Oceanic Source Research Articles

Mesozoic felsic magmatism along the Bangong–Nujiang suture zone, Tibet: Temporospatial variations and tectonic implications

The subduction history and closure of the Meso-Tethys Ocean have not yet been well constrained using data from felsic rocks along the Bangong–Nujiang suture zone. Here we present geochronological, geochemical, and isotopic data from Early Jurassic–Late Cretaceous felsic rocks in the Laguo Co area of central Tibet. We combine our results with published data from coeval felsic rocks to explore the temporospatial variations in magmatism and the implications for subduction in and closure of the Meso-Tethys Ocean. The studied rocks include 182–180 Ma granodiorite, 109 Ma granite porphyry, and 68 Ma rhyolite, and zircon grains from each yield different εHf(t) values (+8.9 to +14.0, −5.5 to +0.7, and −4.9 to +1.1, respectively). The rocks have low-K tholeiitic to medium-K calc-alkaline compositions, low Y and Yb contents, and positive Sr anomalies. These data suggest an oceanic source for the Early Jurassic granodiorite and a crustal source for the Cretaceous granite porphyry and rhyolite, as well as a tectonic transition from an oceanic arc during the Early Jurassic to continental collision during the Cretaceous. The temporospatial variation in felsic magmatism corresponds to intra-oceanic subduction, bidirectional subduction, oceanic ridge or flat subduction, slab rollback, slab breakoff or sinking, and lithospheric delamination. The timing of closure of the Meso-Tethys Ocean is constrained to the Jurassic–Cretaceous, as evidenced by the major differences of the magma sources and formation processes between the Jurassic and Cretaceous felsic rocks. Finally, we present a model showing that oceanic closure occurred earlier in the east and north and later in the west and south.

Influence of natural and anthropogenic aerosols on cloud base droplet size distributions in clouds over the South China Sea and West Pacific

Abstract. Cumulus clouds are common over maritime regions. They are important regulators of the global radiative energy budget and global hydrologic cycle, as well as a key contributor to the uncertainty in anthropogenic climate change projections due to uncertainty in aerosol–cloud interactions. These interactions are regionally specific owing to their strong influences on aerosol sources and meteorology. Here, our analysis focuses on the statistical properties of marine boundary layer (MBL) aerosol chemistry and the relationships of MBL aerosol to cumulus cloud properties just above cloud base as sampled in 2019 during the NASA Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex). The aerosol and clouds were sampled by instruments on the NASA P-3 aircraft over three distinct maritime regions around the Philippines: the West Pacific, the South China Sea, and the Sulu Sea. Our analysis shows three primary sources influenced the aerosol chemical composition: clean marine (ocean source), industrial (Southeast Asia, Manila, and cargo and tanker ship emissions), and biomass burning (Borneo and Indonesia). The clean marine aerosol chemical composition had low values of all sampled chemical signatures, specifically median values of 2.2 µg m−3 of organics (ORG), 2.3 µg m−3 of SO4, 0.3 µg m−3 of NO3, 1.4 µg m−3 of NH4, 0.04 µg m−3 of Cl, and 0.0074 µg m−3 of refractory black carbon (BC). Chemical signatures of the other two aerosol source regions were industrial, with elevated SO4 having a median value of 6.1 µg m−3, and biomass burning, with elevated median concentrations of ORG 21.2 µg m−3 and BC 0.1351 µg m−3. Based on chemical signatures, the industrial component was primarily from ship emissions, which were sampled within 60 km of ships and within projected ship plumes. Normalized cloud droplet size distributions in clouds sampled near the MBL passes of the P-3 showed that clouds impacted by industrial and biomass burning contained higher concentrations of cloud droplets, by as much as 1.5 orders of magnitude for diameters < 13 µm compared to clean marine clouds, while at size ranges between 13.0–34.5 µm the median concentrations of cloud droplets in all aerosol categories were nearly an order of magnitude less than the clean marine category. In the droplet size bins centered at diameters > 34.5 µm concentrations were equal to, or slightly exceeded, the concentrations of the clean marine clouds. These analyses show that anthropogenic aerosols generated from industrial and biomass burning sources significantly influenced cloud base microphysical structure in the Philippine region enhancing the small droplet concentration and reducing the concentration of mid-sized droplets.

