We perform a sensitivity study with the Biogeochemical Elemental Cycling (BEC) ocean model to understand the impact of atmospheric inorganic nitrogen deposition on marine biogeochemistry and air-sea CO₂ exchange. Simulations involved examining the response to three different atmospheric inorganic nitrogen deposition scenarios namely, Pre-industrial (22 Tg N/year), 1990s (39 Tg N/year), and an Intergovernmental Panel on Climate Change (IPCC) prediction for 2100, IPCC-A1FI (69 Tg N/year). Globally, the increasing N deposition had widespread, but modest effects on export production and air-sea CO₂ exchange. The maximum increase in N deposition was 47 Tg N/year since Pre-industrial control for the IPCC-A1FI case, which had an increase in primary production (0.98 Gt C/year or 2%), export production (0.16 Gt C/year or 3%) and a decrease in atmospheric pCO₂ of 1.66 ppm (0.6%) relative to the Pre-industrial control. In some regions, atmospheric N inputs supported >20% of the export production in the current era and >50% of the export production in the IPCC-A1FI case. As nitrogen deposition increased, N fixation decreased because the diazotrophs were outcompeted by diatoms and small phytoplankton under more N-replete conditions. This decrease in N fixation could partially counteract the ongoing increase in new nitrogen inputs via atmospheric N deposition.

 We perform a sensitivity study with the Biogeochemical Elemental Cycling (BEC) ocean model to understand the impact of atmospheric inorganic nitrogen deposition on marine biogeochemistry and air-sea CO₂ exchange. Simulations involved examining the response to three different atmospheric inorganic nitrogen deposition scenarios namely, Pre-industrial (22 Tg N/year), 1990s (39 Tg N/year), and an Intergovernmental Panel on Climate Change (IPCC) prediction for 2100, IPCC-A1FI (69 Tg N/year). Globally, the increasing N deposition had widespread, but modest effects on export production and air-sea CO₂ exchange. The maximum increase in N deposition was 47 Tg N/year since Pre-industrial control for the IPCC-A1FI case, which had an increase in primary production (0.98 Gt C/year or 2%), export production (0.16 Gt C/year or 3%) and a decrease in atmospheric pCO₂ of 1.66 ppm (0.6%) relative to the Pre-industrial control. In some regions, atmospheric N inputs supported >20% of the export production in the current era and >50% of the export production in the IPCC-A1FI case. As nitrogen deposition increased, N fixation decreased because the diazotrophs were outcompeted by diatoms and small phytoplankton under more N-replete conditions. This decrease in N fixation could partially counteract the ongoing increase in new nitrogen inputs via atmospheric N deposition.

To better understand the role of iron in driving marine ecosystems, the Southern Ocean Iron Experiment (SOFeX) fertilized two surface water patches with iron north and south of the Antarctic Polar Front Zone (APFZ). Using 1-D coupled biological-physical simulations, we examine the biogeochemical dynamics that occurred both inside and outside of the fertilized patches during and shortly after the SOFeX field campaign. We focus, in particular, on three main issues governing the biological response to deliberate iron fertilization: the interaction among phytoplankton, light, macronutrient and iron limitation; dilution and lateral mixing between the fertilized patch and external, unfertilized waters; and the effect of varying mixed layer depth on the light field. At the patch south of the APFZ, sensitivity simulations with no dilution results in the maximum bloom magnitude, whereas dilution with external water extends the development of the north patch bloom by relieving silicon limitation. In model sensitivity studies for both sites, maximum chlorophyll concentration and dissolved inorganic carbon depletion inside the fertilized patches are inversely related to mixed layer depth, similar to the patterns observed across a number of iron fertilization field experiments. Our results suggest that Southern Ocean phytoplankton blooms resulting from natural or deliberate iron fertilization will tend to become iron-light co-limited unless the mixed layer depth is quite shallow. © 2007 Elsevier B.V. All rights reserved.

The primary nutrients that limit marine phytoplankton growth rates include nitrogen (N), phosphorus (P), iron (Fe), and silicon (Si). Atmospheric transport and deposition provides a source for each of these nutrients to the oceans. We utilize an ocean biogeochemical model to examine the relative importance of these atmospheric inputs for ocean biogeochemistry and export production. In the current era, simulations with the biogeochemical elemental cycling ocean model suggest that globally, atmospheric Fe inputs could support roughly 50% of the Fe exported from the euphotic zone by sinking organic and inorganic particles. Variations in atmospheric iron inputs strongly impact spatial patterns of phytoplankton growth limitation and the areal extent of the high-nutrient, low-chlorophyll regions. Atmospheric inputs of N, Si, and P have smaller impacts, potentially accounting for 5.1%, 0.21%, and 0.12% of the biogenic export of these elements from the euphotic zone, respectively. Soluble Fe input from the atmosphere is sufficient to support most of the export production in many ocean regions, whether we use a spatially variable aerosol Fe solubility, or a globally constant 2% solubility. Regionally atmospheric N inputs can have significant impacts on marine biogeochemistry, potentially supporting >25% of the export production, an impact that is increasing due to human activities. Atmospheric Si and P inputs have only minimal impacts on marine ecosystem productivity and biogeochemistry, as these inputs are typically quite small relative to the flux of these nutrients from below the euphotic zone.

