Global budgets of methyl halides are not balanced between currently identified sources and sinks. Among biological sources, rapeseed is regarded as the second largest terrestrial source of CH 3 Br, extrapolated from laboratory-based incubations and limited field measurements. This study analyzes the CH 3 Br budget from rapeseed (Brassica napus "Empire"), using field-based life cycle measurements, yielding a globally scaled emission rate of 2.8 ± 0.7 Gg year −1. Though this verifies that rapeseed is a significant global source, it is just half of the previous estimation, even after accounting for the doubling of global annual rapeseed production since then. The ozone-depleting potential of rapeseed is further sustained through CH 3 Cl and CH 3 I emissions, which were measured for the first time and scaled to 5.3 ± 1.3 and 4.0 ± 0.8 Gg year −1 globally. Plain Language Summary Stratospheric ozone absorbs incoming solar UV radiation, attenuating the harmful radiation exposure for life on Earth's surface. Halogen atoms transported via halocarbons, including methyl halides, can catalyze ozone destruction efficiently in the stratosphere. Anthropogenic sources of halocarbons have been decreasing consistently since the implementation of the 1987 Montreal Protocol and its amendments. However, some natural sources, especially those influenced by anthropogenic activities, may offset some of the achievement of reduced halocarbon emissions. This study quantifies methyl halide emissions from cultivated rapeseed (Brassica napus, cultivar: Empire), based on life cycle measurements and normalized to seed production. This yields a global crop contribution of 2.8 ± 0.7 Gg of methyl bromide (CH 3 Br) annually, which is smaller than previous estimates (5.1-6.6 Gg), supporting the conventional view that there must be other unidentified or underestimated sources for CH 3 Br. This study also quantifies for the first time that rapeseed emits 5.3 ± 1.3 Gg of methyl chloride (CH 3 Cl) and 4.0 ± 0.8 Gg of methyl iodide (CH 3 I) each year. Due to the increasing demand on rapeseed products such as canola oil, its global methyl halide emissions are expected to grow in the future.

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are major carriers of atmospheric bromine and chlorine, respectively, which can catalyze stratospheric ozone depletion. However, in our current understanding, there are missing sources associated with these two species. Here we investigate the effect of copper(II) on CH3Br and CH3Cl production from soil, seawater and model organic compounds: catechol (benzene-1,2-diol) and guaiacol (2-methoxyphenol). We show that copper sulfate (CuSO4) enhances CH3Br and CH3Cl production from soil and seawater, and it may be further amplified in conjunction with hydrogen peroxide (H2O2) or solar radiation. This represents an abiotic production pathway of CH3Br and CH3Cl perturbed by anthropogenic application of copper(II)-based chemicals. Hence, we suggest that the widespread application of copper(II) pesticides in agriculture and the discharge of anthropogenic copper(II) to the oceans may account for part of the missing sources of CH3Br and CH3Cl, and thereby contribute to stratospheric halogen load.

Methyl chloride (CH 3 Cl) and methyl bromide (CH 3 Br) are the predominant carriers of natural chlorine and bromine from the troposphere to the stratosphere, which can catalyze the destruction of stratospheric ozone. Here, penguin colony soils (PCS) and the adjacent tundra soils (i.e., penguin-lacking colony soils, PLS), seal colony soils (SCS), tundra marsh soils (TMS), and normal upland tundra soils (UTS) in coastal Antarctica were collected and incubated for the first time to confirm that these soils were CH 3 Cl and CH 3 Br sources or sinks. Overall, tundra soil acted as a net sink for CH 3 Cl and CH 3 Br with potential flux ranges from −18.1 to −2.8 pmol g −1 d −1 and −1.32 to −0.24 pmol g −1 d −1 , respectively. The deposition of penguin guano or seal excrement into tundra soils facilitated the simultaneous production of CH 3 Cl and CH 3 Br and resulted in a smaller sink in PCS, SCS, and PLS. Laboratory-based thermal treatments and anaerobic incubation experiments suggested that the consumption of CH 3 Cl and CH 3 Br was predominantly mediated by microbes while the production was abiotic and O 2 independent. Temperature gradient incubations revealed that increasing soil temperature promoted the consumption of CH 3 Cl and CH 3 Br in UTS, suggesting that the regional sink may increase with Antarctic warming, depending on changes in soil moisture and abiotic production rates.