Temporal variability in seawater Sr/Ca ratios within a coral atoll as an indicator of marine calcifier community diversity

Coral reefs are marine environments where calcium carbonate production and dissolution along with photosynthesis and respiration can have a large impact on the daily biogeochemical cycles of seawater dissolved inorganic carbon (DIC), total alkalinity (TA), oxygen (O2), and major nutrients. Using seawater samples from Tetiaroa Atoll, French Polynesia, we apply isotope dilution thermal ionization mass spectrometry (ID-TIMS) to show that these daily cycles of variability extend to the dissolved seawater Sr/Ca ratio (Sr/Casw). Hourly measurements over a 27+ hour period indicate that Sr/Casw covaries with DIC and TA and exhibits up to a 2% relative difference compared to the regional Pacific Ocean source water Sr/Casw value of 8.53 mmol/mol. We hypothesize that the primary mechanism of hourly variability in Sr/Casw is carbonate precipitation/dissolution by corals and other marine calcifiers on the Tetiaroa reef, while sedimentary redox processes may significantly contribute to an apparent decoupling between net calcification rates estimated from TA compared to dissolved calcium [Ca]sw concentrations. Using a simple Rayleigh distillation model and a two-member mixing equation, we estimate the net partition coefficient of Sr (KD-Sr) for each hourly sample as a mixture of coral (aragonite; KD-Sr ∼ 1.06) and crustose coralline algae (high Mg-calcite; KD-Sr ∼ 0.39) contributions to the measured variability of [Ca]sw and Sr/Casw. As the high Mg-calcites of crustose coralline algae are (1) integral components to the structure and stability of the reef framework and (2) more soluble than aragonite under more acidic conditions, we propose that continued analyses of Sr/Casw within coral reef environments could be a useful tool for monitoring the ecological distribution and contributions of marine calcifiers on reefs as ocean warming and acidification intensify in response to anthropogenic climate change. Additionally, seasonal, interannual, and/or centennial-scale offsets between the Sr/Casw of open ocean source seawater and ambient reef seawater may have significant implications for interpreting past changes in sea surface temperatures derived from the coral Sr/Ca paleothermometer.

Warm Season Extreme Flood Events in the Midwestern US—Sources of Moisture and Physical Mechanisms

AbstractA comprehensive picture of the development of warm season extreme floods in the Midwestern US is presented. We first identify the climatological moisture sources for precipitation in the Midwest using the two‐layer dynamic recycling model (2L‐DRM) with ECMWF Reanalysis v5 (ERA5) data. Terrestrial sources supply most of the moisture for Midwestern US precipitation during the warm season, while oceanic sources dominate during the cold season. The Empirical Orthogonal Function (EOF) analysis is used to select extreme flood events characterized by both positive soil moisture and precipitation anomalies. During the warm season flood events, moisture coming from oceanic sources increases by more than 45% compared to the climatology. In addition, our results show that moisture can come from remote regions due to sustained anomalous circulation. Low‐level circulation anomalies associated with wave trains that traverse the continent enhance moisture contributions from terrestrial sources along narrow paths. However, moisture budget analysis reveals that the primary flood‐producing mechanism is the convergence of moisture due to intense circulation anomalies. Moisture advection and thermodynamic terms are responsible for flood termination. Our results suggest that knowledge of antecedent wet soil moisture conditions is unlikely to improve the predictability of flood‐producing storms.

