225
In this scenario, and in contrast to the hypothesis of Smetacek (1985) the phytoplankton cells are
actually dying under the stress of competition and hydrolytic attack; they may begin to autolyse
and lose their organic matter as DOM during descent through the water column. Our scenario
is not one of serene descent of phytoplankton escaping the vicissitudes of nutrient limitation in
the surface layer, but rather mass mortality on the hands of unforgiving and biochemically
- :0:
- - - ~- -
_. .
Aggregation
~ ._ • : 8 ..
- .. : ' -. ~ -. - - 0<
Fragmentation
I
:0: •
.- .
Sinking Flux
- 0<
~:.~ .
Figure 4. Cartoon depicting phytoplankton cells, producing extracellular mucopolysaccharides under nutrient stress,
aggregating and sinking. Bacterial mineralization and protozoan bactivory on these aggregates results in
intense mineralization supporting cryptic growth of some algal cells. These cells may avoid sinking out of
the euphotic zone as the aggregate fragments due to hydrolytic enzyme activity.
In this scenario, and in contrast to the hypothesis of Smetacek (1985) the phytoplankton cells are
actually dying under the stress of competition and hydrolytic attack; they may begin to autolyse
and lose their organic matter as DOM during descent through the water column. Our scenario
is not one of serene descent of phytoplankton escaping the vicissitudes of nutrient limitation in
the surface layer, but rather mass mortality on the hands of unforgiving and biochemically
- :0:
- - - ~- -
_. .
Aggregation
~ ._ • : 8 ..
- .. : ' -. ~ -. - - 0<
Fragmentation
I
:0: •
.- .
Sinking Flux
- 0<
~:.~ .
Figure 4. Cartoon depicting phytoplankton cells, producing extracellular mucopolysaccharides under nutrient stress,
aggregating and sinking. Bacterial mineralization and protozoan bactivory on these aggregates results in
intense mineralization supporting cryptic growth of some algal cells. These cells may avoid sinking out of
the euphotic zone as the aggregate fragments due to hydrolytic enzyme activity.