The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime.

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020.

The Arctic Ocean has experienced rapid warming and sea ice loss in recent decades, becoming the first open-ocean basin to experience widespread aragonite undersaturation [saturation state of aragonite (Ωarag) < 1]. However, its trend toward long-term ocean acidification and the underlying mechanisms remain undocumented. Here, we report rapid acidification there, with rates three to four times higher than in other ocean basins, and attribute it to changing sea ice coverage on a decadal time scale. Sea ice melt exposes seawater to the atmosphere and promotes rapid uptake of atmospheric carbon dioxide, lowering its alkalinity and buffer capacity and thus leading to sharp declines in pH and Ωarag. We predict a further decrease in pH, particularly at higher latitudes where sea ice retreat is active, whereas Arctic warming may counteract decreases in Ωarag in the future.

Evidence for the growing importance of Eurasian local source to PAHs in the Arctic central basin.

Polycyclic aromatic hydrocarbons (PAHs) are traditionally considered to enter the Arctic Ocean through long-range transport. Arctic warming, especially sea ice retreat, will certainly increase the contribution from local source (such as river input and ice melting). However, this hypothesis remains poorly constrained for lack of quantitative evidence. Here PAHs in surface seawater (67°N-89°N, 152°E-177°E) and sea ice (82°N-89°N) were collected in the western Arctic in 2010. Dissolved concentrations of 15 PAHs (Σ15PAHs) in surface layer ice (26.2 to 49.8 ng/L) were one order of magnitude higher than the underlying seawater. The content of dissolved Σ15PAHs was significantly higher in the marginal ice zone than those in the Chukchi Sea shelf, and the dissolved Σ15PAHs concentration differed by nearly an order of magnitude in two closely adjacent sections in the basin area, which both showed high fraction of river water and sea ice meltwater. This pattern could be explained by the different local inputs from Eurasia and North America. This scenario was further visualized by ice back trajectories capturing significantly higher PAH signals from the Eurasian margin than those from North America and stable oxygen isotopic data finding a positive correlation of PAH levels with the fractions of river runoff and ice-melting water coming from the Eurasia. The PAHs budget of the Arctic Ocean was also dominated by local sources (river and ice melting) as inputs (76 %) and volatilization as outputs (47 %). This study reveals the importance of Eurasian local inputs in supplying PAHs to the central Arctic Ocean. Those processes, which have not been well recognized for PAHs previously, are expected to increase and will undermine global efforts to reduce exposure by remobilizing PAHs stored in permafrost and ice.

Microplastics in three typical benthic species from the Arctic: Occurrence, characteristics, sources, and environmental implications.

Microplastics (MPs) in the Arctic have raised increasing concern, but knowledge on MP contamination in benthic organisms from Arctic shelf regions, e.g., the Chukchi Sea is still limited. Therefore, the present study investigated the occurrence, characteristics, sources, and environmental implications of MPs in the three most common benthic species, namely sea anemone (Actiniidae und.), deposit-feeding starfish (Ctenodiscus crispatus), and snow crab (Chionoecetes opilio), from the Chukchi Sea. The abundances of MPs in the three benthic species were significantly greater than those from the Bering Sea, but lower than those from other regions globally. The top three compositions of MPs in the three species were polyester, nylon, and polyethylene terephthalate. The detection limit for MP size in the present study was 0.03 mm and the mean size of MP in the three species was 0.89 ± 0.06 mm. The surfaces of MPs found in the starfish and crabs were covered with many attachments, cracks, and hollows, while the surfaces of MPs found in the sea anemones were smooth, which was likely a consequence of different feeding behaviors. There was a significantly positive correlation between the abundances of MPs and other anthropogenic substances. The mean MP abundances in the sea anemones ranged from 0.2 items/individual to 1.7 items/individual, which was significantly higher than that in the deposit-feeding starfish (0.1-1.4 items/individual) and snow crabs (0.0-0.6 items/individual). Sea anemones inhabiting lower latitudes ingested relatively higher levels of MPs than those inhabiting higher latitudes. The MP abundances in the sea anemones are significantly and positively correlated with the seasonal reduced ratio of sea ice coverage from August to September. Our findings indicate that sea anemones could function as a bioindicator of MP pollution, and that the MPs in the benthos from the Chukchi Sea might originate from the melting sea ice, fishery activities and ocean currents.

Discrimination Algorithm and Procedure of Snow Depth and Sea Ice Thickness Determination Using Measurements of the Vertical Ice Temperature Profile by the Ice-tethered Buoys.