Seasonal and regional variations of atmospheric ammonia across the South Korean Peninsula

This study aimed to identify the factors causing NH3 emissions in the South Korean Peninsula and West Sea region. To analyze the trends of NH3 and other air pollutants, such as NOx, CO, and NR-PM1, we collected samples from six supersites across the peninsula, a roadside in Seoul, and the West Sea over different sampling periods, ranging from 1 month to 1 year. The highest NH3 concentrations were found at rural areas, ascribed to agricultural activities, particularly NH4NO3 decomposition at high summer temperatures. Areas with low population densities recorded the lowest NH3 concentrations, attributed to the lack of anthropogenic activities. A roadside field experiment confirmed the close link between ambient NH3 and vehicle emissions in urban regions by showing a strong correlation between CO and NOx concentrations and that of NH3. Moreover, we examined oceanic emissions near the eastern coast of South Korea in the West Sea. Long-range transportation studies confirmed that most of the pollutants (NH3, CO, and PM1) were transported by wind from the northeastern region of China. A maritime origin study showed that oceanic emissions and NH4NO3 decomposition in the atmosphere owing to high temperatures were the causing NH3 pollution. These findings provided valuable insights into the emission sources of NH3 in primary air pollutants in South Korea, highlighting the contributions of land-based and oceanic sources. Our study can help inform policymakers and stakeholders for developing effective regional air pollution control strategies.

Recruitment of Psostlarval Spiny Lobster, Stone Crabs, and Larval Fish to Back-Reef Nursery Habitats in the Florida Keys, USA

Back reef areas contain a mosaic of relatively shallow habitats that serve as a key nursery for reef species. Expansive back reef habitats in the lower Florida Keys, USA border the Atlantic Ocean and the Gulf of Mexico. A combination of floating, artificial settlement substrates and plankton nets moored in channels connecting coastal waters and back reef habitats quantified spiny lobster (Panulirus argus) and stone crab (Menippe sp.) settlement, and larval fish ingress, respectively, during 1999 and 2002–2003. The key finding was that channels connecting coastal waters with back reef areas serve as conduits for ingressing larval spiny lobster, stone crabs, and fishes. The results highlight the important role of Atlantic Ocean sources of spiny lobster pueruli and lutjanid fish larvae in this back reef system, and Gulf sources of stone crabs. Spiny lobster settlement generally peaked in August and September and occurred on the Atlantic Ocean side of this back reef system; settlement of stone crabs peaked at the same time as spiny lobster yet occurred predominantly on the Gulf side. Recruitment of larval fish was higher on the Atlantic than the Gulf side, with 37% of fish species collected nearly exclusively on the Atlantic side and about 25% collected nearly exclusively on the Gulf side. Channel habitats appear critical to supporting the nursery role of back reef habitats and should receive special consideration in future ecosystem studies, as well as during spatial planning and evaluations of essential fish habitat.

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Quantification of the Emission of Atmospheric Microplastics and Nanoplastics via Sea Spray

There is growing interest in the transfer of micro- and nanoplastics (MNP) to the atmosphere from the ocean via sea spray, and a limited number of studies have quantified this emission. This study addresses the uncertainty surrounding existing global oceanic MNP emission estimates by developing an experimentally based emission parametrization. We conducted systematic laboratory experiments to understand the impact of MNP size, density, and concentration in water on their aerosolization. The results show that the MNP considered in this study, with a diameter of ≤10 μm, can be emitted via bubble bursting, with the aerosolization increasing monotonically with an increase in the concentration in water and decreasing with an increase in the particle size. Floating polyethylene MNP are observed to be less effectively aerosolized than polystyrene MNP dispersed in bulk water. Using the developed emission parametrization, we estimate that the upper limit of yearly MNP oceanic emission is 50.7 (14.2–93.4) quadrillion (1015) pieces year–1 and 1.66 (0.72–4.13) t year–1. The experimental measurements and ensuing parametrization developed in this study are a timely contribution to the atmospheric microplastic modeling community and will help in further constraining the oceanic source of atmospheric MNP and their potential climatic, environmental, and health implications.

