Estuaries are a major boundary in the land-ocean interaction zone where organic carbon (OC) and nutrients are being processed, resulting in a high water-to-air carbon dioxide (CO2) flux ...(approximately 0.25 Pg C y(-1)). The continental shelves, however, take up CO2 (approximately 0.25 Pg C y(-1)) from the atmosphere, accounting for approximately 17% of open ocean CO2 uptake (1.5 Pg Cy(-1)). It is demonstrated here that CO2 release in estuaries is largely supported by microbial decomposition of highly productive intertidal marsh biomass. It appears that riverine OC, however, would bypass the estuarine zone, because of short river-transit times, and contribute to carbon cycling in the ocean margins and interiors. Low-latitude ocean margins release CO2 because they receive two-thirds of the terrestrial OC. Because of recent CO2 increase in the atmosphere, CO2 releases from low latitudes have become weaker and CO2 uptake by mid- and high-latitude shelves has become stronger, thus leading to more dissolved inorganic carbon export to the ocean.
The exploration of high nuclearity molecular metal oxide clusters and their reactivity is a challenge for chemistry and materials science. Herein, we report an unprecedented giant molecular ...cerium–bismuth tungstate superstructure formed by self‐assembly from simple metal oxide precursors in aqueous solution. The compound, {W14CeIV6O61(W3Bi6CeIII3(H2O)3O14B‐α‐BiW9O333)2}34− was identified by single‐crystal X‐ray diffraction and features 104 metal centers, a relative molar mass of ca. 24 000 and is ca. 3.0×2.0×1.7 nm3 in size. The cluster anion is assembled around a central {Ce6} octahedron which is stabilized by several molecular metal oxide shells. Six trilacunary Keggin anions (B‐α‐BiW9O339−) cap the superstructure and limit its growth. In the crystal lattice, water‐filled channels with diameters of ca. 0.5 nm are observed, and electrochemical impedance spectroscopy shows pronounced proton conductivity even at low temperature.
A giant cerium–bismuth tungstate cluster featuring more than 100 metal ions and a relative molar mass of approximately 24 000 is structurally characterized. The cluster anions form a highly 3D‐porous crystalline lattice featuring water‐filled channels. Proton conductivity measurements show high proton mobility within the framework.
The hierarchical aggregation of molecular nanostructures from multiple components is a grand synthetic challenge, which requires highly selective linkage control. We demonstrate how two orthogonal ...linkage groups, that is, organotin and lanthanide cations, can be used to drive the aggregation of a giant molecular metal oxide superstructure. The title compound {(Sn(CH3)2)2O4{CeW5O18 TeW4O16CeSn(CH3)24TeW8O314}2}46− (1 a) features dimensions of ca. 2.2×2.3×3.4 nm3 and a molecular weight of ca. 25 kDa. Structural analysis shows the hierarchical aggregation from several independent subunits. Initial biomedical tests show that 1 features an inhibitory effect on the proliferation of HeLa cells based on an apoptosis pathway. In vivo experiments in mice reveal the antiproliferative activity of 1 and open new paths for further development of this new compound class.
Hierarchical assembly of a giant heterometallic polyoxotungstate supercluster with a molecular weight of ca. 25 kDa is reported. Geometrically unrestricted cerium(III) and geometrically restricted dimethyl tin cation linkers are used to gain access to a giant molecular species featuring three different polyoxometalate building units. The compound demonstrates in vitro and in vivo antiproliferative activity against HeLa cervical cancer cell lines.