Snow depth and sea ice thickness in the Polar Regions are significant indicators of climate change and have been measured over several decades by ice-tethered buoys. However, sea ice temperature profiles measured by ice-tethered buoys are rarely used to infer snow depth and sea ice thickness owing to the lack of automatic discrimination algorithms, restricting the use of the data for sea ice thermodynamics studies. In this study, snow depth and sea ice thickness were retrieved through the measurements of sea ice temperature profiles using discrimination algorithms of the change point and the maximum likelihood detection methods. The data measured by 50 ice-tethered buoys were used to evaluate the accuracy of the results determined by the algorithm. Influences on the seasonal sea ice thermodynamic state, vertical interval of temperature sensors on the buoys, and initial ice thickness on the estimation errors were also evaluated. The performance of the discrimination algorithm for the data from the Arctic and Antarctic regions was also compared. There were no identifiable differences between the estimation errors from the Arctic and Antarctica. Increases in both the interval of the temperature sensors and the initial ice thickness enlarged the error for the estimation of ice thickness. A procedure developed in this study strengthens the potential application of measurements from the ice-tethered buoys only with the measurements of the vertical temperature profile of the layer of snow-covered ice, but not the measurements of ice basal and surface positions using acoustic sounding.

[Spectral features analysis of sea ice in the Arctic Ocean].

Sea ice in the Arctic Ocean plays an important role in the global climate change, and its quick change and impact are the scientists' focus all over the world. The spectra of different kinds of sea ice were measured with portable ASD FieldSpec 3 spectrometer during the long-term ice station of the 4th Chinese national Arctic Expedition in 2010, and the spectral features were analyzed systematically. The results indicated that the reflectance of sea ice covered by snow is the highest one, naked sea ice the second, and melted sea ice the lowest. Peak and valley characteristics of spectrum curves of sea ice covered by thick snow, thin snow, wet snow and snow crystal are very significant, and the reflectance basically decreases with the wavelength increasing. The rules of reflectance change with wavelength of natural sea ice, white ice and blue ice are basically same, the reflectance of them is medium, and that of grey ice is far lower than natural sea ice, white ice and blue ice. It is very significant for scientific research to analyze the spectral features of sea ice in the Arctic Ocean and to implement the quantitative remote sensing of sea ice, and to further analyze its response to the global warming.

Simultaneous nitrogen and phosphorus removal by a novel sequencing batch moving bed membrane bioreactor for wastewater treatment.

Biological nutrient removal (BNR) was investigated in a sequencing batch membrane bioreactor which used carriers instead of activated sludge named a sequencing batch moving bed membrane bioreactor (SBMBMBR). The SBMBMBR performed well on carbon and nitrogen removal at different COD/TN ratios. COD, TN and ammonium nitrogen removal efficiencies averaged at 93.5%, 82.6% and 95.6%, respectively. The TP removal was closely correlated with the length of anaerobic phase and aerobic phase. When anaerobic time and aerobic time were both 2h, the average TP removal efficiency reached to 84.1% at influent TP concentration of 12.4 mg/L. DO in aerobic phase was an important factor affecting nutrient removal, and the optimal DO was about 3mg/L. There was a small amount of denitrifying phosphorus accumulating organisms (DPAOs) in SBMBMBR which resulted from the anoxic microenvironment existed in the inner of the biofilm. Fluorescence in situ hybridization (FISH) results of microbes showed the composition and spatial structure of the microbial community in the reactor. Furthermore, sequencing batch mode operation was propitious to retard membrane fouling.

Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on membrane fouling.

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated to minimize the effect of suspended solids on membrane fouling. The MBMBR and a conventional membrane bioreactor (CMBR) were operated in parallel for about two months. Unexpectedly, the rate of membrane fouling in MBMBR was about three times of that in CMBR. MBMBR showed a higher cake layer resistance than CMBR due to plenty of filamentous bacteria inhabited in suspended solids in MBMBR. Protein and polysaccharide contents of soluble EPS in MBMBR were obviously larger than those in CMBR. It could be speculated that the overgrowth of filamentous bacteria in MBMBR resulted in severe cake layer and induced a large quantity of EPS, which deteriorated the membrane fouling.

Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on organic carbon and nitrogen removal.

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated for simultaneously removing organic carbon and nitrogen in wastewater. Its performance was compared with a conventional membrane bioreactor (CMBR) at various influent COD/TN ratios of 8.9-22.1. The operational parameters were optimized to increase the treatment efficiency. COD removal efficiency averaged at 95.6% and 96.2%, respectively, for MBMBR and CMBR during the 4 months experimental period. The MBMBR system demonstrated good performance on nitrogen removal at different COD/TN ratios. When COD/TN was 8.9 and the total nitrogen (TN) load was 7.58 mg/l h, the TN and ammonium nitrogen removal efficiencies of the MBMBR were maintained over 70.0% and 80.0%, respectively, and the removed total nitrogen (TN) load reached to 5.31 mg/l h. Multifunctional microbial reactions in the carrier, such as simultaneous nitrification and denitrification (SND), play important roles in nitrogen removal. In comparison, the CMBR did not perform so well. Its TN removal was not stable, and the removed total nitrogen (TN) load was only 1.02 mg/l h at COD/TN ratio 8.9. The specific oxygen utilization rate (SOUR) showed that the biofilm has a better microbial activity than an activated sludge. Nevertheless, the membrane fouling behavior was more severe in the MBMBR than in the CMBR due to a thick and dense cake layer formed on the membrane surface, which was speculated to be caused by the filamentous bacteria in the MBMBR.