Tidal Transport Research Articles

Tidal transports from satellite observations of earth’s magnetic field

The tides are a major driver of global oceanic mixing. While global tidal elevations are very well observed by satellite altimetry, the global tidal transports are much less well known. For twenty years, magnetic signals induced by the ocean tides have been detectable in satellite magnetometer observations, such as Swarm or CHAMP. Here, we demonstrate how satellite magnetometer observations can be used to directly derive global ocean tidal transports. As an advantage over other tidal transport estimates, our tidal estimates base on very few and very loose constraints from numerical forward models.

Evolution of sedimentary dynamic process/pattern in the Quanzhou Bay under impact of Typhoon Matmo (2014)

Typhoons are one of the most dramatic weather events affecting the nearshore environment, which significantly affect the processes of sediment erosion, transport, and redeposition in a short period of time. In this study, the hydrodynamic evolution and sedimentary source and sink processes in the Quanzhou Bay after the typhoon’s passing were systematically studied by using the water column observation data (flow field and turbidity) and the surface sediment grain-size analysis results obtained in two surveys: 3–4 days and 1 month after Typhoon Matmo (2014), respectively. The results show that the typhoon process significantly increased the sediment flux input from the Jinjiang River and expanded the sediment “sink” in the Jinjiang River estuary. After the typhoon’s passing, the sediments in the bay were redistributed under the stable tidal transport, and the estuarine sediments were transformed from a sink of riverine material into a source of sediment transport and diffusion. Typhoon processes play an important role in the evolution of estuarine sediments and sedimentary environment.

Salt Transport Regimes Caused by Tidal and Subtidal Processes in Narrow Estuaries

AbstractTidally averaged transport of salt in estuaries is controlled by various subtidal and tidal processes. In this study, we show the relative importance of various subtidal and tidal transport processes in a width‐averaged sense. This is done for a large range of forcing and geometric parameters, which describe well‐mixed to salt wedge estuaries. To this end, we develop a width‐averaged process‐based model aimed at conducting and analyzing a large number of experiments (∼40,000). We find that the salt transport is dominated by one of seven salt transport balances, or regimes. Four of these regimes are dominated by subtidal processes, while the other three are dominated by tidal processes. Which regime occurs in a part of an estuary depends on four dimensionless parameters, representing local geometry, and forcing conditions. One of the regimes features salt import by correlations between the depth‐averaged tidal velocity and salinity. While this mechanism was previously only associated with along‐channel geometric variations, we find it can also be a dominant mechanism in a significant part of the parameter space due to river‐induced tidal asymmetry, independent of river geometry. We apply our classification to a case study of part of the Dutch Rhine delta and compare to decomposition results of a fully realistic three‐dimensional model. We find the estuary features two regimes, with import dominated by subtidal shear transport in the seaward part of the estuary and by depth‐averaged tidal correlations in the landward part of the estuary.

Using Different Classic Turbulence Closure Models to Assess Salt and Temperature Modelling in a Lagunar System: A Sensitivity Study

Turbulence modelling is an important issue when dealing with hydrodynamic and transport models for better simulation of the transport of dissolved or suspended substances in a body-water. It controls processes involving physical balances (salt and water temperature) and, therefore, the ecosystem equilibrium. The study arises from the need to model the turbulence more efficiently when dealing with extreme situations on the Ria de Aveiro (Portugal), a coastal lagoon shallow water system dominated by tidal transport. Because the turbulence model is coupled to the hydrodynamic and transport models, a correct estimation of the eddy viscosity is important in simulating the salt and the heat transports. The aim is to assess the performance of four turbulence schemes/models (k, k-ε, Smagorinsky’s, and k-ε/Smagorinsky’s (k-ε/Sma), where k is turbulent kinetic energy and ε the dissipation rate of the turbulent kinetic energy) associated to a coupled hydrodynamic and transport models to simulate the eddy viscosity, the salinity, and the temperature. Overall, the results point out that among the different models/schemes used, the is the one which provides a more realistic value of the eddy viscosity within the range (1–6) m2 s−1, but most probably (1–3) m2 s−1. The application of the sensitivity analysis to some non-universal k-ε/Sma parameters evidenced significant sensitivity for the eddy viscosity and the salinity and moderate sensitivity for the water temperature. A 100% adjustment of the parameter values relative to the reference, translated into variations within the range of (1, 4) m2 s−1, (0, 13) PSU, and (1, 2.20) °C, for the eddy viscosity, salinity, and water temperature, respectively.

