Spiral ganglion neurons (SGNs) extend processes that interact with Schwann cells (SCs) and with oligodendrocytes (OLs) and astrocytes (ACs). We investigated the ability of these glial cells to support SGN neurite growth. In the presence of cultured ACs, OLs and SCs, SGN neurites tended to follow SCs and OLs and cross-over ACs. Most neurites initially followed the type of glial cell on which the neuronal cell body was found. To determine the influence of homogeneous populations of glia on neurite growth, SG explants were plated on cultured SCs, ACs or OLs. The number of neurites/explant extending onto SCs (463.89±16.25) was significantly greater than the number extending onto ACs (111.38±38.73) or OLs (6.75±2.21), indicating that populations of central glia inhibit SGN neurite growth. Treatment with cell-permeant cpt-cAMP or forskolin (FSK) each significantly increased the number of neurites on OLs (133.54±25.59 and 292.25±83.57, respectively). cpt-cAMP and FSK each also increased the number of neurites on ACs (213.19± 36.06 and 208.64±59.25, respectively), however the difference was not significant compared with control. The neurites on ACs and OLs failed to grow radially in a well-fasciculated pattern as on SCs. In explants plated on the borders of cultured OL-SC or AC-SC groups, more neurites extended onto SCs compared with OLs and ACs. Conditioned media from OL or AC cultures did not reduce neurite length, implying that the inhibition of neurite growth by central glia is not due to soluble factors. Taken together, these results demonstrate that homogeneous populations of central glia inhibit SGN neurite growth.
Satellite data show that typhoon Chan‐hom did trigger an algal bloom several days after passing by the East China Sea. To investigate dynamic connections between this enhanced chlorophyll‐a and phosphate‐rich Kuroshio subsurface water (KSSW), we set up a fine‐resolution coupled physical‐biological model, which effectively reproduced the oceanic conditions during this typhoon. Furthermore, we released a passive tracer along a zonal transect northeast of Taiwan. The modeled surface tracer variations along the coast of Zhejiang agreed very well with satellite data and chlorophyll‐a changes in the biological model. The lowest structural similarity index between chlorophyll‐a and KSSW was 0.77. Model results along a coastal section imply that typhoon Chan‐hom induced additional upwellings and enhanced vertical mixing, leading to more KSSW outcropping. Through horizontal dynamic diagnostic and vertical velocity decomposition, we distinguished three types of dynamical mechanisms for the upward motions. At first, the linear wind Ekman effect existed around the coastal areas and led to intense Ekman pumping. Second, a pronounced nonlinear effect led to upwellings, and spectrum analysis revealed that this nonlinearity consisted of high‐frequency near‐inertial waves and low‐frequency coastal shelf waves. At last, an eddy field remained after the typhoon, continuously supplying nutrients upward to the surface layer by eddy‐induced Ekman pumping. This study reveals that these mechanisms may be general on the continental shelf, where typhoons can pump phosphate‐rich bottom water into the upper layer and enhance primary productivity there. The results also prove typhoon‐induced nonlinear wave motions on the continental shelf contribute to the outcrop of nutrients.
The Kuroshio intrusion plays a vitally important role in carrying nutrients to marginal seas. However, the key mechanism leading to the Kuroshio intrusion remains unclear. In this study we postulate a mechanism: when the Kuroshio runs onto steep topography northeast of Taiwan, the strong inertia gives rise to upwelling over topography, leading to a left‐hand spiral in the stratified ocean. This is called the topographic beta spiral, which is a major player regulating the Kuroshio intrusion; this spiral can be inferred from hydrographic surveys. In the world oceans, the topographic beta spirals can be induced by upwelling generated by strong currents running onto steep topography. This is a vital mechanism regulating onshore intruding flow and the cross‐shelf transport of energy and nutrients from the Kuroshio Current to the East China Sea. This topographic beta spiral reveals a long‐term missing link between the oceanic general circulation theory and shelf dynamic theory.
