Abstract
The aim of this thesis was the study of respiration in ocean margin
sediments and the assessments of tools needed for this purpose.
The first study was on the biological pump and global respiration
patterns in the deep ocean using an empirical model based
on sediment oxygen consumption data. In this thesis the depth
dependence
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of respiration patterns was modelled using a compiled data
set of sediment oxygen consumption rates. We showed that the depth
relationship can best be described by a double exponential model. By
assuming a uniform flux laterally across the global ocean the depth
attenuation of POC could be derived. The results from this study imply
a more efficient biological pump.
The second study was on the short-term fate of phytodetritus,
investigated across the Pakistan margin of the Arabian Sea. Stations
ranged in water depths from 140 to 1850 m, encompassing the oxygen
minimum zone. Phytodetritus sedimentation events were simulated by
adding 13C-labelled algal material to surface sediments. The labelled
carbon was subsequently traced into bacterial lipids as a proxy of
bacterial biomass, foraminiferan and macrofaunal biomass as well as
into dissolved organic and inorganic pools. The largest pool of
processed carbon was found in dissolved inorganic carbon, attributed
to respiration. Macrofaunal influence was most pronounced at the lower
part of the oxygen minimum zone.
The third study was on benthic respiration rates in the Gulf of
Finland, Baltic Sea. Rates were based on in situ incubations
using benthic chamber landers. Three contrasting stations with
different sediment accumulation regimes were visited. The effect of
changes in water masses on the benthic fluxes was investigated with a
dynamic diagenetic model. Fluxes of dissolved inorganic carbon were
highest at the station with accumulation bottom, intermediate at the
station with transport bottom and lowest at the station with erosion
sediments.
The fourth study was primarily a theoretical investigation of how well
a certain model parameter can be constrained based on a certain
dataset. A model of bio-irrigation was used as a good example of this.
The interpretation is based on fitting observed data with a model
containing several parameters, where some parameters are a
priori unknown. In this chapter, it was tested under what
conditions the results obtained through this fitting are robust. The
results from this study imply that using only the concentration
change in the overlying water, it is not possible to constrain both
the rate and the mechanism of bio-irrigation, thus, sampling the
porewaters at the end of the incubation is a necessity.
The fifth study was an an evaluation of the performance of an oxygen
optode. The performance of the sensor was evaluated and compared with
data obtained by other methods. The principal conclusion was that,
owing to high accuracy, long-term stability (more
than 20 months), lack of pressure hysteresis and limited
cross-sensitivity, this method is overall more suitable for oxygen
monitoring in the aquatic environment than other methods.
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