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Eight‐year ocean color observations between 2002 and 2009 from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite are used to quantitatively assess the spring‐neap tidal effects on variability of ocean optical and biogeochemical properties in the Bohai Sea, Yellow Sea, and East China Sea. We demonstrate that spring‐neap tidal variation is one of important ocean processes that drive both the synoptic‐scale and mesoscale changes of the ocean optical, biological, and biogeochemical properties in the coastal region. Normalized water‐leaving radiance spectra (nLw(λ)), water diffuse attenuation coefficient at the wavelength of 490 nm (Kd(490)), and total suspended matter (TSM) concentration show significant spring‐neap variations in the coastal region within a lunar cycle of 29.53 days. In the open ocean, however, spring‐neap tidal effects on ocean color data are negligible. The entire areal coverage of the turbid waters (Kd(490) > 0.3 m−1) showing significant spring‐neap tidal variations is ∼4–5 × 105 km2. Similar coverage of moderately turbid waters (0.1 < Kd(490) ≤ 0.3 m−1) is also impacted by the spring‐neap tides. The magnitude of the spring‐neap tidal effects on the variations of the satellite ocean color properties, e.g., Kd(490) and TSM, is in the same order as the seasonal variations in the coastal region. Highest Kd(490) and largest turbid water coverage lag the new moon (or full moon) about 2–3 days, while the lowest Kd(490) and smallest turbid water coverage are also ∼2–3 days behind the one‐quarter (or three‐quarter) moon. This is attributed to the seawater inertia and the friction against the seabed as well as the sediment resuspension process. Key Points Evaluation of the spring‐neap tidal effects on variability of ocean properties Significant tidal effects on remote sensing products in coastal regions Phase shifts in tidal effects for Bohai Sea, Yellow Sea, and East China Sea

We investigated the spatio-temporal variability of chlorophyll-a (Chl-a) and total suspended matter (TSM) associated with spring–neap tidal cycles in the Ariake Sea, Japan. Our study relied on significantly improved, regionally-tuned datasets derived from the ocean color sensor Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua over a 16-year period (2002–2017). The results revealed that spring–neap tidal variations in Chl-a and TSM within this macrotidal embayment (the Ariake Sea) are clearly different regionally and seasonally. Generally, the spring–neap tidal variability of Chl-a in the inner part of the Ariake Sea was controlled by TSM for seasons other than summer, whereas it was controlled by river discharge for summer. On the other hand, the contribution of TSM to the variability of Chl-a was not large for two areas in the middle of Ariake Sea where TSM was not abundant. This study demonstrates that ocean color satellite observations of Chl-a and TSM in the macrotidal embayment offer strong advantages for understanding the variations during the spring–neap tidal cycle.

Mangrove ecosystems are nursery habitats for several snapper species worldwide. Yet the short-term dynamics in nursery habitat use of Lutjanidae remain poorly understood, with knowledge biased toward clear water, nonestuarine mangroves. Here, we document the effects of tidal-diel cycles and salinity on patterns in abundance and feeding of the yellow snapper, Lutjanus argentiventris, using samples collected from intertidal creeks in a macrotidal estuarine mangrove during 2009—2010 from Colombia, in the Tropical Eastern Pacific (TEP) region. Abundance and biomass were significantly higher in medium salinity versus low salinity creeks. Contrasting tidal-diel patterns of abundance-densities versus catch mass-biomass were due to a size-based intraspecific variation in mangrove use: fish <10 cm visited intertidal creeks mainly during daytime at neap tides, whereas fish >20 cm entered at night during both spring and neap tides. L. argentiventris had a generalist diet (mainly fish and porcellanid crabs). Fish <10 cm displayed a narrower diet breadth than larger size classes, with decreasing importance of fish size during ontogeny. The highest stomach fullness index values (especially of individuals <20 cm) during neap tide-daytime inundations contradicted the common assumption that snappers are nocturnal feeders and highlight the role of tidal-diel cycles in determining fish feeding preferences in macrotidal mangrove systems. Comparisons with other studies showed that habitat use and feeding patterns of this and other Lutjanids vary significantly according to size, tidal-diel dynamics, and mangrove settings, e.g., marine microtidal versus estuarine macrotidal systems. Therefore, generalized conclusions derived from a single mangrove setting should be drawn with caution.

Turbidity is an indicator of the quality of water and usually exhibits variability associated with changing hydrodynamic conditions, which can be reflected in the sediment dynamics in coastal regions. Darwin Harbour is a typical macro-tidal, well mixed, and complex environment influenced by industries, human activities, and natural factors—including winds, currents, river discharges, waves, and tides. As a case study, hydrodynamics and sediment dynamics in Darwin Harbour are investigated using moderate resolution imaging spectroradiometer (MODIS) measurements. This study focuses on understanding the variability of turbidity, mechanisms that control the variations of turbidity and analyzing field data to determine the main factors that influence the sediment dynamics in Darwin Harbour. The results of this study illustrate the seasonal turbidity variation is mainly influenced by the wind waves. The dredging campaigns in 2013 and 2014 wet seasons contributed to the rise of turbidity in Darwin Harbour. The action of tidal currents appears to be the dominant factor controlling the turbidity pattern in a spring–neap cycle and the turbidity intra-tidal variation. In addition, the turbidity maximum zone (TMZ) near Charles Point is formed by the tidal current convergence based on the results of current modelling.

