Laughing gas from the Pacific
three expeditions of the vessel METEOR. (© H. Bange, GEOMAR)
Although nitrous oxide emissions do not appear to be anything to be too overly concerned about, it is certainly no laughing matter – for nitrous oxide is one of the gases responsible for the greenhouse effect; and excess emissions would worsen the effects of global warming.
Besides being used by dentists as an anaesthetic gas, nitrous oxide – or chemically correct nitrous oxide – is also found in nature in large quantities. Its heat-absorbing properties means that it is a powerful greenhouse gas in the lower atmosphere, while at the higher levels in the atmosphere, it contributes indirectly to ozone depletion.
Until recently, the methods used for measuring oceanic nitrous oxide sources could only yield rough estimates. "A global assessment of nitrous oxide emissions [...] is difficult because we do not know exactly where and how much of it is produced in nature" said Damian Arévalo-Martínez, a marine chemist from GEOMAR Helmholtz Centre for Ocean Research Kiel.
The latest research – based on the findings of three expeditions using a new measurement technology – shows that the Southeast Pacific has been significantly underestimated as a source of nitrous oxide. In fact, the new data showed the highest ever measured nitrous oxide concentrations in the surface waters of the ocean.
Together with colleagues from GEOMAR and the Kiel University (Christian-Albrechts-Universität zu Kiel [CAU]), he presented their findings in the scientific journal Nature Geoscience.
Oxygen depletion also affects Nitrogen cycle
in the tropical oceans (© Geomar).
This movement of water brings much plankton growth close to the surface, which sinks on the water column upon death. Then, when this biomass decomposes, the microorganisms would consume more oxygen than what the surrounding waters could supply. As a result, the oxygen level drops.
Of all the tropical OMZs, the one in the Pacific is the largest. "We know that oxygen depletion also affects the nitrogen cycle and favours the production of nitrous oxide” said Arévalo-Martínez. During the expeditions, the scientists had the opportunity of periodically measuring the nitrous oxide concentrations in surface water for the first time.
"Before, the ship had to stop every few miles. We took seawater samples, analysed them and had data for one point only. With the new, continuous measurement method we get a lot more data, which also enables us to make better extrapolations for the whole area.” explained Bange.