentrations were highly correlated with solar radiance levels, increasing during the morning to twice the night-time level and declining after noon. Regions to the south showed no evidence of diurnal periodicity, and profiles observed in the same region as the surface diurnal effect revealed a H 2 gradient within the mixed layer. Production of H 2 may be due to the nitrogenase activity of N 2-fixers, while the afternoon decline of H 2 levels may be explained by downward transport into the mixed layer accompanied by loss to the near-surface atmosphere. Observations of H 2 in the oceans show a strong relationship to in situ biological activity, particularly photosynthetic nitrogen fixation. Yet the dynamics of the relationships have up to now been masked by inadequate sampling and the long time constants of H 2 processes. The diurnal H 2 cycle is thus a phenomenon that may prove H 2 to be a sensitive chemical tracer of microbiological activity.
- Publication:
-
Deep Sea Research A
- Pub Date:
- January 1984
- DOI:
- 10.1016/0198-0149(84)90069-4
- Bibcode:
- 1984DSRA...31...13H