In order to examine the influence of forcing (river flow and tides) and anthropogenic activities (dredging and dam regulation) on stratification, a study was conducted over a period of 19 months (June 2008–December 2009) in the Gautami–Godavari estuary (G–GE) during spring and neap tide periods covering entire spectrum of discharge over a distance of 36 km from the mouth. The bathymetry of the estuary was recently changed due to dredging of ∼20 km of the estuary from the mouth for transportation of barges. This significantly changed the mean depth and salinity of the estuary from its earlier state. The variations in the distribution of salinity in the Godavari estuary are driven by river discharge during wet period (June–November) and tides during dry period (December–May). The weak stratification was observed during high discharge (July–August) and no discharge (January–June) periods associated with dominant fresh water and marine water respectively. The strong stratification was developed associated with decrease in discharge during moderate discharge period (October–December). Relatively stronger stratification was noticed during neap than spring tides. The 15 psu isohaline was observed to have migrated ∼2–3 km more towards upper estuary during spring than neap tide suggesting more salt enters during former than latter period. Total salt content was inversely correlated with river discharge and higher salt of about 400×10 6 m 3 psu was observed during spring than neap tide. Flushing times varied between less than a day and more than a month during peak and no discharge periods respectively with lower times during spring than neap tide. The flushing times are controlled by river discharge during high discharge period, tides during dry period and both (river discharge and tides) under moderate discharge period. This study suggests that modification of discharge, either natural due to weak monsoon, or artificial such as dam constructions and re-routing the river flow, may have significant impact on the stratification and biogeochemistry of the Godavari estuary.

Intra-tidal variability in the transport of materials through the Cochin estuary was studied over successive spring and neap tides to estimate the export fluxes of nutrients and chlorophyll a into the adjoining coastal zone. The results showed that there was a substantial increase in the freshwater flow into the estuary following heavy rains (~126 mm) prior to the spring tide observations. The estuary responded accordingly with a relatively larger export through the Cochin inlet during spring tide over neap tide. Despite an increased freshwater discharge during spring tide, the export fluxes of phosphate and ammonia were high during neap tide due to their input into the estuary through anthropogenic activities. The significance of this study is that the export fluxes from the Cochin estuary could be a major factor sustaining the spectacular monsoon fishery along the southwest coast of India.

Monteiro, M.C.; Pereira, L.C.C., and Jiménez, J.A., 2016. The trophic status of an Amazon estuary under anthropic pressure (Brazil). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. XX-XX. Coconut Creek (Florida), ISSN 0749-0208. The effects of the anthropogenic process on the trophic status of the Caeté estuary (located 150 km southwest of the Amazon delta) were undertaken under different climate conditions. To do this, oceanographic data were carried out, covering the dry season of 2010 (August–December: rainfall 363 mm), and the wet (January–July, rainfall 2483 mm) and dry seasons of 2011 (August–October, rainfall 135 mm). During the dry season (2010 and 2011) the mean discharge of the Caeté River was less than 20.0 m3 s−1, while, during the wet season, the mean discharge increased to 73.6 m3 s−1. Tidal ranges oscillated between 2.2 and 3.8 m, and current speeds varied from 0.6 and 0.7 m s−1 in both seasons (wet and dry). Salinity (under 3.0) and pH (under 6.0) were typical of fluvial systems. Turbidity (up to 150 NTU), dissolved oxygen (6.7 mg L−1) and dissolved nutrient (nitrite, nitrate, phosphate and silicate, but not ammonium) concentrations reached their maximum levels during the dry season, when the runoff decreased. The high chlorophyll a concentrations (values of up to 10.0 mg m−3) were typical of environments with high levels of primary productivity. According to the trophic index (TRIX), the waters of the Caeté estuary were characterized by moderate levels of eutrophication and good water quality during the wet season, shifting to high levels of eutrophication and bad water quality during the dry season. A comparative analysis indicates that eutrophication is less intense during neap tides in comparison with spring tides.