Surfing the tide: Homeward migration of sea trout (Salmo trutta) in a Patagonian river

This study evaluates the influence of marine and freshwater conditions on the timing of river entry and upstream migration of sea trout (Salmo trutta) in the Grande River of Tierra del Fuego, Patagonia. We analysed the in-river catch-and-release records from a group of fishing lodges that dominate the Grande River fishery during January-April 2008 (n=5029 fish) as a function of environmental variables: tidal amplitude, stage in the lunar cycle, river discharge, and river water temperature along the homeward migration season. We discuss the value of the daily catch rate as an abundance index in the Grande river, then analyse the temporal structure of the tidal cycle in the Grande River estuary, a macro-tidal environment with a mean tidal amplitude of 5.7m, and analyse the fit of a generalized additive model to trout catches on a daily basis in four sections along the river to identify the environmental variables that may affect trout abundance throughout the homeward migration. Fish catches in each section of the river were differentially affected by specific environmental variables: tidal amplitude had a positive and significant effect on catches in the lower river sections, whereas water temperature and river discharge significantly affected catches in upper sections (positive effect of temperature; negative effect of discharge). Catches in the lower section clearly reflect the river entry stage of the homeward migration, with a bi-modal shape significantly correlated with the tidal cycle. The first peak was composed mainly of larger multi-sea-winter trout that move upstream, whereas the second one had a wider range of fish lengths, including a large proportion of small and maybe nonreproductive trout that overwinter in the lower river. Based on our results, we conclude that the large tides in the Grande River estuary strongly affect the river entry timing of sea trout. The underlying mechanisms of this effect may be a combination of increased olfactory recognition and increased tidal transport modulated by the seasonal tidal cycle, which operates on trout during coastal migration to produce the pulses observed in the Grande River sea trout run. In the middle and upper sections of the river, where the tidal effect at river entry was dissipated as upstream migration progressed, trout catches increased with water temperature and decreased with river discharge, which may operate through their influence on in-river migration rate and abundance, but also through changes in catchability.

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Tidal flat system is composed of multiple sub-scale geomorphological units. We found a new mesoscale geomorphological unit on sand-mud mixed intertidal zone along China coast, which was defined as hummocky patches. Hummock patches are most developed in middle tidal flat, with horizontal magnitude of 10–20 m and vertical magnitude of ∼15 cm. Hummocky patches significantly influence local sediment transport, thus affect morphological evolution of tidal flats. In order to understand the formation and development mechanisms of hummocky patches, we collected hydrodynamics, topography, sediment properties, and substrate erosion thresholds data through an in-situ field observation covering a spring-neap tidal cycle over an accretional intertidal flat in Jiangsu, China. We found that sediment characteristics including sorting coefficient (σ: measuring the uniformity of sediment particles) and silt/clay/organic matter/water content are essentially different between hummocky patches and nearby seabed, which leads to spatially varied substrate erosion resistance. The measured erosion thresholds for patches are two times higher comparing to surrounding seabed sediment, which provides foundation for the formation of hummocky patches. Under the impact of periodical tidal currents and waves, surrounding seabed experiences considerably more erosion than patch area, which finally develops to hummocky patches. Therefore, hydrodynamic forces drive the formation and development of patches. The erosion resistance of patches decreases vertically from seabed surface to sublayer, causing initial erosion in the lower sublayer, followed by a mass collapse of the seabed surface layer. Hummocky patches are commonly found in middle tidal zone and their sizes decrease to the shore as tidal currents and waves attenuate with shoreward propagation. Hummocky patches have distinct seasonal variations, which only appear in summer and autumn when wind waves are comparatively lower than winter and spring. We infer the reason is that the strong hydrodynamics caused by winter storms cause larger bottom shear stress than the erosion threshold of hummocky patches, leading to destruction of hummocky patches and a smooth tidal flat surface. This study shed new insight on the knowledge of mesoscale geomorphological units and their formation and development in intertidal flats, which provides crucial information for developing more realistic tidal flat sediment transport and morphological models.