The primary nutrients that limit marine phytoplankton growth rates include nitrogen (N), phosphorus (P), iron (Fe), and silicon (Si). Atmospheric transport and deposition provides a source for each of these nutrients to the oceans. We utilize an ocean biogeochemical model to examine the relative importance of these atmospheric inputs for ocean biogeochemistry and export production. In the current era, simulations with the biogeochemical elemental cycling ocean model suggest that globally, atmospheric Fe inputs could support roughly 50% of the Fe exported from the euphotic zone by sinking organic and inorganic particles. Variations in atmospheric iron inputs strongly impact spatial patterns of phytoplankton growth limitation and the areal extent of the high-nutrient, low-chlorophyll regions. Atmospheric inputs of N, Si, and P have smaller impacts, potentially accounting for 5.1%, 0.21%, and 0.12% of the biogenic export of these elements from the euphotic zone, respectively. Soluble Fe input from the atmosphere is sufficient to support most of the export production in many ocean regions, whether we use a spatially variable aerosol Fe solubility, or a globally constant 2% solubility. Regionally atmospheric N inputs can have significant impacts on marine biogeochemistry, potentially supporting >25% of the export production, an impact that is increasing due to human activities. Atmospheric Si and P inputs have only minimal impacts on marine ecosystem productivity and biogeochemistry, as these inputs are typically quite small relative to the flux of these nutrients from below the euphotic zone.

We present results from transient sensitivity studies with the Biogeochemical Elemental Cycling (BEC) ocean model to increasing anthropogenic atmospheric inorganic nitrogen (N) and soluble iron (Fe) deposition over the industrial era. Elevated N deposition results from fossil fuel combustion and agriculture, and elevated soluble Fe deposition results from increased atmospheric processing in the presence of anthropogenic pollutants and soluble Fe from combustion sources. Simulations with increasing Fe and increasing Fe and N inputs raised simulated marine nitrogen fixation, with the majority of the increase in the subtropical North and South Pacific, and raised primary production and export in the high-nutrient low-chlorophyll (HNLC) regions. Increasing N inputs alone elevated small phytoplankton and diatom production, resulting in increased phosphorus (P) and Fe limitation for diazotrophs, hence reducing nitrogen fixation (∼6%). Globally, the simulated primary production, sinking particulate organic carbon (POC) export. and atmospheric CO₂ uptake were highest under combined increase in Fe and N inputs compared to preindustrial control. Our results suggest that increasing combustion iron sources and aerosol Fe solubility along with atmospheric anthropogenic nitrogen deposition are perturbing marine biogeochemical cycling and could partially explain the observed trend toward increased P limitation at station ALOHA in the subtropical North Pacific. Excess inorganic nitrogen ([NO₃ ⁻] + [NH₄ ⁺] − 16[PO₄ ³⁻]) distributions may offer useful insights for understanding changing ocean circulation and biogeochemistry.

UNLABELLED: Infections caused by antimicrobial-resistant Escherichia coli are the leading cause of death attributed to antimicrobial resistance (AMR) worldwide, and the known AMR mechanisms involve a range of functional proteins. Here, we employed a pan-genome wide association study (GWAS) approach on over 1,000 E. coli isolates from sick dogs collected across the US and Canada and identified a strong statistical association (empirical P < 0.01) of AMR, involving a range of antibiotics to a group 1 capsular (CPS) gene cluster. This cluster included genes under relaxed selection pressure, had several loci missing, and had pseudogenes for other key loci. Furthermore, this cluster is widespread in E. coli and Klebsiella clinical isolates across multiple host species. Earlier studies demonstrated that the octameric CPS polysaccharide export protein Wza can transmit macrolide antibiotics into the E. coli periplasm. We suggest that the CPS in question, and its highly divergent Wza, functions as an antibiotic trap, preventing antimicrobial penetration. We also highlight the high diversity of lineages circulating in dogs across all regions studied, the overlap with human lineages, and regional prevalence of resistance to multiple antimicrobial classes. IMPORTANCE: Much of the human genomic epidemiology data available for E. coli mechanism discovery studies has been heavily biased toward shiga-toxin producing strains from humans and livestock. E. coli occupies many niches and produces a wide variety of other significant pathotypes, including some implicated in chronic disease. We hypothesized that since dogs tend to share similar strains with their owners and are treated with similar antibiotics, their pathogenic isolates will harbor unexplored AMR mechanisms of importance to humans as well as animals. By comparing over 1,000 genomes with in vitro antimicrobial susceptibility data from sick dogs across the US and Canada, we identified a strong multidrug resistance association with an operon that appears to have once conferred a type 1 capsule production system.