3. Sulfur Cycling in Coastal Upwelling Systems
Dimethylsulfide
43
Dimethylsulfide is a volatile sulfur compound that forms the majority of
non-sea-salt sulfates (NSS-SO/-), which over ocean areas are almost
exclusively responsible for cloud condensation nuclei (CCN) (Charlson,
Lovelock , Andreae, & Warren, 1987). In addition to DMS, a wide range
of other sulfur compounds is derived from marine biogenic sources (e.g.,
hydrogen sulfide), but DMS and its precursor, dimethylsulfonium propionate (DMSP), usually predominate (Charlson et aI., 1987). Hedin and
Hetherington (this volume) note that sea salts are the major route by
which near-coastal terrestrial temperate rainforests acquire S04' though
marine emissions of DMS enhance atmospheric inputs of sulfur.
DMS is produced predominantly by marine phytoplankton; although
the first discussion of DMS occurred in 1935 (Haas, 1935) the precise
causes are still unclear. The factors affecting the production of DMS and
its effects upon the sulfur cycle and the earth's environment are still
poorly understood. In evaluating the causes of DMS production, the
quantities produced in different environments may be determined. The
factors affecting the production of DMS can be classified according to two
factors. Abiotic factors such as temperature and salinity indicate the
adaptive features of the phytoplankton to their environment. For
example, Iida, Nakamura, and Tokunaga (1985) partially purified an
enzyme from one phytoplankton species and noted that the optimum
temperature for the production of DMS from this enzyme is around 40°C
and the maximal pH is between 7.0 and 7.5. Vairavamurthy, Andreae,
and Iverson (1985) have shown that DMSP, the substance from which
DMS originates, may be associated with internal neutralization of phytoplankton's ionic charges, rendering their salty environment less of a toxic
hazard . However, it is unlikely that DMS is a buoyancy control, despite
the effect of different salinities on DMS production, as it is such a small
proportion of the total amount of the organic matter excreted (Barnard,
Andreae, & Iverson, 1984). In addition, as large amounts of sulfur reside
in the oceans, marine organisms must find a way to rid themselves of
excess amounts; excreting sulfur as a methylated compound ensures quick
removal in the form of a gas or vapor.
Biotic factors affecting DMS production include species type and predation ; yet information about this is still limited. Dacey (1987) proposed
that the rate of DMS release increases when phytoplankton are grazed by
zooplankton. However, Chameides and Davis (1982) proposed that DMS
may be a defense against predation ; this view is supported by observations
in the south Bering Sea (Barnard et aI., 1984). In addition, different
groups of phytoplankton produce different amounts of DMS; for example,
coccolithophorids have the highest rate of DMS excretion per unit biomass
(Charlson et aI., 1987).
Dimethylsulfide
43
Dimethylsulfide is a volatile sulfur compound that forms the majority of
non-sea-salt sulfates (NSS-SO/-), which over ocean areas are almost
exclusively responsible for cloud condensation nuclei (CCN) (Charlson,
Lovelock , Andreae, & Warren, 1987). In addition to DMS, a wide range
of other sulfur compounds is derived from marine biogenic sources (e.g.,
hydrogen sulfide), but DMS and its precursor, dimethylsulfonium propionate (DMSP), usually predominate (Charlson et aI., 1987). Hedin and
Hetherington (this volume) note that sea salts are the major route by
which near-coastal terrestrial temperate rainforests acquire S04' though
marine emissions of DMS enhance atmospheric inputs of sulfur.
DMS is produced predominantly by marine phytoplankton; although
the first discussion of DMS occurred in 1935 (Haas, 1935) the precise
causes are still unclear. The factors affecting the production of DMS and
its effects upon the sulfur cycle and the earth's environment are still
poorly understood. In evaluating the causes of DMS production, the
quantities produced in different environments may be determined. The
factors affecting the production of DMS can be classified according to two
factors. Abiotic factors such as temperature and salinity indicate the
adaptive features of the phytoplankton to their environment. For
example, Iida, Nakamura, and Tokunaga (1985) partially purified an
enzyme from one phytoplankton species and noted that the optimum
temperature for the production of DMS from this enzyme is around 40°C
and the maximal pH is between 7.0 and 7.5. Vairavamurthy, Andreae,
and Iverson (1985) have shown that DMSP, the substance from which
DMS originates, may be associated with internal neutralization of phytoplankton's ionic charges, rendering their salty environment less of a toxic
hazard . However, it is unlikely that DMS is a buoyancy control, despite
the effect of different salinities on DMS production, as it is such a small
proportion of the total amount of the organic matter excreted (Barnard,
Andreae, & Iverson, 1984). In addition, as large amounts of sulfur reside
in the oceans, marine organisms must find a way to rid themselves of
excess amounts; excreting sulfur as a methylated compound ensures quick
removal in the form of a gas or vapor.
Biotic factors affecting DMS production include species type and predation ; yet information about this is still limited. Dacey (1987) proposed
that the rate of DMS release increases when phytoplankton are grazed by
zooplankton. However, Chameides and Davis (1982) proposed that DMS
may be a defense against predation ; this view is supported by observations
in the south Bering Sea (Barnard et aI., 1984). In addition, different
groups of phytoplankton produce different amounts of DMS; for example,
coccolithophorids have the highest rate of DMS excretion per unit biomass
(Charlson et aI., 1987).