Observations indicate a seasonal variation of the Kuroshio subsurface water (KSSW) intrusion into the coastal region off the Zhejiang Province of China. The observed temperature and salinity distributions suggest a stronger intrusion in June and weaker intrusion in December. A hydrodynamic model well reproduces the seasonal variation of temperature and salinity characteristics and the current structure over the continental shelf. A passive tracer in the subsurface layer is used to investigate the movement of the KSSW. Tracer experiments confirm the seasonal variation of the KSSW intrusion, showing that the intrusion is stronger in summer and weaker in autumn and winter. Moreover, tracer concentrations suggest that in general it takes at least 1.5 months for the KSSW from east of Taiwan to reach the Zhejiang coastal area. Analyses of the momentum balances indicate that the KSSW's northward movement is regulated by the geostrophic current, while the shoreward intrusion results from the bottom Ekman effect. The seasonal changes in pressure gradients and vertical eddy viscosities contribute to the KSSW intrusion into the Zhejiang coastal area in June rather than in December. Sensitivity experiments show that the seasonal variation of the KSSW intrusion is mainly induced by the different wind stresses in summer and winter. The stronger southerly monsoon, the weaker and warmer Taiwan Warm Current, and the stronger and colder Kuroshio Current are favorable to the KSSW intrusion.
The Changjiang Estuary and adjacent sea area in the East China Sea suffer from frequent harmful algal blooms. However, the relative importance of riverine nutrient input from the Changjiang River and oceanic nutrient input from the Taiwan Warm Current and Kuroshio Current to the development and distribution of summer phytoplankton blooms in this area remains unclear. To address this problem, we deployed a coupled physical-biological model. The coupled model successfully reproduces the main hydrographic and biogeochemical features in this domain. Both satellite observations and model results show two regions of elevated chlorophyll concentrated in this site. Simulated results show that harmful algal blooms in the region north of the Zhoushan Islands are mainly driven by riverine nutrients from the Changjiang River, while algal blooms in the region south of the Zhoushan Islands are mainly controlled by nutrients from the open ocean. Nutrient input, particularly phosphate, from the Kuroshio subsurface water contributes most to the accumulation of dinoflagellate biomass and chlorophyll in the southern region, while the Taiwan Warm Current has less influence. This has implications for nutrient control and land management practices: Although reducing riverine nutrient loads may significantly reduce phytoplankton growth north of the Zhoushan Islands, it will have little effect in the area to the south. Plain Language Summary Blooms of microscopic algae that can be harmful to marine ecosystems and commercial fisheries are increasingly common during the summer months in the Changjiang Estuary and adjacent sea area in the East China Sea. The Changjiang River is traditionally considered as the dominant source of nutrients driving these harmful algal blooms. In this study, we show that although this appears to be true for algal blooms occurring to the north and northeast of the river estuary, algal blooms that occur along the coast to the south of the river estuary are mainly regulated by nutrient input from the open ocean. Intrusion of the Kuroshio subsurface water to the south of the Changjiang Estuary is shown to be particularly important in supplying the dissolved phosphate necessary for the algae in the southern region to bloom in large quantities.
The Kuroshio Current plays a crucial role in the subtropical gyre of the Pacific circulation by compensating for southward transport in the ocean interior induced by the negative wind stress curl; this current brings nutrients, high salinity, and high-temperature water downstream (
In the past decade (2010–2019), the annual maximum typhoon storm surge (AMTSS) accounted for 46.6% of the total direct economic loss caused by marine disasters in Chinese mainland, but its prediction in advance is challenging. By analyzing records of 23 tide-gauge stations, we found that the AMTSSs in Shanghai, Zhejiang and Fujian show significant positive correlations with the El Niño-Southern Oscillation (ENSO). For the 1987–2016 period, the maximum correlation is achieved at Pingtan station, where correlation coefficient between the AMTSS and Niño-3.4 is 0.55. The AMTSS occurring in El Niño years are stronger than those in non-El Niño years by 9–35 cm in these areas. Further analysis suggests that a developing El Niño can greatly modulate the behaviors of Northwest Pacific typhoons. Strong typhoons tend to make landfall in southeast China with stronger intensities and northward shifted landfall positions. This study indicates that the modulation effect by ENSO may provide potential predictability for the AMTSS, which is useful for the early alert and reduction of storm surge damages.
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