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|Title: ||Assessing uncertainty in models of the ocean carbon cycle|
|Authors: ||Scott, Vivian|
|Supervisor(s): ||Kettle, Helen|
|Issue Date: ||2010|
|Publisher: ||The University of Edinburgh|
|Abstract: ||In this thesis I explore the effect of parameter uncertainty in ocean biogeochemical models on
the calculation of carbon uptake by the ocean. The ocean currently absorbs around a quarter
of the annual anthropogenic CO2 emissions to the atmosphere [Scholes et al., 2009], slowing
the increase in radiative forcing associated with the increasing atmospheric CO2 concentration.
Ocean biogeochemical models have been developed to study the role of the ocean ecosystem in
this process. Such models consist of a greatly simplified representation of the hugely complex
ocean ecosystem. This simplification requires extensive parameterisation of the biological
processes that convert inorganic carbon to and from organic carbon in the ocean.
The HadOCC ocean biogeochemical model is a Nutrient-Phytoplankton-Zooplankton-Detritus
(NPZD) model that is used to represent the role of the ocean ecosystem in the global carbon cycle
in the HadCM3 and FAMOUS GCMs. HadOCC uses twenty parameters to control the processes
of biological growth, mortality, grazing and detrital sinking that control the uptake and cycling
of carbon in the ocean ecosystem. These parameters represent highly complex and in some cases
incompletely understood biological processes, and as a result are uncertain in value.
A sensitivity analysis is performed to identify the HadOCC parameters that due to uncertainty in
value have the greatest possible effect on the exchange of CO2 between the atmosphere and the
ocean—the air-sea CO2 flux. These are found to be the parameters that control phytoplankton
growth in the well lit surface ocean, the formation of carbonate by marine organisms and the
sinking of biological detritus.
The uncertainty in these parameters is found to cause changes to the air-sea CO2 flux calculated
by the FAMOUS GCM. The initial effect of these changes is equivalent to the order of the error
of current estimates of the net annual carbon uptake by the ocean (2.2 ± 0.3 Pg C y−1 [Gruber
et al., 2009], 2.2 ± 0.5 Pg C y−1 [Denman et al., 2007]). This indicates that while the effect
of ocean biogeochemical parameter uncertainty is non-negligible, it is within the bounds of
the uncertainty of the total (inorganic and organic) ocean carbon system, and is considerably
less than the uncertainty in the carbon uptake of the terrestrial biosphere [Houghton, 2007].
However, as the ocean plays a crucial role in the global carbon cycle and the regulation of
the Earth’s climate, further understanding and better modelling of the role of the ocean ecosystem
in the global carbon cycle and its reaction to anthropogenic climate forcing remains important.|
|Sponsor(s): ||Natural Environment Research Council (NERC)|
|Keywords: ||ocean biogeochemical models|
|Appears in Collections:||Global Change Research Institute PhD thesis collection|
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