Simulation of freshwater transport network and salt flux in the Bangladesh delta

Circulation of saline water is important for maintaining water quality in the Ganges-Brahmaputra-Meghna (GBM) delta because of its vulnerability to the threat of climate change. We applied a numerical model to examine the volume and salt transports within the GBM delta, Bangladesh. To understand the components of salt water intrusion driven by tidal and subtidal (residual) transports, we selected 19 cross-sections to represent the complex delta circulation in a simplified network model. Our results show that over 82.51% of GBM river water drains through the eastern estuarine system (EES) in the wet season, increasing to 98.37% in the dry season. Residual transport can be comparable in size with the tidal transport in the wet season, and one order of magnitude smaller in the dry season. The western estuarine system (WES) experiences serious salinity intrusion in the dry season, and strong seasonal variability in both tidal and subtidal transport, with suppression of tide-driven transport observed during the wet season. Our results show the sub-channels area of the Lower Meghna River also faces the risk from salinity intrusion issues, as stronger tidal salt flux is estimated in the dry season. Tidal volume transport varies seasonally, corresponding to the variability of river discharge. A simplified solution by means of polynomial expansion was applied to describe the tidal propagation within river channels. Inland penetration of tidal energy is reduced with large river discharge, and additionally the propagation speed of the tidal wave increases in the wet season. Our analysis helps understand the response of the three estuarine systems to seasonal and tidal controls, and can be used to inform river management about the upstream-downstream linkages.

The Properties of the Tide Current and Sediment at a Port of Southern China

Environmental factors of projects in the sea area, such as tidal current characteristics and sediment transport patterns, play a decisive role in the safe operation of the harbor. Based on the observation data of tide level, tidal current, suspended sediment, and surface sediment in the Port of Shenquan, this paper focuses on the study of the characteristics of tidal current and sediment of projects in the sea area. According to the measured tide hydrograph, it can be concluded that the tide in the Port of Shenquan is irregular diurnal, and the flow of rising and falling tides is basically rectilinear. The velocity of the neap tide is higher than that of spring tide, which is mainly related to the strong winds and waves. The sand source is limited, and the sediment concentration in the water is very low. The hourly sediment concentration in each station fluctuates within a narrow range, independent of hourly velocity change. The sediment is coarse and fine, with a distribution pattern of coarse near shore, fine in deep water, coarse in East and West, and fine in the middle, and the sorting coefficient of sediment is medium to well.

Rectified tidal transport in Lofoten–Vesterålen, northern Norway

Abstract. Vestfjorden in northern Norway, a major spawning ground for the northeast Arctic cod, is sheltered from the continental shelf and open ocean by the Lofoten–Vesterålen archipelago. The archipelago, however, is well known for hosting strong and vigorous tidal currents in its many straits, currents that can produce significant time-mean tracer transport from Vestfjorden to the shelf outside. We use a purely tidally driven unstructured-grid ocean model to look into non-linear tidal dynamics and the associated tracer transport through the archipelago. Of particular interest are two processes: tidal pumping through the straits and tidal rectification around islands. The most prominent tracer transport is caused by tidal pumping through the short and strongly non-linear straits Nordlandsflaget and Moskstraumen near the southern tip of the archipelago. Here, tracers from Vestfjorden are transported tens of kilometers westward out on the outer shelf. Further north, weaker yet notable tidal pumping also takes place through the longer straits Nappstraumen and Gimsøystraumen. The other main transport route out of Vestfjorden is south of the island of Røst. Here, the transport is primarily due to tracer advection by rectified anticyclonic currents around the island. There is also an anticyclonic circulation cell around the island group Mosken–Værøy, and both cells have flow speeds up to 0.2 m s−1, magnitudes similar to the observed background currents in the region. These high-resolution simulations thus emphasize the importance of non-linear tidal dynamics for transport of floating particles, like cod eggs and larvae, in the region.

Flows, Transport, and Effective Drag in Intertidal Salt Marsh Creeks

AbstractIntertidal creeks (channel width <5 m) weave through salt marshes, delivering water, nutrients, and sediments into the marsh interior and affecting spatial heterogeneity in plant and animal distributions. Despite their global prevalence, creek connectivity, and the mechanisms controlling cross‐marsh hydrodynamics, remain poorly resolved. In this study, we measured flow and total suspended solids transport in three intertidal creeks within a confined drainage basin in a Georgia, USA salt marsh. We discovered that the effective drag is 3–12 times greater than bed drag, reaching levels similar to those observed in coral reefs. Furthermore, the drag between tidal flood and ebb phases differs, indicating an asymmetric drag. Analyses of along‐channel momentum reveal that pressure gradient m/s2 and friction m/s2 dominate creek momentum balance. Divergence in tidal and suspended solids transport between adjacent creeks revealed contrasting tidal transport asymmetries (i.e., flood or ebb dominated) within this confined basin. We discuss how these differences may alter the eco‐geospatial evolution of salt marshes and their response to sea‐level rise.

