A global dataset of atmospheric ⁷Be and ²¹⁰Pb measurements: annual air concentration and depositional flux

7Be and 210Pb air concentration and depositional flux data provide key information on the origins and movements of air masses, as well as atmospheric deposition processes and residence time of aerosols. After their deposition onto the Earth's surface, they are utilized for tracing soil redistribution processes on land, particle dynamics in aquatic systems, and mixing processes in open ocean. Here we present a global dataset of air concentration and depositional flux measurements of atmospheric 7Be and 210Pb made by a large number of global research communities. Data were collected from published papers between 1955 and early 2020. It includes the annual surface air concentration data of 7Be from 367 sites and 210Pb from 270 sites, the annual depositional flux data of 7Be from 279 sites and 210Pb from 602 sites. When available, appropriate metadata have also been summarized, including geographic location, sampling date, methodology, annual precipitation, and references. The dataset is archived at https://doi.org/10.5281/zenodo.4785136 (Zhang et al., 2021) and is freely available for the scientific community. The purpose of this paper is to provide an overview of the scope and nature of this dataset and its potential utility as baseline data for future research.

A comprehensive global dataset of atmospheric ⁷Be and ²¹⁰Pb measurements: air concentration and depositional flux

7Be and 210Pb air concentration and depositional flux data provide key information on the origins and movements of air masses, as well as deposition processes and residence time of aerosols. After their deposition onto the Earth's surface, they are utilized for tracing soil redistribution processes on land and particle dynamics and mixing processes in the ocean. Here we present a global dataset of air concentration and depositional flux measurements of atmospheric 7Be and 210Pb made by a large number of researchers and laboratories. Data were collected from published papers between 1955 and early 2020. It includes the annual surface air concentrations data of 7Be from 367 sites and of 210Pb from 270 sites, the annual depositional flux of 7Be from 279 sites, and of 210Pb from 602 sites. When available, appropriate metadata have also been summarized, including geographic location, sampling date, methodology, annual precipitation, and references. The dataset is available at https://doi.org/10.5281/zenodo.4521649 (Zhang et al., 2021). The purpose of this paper is to have the published data available in one place for future researchers' public consumption in their research and provide an overview of the scope and nature of this dataset holdings.

Bidirectional air–sea exchange and accumulation of POPs (PAHs, PCBs, OCPs and PBDEs) in the nocturnal marine boundary layer

As a consequence of long-range transported pollution, air–sea exchange can become a major source of persistent organic pollutants in remote marine environments. The vertical gradients in the air were quantified for 14 species, i.e. four parent polycyclic aromatic hydrocarbons (PAHs), three polychlorinated biphenyls (PCBs), three organochlorine pesticides (OCPs) and two polybrominated diphenylethers (PBDEs) in the gas-phase at a remote coastal site in the southern Aegean Sea in summer. Most vertical gradients were positive (Δc∕Δz > 0), indicating downward (net depositional) flux. Significant upward (net volatilisational) fluxes were found for three PAHs, mostly during daytime, and for two OCPs, mostly during night-time, as well as for one PCB and one PBDE during part of the measurements. While phenanthrene was deposited, fluoranthene (FLT) and pyrene (PYR) seem to undergo flux oscillation, hereby not following a day–night cycle. Box modelling confirms that volatilisation from the sea surface has significantly contributed to the night-time maxima of OCPs. Fluxes were quantified based on eddy covariance. Deposition fluxes ranged from −28.5 to +1.8 µg m−2 day−1 for PAHs and −3.4 to +0.9 µg m−2 day−1 for halogenated compounds. Dry particle deposition of FLT and PYR did not contribute significantly to the vertical flux.

Bi-directional air-sea exchange and accumulation of POPs (PAHs, PCBs, OCPs and PBDEs) in the nocturnal marine boundary layer

As a consequence of long-range transported pollution air-sea exchange can become a major source of persistent organic pollutants in remote marine environments. The vertical gradients in air of 14 species i.e., 4 parent polycyclic aromatic hydrocarbons (PAHs), 3 polychlorinated biphenyls (PCBs), 3 organochlorine pesticides (OCPs) and 2 polybrominated diphenylethers (PBDEs) in the gas-phase were quantified at a remote coastal site in the southern Aegean Sea in summer. Most vertical gradients were positive (Δc/Δz > 0) indicating downward (net depositional) flux. Significant upward (net volatilisational) fluxes were found for 3 PAHs, mostly during day-time, and for 2 OCPs, mostly during night-time, as well as for 1 PCB and 1 PBDE during part of the measurements. While phenanthrene was deposited, fluoranthene (FLT) and pyrene (PYR) seem to undergo flux oscillation, hereby not following a day/night cycle. Box modelling confirms that volatilisation from the sea surface has significantly contributed to the night-time maxima of OCPs. Fluxes were quantified based on Eddy covariance. Deposition fluxes ranged −28.5 − +1.8 μg m−2 d−1 for PAHs and −3.4 − +0.9 μg m−2 d−1 for halogenated compounds. Dry particle deposition of FLT and PYR did not contribute significantly to the vertical flux.

Dissolved inorganic carbon and alkalinity fluxes from coastal marine sediments: model estimates for different shelf environments and sensitivity to global change

We present a one-dimensional reactive transport model to estimate benthic fluxes of dissolved inorganic carbon (DIC) and alkalinity (AT) from coastal marine sediments. The model incorporates the transport processes of sediment accumulation, molecular diffusion, bioturbation and bioirrigation, while the reactions included are the redox pathways of organic carbon oxidation, re-oxidation of reduced nitrogen, iron and sulfur compounds, pore water acid-base equilibria, and dissolution of particulate inorganic carbon (calcite, aragonite, and Mg-calcite). The coastal zone is divided into four environmental units with different particulate inorganic carbon (PIC) and particulate organic carbon (POC) fluxes: reefs, banks and bays, carbonate shelves and non-carbonate shelves. Model results are analyzed separately for each environment and then scaled up to the whole coastal ocean. The model-derived estimate for the present-day global coastal benthic DIC efflux is 126 Tmol yr−1, based on a global coastal reactive POC depositional flux of 117 Tmol yr−1. The POC decomposition leads to a carbonate dissolution from shallow marine sediments of 7 Tmol yr−1 (on the order of 0.1 Pg C yr−1. Assuming complete re-oxidation of aqueous sulfide released from sediments, the effective net flux of alkalinity to the water column is 29 Teq. yr−1, primarily from PIC dissolution (46%) and ammonification (33%). Because our POC depositional flux falls in the high range of global values given in the literature, the reported DIC and alkalinity fluxes should be viewed as upper-bound estimates. Increasing coastal seawater DIC to what might be expected in year 2100 due to the uptake of anthropogenic CO2 increases PIC dissolution by 2.3 Tmol yr−1and alkalinity efflux by 4.8 Teq. yr−1. Our reactive transport modeling approach not only yields global estimates of benthic DIC, alkalinity and nutrient fluxes under variable scenarios of ocean productivity and chemistry, but also provides insights into the underlying processes.