The cold and windy Southern Ocean favors the exchange of CO2 with the atmosphere. At high latitudes (photo), a recent and persistent increase in winds has produced a saturation of the Southern Ocean sink for CO2. Photo: N.Metzl, August 2000, oceanographic cruise OISO-5. |
An
organic compound that smells like cabbage and has been called the “smell
of the sea” could be more sensitive to global climate change than commonly
believed.
In
a recent report, a Livermore researcher, along
with colleagues from Los Alamos and Oak
Ridge national laboratories and the New Mexico
Institute of Mining and Technology, found through computer modeling that
dimethyl sulfide (DMS) will increase significantly in certain parts of the
ocean and decrease in others if the world continues with a business-as-usual
fossil fuel dependency.
DMS,
a sulfur-containing compound that affects the heat balance of the Earth, is one
of the major precursors for aerosols and cloud condensation in the marine
boundary layer over much of the remote ocean. DMS is produced by marine
plankton and represents the largest source of natural sulfur emissions. Upon
reaching the atmosphere, DMS is converted into sulfate aerosols, which reflect
sunlight and can stimulate cloud formation.
“We
found that DMS is locally much more sensitive to climate change than in
previous modeling studies,” said LLNL’s Philip Cameron-Smith. “The
shift in emissions will change the heating patterns.”
The
Southern Ocean is a locale where the effects of global climate change are
noticeable. In this region, there is substantial biological production, carbon
drawdown and convective return of nutrients.
Using
climate simulations with a global ocean biogeochemical model, scientists looked
at the impact of present-day (355 ppm) and future (970 ppm) concentrations of
carbon dioxide in the atmosphere on DMS levels and emissions in the Southern
Hemisphere.
What
they found was quite a surprise: In the future scenario, the average DMS
emission to the atmosphere was 150% more than current levels in the Southern
Ocean. Team members found that sea ice changes and ocean ecosystem composition
shifts caused by changes in temperature, mixing, nutrient, and light regimes
caused the increase in DMS in their simulation.
“DMS
emissions in the Southern Ocean are significantly more sensitive to climate
change than previously thought,” Cameron-Smith said. “The melting of
the southern sea-ice has a large impact on DMS flux in the model, because it
opens up a lot of cold open water in which the DMS-producing plankton thrive
(particularly a species called Phaeocystis). This compensates for the warming
of the ocean in other areas where Phaeocystis stops growing so well.”
In
the future, scientists may have to consider how ocean acidification, which is
tied directly to climate warming, could affect the plankton community, and
therefore DMS production.
The
research appears in Geophysical Research Letters.