Nutrient inputs from the Mississippi/Atchafalaya River system into the northern Gulf of Mexico promote high phytoplankton production and lead to high respiration rates. Respiration coupled with water ...column stratification results in seasonal summer hypoxia in bottom waters on the shelf. In addition to consuming oxygen, respiration produces carbon dioxide (CO2), thus lowering the pH and acidifying bottom waters. Here we present a high‐resolution biogeochemical model simulating this eutrophication‐driven acidification and investigate the dominant underlying processes. The model shows the recurring development of an extended area of acidified bottom waters in summer on the northern Gulf of Mexico shelf that coincides with hypoxic waters. Not reported before, acidified waters are confined to a thin bottom boundary layer where the production of CO2 by benthic metabolic processes is dominant. Despite a reduced saturation state, acidified waters remain supersaturated with respect to aragonite.
Key Points
A biogeochemical model realistically simulates eutrophication‐induced acidification in the northern Gulf of Mexico
The sediments, which are a major source of dissolved inorganic carbon (DIC), cause low pH that is restricted to the bottom boundary layer
The contribution of river‐derived organic matter to DIC production and acidification is small in the river outflow region
It has been speculated that the partial pressure of carbon dioxide (pCO
) in shelf waters may lag the rise in atmospheric CO
. Here, we show that this is the case across many shelf regions, implying ...a tendency for enhanced shelf uptake of atmospheric CO
. This result is based on analysis of long-term trends in the air-sea pCO
gradient (ΔpCO
) using a global surface ocean pCO
database spanning a period of up to 35 years. Using wintertime data only, we find that ΔpCO
increased in 653 of the 825 0.5° cells for which a trend could be calculated, with 325 of these cells showing a significant increase in excess of +0.5 μatm yr
(p < 0.05). Although noisier, the deseasonalized annual data suggest similar results. If this were a global trend, it would support the idea that shelves might have switched from a source to a sink of CO
during the last century.
Recent interest in the ocean's capacity to absorb atmospheric CO2 and buffer the accompanying “ocean acidification” has prompted discussions on the magnitude of ocean margin alkalinity production via ...anaerobic processes. However, available estimates are largely based on gross reaction rates or misconceptions regarding reaction stoichiometry. In this paper, we argue that net alkalinity gain does not result from the internal cycling of nitrogen and sulfur species or from the reduction of metal oxides. Instead, only the processes that involve permanent loss of anaerobic remineralization products, i.e., nitrogen gas from net denitrification and reduced sulfur (i.e., pyrite burial) from net sulfate reduction, could contribute to this anaerobic alkalinity production. Our revised estimate of net alkalinity production from anaerobic processes is on the order of 4–5 Tmol yr−1 in global ocean margins that include both continental shelves and oxygen minimum zones, significantly smaller than the previously estimated rate of 16–31 Tmol yr−1. In addition, pyrite burial in coastal habitats (salt marshes, mangroves, and seagrass meadows) may contribute another 0.1–1.1 Tmol yr−1, although their long‐term effect is not yet clear under current changing climate conditions and rising sea levels. Finally, we propose that these alkalinity production reactions can be viewed as “charge transfer” processes, in which negative charges of nitrate and sulfate ions are converted to those of bicarbonate along with a net loss of these oxidative anions.
Key Points
Ocean margin anaerobic alkalinity production is less than previously estimated
Anaerobic alkalinity production can be viewed through a charge transfer process
During the summers of 2009 and 2013, seawater pH and concentrations of dissolved oxygen, inorganic carbon, and nutrients were measured off the Changjiang estuary in the East China Sea. The 2009 ...cruise captured the effects of Typhoon Morakot; the 2013 cruise sampled more typical conditions (no typhoon). Data from both years indicate a close correlation between high primary productivity in surface waters and hypoxia in bottom waters. Based on these observations, we developed a conceptual model to guide an exploration of processes contributing to the formation of summertime bottom hypoxia. A mixing-model analysis of the 2009 data identified a surface diatom bloom as the major (70–80%) source of the organic carbon that decomposed and ultimately led to bottom water hypoxia. Within the Changjiang River plume, depth-integrated net biological production in the water column was 1.8 g C m−2 d−1, indicating strong autotrophic production, which in turn led to a high respiration rate of 1.2 g C m−2 d−1 in the bottom water. During both cruises, strong surface-to-bottom physical and metabolic coupling was evident. In 2009, storm-driven inputs of nutrients from elevated river discharge and strong vertical mixing helped to fuel the rapid development of a surface diatom bloom. Afterwards, stratified conditions re-established, newly formed labile organic matter sank, and bottom water oxygen was quickly consumed to an extent that hypoxia and acidification developed. To our knowledge, the observed rate of hypoxia and acidification development (within 6 d) is the fastest yet reported for the Changjiang River plume.
