# Evaluating Uncertainties in Marine Biogeochemical Models: Benchmarking Aerosol Precursors
## 1 Introduction
### Background  
Even as several of the most crucial global biogeochemical cycles are being implemented in ESMs [16; 17], remote aerosol remains a continuing challenge to the community. 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]. However, 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]. Both primary and secondary atmospheric particulates influence cloud microphysical properties and ultimately impact incoming solar radiation and Earth's albedo. Although anthropogenic emissions tend to dominate the net contributions of atmospheric particles to radiative forcing, about 90% by mass of the total global aerosol is of natural origin. Volcanoes, plant emissions, and marine sea-air fluxes all play a role. Uncertainty derived from these natural sources is responsible for roughly half the variance exhibited by aerosol forcing since the onset of the industrial era [18]. On a net basis, the atmospheric aerosol leads to reflection of incoming shortwave radiation [19; 20; 21]. Although much has been learned since this effect was originally recognized [22], many questions are yet to be answered or even addressed. The most pressing regard the biology of cloud albedo, because it exerts strong leverage on the global radiation balance [9; 18; 20]. Such issues limit our ability to predict climate sensitivity, for example due to the better-known and ever increasing atmospheric concentrationsof greenhouse gases (GHGs). For decades now, there has been a singular focus on anthropogenic aerosol as a major uncertainty driver [21; 23]. However, progress in quantifying climate sensitivity has been irregular, and attention gradually shifted toward the evaluation of natural emissions (volcanic aerosols, natural sulfate, sea salt, and others). There is a strong need to determine the baseline of pre-industrial emissions, as well as the uncertainties introduced by shifts in global biota over the past century [18]. The marine environment is biologically active and a major player in the cycling of natural atmospheric aerosols due to its vast extent [1]. The vertical transport of trace gases and particles from the global ocean surface into the lower atmosphere constitutes a constant dynamic maintaining and controlling aerosol loading in the marine boundary layer (MBL). The composition and strength of oceanic emissions control the formation of both primary and secondary aerosols in the MBL, ultimately dictating the magnitude of planetary scale cloud albedo [9; 24]. There continue to be open questions concerning the atmospheric inventory of natural aerosols worldwide, such that marine precursor-to-cloud relationships are even less well constrained than the major greenhouse gas relationships. This leads to significant uncertainty in aerosol-cloud interactions and creates challenges for the representation of natural aerosol distributions and general oceanic climate in Earth System Models [11; 25]. The biogenic volatile organic compounds (BVOCs) represent a crucial subset of the overall marine aerosol challenge. Vertical flux-transport of trace gases such as DMS, isoprene, and the monoterpenes influences the formation of secondary organic aerosols (SOA), which modify cloud microphysics [9; 26]. Other modes of uncertainty regard the organic chemistry of less volatile constituents among the dissolved organics [12]. Primary organic aerosols (POA) introduced along with sea spray are really marine macromolecules that are derived from the degradation of phytoplankton cells; otherwise, they are downstream oxidation products that are also high in molecular weight [5; 6].