Search

A simple, convenient, and efficient method for the formation of functionalized dibenzo[ b, f]oxepins and their analogs bearing both electron-donating and electron-withdrawing groups has been developed via a one-pot cascade reaction. Most starting materials are commercially available 2-(2-hydroxyphenyl)acetonitriles and 2-haloarylaldehydes. The procedure makes use of Cs2CO3 as the base, and DMF as solvent under copper-assisted/copper-free conditions. The reaction has a comprehensive group tolerance for substrates. Most of the reactions were complete within 1 h in good-to-excellent yields, and the reaction temperatures were relatively low. The protocol could be scaled up to grams without lowering the yield. A reaction mechanism was also proposed. [ABSTRACT FROM AUTHOR]

An efficient palladium/copper-catalyzed domino reaction was developed to yield functionalized naphthalenes, quinolines, and isoquinolines. The reactions of various substituted 1-phenylprop-2-yn-1-ols containing electron-donating (EDG) and electron-withdrawing (EWG) groups and 1-heteroarylprop-2-yn-1-ols worked well with this procedure. Both electron-rich and -deficient aryl halides were satisfactory substrates for this reaction. This domino benzannulation process involves a Sonogashira cross-coupling reaction, followed by isomerization to a chalcone, and finally an intramolecular condensation reaction. [ABSTRACT FROM AUTHOR]

Seasonal patterns of phytoplankton biomass and primary production (PP) are important features characterizing a marine ecosystem. The South China Sea (SCS) has been arbitrarily illustrated as an ecosystem with low PP in summer and high PP in winter. However, there is an emerging consensus about a lack of unity of PP seasonality in the SCS even in the northern SCS shelf-sea. Through analysis of the distributions of the remotely sensed colored dissolved organic matter absorption coefficient, a river-dominated ocean margin in the northern SCS (NSCS-RiOMar) with the 50 m isobath as its southeastern boundary has been defined. The difference in PP seasonality between the NSCS-RiOMar and the whole shelf-sea was evaluated by both the measured and the remotely sensed depth-integrated primary production (ΣPP). A diagnostic analysis found that euphotic depth and a function of the half-saturation light intensity accounted for the seasonal variation of ΣPP in the NSCS-RiOMar. Accordingly, the Platt and Sathyendranath (1993) model plus the nearest neighbor method and the semi-analytical estimates of euphotic depth were used to compute the remotely sensed ΣPP. The average ΣPP in the NSCS-RiOMar were 1146.4, 1604.7, 979.5, and 891.3 mg C m−2 d−1 in spring, summer, autumn, and winter, respectively, contrasted with small seasonal variations in the whole shelf-sea. The unimodal ΣPP peak was in June-July in accordance with the peak of Pearl River discharge. This result was striking because previous remote sensing studies all showed the reversed seasonal pattern of ΣPP in both the NSCS-RiOMar and the whole shelf-sea. The annual PP was estimated to be 33.5 ± 2.3 Mt C yr−1 and 56.2 ± 3.2 Mt C yr−1 in the NSCS-RiOMar and the whole shelf-sea, respectively. The nutrients inputted by the China Coastal Current might account for 4–23% of ΣPP in the NSCS-RiOMar between December and February. [ABSTRACT FROM AUTHOR]

Sinking particles play a crucial role in transferring carbon from the atmosphere to the deep ocean. However, due to intensive particle transformations such as aggregation, disaggregation, and remineralization, only a small portion of the organic carbon produced in the euphotic zone ends up being sequestered in the deep ocean or sediment. Mesoscale eddies can significantly impact the surface ocean nutrient budget, primary production, and carbon export. Despite this, there is still a lack of research on how particle dynamics in eddy-impacted regions affect the efficiency of carbon export. In this study, we used observations of thorium isotopes (234Th and 228Th) and particulate organic carbon (POC) at two stations in the South China Sea (TS1: a decaying-eddy-impacted station and SEATS: an oligotrophic station) and an inverse model to investigate the impact of particle dynamics on particle export efficiency. Our findings indicate that particle remineralization/fragmentation was enhanced inside the eddy, which counteracted the nutrient pumping effect that promotes surface ocean productivity and eventually led to even lower carbon flux compared to the oligotrophic station. • Particle dynamics was studied at two stations in the South China Sea using inverse method. • Particle disaggregation and remineralization decrease carbon flux in the eddy station. • The finding has implications for the observed high-production and low-export efficiency. [ABSTRACT FROM AUTHOR]

The cyanobacterium Trichodesmium is responsible for approximately half of the ocean's nitrogen input through nitrogen fixation. Although it was first recorded near Australia in the 18th century, the knowledge of where and when large quantity of Trichodesmium around Australia could be found is still lacking. Here, using multi‐band satellite imagery acquired between 2012 and 2021, we fill this knowledge gap through the use of deep learning, designed to recognize both the spectral shapes of individual pixels and spatial morphology of surface aggregations (scums) of Trichodesmium. Trichodesmium scums were found nearly everywhere around Australia, with a cumulative footprint (i.e., where the 10‐year average density is >0.001‰) exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. Furthermore, temperature, iron‐rich dust and black carbon aerosols, with the latter being a result of frequent bushfires, play major roles in determining the spatial distributions and seasonality of Trichodesmium. Plain Language Summary: Responsible for half of the ocean's nitrogen input through nitrogen fixation, the saltwater cyanobacterium Trichodesmium is ubiquitous in global tropical and subtropical oceans but particularly abundant around Australia. However, although the earliest report goes back to the 18th century, the knowledge of where and when large quantities of Trichodesmium can be found around Australia is still incomplete. Based on satellite imagery and deep learning, we quantified relative abundance of Trichodesmium around Australia for the period of 2012–2021. Surface aggregations of Trichodesmium were found almost everywhere except the southern coast, with a cumulative footprint exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. The spatial distributions and seasonality were found to correlate well with water temperature, iron‐rich dust from Australian desert, and black carbon aerosols from frequent bushfires. With the projected ocean warming in the coming century, Trichodesmium may expand further south, making the cumulative footprint even larger. Key Points: Deep learning was applied to multi‐band satellite images to detect and quantify Trichodesmium surface scums around AustraliaTrichodesmium scums were found nearly everywhere around Australia with a seasonality and a cumulative footprint exceeding 4.6 million km2Distribution and seasonality of Trichodesmium were driven by temperature, iron‐rich dust and black carbon from the mainland bushfires [ABSTRACT FROM AUTHOR]