Tracing Oceanic Sources of Heat Content Available for Atlantic Hurricanes

AbstractIn the Main Development Region (MDR) for Atlantic hurricanes, the volume of water warmer than 26.5°C quantifies the potential source of energy for major storms. Taking a Lagrangian perspective, this warm water is backtracked on seasonal timescales in an eddy‐resolving ocean model hindcast spanning 1988–2010. Being confined near the surface and assuming a mixed layer depth of 50 m, net heat fluxes into or out of water parcels advected toward the MDR are inferred from along‐trajectory temperature tendencies. To first order, these heat fluxes match surface net heat fluxes during the months over which water advects into the region. Contributions to this warm water in the preceding 6 months include water resident in the MDR (20%–40%), arriving via the North Brazil Current (NBC, 5%–15%), or via Ekman drift across 10°S. In relative terms, decreased contributions from the NBC and Ekman drift and more in situ warming within the MDR lead to warmer, more active hurricane seasons.

The rare case of Hurricane Catarina (2004) over the South Atlantic Ocean: The origin of its precipitation through a Lagrangian approach

AbstractTropical cyclones (TCs) are extremely rare over the South Atlantic Ocean (SATL) due to predominantly unfavourable conditions, that is, cool sea‐surface temperature and strong vertical wind shear. Nevertheless, unusual conditions over SATL associated with a blocking system promoted the formation of Hurricane Catarina from an extratropical precursor in late March 2004, which produced heavy rainfall over the states of Santa Catarina and the Rio Grande do Sul in south Brazil. This work identifies the moisture sources for the precipitation produced by Catarina along its 6‐hourly trajectory, through a Lagrangian moisture‐tracking method. We extracted the pathways of precipitating air parcels within the cyclone's outer radius from the global outputs of the FLEXPART model forced with the ERA‐Interim reanalysis. Our findings revealed the terrestrial source in south‐southeastern Brazil (SEB) and the oceanic source limited by the box between 20‐40°S and 30–50°W over SATL (WSATL) as the principal moisture sources, with the overall support of ∼27% and ∼66%, respectively. However, their contribution varied according to the development phase of Catarina. While the moisture uptake from SEB decreased from ∼75% during the extratropical phase to ∼8% during the hybrid stage, the moisture contribution from WSATL notable increased from ∼20% to 87%, respectively. Likewise, the contributions from SEB and WSATL during the tropical phase of the cyclone accounted for ∼13% and ∼85%, respectively. The tracked air parcels achieved the high water content in a short period before the precipitation, leading to a reduction of the mean water vapour residence time to ∼3.1 days. Additionally, the precipitating moisture uptake along the Catarina trajectory was noticeably higher than the climatological value.

Intercomparison of Atmospheric Carbonyl Sulfide (TransCom‐COS; Part One): Evaluating the Impact of Transport and Emissions on Tropospheric Variability Using Ground‐Based and Aircraft Data

AbstractWe present a comparison of atmospheric transport model (ATM) simulations for carbonyl sulfide (COS), within the framework of the atmospheric tracer transport model intercomparison project “TransCom‐COS.” Seven ATMs participated in the experiment and provided simulations of COS mixing ratios over the years 2010–2018, using state‐of‐the‐art surface fluxes for various components of the COS budget: biospheric sink, oceanic source, sources from fire and industry. The main goal of TransCom‐COS is to investigate the impact of the transport uncertainty and emission distribution in simulating the spatio‐temporal variability of tropospheric COS mixing ratios. A control case with seasonal surface fluxes of COS was constructed. The results indicate that the COS mixing ratios are underestimated by at least 50 parts per trillion (ppt) in the tropics, pointing to a missing tropical source. In summer, the mixing ratios are overestimated by at least 50 ppt above 40°N, pointing to a likely missing sink in the high northern latitudes. Regarding the latitudinal profile, the model spread is greater than 60 ppt above 40°N in boreal summer. Regarding the seasonal amplitude, the model spread reaches 50 ppt at 6 out of 15 sites, compared to an observed seasonal amplitude of 100 ppt. All models simulated a too late minimum by at least 2–3 months at two high northern‐latitude sites, likely owing to errors in the seasonal cycle in the ocean emissions. This study highlighted the shortcomings in the COS global budget that need to be resolved before using COS as a photosynthesis tracer.

