Publication Date:
2019-07-17
Description:
Several pelagic ecosystem models now allow for flexibility in the
elemental composition of the modelled plankton functional types.
Often they are based on some variant of the model for phytoplankton
photoacclimation by Geider et al. (1998) that has been shown to reproduce
C:N and C:Chl ratios in laboratory experiments both for constant
nutrient and light conditions, and for a transition to nutrient
limitation well. Based on that success, the predicted stoichiometries in
ecosystem models employing the Geider model or one of its competitors
have not received much attention.
Here we first investigate how well the two physiologically-based
models by Geider et al. (1998), and by Pahlow (2005) are able to
describe observed changes in biomass stoichiometry in a laboratory
experiment with a more dynamic nutrient regime, namely a sudden resupply of
nitrogen after a bloom, as would be expected after a brief mixing event.
We show that both the Geider et al. (1998), and the Pahlow (2005) model are
able to describe shifts on C:N stoichiometry over the course of a
bloom, albeit not equally well, but that both have problems describing
the recovery from nutrient starvation.
We then discuss the patterns of phytoplankton stoichiometry and
their sensitivity to some assumptions on physiology in a global ecosystem
model. Our model allows for flexible stoichiometry in both non-diatoms and
diatoms, with an extension of the Geider model for diatom Si:C variations.
Globally, largest deviations of the C:N ratio from
Redfield are modelled in the nutrient-depleted subtropical gyres, but
they contribute little to vertical export. Lab-observed changes in
C:Chl ratio are described well by the Geider model. Modelled global
patterns in C:Chl are consistent with a number of field- and
satellite-based observations. It remains a challenge,
however, to distinguish between variations in stoichiometry due to
physiological acclimation and to community composition.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Conference
,
notRev
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