Interactions between biotic and abiotic processes determine biogeomorphology in Yangtze Estuary coastal marshes: Observation with a modeling approach

Coastal salt marshes are biogeomorphic ecosystems with coupled vegetation and hydro-sedimentary processes. A significant biogeomorphic feature with a positive loop between vegetation colonization, sedimentary accretion, and edge scarp progradation can be found in coastal marshes with a highly depositional environment, such as the Yangtze Estuary. Together with field surveys, we used a process-based salt marsh model to characterize the spatiotemporal dynamics of vegetation and geomorphology in a tidal wetland in the Yangtze Estuary from 2014 to 2019. This model incorporated interactions between biotic processes (plant growth, colonization, and hydrological resilience) and abiotic processes (tidal transport of propagules, sediment inputs, and habitat-specific sediment deposition). Comparisons with field measurements showed that the model satisfactorily described the interannual variations in vegetation growth and lateral expansion, sedimentary dynamics and elevation change, and formation of marsh-edge scarps at two investigation sites. In particular, both observation and simulation revealed that the degree of sediment supply regulated the rates of vegetation behavior and geomorphic changes. The rates of plant establishment and growth were higher at the site with high sediment supply, and a higher rate of vegetation expansion and sedimentary accretion drove a faster seaward progradation of marsh-edge scarps, compared to the site with low sediment supply. Our results indicate that the interactions between biotic and abiotic processes, together with sediment supply, strongly determine the heterogeneity of marsh biogeomorphology in a highly depositional system. Thus, there is a vast potential for application of process-based models in formulating tidal wetland management and assessing future system resilience.

Extreme Meteorological Events in a Coastal Lagoon Ecosystem: The Ria de Aveiro Lagoon (Portugal) Case Study

Extreme weather events (EWEs) represent meteorological hazards for coastal lagoon hydrodynamics, of which intensity and frequency are increasing over the last decades as a consequence of climate changes. The imbalances they generated should affect primarily vulnerable low-lying areas while potentially disturbing the physical balances (salt and water temperature) and, therefore, the ecosystem equilibrium. This study arises from the need to assess the impact of EWEs on the Ria de Aveiro, a lagoon situated in the Portuguese coastal area. Furthermore, it was considered that those events occur under the frame of a future sea-level rise, as predicted by several climate change scenarios. Two EWEs scenarios, a dry and an extremely wet early summer reflecting past situations and likely to occur in the future, were considered to assess the departure from the system baseline functioning. It was used as a biogeochemistry model that simulates the hydrodynamics, as well as the baseline physical and biogeochemistry state variables. The dry summer scenario, corresponding to a significant reduction in the river’s inflow, evidences a shift of the system to a situation under oceanic dominance characterized by colder and saltier water (~18 °C; 34 PSU) than the baseline while lowering the concentration of the nutrients and reducing the phytoplankton population to a low-level limit. Under a wet summer scenario, the lagoon shifted to a brackish and warmer situation (~21 °C, <15 PSU) in a time scale of some tidal periods, driven by the combining effect of the tidal transport and the river’s inflow. Phytoplankton patterns respond to variability on local and short-term scales that reflect physical conditions within the lagoon, inducing nutrient-supported growth. Overall, the results indicate that EWEs generate local and transient changes in physical conditions (namely salinity and water temperature) in response to the characteristic variability of the lagoon’s hydrodynamics associated with a tidal-dominated system. Therefore, in addition to the potential impact of changing physical conditions on the ecosystem, saline intrusion along the lagoon or the transfer of brackish water to the mouth of the system are the main consequences of EWEs, while the main biogeochemistry changes tend to remain moderate.