Saltwater intrusion is a serious environmental problem in the Zhujiang River Estuary（ZRE）,which threatens the water supply of fifteen million people.The hydrological observations as well as meteorological and tidal forcing in the winter of 2007/2008 were analyzed to examine the saltwater intrusion in the ZRE.The observational results suggest that the maximum vertical difference of salinity can reach 10 in the Humen Channel during neap tide,but is very small in the Hengmen Channel.The vertically averaged salinity from time series stations during spring tide is higher than that during neap tide.A three-dimensional finite difference model was developed based on the environmental fluid dynamic code（EFDC） to study the mechanism of saltwater intrusion and salinity stratification in the ZRE.By analyzing the salt transport and the temporal variation of saltwater intrusion,the authors found that the net salt transport due to the estuarine circulation during neap tide was more than that during spring tide.This caused salt to advance more into the estuary during neap tide.However,saltwater intrusion was stronger during spring tide than that during neap tide because the spring-neap variation in salt transport was small relative to the total length of the saltwater intrusion.The physical mechanism causing this saltwater intrusion was investigated by a series of sensitivity experiments,in order to examine saltwater intrusion in response to river discharge and winds.The freshwater source was a dominant influencing factor to the saltwater intrusion and controlled salinity structure,vertical stratification and length of the saltwater intrusion.The prevailing northeast monsoon during winter could increase the saltwater intrusion in the ZRE.Though the southwest wind was unfavorable to saltwater intrusion during spring tide,it could increase stratification and saltwater intrusion during neap tide.

Tide currents are important for mixing in ocean, especially they flow through straits, generating turbulence that facilitates the mixing of surface and deep waters. To further investigate the tidal current distribution patterns in the coastal waters of Zhanjiang and study the effect of Qiongzhou Strait (QS) on the features of tidal current, a quasiharmonic analysis method was employed to analyze the measured ocean current data collected during the periods of spring and neap tides in both the winter and the summer of 2018 in the study area. The analysis aimed to explore the tidal nature, tidal movement characteristics, and residual current distribution features of this region. The research results indicate that topography influence is dominant factor for tidal current variations in the study area. The northern stations C1, C2, C3, and C7 exhibit irregular semidiurnal tides, whereas southern stations C4, C5, C6, C8, and C9 display irregular diurnal tides. The dominant tidal constituents at all the stations are M 2 , K 1 , and O 1 . The tidal currents mainly flow in a reciprocating manner, with the dominant current direction during both flooding and ebbing tides being southwest-northeast at most stations. The vertically averaged current speeds during spring tides are significantly higher than those during neap tides. The tidally averaged current speeds decrease from the surface to the bottom. Southern stations C4, C5, C6, C8, and C9, which are located close to the QS, present relatively high tidally averaged current speeds. The directions of the residual currents at various depths are similar and are mainly southern biased. In summer, the residual currents are less affected by wind stress, whereas in winter, during neap tides, the residual currents are significantly influenced by northeasterly winds, resulting in velocities that are notably greater than those during spring tides.

Predicting the occurrence of internal solitary‐like waves (ISWs) is important for parameterizing turbulent dissipation. ISWs in the northern South China Sea (SCS) are well understood to mainly originate from the Luzon Strait (LS). They are generally predictable due to their phase‐locked relation with tidal forcing in the LS. However, irregular occurrence of ISWs is noted from our 9‐day moored measurements on the SCS shelf. More energetic ISWs unexpectedly appeared during the neap tide than the spring tide. Their occurrence was related to subtidal shelf flows. The tidal and shelf flows had comparable magnitudes. We thus hypothesize that when the total flow meets critical conditions ISWs are generated locally over irregular seafloor. This hypothesis is supported by numerical experiments and validated by observations. Consequently, local generation of ISWs enhances both the intensity and complexity of internal wave field on the shelf, and thus the unpredictability of ISW occurrence. Plain Language Summary Internal solitary‐like waves (ISWs) are ubiquitous in the ocean. They can propagate several hundreds of kilometers, and induce strong turbulence and mixing. Revealing generation mechanisms and propagation of ISWs is key to further investigating their influence on the distributions of energy dissipation, heat, nutrients, sediment, and pollutants, as well as the safety of submarine voyages and offshore drilling. In this paper, ISWs in the northern South China Sea (SCS), where the most energetic ISWs in the world's oceans are generated, are studied. It is widely accepted that these ISWs generally originate from the Luzon Strait (LS). They usually have regular occurrence, and are phase‐locked to tidal forcing in the LS. However, we present field measurements showing irregular occurrence of ISWs on the northern shelf of the SCS. This irregular occurrence is in striking contrast to the prominent predictability of ISWs originated from the LS. We reveal that the intermittent nature of the occurrence is due to the local generation of ISWs on the shelf; the coupling of different flow components seems to play a significant role in ISW generation on the shelf. The results reported here are expected to be applicable to other shelf regions of the world's oceans. Key Points Field measurements documented large numbers of internal solitary‐like waves (ISWs) with irregular occurrence on the northeastern shelf of the South China Sea More energetic and larger numbers of ISWs are observed during the neap tide than during the spring tide as modulated by shelf flows ISWs are locally generated due to the joint effects of tidal and subtidal shelf flows