Manganese (Mn) is a key cofactor in enzymes responsible for lignin decay (mainly Mn peroxidase), regulating the rate of litter degradation and carbon (C) turnover in temperate and boreal forest biomes.While soil Mn is mainly derived from bedrock, atmospheric Mn could also contribute to soil Mn cycling, especially within the surficial horizon, with implications for soil C cycling. However, quantification of the atmospheric Mn cycle, which comprises emissions from natural (desert dust, sea salts, volcanoes, primary biogenic particles, and wildfires) and anthropogenic sources (e.g. industrialization and land-use change due to agriculture) transport, and deposition into the terrestrial and marine ecosystem, remains uncertain. Here, we use compiled emission datasets for each identified source to model and quantify the atmospheric Mn cycle with observational constraints. We estimated global emissions of atmospheric Mn in aerosols (<10 µm in aerodynamic diameter) to be 1500 Gg Mn yr-1. Approximately 32% of the emissions come from anthropogenic sources. Deposition of the anthropogenic Mn shortened soil Mn “pseudo” turnover times in surficial soils about 1-m depth (ranging from 1,000 to over 10,000,000 years) by 1-2 orders of magnitude in industrialized regions. Such anthropogenic Mn inputs boosted the Mn-to-N ratio of the atmospheric deposition in non-desert dominated regions (between 5×10-5 and 0.02) across industrialized areas, but still lower than soil Mn-to-N ratio by 1-3 orders of magnitude. Correlation analysis revealed a negative relationship between Mn deposition and topsoil C density across temperate and (sub)tropical forests, illuminating the role of Mn deposition in these ecosystems.

Aircraft measurement campaigns have revealed that super coarse dust (diameter > 10 um) surprisingly accounts for approximately a quarter of aerosols by mass in the atmosphere. However, most global aerosol models either underestimate or do not include super coarse dust abundance. To address this problem, we use brittle fragmentation theory to develop a parameterization for the emitted dust size distribution that includes emission of super coarse dust. We implement this parameterization in the Community Earth System Model (CESM) and find that it brings the model in good agreement with measurements of super coarse dust close to dust source regions. However, the model still underestimates super coarse dust in dust outflow regions. Thus, we conclude that model underestimation of super coarse atmospheric dust is in part due to the underestimation of super coarse dust emission and likely in part due to errors in deposition processes.

A key challenge in accurate simulations of desert dust emission is the parameterization of the threshold wind speed above which dust emission occurs. However, the existing parameterizations yield a unrealistically low dust emission threshold in some climate models such as the Community Earth System Model (CESM), leading to higher simulated dust source activation frequencies than observed and requiring global tuning constants to scale down dust emissions. Here we develop a more realistic parameterization for the dust emission threshold in CESM. In particular, we account for the dissipation of surface wind momentum by surface roughness elements such as vegetation, rocks, and pebbles, which reduce the wind momentum exerted on the bare soil surface. We achieve this by implementing a dynamic wind drag partition model by considering the roughness of the time-varying vegetation as quantified by the leaf area index (LAI), as well as the time-invariant rocks and pebbles using satellite-derived aeolian roughness length. Furthermore, we account for the effect of soil size on dust emission threshold by replacing the currently used globally constant soil median diameter with a spatially varying soil texture map. Results show that with the new parameterization dust emissions decrease by 20–80% over source regions such as Africa, Middle East, and Asia, thereby reducing the need for the global tuning constant. Simulated dust emissions match better in both spatiotemporal variability and emission frequency when compared against satellite observed dust activation frequency data. Our results suggest that including more physical dust emission parameterizations into climate models can lessen bias and improve simulation results, possibly eliminate the use of empirical source functions, and reduce the need for tuning constants. This development could improve assessments of dust impacts on the Earth system.

14 15 Key Points: 16 (1) E3SMv1 captures spatial and temporal variability in the observed dust aerosol optical 17 depth, but underestimates long-range transport. 18 (2) The net direct radiative effect of dust simulated by E3SMv1 is-0.42 Wm-2 with a smaller 19 longwave warming than other recent studies. 20 (3) In addition to emission, dry removal of dust are highly sensitive to the increase of 21 horizontal or vertical model resolution. 22 23 24

Dissolved iron (dFe) plays an important role in regulating marine biological productivity. In high nutrient, low chlorophyll (HNLC) regions (> 33% of the global ocean) iron is the primary growth limiting nutrient, and elsewhere can regulate nitrogen fixation and growth by diazotrophs. Overall, dFe supply potentially impacts half of global ocean productivity. The link between iron availability and carbon export is strongly dependent on the phytoplankton iron quotas, or cellular Fe:C ratios. This ratio can vary by more than an order of magnitude in the open ocean and is positively correlated with ambient dFe concentration in sparse field observations. The Community Earth System Model (CESM) ocean component has been modified to simulate dynamic, group-specific, phytoplankton iron quotas (Fe:C) that vary as a function of ambient iron concentration. The simulated Fe:C ratios match the spatial trends in the observations and improve the correlation with global-scale, observed nutrient distributions. Acclimation of phytoplankton Fe:C ratios dampens the biogeochemical response to varying atmospheric deposition fluxes of soluble iron, compared to a model with fixed Fe:C. However, varying atmospheric soluble iron supply still has first order impacts on global carbon and nitrogen fluxes, and on the spatial patterns of nutrient limitation; both of which are strongly sensitive to changes in pyrogenic sources of iron. Accounting for dynamic, phytoplankton iron quotas is critical for capturing the ocean biogeochemical responses to varying atmospheric soluble iron inputs, including expected changes in both the mineral dust and pyrogenic sources with climate warming and anthropogenic activity.

If the university can be thought of as an incubator for ideas and thought leadership, then each department is a learning ecosystem unto itself. The IDEEAS (Inclusion, Diversity, and Equity in Earth and Atmospheric Sciences) Working Group formed organically in Cornell’s Earth and Atmospheric Sciences department as a grassroots group with a desire to improve the department ecosystem. Self-selected from the full cross-section of the department, our members comprise students, staff, researchers, faculty, and emeriti. IDEEAS is a non-hierarchical group within the very hierarchical setting of academia, and our work provides a model for disrupting traditional power structures while leveraging their influence to reimagine how an academic unit could and should function. IDEEAS is not a committee; we are a collective. We believe that, irrespective of rank or role, every member of the department community has the capacity to practice leadership. As such, we lead by action. Each IDEEAS project or initiative is organized around an action team, who collectively carry out a community-informed vision of the culture we would like to co-create with the rest of the department. Our commitment to collective leadership empowers constituencies (e.g., students, non-academic staff, post-docs) who have traditionally lacked a pathway to provide input or participate in department-level decision making. IDEEAS is developing formal channels of communication between the group and department leadership in an effort to develop a sustainable ecosystem that will outlive its founders. IDEEAS events combine community building and intentional learning opportunities to promote critical reflection and foster connections. Events included a well-attended kickoff party with facilitated conversation that drew 56 attendees (~40% of the department), and community conversations about implicit bias and structural racism. IDEEAS organizers have been critically responsive during ongoing COVID19 isolation, providing numerous opportunities for social connection and using the disruption as a catalyst to cultivate connection and build community resilience that will outlast the pandemic. We invite discussion and collaboration with those engaged in similar justice, equity, diversity, and inclusion work in the geosciences.