Evaluating Uncertainties in Marine Biogeochemical Models: Benchmarking Aerosol Precursors

Oluwaseun Ogunro,Nathan Collier,Forrest Hoffman,Scott Elliott,Weiwei Fu,Oliver Wingenter,Clara Deal

doi:10.3390/atmos9050184

Abstract

The effort to accurately estimate global radiative forcing has long been hampered by a degree of uncertainty in the tropospheric aerosol contribution. Reducing uncertainty in natural aerosol processes, the baseline of the aerosol budget, thus becomes a fundamental task. The appropriate representation of aerosols in the marine boundary layer (MBL) is essential to reduce uncertainty and provide reliable information on offsets to global warming. We developed an International Ocean Model Benchmarking package to assess marine biogeochemical process representations in Earth System Models (ESMs), and the package was employed to evaluate surface ocean concentrations and the sea–air fluxes of dimethylsulfide (DMS). Model performances were scored based on how well they captured the distribution and variability contained in high-quality observational datasets. Results show that model-data biases increased as DMS enters the MBL, but unfortunately over three-quarters of the models participating in the fifth Coupled Model Intercomparison Project (CMIP5) did not have a dynamic representation of DMS. When it is present, models tend to over-predict sea surface concentrations in the productive region of the eastern tropical Pacific by almost a factor of two, and the sea–air fluxes by a factor of three. Systematic model-data benchmarking as described here will help to identify such deficiencies and subsequently lead to improved subgrid-scale parameterizations and ESM development.

Highlights

The global natural aerosol system is dominated on an areal basis by remote oceanic processes driven by phytoplankton that lead to the formation of an array of chemical cloud condensation nucleus types [1,2,3,4,5,6]
We have recently developed a set of Earth System Models (ESMs) analysis methods and metrics specific to the marine biogeochemistry realm, as part of the ongoing International Ocean Model Benchmarking (IOMB)
We demonstrate the ability of IOMB to evaluate model outcomes for nitrate and net primary production, and use DMS as a proxy for volatile organic compounds (VOCs)

Summary

Introduction

The global natural aerosol system is dominated on an areal basis by remote oceanic processes driven by phytoplankton that lead to the formation of an array of chemical cloud condensation nucleus types [1,2,3,4,5,6]. Uncertainty in the aerosol forcing and feedbacks associated with ocean biota have long been suspected contributors in the era of global change, due to their effects on particle chemistry and cloud albedo [4,9]. Their complex ecological geography means they are extremely difficult to quantify. A related issue is the isolation of anthropogenic effects relative to any natural counterparts Uncertainty in these areas undermines the continuing international effort to appropriately simulate the aerosol mitigation of the global greenhouse effect—or amplification, as the case may be [4,9]. Plant emissions, and marine sea–air fluxes all play a role

Methods

Results

Discussion

Conclusion