Sources of water vapor and their effects on water isotopes in precipitation in the Indian monsoon region: a model-based assessment

Climate records of ratios of stable water isotopes of oxygen (δ18O) are used to reconstruct the past Indian monsoon precipitation. Identifying the sources of water vapor is important in understanding the role of monsoonal circulation in the δ18O values, to aid in monsoon reconstructions. Here, using an isotope-enabled Earth system model, we estimate the contributions of oceanic and terrestrial water vapor sources to two major precipitation seasons in India—the Southwest monsoon and the Northeast monsoon, and their effects on the δ18O in precipitation (δ18Op). We find that the two monsoon seasons have different dominant sources of water vapor because of the reversal in atmospheric circulation. While Indian Ocean regions, Arabian Sea, and recycling are the major sources of the Southwest monsoon precipitation, North Pacific Ocean and recycling are two crucial sources of Northeast monsoon precipitation. The δ18Op of the Southwest monsoon precipitation is determined by contributions from the Indian Ocean sources and recycling. Despite reduced precipitation, more negative δ18Op values are simulated in the Northeast monsoon season due to larger negative δ18Op contributions from the North Pacific. Our results imply that changes in atmospheric circulation and water vapor sources in past climates can influence climate reconstructions using δ18O.

The challenges of driving Charon's cryovolcanism from a freezing ocean

A combination of geological interpretations and thermal-orbital evolution models imply that Pluto's large moon, Charon, had a subsurface water (and possibly ammonia) ocean that eventually froze. Ocean freezing generates large tensile stresses in the upper part of the ice shell and pressurizes the ocean below, perhaps leading to the formation of Charon's large canyons and putative cryovolcanic flows. Here, we identify the conditions in which a freezing ocean could create fractures that fully penetrate its ice shell, linking Charon's surface with its ocean and facilitating ocean-sourced cryovolcanism. We find that current models of Charon's interior evolution predict ice shells that are far too thick to be fully cracked by the stresses associated with ocean freezing. Either Charon's ice shell was <10 km thick when the flows occurred (as opposed to >100 km) or the surface was not in direct communication with the ocean as part of the eruptive process. If Charon's ice shell had been thin enough to be fully cracked, it would imply substantially more ocean freezing than is indicated by the canyons, Serenity and Mandjet Chasma. Due to the low radiogenic heating within Charon and the loss of tidal heating early in its history, a thin ice shell should have been short-lived, implying that ocean-sourced cryovolcanic flows would have ceased relatively early in Charon's history, consistent with interpretations of its surface geology. An additional (and perhaps implausibly large) heat source would be required to generate the substantially larger ocean implied by through-going fractures. We also find that ocean freezing can easily generate deep fractures that do not fully penetrate to the ocean, which may be the foundation of Charon's canyons. Plain language summaryWhen ocean-bearing moons begin to cool down, their oceans can freeze. As new ice accretes to the bottom of the existing ice shell, the added volume of the ice can stress the shell. Pluto's largest moon, Charon, has canyons and cryovolcanic flows that may have formed in response to a freezing ocean. Here, we model the formation of fractures within Charon's ice shell as the ocean underneath it freezes to explore the evolution of Charon's interior and surface. We find that an ocean source for cryovolcanic flows is unlikely because the ice shell would have had to be much thinner than current thermal evolution models imply. However, freezing the ocean may have produced the stresses that formed canyons later in Charon's history.

