Measuring the transport of the Changjiang (also known as the Yangtze) River-derived buoyant coastal current, that is, the Min-Zhe Coastal Current, is of great importance for understanding the fate of terrestrial materials from this large river into the open ocean, but it is usually difficult to achieve because of the energetic tidal currents along the Chinese coast. In February 2012, a detiding cruise survey was carried out using the phase-averaging method. For the first time, this coastal current has been quantified with in situ data and has been shown to have a volume transport of 0.215 Sv (1 Sv [ 10 6 m 3 s 21 ) and a maximum surface velocity of ;50 cm s 21 . The ratio between the volume transport of the buoyant coastal current and that of the Changjiang is O(10). Freshwater transport by the buoyant coastal current accounts for over 90% of the Changjiang River's discharge. Buoyancy and winds are both important in driving this current.
Coastal currents generally flow downshelf with land on the right side (Northern Hemisphere) under the geostrophic balance, and are often strengthened by downwelling‐favorable winds. However, the recent mooring observation in the inner southwestern Yellow Sea showed that coastal transport direction can be substantially changed by tidal forcing. In the survey, the tidal‐averaged transports at two out of three sites remained northward (i.e., in the upshelf direction) and opposite the downwelling‐favorable northerly wind, except during a brief neap tide period. Numerical experiments showed that the incoming Poincaré wave tide from the East China Sea plays a key role in forming this counter‐wind transport system. This tidal wave produces a shoreward tidal stress south of 33.5°N in the inner southwestern Yellow Sea, driving an upshelf transport under the Earth's rotation. Counterpropagating tidal waves from the East China Sea and the northern Yellow Sea collide in coastal water in 32.5–34°N, which produce a standing tidal wave and therefore a mean sea‐surface setup with alongshore and cross‐shelf scales of both >100 km. This sea‐surface setup causes an alongshore sea surface gradient, which veers the upshelf transport to the offshore direction under geostrophic balance. The strong tidal current increases the tidal‐mean bottom resistance in the SCW, thus reduces the wind‐driven current to a magnitude smaller than the tide‐induced residual transport velocity. Therefore, upshelf transport persists in the inner southwestern Yellow Sea, and the Changjiang River Estuary becomes a major source area for the inner southwestern Yellow Sea.
Summary Pollution of soil by the heavy metal cadmium (Cd) is a global environmental problem. The glutathione (GSH)‐dependent phytochelatin (PC) synthesis pathway is one of the most important mechanisms contributing to Cd accumulation and tolerance. However, the regulation of this pathway is poorly understood. Here, we identified an Arabidopsis thaliana cadmium‐tolerant dominant mutant xcd1‐D (XVE system‐induced cadmium‐tolerance 1) and cloned XCD1 gene (previously called MAN3), which encodes an endo‐β‐mannanase. Overexpression of MAN3 led to enhanced Cd accumulation and tolerance, whereas loss‐of‐function of MAN3 resulted in decreased Cd accumulation and tolerance. In the presence of estradiol, enhanced Cd accumulation and tolerance in xcd1‐D was associated with GSH‐dependent, Cd‐activated synthesis of PCs, which was correlated with coordinated activation of gene expression. Cd stress‐induced expression of MAN3 and the consequently increased mannanase activity, led to increased mannose content in cell walls. Moreover, mannose treatment not only rescued the Cd‐sensitive phenotype of the xcd1‐2 mutant, but also improved the Cd tolerance of wild‐type plants. Significantly, this mannose‐mediated Cd accumulation and tolerance is dependent on GSH‐dependent PC concentrations via coordinated control of expression of genes involved in PC synthesis. Our results suggest that MAN3 regulates the GSH‐dependent PC synthesis pathway that contributes to Cd accumulation and tolerance in A. thaliana by coordinated control of gene expression.
The concentrated benthic suspension (CBS) of mud, as a major contributor of sediment transport in the turbidity maximum of the estuary, is of great challenge to be correctly monitored through field measurements, and its formation mechanism is not well understood. A tripod system equipped with multiple instruments was deployed to measure the near‐bed hydrodynamics and sediments in the North Passage of the Changjiang Estuary, with the aim at determining the formation mechanisms of CBS. The measurements detected a significant dominance of high sediment concentration in the near‐bed 1‐m layer: ~20 g/L at the southern site and ~47 g/L at the northern site. Strong CBS occurred under weak tidal mixing condition and was directly relevant to the sediment‐induced suppression of turbulent kinetic energy and the enhanced water stratification due to saltwater intrusion and sediment suspension. During the weak‐mixing neap period, the typical thickness of CBS was about 0.2–0.3 m, with a life time of ~2.83 hr (suspended‐sediment concentration > 15.0 g/L). Enhanced water stratification reduced vertical mixing and confined the sediment entrainment from the near‐bed layer to the upper column. This enhancement was due to the suppression of turbulent kinetic energy as a result of the sediment accumulation in the near‐bottom column during the slack waterand also due to the appearance of a two‐layer salinity structure in the vertical as a result of saltwater intrusion near the bottom. These physical processes worked as a positive feedback loop during the formation of CBS and can be simulated with a process‐oriented, one‐dimensional vertical CBS model.
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