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Abstract Marine fish precipitate carbonates in their intestines that they subsequently excrete as part of an osmoregulatory strategy. While fish carbonates are proposed to be volumetrically significant to the global carbonate budget, no study has presented direct evidence of fish carbonates in the open ocean. Here we examine sediment trap material collected by the Oceanic Flux Program (OFP) in the North Atlantic and observe the episodic occurrence of enigmatic blue particles since 1992. The blue particles are comprised of calcite with unusually high magnesium content (up to 46 mol%) with distinctively depleted δ¹³C and enriched δ¹⁸O compared with calcite produced by common marine calcifiers. Based on the mineralogical, isotopic, and textural similarities between the blue particles and fish carbonates, we propose that the blue particles are produced by pelagic fish. Our data suggest that fish modify their intestinal fluids to create a concentrated, highly supersaturated,¹³C depleted solution capable of precipitating calcite with high magnesium content and low δ¹³C. Collectively, our data imply that fish carbonate production is an open‐ocean phenomenon, opening up the possibility that fish contribute to the production, dissolution, and export of carbonates globally. 

There is an ongoing debate on the different transmission modes of SARS-CoV-2 and their relative contributions to the pandemic. In this paper, we employ a simple mathematical model, which incorporates both the human-to-human and environment-to-human transmission routes, to study the transmission dynamics of COVID-19. We focus our attention on the role of airborne transmission in the spread of the disease in a university campus setting. We conduct both mathematical analysis and numerical simulation, and incorporate published experimental data for the viral concentration in the air to fit model parameters. Meanwhile, we compare the outcome to that of the standard SIR model, utilizing a perturbation analysis in the presence of multiple time scales. Our data fitting and numerical simulation results show that the risk of airborne transmission for SARS-CoV-2 strongly depends on how long the virus can remain viable in the air. If the time for this viability is short, the airborne transmission route would be inconsequential in shaping the overall transmission risk and the total infection size. On the other hand, if the infectious virus can persist in aerosols beyond a few hours, then airborne transmission could play a much more significant role in the spread of COVID-19. 

Abstract. Here we present measurement results of temporal distributions of nitrous acid (HONO) along with several chemical and meteorologicalparameters during the spring and the late summer of 2019 at Tudor Hill Marine Atmospheric Observatory in Bermuda. Large temporal variations inHONO concentration were controlled by several factors including local pollutant emissions, air mass interaction with the island, andlong-range atmospheric transport of HONO precursors. In polluted plumes emitted from local traffic, power plant, and cruise ship emissions,HONO and nitrogen oxides (NOx) existed at substantial levels (up to 278 pptv and 48 ppbv, respectively),and NOx-related reactions played dominant roles in daytime formation of HONO. The lowest concentration of HONO wasobserved in marine air, with median concentrations at ∼ 3 pptv around solar noon and < 1 pptv during thenighttime. Considerably higher levels of HONO were observed during the day in the low-NOx island-influenced air([NO2] < 1 ppbv), with a median HONO concentration of ∼ 17 pptv. HONO mixing ratios exhibiteddistinct diurnal cycles that peaked around solar noon and were lowest before sunrise, indicating the importance of photochemical processes forHONO formation. In clean marine air, NOx-related reactions contribute to ∼ 21 % of the daytime HONOsource, and the photolysis of particulate nitrate (pNO3) can account for the missing source assuming a moderate enhancement factorof 29 relative to gaseous nitric acid photolysis. In low-NOx island-influenced air, the contribution from bothNOx-related reactions and pNO3 photolysis accounts for only ∼ 48 % of the daytime HONOproduction, and the photochemical processes on surfaces of the island, such as the photolysis of nitric acid on the forest canopy, might contributesignificantly to the daytime HONO production. The concentrations of HONO, NOx, and pNO3 were lowerwhen the site was dominated by the aged marine air in the summer and were higher when the site was dominated by North American air in the spring,reflecting the effects of long-range transport on the reactive nitrogen chemistry in background marine environments.