Sediment carbon sequestration and sources in peri-urban tidal flats and adjacent wetlands in a megacity

We investigated the sediment carbon (C) stocks, sequestration and sources in tidal flats and their adjacent mangroves in two coastal wetlands in Hong Kong (the Mai Po Nature Reserve (MPNR) and Ting Kok (TK)), part of a megacity of ∼20 million. At both locations, the C stock of tidal flats was lower than that of mangroves. In MPNR, tidal flats indicated a higher C burial rate (75.2 g C m−2 yr−1) compared to mangroves (64.3 g C m−2 yr−1). The C of tidal flats mainly originated from mangroves and riverine sources, while those in deeper sediments (below 60 cm) in the mangroves originated from the tidal flats. In TK, the C of tidal flats was dominated by oceanic sources. Our study indicates that tidal flats are also important in coastal C sequestration. On highly urbanized coasts, tidal flats and their connected mangroves can play a critical role for C mitigation.

Spatial variations of particulate-bound mercury in the atmosphere along a transect from the mid-Northern Hemisphere to the high southern latitudes

Particulate-bound mercury (PBM) measurements in the boundary layer were performed during the 2015–2016 Chinese Antarctic Research Expedition from the middle Northern Hemisphere (Shanghai, China) to the Antarctic Ice Sheet summit, Dome A. A significant latitudinal gradient in PBM was observed. PBM over the Northern Hemisphere oceans was influenced by both continental and oceanic sources, with elevated PBM levels associated with continental inputs. PBM over this region was significantly higher in November than that in April, which could be related to the continental Hg carried by the strong East Asian winter monsoon. Far away from the continental sources, extremely low PBM was observed over the Southern Ocean (2.6 ± 1.6 pg m−3). Elevated PBM was found across the Antarctic Ice Sheet (79.1 ± 43.4 pg m−3), and the highest PBM observed at Dome A (143.4 ± 27.0 pg m−3) was likely associated with GEM emissions from snow and enhanced oxidation of GEM due to snow photochemistry. Across the Antarctic Ice Sheet, PBM increased significantly with the increasing distance from the coast, which may have resulted from the mixing of air masses from the Antarctic plateau and the ocean. GEM emissions from inland Antarctic snow can influence atmospheric PBM concentrations over the Antarctic coastal seas via the transport by katabatic winds, and thus play an important role in atmospheric Hg cycle in the high southern latitudes.

Seasonal characteristics of biogenic secondary organic aerosol tracers in a deciduous broadleaf forest in northern Japan

We collected total suspended particulate (TSP) samples from January 2010 to December 2010 at Sapporo deciduous forest to understand the oxidation processes of biogenic volatile organic compounds (BVOCs). The gas chromatography-mass spectrometric technique was applied to determine biogenic secondary organic aerosols (BSOAs) in the TSP samples. We found the predominance of the isoprene SOA (iSOA) tracers (20.6 ng m−3) followed by α/β-pinene SOA (pSOA) tracers (8.25 ng m−3) and β-caryophyllene SOA (cSOA) tracer (1.53 ng m−3) in the forest aerosols. The results showed large isoprene fluxes and relatively high levels of oxidants in the forest atmosphere. The iSOA and pSOA tracers showed a clear seasonal trend with summer and autumn maxima and winter and spring minima. Their seasonal trends were mainly controlled by BVOCs emission from the local broadleaf deciduous forest. Additionally, the regional level of isoprene emissions from the oceanic sources may also be contributed during summertime aerosols. cSOA tracer showed high concentrations in the winter and spring, possibly due to an additional contribution of biomass burning (BB) aerosols from the local or regional BB activities. The biogenic secondary organic carbon (BSOC) was contributed mainly by the oxidation products of isoprene (136 ngC m−3) followed by β-caryophyllene (63.0 ngC m−3) and α/β-pinene (35.9 ngC m−3). The mass concentration ratio (0.92) of pinonic acid + pinic acid and 3-methyl-1,2,3-butanetricarboxylic acid ((PNA + PA)/3-MBTCA) indicates the photochemical transformation of first-generation oxidation products to the higher generation oxidation products. The average ratios of isoprene to α/β-pinene (1.64) and β-caryophyllene (18.6) oxidation products suggested a large difference in the emissions of isoprene and α/β-pinene compared to β-caryophyllene. The cSOA tracers in the forest aerosols are also contributed by BB during the winter and spring. Positive matrix factorization analyses of the BSOA tracers confirmed that organic aerosols of deciduous forests are mostly related to isoprene emissions. This study suggests that isoprene is a more significant precursor for the BSOA than α/β-pinene and β-caryophyllene in a broadleaf deciduous forest.

