Owing to its highly unsaturated nature, the CtC triple bond is one of the most fascinating fragments in chemistry. Possessing characteristic two-coordinate sp-hybridized carbon atoms, acetylene, the simplest yet most important alkyne, is exceptional as it may be utilized to prepare a wide variety of important organic compounds. Even as there are few inorganic or organometallic congeners which offer a convenient comparison with acetylene, herein we report the synthesis 1 and molecular structure 2 of Na 2 [Mes* 2 C 6 H 3 -GatGa-C 6 H 3 Mes* 2 ] (Mes* ) 2,4,6-i-Pr 3 C 6 H 2 ), isolated as deep red (almost black) crystals from the sodium metal reduction of (Mes* 2 C 6 H 3 )GaCl 2 (eq 1). In addition to being the first organometallic compound

To simulate and help interpret the nature of the newly synthesized Ga 2 R 2 Na 2 molecule with bulky groups, ab initio and density functional quantum mechanical methods were applied to study the structures and bonding of the model [HGaGaH] 2-, [H 2 GaGaH 2 ] 2-, and [H 3 CGaGaCH 3 ] 2dianions, as well as the neutral Na 2 [H 2 GaGaH 2 ], Na 2 [H 3 CGaGaCH 3 ], Ga 2 H 2 , and Ga 2 H 4 species. Basis sets of triple-ζ plus double polarization quality augmented with diffuse functions were employed. No general bond lengthsbond order relationship is found. Bending from linearity of the acetylene analogues increases the GaGa separation more than the bond order is decreased. The GaGa bonding in the experimental molecule is concluded to be between triple and double in character despite the relatively long bond length.

Reaction of disodium tetracarbonylferrate, Na2[Fe(CO)4], with [2,6-bis(2,4,6-triisopropylphenyl)phenyl]gallium dichloride, (Mes*2C6H3)GaCl2 (Mes* = 2,4,6-triisopropylphenyl), affords tetracarbonyliron [2,6-bis(2,4,6-triisopropylphenyl)phenyl]gallyne, (CO)4Fe⋮Ga(C6H3Mes*2), as anaerobically stable yellow prism crystals. The title compound offers evidence in support of an iron−gallium triple bondthe first ferrogallyne.

Abstract. We assess the relative contributions of different sources of organic matter, marine vs. terrestrial, to oxygen consumption in an emerging hypoxic zone in the lower Pearl River Estuary (PRE), a large eutrophic estuary located in Southern China. Our cruise, conducted in July 2014, consisted of two legs before and after the passing of Typhoon Rammasun, which completely de-stratified the water column. The stratification recovered rapidly, within 1 day after the typhoon. We observed algal blooms in the upper layer of the water column and hypoxia underneath in bottom water during both legs. Repeat sampling at the initial hypoxic station showed severe oxygen depletion down to 30 µmol kg −1 before the typhoon and a clear drawdown of dissolved oxygen after the typhoon. Based on a three endmember mixing model and the mass balance of dissolved inorganic carbon and its isotopic composition, the δ 13 C of organic carbon remineralized in the hypoxic zone was −23.2 ± 1.1 ‰. We estimated that 65 ± 16 % of the oxygen-consuming organic matter was derived from marine sources, and the rest (35 ± 16 %) was derived from the continent. In contrast to a recently studied hypoxic zone in the East China Sea off the Changjiang Estuary where marine organic matter dominated oxygen consumption, here terrestrial organic matter significantly contributed to the formation and maintenance of hypoxia. How varying amounts of these organic matter sources drive oxygen consumption has important implications for better understanding hypoxia and its mitigation in bottom waters.

The study of acidification in Chesapeake Bay is challenged by the complex spatial and temporal patterns of estuarine carbonate chemistry driven by highly variable freshwater and nutrient inputs. A new module was developed within an existing coupled hydrodynamic‐biogeochemical model to understand the underlying processes controlling variations in the carbonate system. We present a validation of the model against a diversity of field observations, which demonstrated the model's ability to reproduce large‐scale carbonate chemistry dynamics of Chesapeake Bay. Analysis of model results revealed that hypoxia and acidification were observed to cooccur in midbay bottom waters and seasonal cycles in these metrics were regulated by aerobic respiration and vertical mixing. Calcium carbonate dissolution was an important buffering mechanism for pH changes in late summer, leading to stable or slightly higher pH values in this season despite persistent hypoxic conditions. Model results indicate a strong spatial gradient in air‐sea CO2 fluxes, where the heterotrophic upper bay was a strong CO2 source to atmosphere, the mid bay was a net sink with much higher rates of net photosynthesis, and the lower bay was in a balanced condition. Scenario analysis revealed that reductions in riverine nutrient loading will decrease the acid water volume (pH < 7.5) as a consequence of reduced organic matter generation and subsequent respiration, while bay‐wide dissolved inorganic carbon (DIC) increased and pH declined under scenarios of continuous anthropogenic CO2 emission. This analysis underscores the complexity of carbonate system dynamics in a productive coastal plain estuary with large salinity gradients.

