ESTIMATION OF PARTICLE (DIS)AGGREGATION RATES FROM THE JOINT INVERSION OF POC, Al, AND Ti CONCENTRATION DATA
ESTIMATION OF PARTICLE (DIS)AGGREGATION RATES FROM THE JOINT INVERSION OF POC, Al, AND Ti CONCENTRATION DATA
Abstract:
The processes of particle aggregation and particle disaggregation are of
paramount importance for the downward transport of particulate material
and of their chemical constituents through the oceanic water column.
Particle aggregation tends to increase the size of particles and thus to
enhance their gravitational settling speed, whereas particle
disaggregation redistributes material into the smaller size classes.
However, our current observational understanding of the rates of
particle (dis)aggregation in oceanic waters remains severely limited as
these processes are difficult to measure directly. Here, following the
work of R. Murnane and colleagues undertaken in the 1990s, we apply an
inverse method to fit the equations of a two particle size class model
to size-fractionated data of particulate organic carbon and lithogenic
material (Ti and Al) from the EXPORTS cruise in the eastern North
Pacific. The outcome of the fit is an estimate of apparent rate
constants of particle (dis)aggregation rates and of their uncertainties
in the upper 500 m of the water column at a number of stations and
depths sampled during the cruise. Our estimates represent the integrated
effects of all processes contributing to particle (dis)aggregation, in
contrast to other projects of the EXPORTS program that are dedicated to
a few of such processes. Our estimates of particle cycling rates deduced
from the inversion of chemical tracer data thus provide a valuable
quantitative constraint to which rates derived from other approaches
could be compared.
paramount importance for the downward transport of particulate material
and of their chemical constituents through the oceanic water column.
Particle aggregation tends to increase the size of particles and thus to
enhance their gravitational settling speed, whereas particle
disaggregation redistributes material into the smaller size classes.
However, our current observational understanding of the rates of
particle (dis)aggregation in oceanic waters remains severely limited as
these processes are difficult to measure directly. Here, following the
work of R. Murnane and colleagues undertaken in the 1990s, we apply an
inverse method to fit the equations of a two particle size class model
to size-fractionated data of particulate organic carbon and lithogenic
material (Ti and Al) from the EXPORTS cruise in the eastern North
Pacific. The outcome of the fit is an estimate of apparent rate
constants of particle (dis)aggregation rates and of their uncertainties
in the upper 500 m of the water column at a number of stations and
depths sampled during the cruise. Our estimates represent the integrated
effects of all processes contributing to particle (dis)aggregation, in
contrast to other projects of the EXPORTS program that are dedicated to
a few of such processes. Our estimates of particle cycling rates deduced
from the inversion of chemical tracer data thus provide a valuable
quantitative constraint to which rates derived from other approaches
could be compared.