Seasonal dependency of the atmospheric oxidizing capacity of the marine boundary layer of Bermuda

In this study, we investigate the atmospheric oxidation capacity in the marine boundary layer during two measurement campaigns in spring and summer 2019 at the Tudor Hill Marine Atmospheric Observatory, Bermuda. Measured species included non-methane hydrocarbons (NMHCs), HONO, HNO3, particulate matter, particulate nitrates, NO, NO2, O3, in addition to the meteorological parameters. Measured concentrations of all species were generally higher in spring than in summer. During the spring and summer, OH initiation sources made 61% and 42% of the total OH production rate (POH) during the daytime, respectively. The higher levels of NMHCs and OH production from ozone photolysis lead to a higher oxidation rate of NMHCs in the spring compared to summer. However, the low NO in the spring and summer leads to inefficient recycling of RO2 and HO2 to OH, with HO2 reaction with NO accounting for only 22% and 42% of POH during spring and summer. Sensitivity analysis suggests that OH reactivity in the MBL can be potentially enhanced by an oceanic source rather than a secondary oxidation product. Including halogen monoxides, BrO and IO were found to decrease HO2 by ∼14 and 18% during spring and summer, respectively, with marginal impact on OH due to the higher loss by aerosol uptake. The results demonstrate the complex multiphase HOx-Halogen chemistry and call for a more comprehensive multiphase investigation.

Circum-Antarctic abundance and properties of CCN and INPs

Abstract. Aerosol particles acting as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs) play a major role in the formation and glaciation of clouds. Thereby they exert a strong impact on the radiation budget of the Earth. Data on abundance and properties of both types of particles are sparse, especially for remote areas of the world, such as the Southern Ocean (SO). In this work, we present unique results from ship-borne aerosol-particle-related in situ measurements and filter sampling in the SO region, carried out during the Antarctic Circumnavigation Expedition (ACE) in the austral summer of 2016–2017. An overview of CCN and INP concentrations over the Southern Ocean is provided and, using additional quantities, insights regarding possible CCN and INP sources and origins are presented. CCN number concentrations spanned 2 orders of magnitude, e.g. for a supersaturation of 0.3 % values ranged roughly from 3 to 590 cm−3. CCN showed variable contributions of organic and inorganic material (inter-quartile range of hygroscopicity parameter κ from 0.2 to 0.9). No distinct size dependence of κ was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between 30 and 110 nm). The contribution of sea spray aerosol (SSA) to the CCN number concentration was on average small. Ambient INP number concentrations were measured in the temperature range from −5 to −27 ∘C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at −16 ∘C from 0.2 to 100 m−3. Elevated values (above 10 m−3 at −16 ∘C) were measured when the research vessel was in the vicinity of land (excluding Antarctica), with lower and more constant concentrations when at sea. This, along with results of backward-trajectory analyses, hints towards terrestrial and/or coastal INP sources being dominant close to ice-free (non-Antarctic) land. In pristine marine areas INPs may originate from both oceanic sources and/or long-range transport. Sampled aerosol particles (PM10) were analysed for sodium and methanesulfonic acid (MSA). Resulting mass concentrations were used as tracers for primary marine and secondary aerosol particles, respectively. Sodium, with an average mass concentration around 2.8 µg m−3, was found to dominate the sampled, identified particle mass. MSA was highly variable over the SO, with mass concentrations up to 0.5 µg m−3 near the sea ice edge. A correlation analysis yielded strong correlations between sodium mass concentration and particle number concentration in the coarse mode, unsurprisingly indicating a significant contribution of SSA to that mode. CCN number concentration was highly correlated with the number concentration of Aitken and accumulation mode particles. This, together with a lack of correlation between sodium mass and Aitken and accumulation mode number concentrations, underlines the important contribution of non-SSA, probably secondarily formed particles, to the CCN population. INP number concentrations did not significantly correlate with any other measured aerosol physico-chemical parameter.