Stable carbon isotope ratios ( 13 C/ 12 C) have been extensively used to trace carbon flow, and partition net ecosystem CO 2 exchange. However, the CO 2 isotopic data are still very limited in terrestrial ecosystems of maritime Antarctica. Here, we chose six tundra sites to investigate the isotopic compositions of CO 2 during ecosystem respiration and photosynthesis, and the relationships with environmental variables using the static chamber method. For all tundra sites, ecosystem respirated-CO 2 was 13 C-depleted while vegetation photosynthesis resulted in the enrichment of 13 C in the chamber headspace, compared with local atmospheric CO 2 . The δ 13 C-CO 2 showed a strong negative correlation with CO 2 concentrations in the chamber headspace both under dark condition (r 2 = 0.70, p < 0.01) and under light condition (r 2 = 0.29, p < 0.05), whereas δ 18 O-CO 2 was almost stable, only with a small fluctuation from − 7.7 to − 8.3‰. The δ 13 C of ecosystem-respired (δ r ) and photoassimilated-CO 2 (δ p ) fluctuated from − 12.4 to − 15.1‰ and − 10.5 to − 12.6‰, respectively, indicating that lower C isotopic discrimination occurred during plant photosynthesis and tundra ecosystem respiration, compared with reported data from other global ecosystems. Overall there was a small but distinct negative carbon isotopic disequilibrium (D: − 1 to − 3‰) between δ r and δ p at the spatial or summertime scale. The δ p and δ r showed consistent summertime variation patterns with significant positive correlation (r 2 = 0.95, p < 0.01). The δ r and δ p significantly negatively correlated with respiration rates (r 2 = 0.91, p < 0.01) and photosynthesis rates (r 2 = 0.86, p < 0.01), respectively, and the δ r , instead of δ p , significantly correlated with net ecosystem exchange fluxes (r 2 = 0.75, p = 0.012). The summertime patterns of δ r , δ p and D sensitively corresponded to changing temperature, precipitation and sunlight intensity, supporting the links between CO 2 isotope fractionation and environmental variables during ecosystem respiration and plant photosynthesis. It was found that penguin activities had no significant effect on δ r and δ p although their activities significantly increased tundra ecosystem respiration and photosynthesis fluxes. The investigation of CO 2 isotopic compositions contributes to better understanding of carbon cycling in maritime Antarctic tundra ecosystems.

No abstract

No abstract

Chlorine-containing halocarbons, such as chloromethane (CH 3 Cl), chloroform (CHCl 3 ), and chlorofluorocarbons (CFCs), can photo-dissociate in the stratosphere, releasing reactive chlorine radicals that catalyze ozone depletion. Among the naturally produced atmospheric chlorocarbons, CHCl 3 is the second-largest natural carrier of chlorine after CH 3 Cl. With an average tropospheric lifetime of 149 days (Engel et al., 2018), it is categorized as a very short-lived substance (VSLS). Hence, the ozone-depleting capacity of CHCl 3 was thought to be minor and was not regulated by the Montreal Protocol. However, observations over the past decade showed its atmospheric molar fractions have been steadily increasing (Engel et al., 2018;Fang et al., 2019). Numerical model simulations also indicated the recovery of stratospheric ozone may be significantly delayed if atmospheric concentrations of VSLSs, including CHCl 3 , continue to grow (Fang et al., 2019).Natural sources of CHCl 3 are believed to predominate over anthropogenic sources, accounting for 50%-90% of global CHCl 3 emissions (McCulloch, 2003;Worton et al., 2006). The natural emissions of CHCl 3 are

&lt;p&gt;Carbonyl sulfide (OCS), the most abundant atmospheric sulfur-carrying gas, can contribute to regulating Earth&amp;#8217;s radiative balance through forming sulfate aerosols. The bryophyte-dominated tundra lying over the ice-free Antarctica is an important terrestrial carbon sink and provides colonies for sea animals, such as penguins and seals, which remains hitherto unexplored concerning OCS biogeochemistry. Here, we measured OCS fluxes from the Antarctic tundra and coupled their fluxes to soil biogeochemical properties to explore OCS production and degradation processes. The bryophyte-dominated normal upland tundra was an OCS sink at -0.97 &amp;#177; 0.57 pmol m&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, resulting from both bryophytes and OCS-metabolizing enzymes (e.g., carbon anhydrase, nitrogenase) secreted by soil microbes, such as &lt;em&gt;Acidobacteria,&lt;/em&gt; &lt;em&gt;Verrucomicrobia&lt;/em&gt;, &lt;em&gt;Chloroflexi&lt;/em&gt;, and &lt;em&gt;Mortierellomycota&lt;/em&gt;. In comparison, tundra within sea animal colonies was an OCS source up to 1.35 &amp;#177; 0.38 pmol m&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, due to the input of organosulfur from sea animals and the animal-induced anaerobic soil environment, which promoted simultaneous abiotic OCS production in soil, and outweighed the biogenic OCS uptake by bryophytes and soil microbes. Furthermore, sea animal colonization shaped the soil microenvironment, affecting nutrient levels, pH and moisture, which may have reduced the abundances of OCS-metabolizing microbes and thereby OCS degradation and further unveiled concurrent OCS production. Basic calculation suggested that sea animals contribute about 107 metric tons yr&lt;sup&gt;-1&lt;/sup&gt; of OCS-S to the atmosphere. The strength of this OCS source is expected to increase in response to Antarctic warming. Overall, tundra ecosystems are important interfaces for OCS exchange and sea animals exert an impact on the sulfur cycle in coastal Antarctica.&lt;/p&gt;