Abstract
Pelagic biogeochemical models (BGCMs) have matured into generic components of Earth System Models. BGCMs mimic the effects of marine biota on oceanic nutrient, carbon and oxygen cycles. They rely on parameters that are adjusted to match observed conditions. Such parameters are key to determining the models’ responses to changing environmental conditions. However, many of these parameters are difficult to constrain and constitute a major source of uncertainty in BGCM projections. Here we use, for the first time, variance-based sensitivity analyses to map BGCM parameter uncertainties onto their respective local manifestation in model entities (such as oceanic oxygen concentrations) for both contemporary climate and climate projections. The mapping effectively relates local uncertainties of projections to the uncertainty of specific parameters. Further, it identifies contemporary benchmarking regions, where the uncertainties of specific parameters manifest themselves, thereby facilitating an effective parameter refinement and a reduction of the associated uncertainty. Our results demonstrate that the parameters that are linked to uncertainties in projections may differ from those parameters that facilitate model conformity with present-day observations. In summary, we present a practical approach to the general question of where present-day model fidelity may be indicative for reliable projections.
Highlights
Pelagic biogeochemical models (BGCMs) have matured into generic components of Earth System Models
Why even bother with BGCM-based projections? The reason is that the pelagic oceanic nutrient, oxygen and carbon cycles were subject to pronounced changes during the past decades[13,14,15] and we anticipate that these will continue as we move further into the Anthropocene
As a side aspect of the presented results, we report that the long-standing problem of a biased Indian Ocean Oxygen Minimum Zones (OMZs), apparently endemic to the current generation of coupled ocean-circulation biogeochemical m odels[34], is in our model related to the representation of vertical mixing processes rather than to unknowns in biogeochemical model parameters
Summary
Pelagic biogeochemical models (BGCMs) have matured into generic components of Earth System Models. BGCMs mimic the effects of marine biota on oceanic nutrient, carbon and oxygen cycles They rely on parameters that are adjusted to match observed conditions. Series are available and satellite observations refer to the sea surface only) and long wall-clock times (weeks to even months) to reach a quasi-equilibrium for each model formulation and parameter set, impede this process[10] This puts these models even further apart from, e.g., the ocean and atmosphere modules of climate models that are built on first order principles such as Newton’s second law of Motion. Among the associated pressing societal questions are the potential future developments of anthropogenic carbon storage in the oceans and oceanic deoxygenation - a term coined to describe the continuous decline of oxygen levels in the ocean which, in turn, may trigger a decline in fish yield[16] and the release of the potent greenhouse gas nitrous oxide[17]. In response to urgent demands for information in order to facilitate mitigation and adaptation strategies, BGCMs are applied to project oceanic carbon and oxygen cycles - despite their limitations
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