The combined effects of anthropogenic and biological CO
inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would ...contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H
S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. We show that a pH minimum occurs in mid-depths where acids are generated as a result of H
S oxidation in waters mixed upward from the anoxic depths. Our analyses also suggest a large synergistic effect from river-ocean mixing, global and local atmospheric CO
uptake, and CO
and acid production from respiration and other redox reactions. Together they lead to a poor acid buffering capacity, severe acidification and increased carbonate mineral dissolution in the USA's largest estuary.The potential contribution of redox reactions to acidification in coastal waters is unclear. Here, using measurements from the Chesapeake Bay, the authors show that pH minimum occurs at mid-depths where acids are produced via hydrogen sulfide oxidation in waters mixed upward from anoxic depths.
In determining global sea‐to‐air CO2 flux from measurements or models, the ocean margin has not been resolved from the land or the open ocean. Recent studies have indicated that shelves can be either ...a large sink or a source for atmospheric CO2. This CO2 sink/source term may substantially alter our current view of the global carbon budget for land and oceans. However, past fieldwork and synthesis have focused on a few shelves in the northern temperate zone while the vast majority of other shelves are ignored. By dividing the highly heterogeneous shelves into seven provinces, we suggest that the continental shelves are a sink for atmospheric CO2 at mid‐high latitudes (−0.33 Pg C a−1) and a source of CO2 at low latitudes (0.11 Pg C a−1). Warm temperature and high terrestrial organic carbon input are most likely responsible for the CO2 release in low latitude shelves.
The western Arctic Ocean is known to be nitrate deficient relative to phosphate but the decadal trend and the processes contributing to the deficit are not clear. To investigate changes in this ...extreme nitrate deficit of over 10 μmol/kg and its causal mechanisms, nutrient concentrations were examined along a transect spanning the Bering Basin, the Bering–Chukchi Shelf, and the western Arctic Ocean Basin over the last two decades (1994–2018). The results show that the extreme nitrate deficit has extended to greater depths and further north during the past two decades, which coincided with the expansion of Pacific water in the western Arctic Ocean. Subsurface nutrient stocks in the basin areas appear to have increased, but are accompanied by a larger nitrate deficit, which may be due to stronger shelf denitrification. This nitrate loss (∆N) caused by shelf denitrification was estimated to be 7.3 ± 0.1 μmol/kg during the interval 2012–2018, which was ∼10% higher than that in 1994. This suggests an intensification of denitrification on this marginal shelf under climatic and environmental change in the Arctic Ocean.
Plain Language Summary
Prominent nitrate deficits relative to phosphate of over 10 μmol/kg in the Arctic Ocean are caused by a combination of nitrate loss by denitrification and a pre‐existing nitrate deficit in the inflowing Pacific waters. Over the last two decades (1994–2018), this extreme nitrate deficit extended to greater depths and further north, which coincided with the expansion of Pacific water into the western Arctic Ocean. Meanwhile, subsurface nutrient stocks have increased, however followed by a larger nitrate deficit, which may be due to stronger shelf denitrification in the western Arctic Ocean.
Key Points
Prominent nitrate deficits of over 10 μmol/kg expanded to greater depths and further north during 1994–2018
Subsurface nutrient stocks have increased in the western Arctic Ocean basin, but with larger nitrate deficit
Denitrifying activity on the marginal shelf might be enhanced as a result of climate change
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