Precipitation Moisture Sources of Ethiopian River Basins and Their Role During Drought Conditions

In this study, we identified and investigated the annual climatological moisture sources for the Ethiopian river basins during 1980–2018. First, according to cluster analysis, the 12 river basins of this country were grouped into four regions: northeast (NE), southeast (SE), southwest (SW), and west (W), which were characterised by similar annual precipitation features. Global outputs from the Lagrangian FLEXPART model were used to investigate the air mass humidity gain before reaching each region. This revealed five main oceanic moisture sources located in the Mediterranean Sea, Red Sea, Indian Ocean, Persian Gulf, and the Arabian Sea, in addition to three main terrestrial moisture sources located in the African continent, Arabian Peninsula, and the regions themselves. Once the main climatological sources of moisture for each region were identified, a forward-in-time analysis of air masses over each source was performed to calculate the moisture contribution to precipitation (E – P) &amp;lt; 0 over the defined regions. The most important source at the annual scale for the NE, SW, and W regions is the African continent, while for the SE, it is the Indian Ocean. Indeed, terrestrial moisture sources are the major contributors (&amp;gt;50%) to the precipitation over the NE, SW, and W, whereas oceanic sources are the major contributors to the SE. Another analysis identified the years affected by drought conditions in the regions. The role of the sources was evaluated for those years affected by severe and extreme drought, revealing the heterogeneous and also direct influences on the regions. Finally, according to the normalised difference vegetation index, the impacts of annual severe and extreme droughts were more prominent in areas of the NE and SE, but also in the SW during 1984.

Organic Aerosols and Source Analysis of Fine Particles in the Background of Shiwanda Mountain, Guangxi

The non-polar compounds in atmospheric fine particles (PM2.5) mainly include polycyclic aromatic hydrocarbons (PAHs) and normal alkanes (n-alkanes), etc., which are usually used to identify the source of the air pollution and have a great important impact on human health and the environment. To study the pollution characteristics and sources of non-polar organic aerosols in the background point PM2.5 in Guangxi, from November 2017 to October 2018, 17 types of PAHs and 20 types of n-alkanes were analyzed on PM2.5 samples collected in the field. It was found that the annual average concentrations of PAHs and n-alkanes were 4.28±4.25 ng·m-3 and 13.7±14.72 ng·m-3, respectively. The seasonal change was as follows:winter[(7.86±5.19) ng·m-3, (27.51±16.90) ng·m-3]>spring[(2.73±1.76) ng·m-3, (7.64±4.71) ng·m-3]>autumn[(2.34±145) ng·m-3, (7.01±4.55) ng·m-3]>summer[(1.91±1.67) ng·m-3, (3.98±3.12) ng·m-3]. In PAHs, 5-ring and 6-ring molecules accounted for more than 60%, followed by low- and medium-ring molecules (4-ring and 3-ring). The high molecular weight of n-alkanes was relatively high (C29>C31>C27), and the odd and even carbon numbers were significantly different. In addition, combined with the feature ratio method, principal component analysis method, and backward trajectory joint verification, it was found that 41.5% of non-organic aerosols in winter were affected by maritime traffic emissions and ocean source transportation, and 36.7% of the pollution was explained by the coal burning and local biomass burning; 25.2% of the pollution in spring came from biomass combustion and transportation, and 45.0% was attributed to marine transportation in the southern part of the study area and higher plant wax emissions pollution; 53.4% of pollution in summer came from polluted ship emissions, and 10.6% of pollution came from transportation in Southwest Thailand Source transportation. The organic aerosols at the background sites in Guangxi were affected by the combined effects of local emissions and transmission sources.