Abstract We conducted hydrothermal experiments at 300°C and at pressure varying from 2.2 to 3.4 kbar to study the effect of fluid salinity on the coupling between molecular hydrogen (H 2 ) formation and olivine serpentinization, where peridotite and olivine with 25–50 μm of starting grain sizes were reacted with pure H 2 O and saline solutions (0.5, 1.5, and 3.3 M NaCl). Serpentine, the main hydrous mineral in most experiments, was quantified according to calibration curves based on Fourier‐transformed infrared spectroscopy and X‐ray diffraction analyses. Compared to pure H 2 O, saline solutions promote the hydrothermal alteration of olivine and peridotite. For experiments with peridotite and pure H 2 O, 67% of reaction extent was achieved after 14 days, which increased to 89% in experiments with medium‐salinity solutions (1.5 M NaCl) over the same period. Medium‐ and high‐salinity solutions inhibit H 2 formation during serpentinization, which is associated with the serpentinization of pyroxene especially clinopyroxene. The redox conditions were constrained according to the equilibrium H 2,aq = H 2,g , and very reducing conditions were achieved during the serpentinization of olivine and peridotite. This study is the first to show iowaite formation directly from peridotite serpentinization, indicating alkaline solutions. Thermodynamic calculations suggest that the hydrolysis of NaCl (NaCl + H 2 O = HCl + NaOH) may yield alkaline solutions, due to higher dissociation constants of NaOH compared to HCl. This study suggests that chlorine greatly influences the serpentinization of olivine and peridotite in natural geological settings. It also indicates that iowaite formation may not require oxidizing conditions as previously thought.
Abstract Great efforts have been made to understand the impacts of the 1997 Indonesian wildfires on land ecology and human health, yet its influences on marine environments are poorly understood owing to sparse observations. Here we present weekly to monthly resolution coral δ 13 C records across the South China Sea in conjunction with a regional ocean general circulation model to study the effects of these cataclysmic wildfires on nearby oceans. Large and persistent negative δ 13 C excursions were found in corals from the interior South China Sea several months after the wildfires. This delay indicates that the 13 C‐depleted ash fallout was distributed by ocean currents rather than direct atmospheric transport, which is supported by the results of our numerical model. Thus, the impacts of tropical wildfires on marine ecology may last for 1 year and extend thousands of kilometers from the burning center.
Abstract The food source of hadal endemic fauna provides an insight into the carbon cycle in trenches and a biological adaptation to the impoverished and harsh trench environment. Here, we present the first Δ 14 C results of hadal amphipods from three trenches in the Pacific to define the organic matter source in these remote ecosystems. Amphipod muscle tissues contain a bomb 14 C signature (Δ 14 C from 10 ± 2‰ to 65 ± 2‰), thereby revealing a dietary preference for labile and fresh organic matter derived from the surface water. Thus, the carbon cycle in the deepest ocean trench has a tight linkage with the surface ocean via the food chain. The bomb 14 C dating result suggests that hadal amphipods have a low tissue turnover rate and an unexpectedly long lifetime (>10 years), at more than 4 times higher than the common longevity (~2 years) of amphipods in shallow waters.
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