Few estuaries have inorganic carbon datasets with sufficient spatial and temporal coverage for identifying acidification baselines, seasonal cycles and trends. The Chesapeake Bay, though one of the most well-studied estuarine systems in the world, is no exception. To date, there have only been observational studies of inorganic carbon distribution and flux in lower bay sub-estuaries. Here, we address this knowledge gap with results from the first complete observational study of inorganic carbon along the main stem. Dissolved inorganic carbon (DIC) and total alkalinity (TA) increased from surface to bottom and north to south over the course of 2016, mainly driven by seasonal changes in river discharge, mixing, and biological carbon dioxide (CO 2 ) removal at the surface and release in the subsurface. Upper, mid-and lower bay DIC and TA ranged from 1000-1300, 1300-1800, and 1700-1900 µmol kg −1 , respectively. The pH range was large, with maximum values of 8.5 at the surface and minimums as low as 7.1 in bottom water in the upper and mid-bay. Seasonally, the upper bay was the most variable for DIC and TA, but pH was more variable in the mid-bay. Our results reveal that low pH is a continuing concern, despite reductions in nutrient inputs. There was active internal recycling of DIC and TA, with a large inorganic carbon removal in the upper bay and at salinities < 5 most months, and a large addition in the mid-salinities. In spring and summer, waters with salinities between 10 and 15 were a large source of DIC, likely due to remineralization of organic matter and dissolution of CaCO 3 . We estimate that the estuarine export flux of DIC and TA in 2016 was 40.3 ± 8.2 × 10 9 mol yr −1 and 47.1 ± 8.6 × 10 9 mol yr −1 . The estuary was likely a large sink of DIC, and possibly a weak source of TA. These results support the argument that the Chesapeake Bay may be an exception to the long-standing assumption that estuaries are heterotrophic. Furthermore, they underline the importance of large estuarine systems for mitigating acidification in coastal ecosystems, since riverine chemistry is substantially modified within the estuary.

This review examines the current understanding of the global coastal ocean carbon cycle and provides a new quantitative synthesis of air-sea CO2 exchange. This reanalysis yields an estimate for the globally integrated coastal ocean CO2 flux of −0.25 ± 0.05 Pg C year−1, with polar and subpolar regions accounting for most of the CO2 removal (>90%). A framework that classifies river-dominated ocean margin (RiOMar) and ocean-dominated margin (OceMar) systems is used to conceptualize coastal carbon cycle processes. The carbon dynamics in three contrasting case study regions, the Baltic Sea, the Mid-Atlantic Bight, and the South China Sea, are compared in terms of the spatio-temporal variability of surface pCO2. Ocean carbon models that range from box models to three-dimensional coupled circulation-biogeochemical models are reviewed in terms of the ability to simulate key processes and project future changes in different continental shelf regions. Common unresolved challenges remain for implementation of these models across RiOMar and OceMar systems. The long-term trends in coastal ocean carbon fluxes for different coastal systems under anthropogenic stress that are emerging in observations and numerical simulations are highlighted. Knowledge gaps in projecting future perturbations associated with before and after net-zero CO2 emissions in the context of concurrent changes in the land-ocean-atmosphere coupled system pose a key challenge. ▪ A new synthesis yields an estimate for globally integrated coastal ocean carbon sink of −0.25 Pg C year−1, with greater than 90% of atmospheric CO2 removal occurring in polar and subpolar regions. ▪ The sustained coastal and open ocean carbon sink is vital in mitigating climate change and meeting the target set by the Paris Agreement. ▪ Uncertainties in the future coastal ocean carbon cycle are associated with concurrent trends and changes in the land-ocean-atmosphere coupled system. ▪ The major gaps and challenges identified for current coastal ocean carbon research have important implications for climate and sustainability policies. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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