ABSTRACT
Topographic Rossby waves (TRWs) dominate the low-frequency variability of deep ocean currents and play a crucial role in energy exchange and material mixing. On the continental slope of the southwestern South China Sea, a deep-water mooring was deployed to observe TRWs for a period of ~ 40 days. The TRWs, with a wavelength of 109 km, account for 41.3% of the subinertial variations. A ray-tracing model was applied to investigate the propagation and energy source. The results showed that the TRWs propagated from the northeast of the mooring location and were most likely caused by the mesoscale eddy disturbances off the Vietnam coast. This study provides a new perspective on examining the impact of mesoscale eddies off Vietnam on abyssal currents.
ABSTRACT
The association between clay minerals and organic carbon is pivotal for understanding transport, burial, and preservation processes of sedimentary organic carbon. However, fine-scale microscopic studies are still limited in assessing the effect of diverse clay mineral structures and properties on organic carbon sequestration. In this study, we employed X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy coupled with energy dispersive spectroscopy and electron energy loss spectroscopy analyses to investigate the nanoscale interaction between clay minerals and organic carbon of two typical fluvial sediment samples with contrasting clay mineral compositions and organic carbon origins. Sample from Taiwan shows abundant illite and chlorite with petrogenic organic carbon, while sample from Luzon has significant smectite with pedogenic organic carbon. We observed that the nanostructure of the clay minerals controls the distribution of organic carbon. In the Luzon sample, the organic carbon is tightly associated with smectite, occupying expandable interlayer spaces. In the Taiwan sample, however, the organic carbon is primarily confined on the surface and edge of illite. These findings offer valuable insights into the selective association of organic carbon with clay minerals and underscore the role of clay mineral nanolayer structures in governing the occurrence and preservation of organic carbon in sediments. A comprehensive understanding of these interactions is crucial for accurate assessments of carbon cycling and sequestration in the natural environment.
ABSTRACT
Molecular dynamics simulations were used to investigate the effects of the external surface of a 2:1 clay mineral with different charge amounts and charge locations on CH4 hydrate formation. The results showed that 512, 51262, 51263, and 51264 were formed away from the clay mineral surface. The surface of the clay mineral with high- and low-charge layers was occupied by Na+ to form various distributions of outer- and inner-sphere hydration structures, respectively. The adsorbed Na+ on the high-charge layer surface reduced the H2O activity by disturbing the hydrogen bond network, resulting in low tetrahedral arrangement of H2O molecules near the layer surface, which inhibited CH4 hydrate formation. However, more CH4 molecules were adsorbed onto the vacancy in the Si-O rings of a neutral-charge layer to form semicage structures. Thus, the order parameter of H2O molecules near this surface indicated that the arrangement of H2O molecules resulted in a more optimal tetrahedral structure for CH4 hydrate formation than that near the negatively charged layer surface. Different nucleation mechanisms of the CH4 hydrate on external surfaces of clay mineral models were observed. For clay minerals with negatively charged layers (i.e., high and low charge), the homogeneous nucleation of the CH4 hydrate occurred away from the surface. For a clay mineral with a neutral-charge layer, the CH4 hydrate could nucleate either in the bulk-like solution homogeneously or at the clay mineral-H2O interface heterogeneously.
ABSTRACT
Diatoms play an important role in marine biogeochemical cycle of aluminum (Al), as dissolved Al is taken up by diatoms to build their siliceous frustules and is involved in the sedimentation of diatomaceous biogenic silica (BSi). The Al incorporation in BSi facilitates decreasing the dissolution of marine BSi and thus substantially influences the biochemical processes driven by diatoms, such as CO2 sequestration. However, the role of lake BSi in the terrestrial biochemical Al cycle has not been explored, though lakes represent the second-largest sink for BSi. By identifying the previously unexplored high Al/Si atomic ratios (up to 0.052) in lake BSi, here we show lake BSi is a large terrestrial Al pool due to its high Al content, and lake sedimentary BSi constitutes a significant global sink for Al, which is on the same magnitude as the Al sink in global oceans.
ABSTRACT
AIM: To investigate the effects of soy isoflavones (SI) on the expression of Bax mRNA and Ca(2+) -ATPase activity in ovaries of perimenopause rats. METHODS: The animal model of perimenopause rats was established by unforced aging. 12 month-old presenilins female Wistar rats were administered by intragastric (ig) with low (500 mg/kg), middle (158 mg/kg) and high (500 mg/kg) does of SI for 8 weeks. The expression of Bax mRNA in ovaries were detected by RT-PCR. Ca(2+) -ATPase activity in ovaries and MDA content and SOD activity in serum were detected by chemi-chromatometry. RESULTS: Intervention of SI could significantly decrease the expression of Bax mRNA in ovaries and MDA content in serum, increase Ca(2+) -ATPase activity in ovaries and SOD activity in serum of presenilins rats (P < 0.05 or P < 0.01). CONCLUSION: Soy isoflavones could down-regulate the expression of Bax mRNA and increase Ca(2+) -ATPase activity in aged ovaries. It is probably one of the mechanisms to improve the function of aged ovaries in perimenopause rats.
