Toward Citizen Science-Based Ocean Acidification Observations Using Smartphone Devices.

pH is a key parameter in many chemical, biological, and biogeochemical processes, making it a fundamental aspect of environmental monitoring. Rapid and accurate seawater pH measurements are essential for effective ocean observation and acidification investigations, resulting in the need for novel solutions that allow robust, precise, and affordable pH monitoring. In this study, a versatile smartphone-based environmental analyzer (vSEA) was used for the rapid measurement of seawater pH in a field study. The feasibility of the use of the vSEA algorithm for pH quantification was explored and verified. When used in conjunction with a three-dimensional (3D)-printed light-proof shell, the quality of captured images is guaranteed. The quantitative accuracy of vSEA pH measurements reached 0.018 units with an uncertainty of <0.01, meeting the requirements of the Global Ocean Acidification Observing Network (GOA-ON) for "weather" goals (permitting a maximum pH uncertainty of 0.02). The vSEA-pH system was successfully applied for on-site pH measurements in coastal seawater and coral systems. The performance of the vSEA-pH system was validated using different real-world samples, and t-test results showed that the vSEA-pH system was consistent with pH measurements obtained using a state-of-the-art benchtop spectrophotometer (t = 1.986, p = 0.7949). The vSEA-pH system is applicable to different types of smartphone devices, making it possible for vSEA-pH to be widely promoted for public citizen use. The vSEA-pH system offers a simple, accurate, and applicable method for the on-site measurement of seawater pH, assisting the large-scale monitoring of ocean acidification by allowing the contribution of citizen science-based data collection.

Seasonal isotopic and isotopomeric signatures of nitrous oxide produced microbially in a eutrophic estuary.

Anthropogenic input of excess nutrients stimulates massive nitrous oxide (N2O) production in estuaries with distinct seasonal variations. Here, nitrogen isotopic and isotopomeric signatures were utilized to investigate the seasonal dynamics of N2O production and nitrification at the middle reach of the eutrophic Pearl River Estuary in the south of China. Elevated N2O production primarily via ammonia oxidation (> 1 nM-N d-1) occurred from April to November, along with increased temperature and decreased dissolved oxygen concentration. This consistently oxygenated water column showed active denitrification, contributing 20-40 % to N2O production. The water column microbial N2O production generally constituted a minor fraction (10-15 %) of the estuarine water-air interface efflux, suggesting that upstream transport and tidal dilution regulated the dissolved N2O inventory in the middle reach of the estuary. Nitrification (up to 3000 nM-N d-1) played a critical role in bioavailable nitrogen conversion and N2O production, albeit with N2O yields below 0.05 %.

Relationships among the climate-relevant gases during the Southern Ocean bloom season.

The ocean plays an essential role in regulating the sources and sinks of climate-relevant gases, like CO2, N2O and dimethyl sulfide (DMS), thus influencing global climate change. Although the Southern Ocean is known to be a strong carbon sink, a significant DMS source and possibly a large source of N2O, our understanding of the interaction among these climate-relevant gases and their potential impacts on climate change is still insufficient in the Southern Ocean. Herein, we analyzed parameters, including surface water pCO2, dissolved inorganic carbon (DIC), alkalinity (TA), DMS and N2O in the water column, collected during the austral summer of 2015-2016 in the 32nd Chinese Antarctic Research Expedition (CHINARE) at the tip of Antarctic Peninsula. A positive correlation between DMS and pCO2 (indicated by deficit of DIC, ∆DIC, refer to values in 100 m) was observed in waters above 75 m, whereas no correlation between N2O saturation anomaly (SA) and DMS, ∆DIC was found. In the area with stable stratification with phytoplankton bloom, significant DMS source and strong CO2 uptake with weak N2O emission were observed. Conversely, strong mixing or upwelling area was shown to be a strong marine CO2 source and significant N2O release with weak DMS source.

Underway mapping of coastal seawater pH using an automated shipboard analyzer with spectrophotometric detection.

The development of field-deployable methods and instruments for the measurement of pH and other carbonate parameters is important for the assessment of the marine carbon cycle, ocean acidification and marine carbon dioxide removal techniques. In this study, a high-precision fully automated integrated syringe-pump-based environmental-water analyzer for pH (iSEA-pH) was developed. The pH is determined spectrophotometrically using purified indicator dye with a high precision (better than ±0.001) and high frequency (3.5 min/sample). For the short-term analysis, the measurement frequency was 18 h-1, which revealed pH = 7.8148 ± 0.0005 (n = 104) for aged surface seawater (S = 35) from the western Pacific. For long-term analysis, the measurement frequency was 2 h-1 for 4 days, and the results showed that pH = 7.8148 ± 0.0010 (n = 200). Three commonly used pH indicators (meta-cresol purple, thymol blue and phenol red) were purified with improved flash chromatography procedures. The autonomous iSEA-pH can automatically correct for the influence of temperature, salinity and other factors on pH measurements to achieve rapid and accurate on-site measurements, which meet the "climate" goal of the Global Ocean Acidification Observing Network (uncertainty is ±0.003). Three identical iSEA-pH systems were developed and successfully applied in mesocosm experiments and several coastal and open ocean cruises with excellent in field performance.

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.