Cm. Turley et al., TRANSFORMATIONS OF BIOGENIC PARTICLES DURING SEDIMENTATION IN THE NORTHEASTERN ATLANTIC, Philosophical transactions-Royal Society of London. Biological sciences, 348(1324), 1995, pp. 179-189
The vertical flux and transformation of biogenic particles are importa
nt processes in the oceanic carbon cycle. Changes in the magnitude of
the biological pump can occur in the north eastern Atlantic on both a
seasonal and interannual basis. For example, seasonal Variations in ve
rtical flux at 47 degrees N 20 degrees W are linked to seasonal ocean
productivity variations such as the spring bloom. The size and organic
and inorganic content of phytoplankton species, their development and
succession also play a role in the scale and composition of the biolo
gical pump. The majority of flux is in the form of fast sinking aggreg
ates. Bacteria and transparent exopolymer particle production by phyto
plankton have been implicated in aggregate production and mass flux ev
ents. Zooplankton grazing and faecal pellet production, their size and
composition and extent of their vertical migration also influence the
magnitude of vertical flux. Aggregates are formed in the upper ocean,
often reaching a maximum concentration just below the seasonal thermo
cline and can be a food resource to mesozooplankton as well as to the
high concentrations of attached bacteria and protozoa. Attached bacter
ia remineralize and solubilize the aggregate particulate organic carbo
n. The degree of particle solubilization is likely to be affected by f
actors controlling enzyme activity and production, for example tempera
ture, pressure or concentration of specific organic molecules, all of
which may change during sinking. Attached bacterial growth is greatest
on particulate organic matter collected at 500 m which is the depth w
here studies of(210)po reveal that there is greatest break-up of rapid
ly sinking particles. Break-up of particles by feeding zooplankton can
also occur. The fraction of sinking poc lost between 150-3100 m at on
e station in the north eastern Atlantic could supply about 90 % of the
bacterial carbon demand. Some larger, faster sinking aggregates escap
e solubilization and disaggregation in the upper 1000 m and arrive in
the deep ocean and on the deep-sea bed. Seasonally varying rates of se
dimentation are reflected at the deep-sea floor by deposition of phyto
detrital material in summer. Approximately 2-4 % of surface water prim
ary production reaches the sea floor in 4500 m depth at 47 degrees N 2
0 degrees W after a sedimentation time of about 4-6 weeks. In this reg
ion, concentrations of chloroplastic pigments increased in summer by a
n order of magnitude, whereas seasonal changes in activity or biomass
parameters were smaller. Breakdown of the generally strongly degraded
organic matter deposited on deep-sea sediments is mainly accomplished
by bacteria. Rates of degradation and efficiency of biomass production
depend largely on the proportion of biologically labile material whic
h decreases with advancing decay. It is likely that different levels o
f organic matter deposition influence the bioturbation rates of larger
benthos, which has an effect on transport processes within the sedime
nt and presumably also on microbial degradation rates.