Influence of Riverbed Incision and Hydrological Evolution on Water Quality and Water Age Based on Numerical Simulation: A Case Study of the Minjiang Estuary

In recent years, problems such as water quality deterioration, saltwater invasion, and low oxygen have appeared in estuaries all over the world. The Minjiang River in Fujian, as a typical tidal estuary area, is facing these thorny problems. In this paper, the effects of topography and hydrologic evolution on the water age and water quality of the lower reaches of the Minjiang River were simulated by building a hydrodynamic and water quality model. The results show that: (1) It was found that the riverbed incision of the lower reaches of the Minjiang River led to the overall decline of river water level, the increase of river volume, and the increase of downstream water age, which eventually led to the decrease of dissolved oxygen (DO) and the deterioration of water quality in the downstream from Shuikou to Baiyantan. However, the decline of topography led to the increase of tidal volume in the estuary, the enhancement of the dilution effect of oxygen-rich water bodies in the open sea, and the increase of DO in the lower reaches of Baiyantan. (2) Under no tidal action, the concentration of pollutants in the water of the North Channel increased, the DO decreased, and the DO decreased from Baiyantan to the offshore water. After the enhancement of tidal action, the dilution of oxygen-enriched water from the offshore water increased, and the DO increased. (3) The hydrological and water quality characteristics of the upper part of the lower reaches of the Minjiang River were mainly controlled by topography, runoff, and pollutant discharge, which were more affected by the tidal current transport operation and pollutant discharge near the open sea. In recent decades, the deterioration of water quality and the aggravation of saltwater intrusion in the Minjiang River were closely related to the serious topographic downcutting. The results provide a scientific basis for revealing the deterioration of estuary water quality and long-term management of the estuary.

Self‐Organization of Coastal Barrier Systems During the Holocene

AbstractUnderstanding the response of coastal barrier systems to sea level rise is a crucial societal need. Despite the problem having been studied extensively, major knowledge gaps remain. For example, neither the sedimentary record nor existing numerical models have been conclusive in explaining the formation of barrier islands. Here I present a comprehensive 2D model that seamlessly couples cross‐shore and along‐shore transport, tidal transport, storm surges, and wind waves, and use it to simulate an idealized passive margin during the last 7,000 years. In the early Holocene, when sea level was rising ∼20 mm/yr, shoals and ephemeral barrier islands formed, periodically drowned, and then formed again at a landward location. Shoal emergence was triggered by the disequilibrium of the recently submerged shelf, especially for large waves and mild shelf slopes. About 5,000 years ago, as sea level rise slowed down to ∼1 mm/yr, barriers stabilized and even prograded seaward. The combination of excess sediment in the nearshore and storm surges allowed barriers to accrete above mean high water. When barriers eventually equilibrated to the new sea level rise rate and started to retreat, their retreat rate was highly variable in space and time due to autogenic processes such as inlet formation and backbarrier channel interception. This variability also included multi‐decadal periods of localized progradation. Both lag dynamics and autogenic processes confound the relationship between barrier retreat and sea level rise rate.

NUMERICAL SIMULATIONS ON INFLUENCE OF LONG-TERM FLUCTUATION OF MEAN WATER LEVEL ON SAND WAVES IN THE KANMON WATERWAY, JAPAN

In this study, the numerical simulation of tidal current and sediment transport in the Kanmon Waterway were performed by using a numerical simulation model FVCOM (Finite Volume Community Ocean Model (Chen et al. 2003)), in order to discuss the influence of the long-term fluctuation of mean water level on the sand waves. The numerical simulation results suggested that the spatial difference of the long-term fluctuation of mean water level in the Kanmon Straits slightly changes the tidal current around Tanoura Area, and consequently affects the development of sand waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kfMfIVGiLKM

Cardinal Buoys: An Opportunity for the Study of Air-Sea CO2 Fluxes in Coastal Ecosystems

From 2015 to 2019 we installed high-frequency (HF) sea surface temperature (SST), salinity, fluorescence, dissolved oxygen (DO) and partial pressure of CO 2 (pCO 2) sensors on a cardinal buoy of opportunity (ASTAN) at a coastal site in the southern Western English Channel (sWEC) highly influenced by tidal cycles. The sensors were calibrated against bimonthly discrete measurements performed at two long-term time series stations near the buoy, thus providing a robust multi-annual HF dataset. The tidal transport of a previously unidentified coastal water mass and an offshore water mass strongly impacted the daily and seasonal variability of pCO 2 and pH. The maximum tidal variability associated to spring tides (>7 m) during phytoplankton blooms represented up to 40% of the pCO 2 annual signal at ASTAN. At the same time, the daily variability of 0.12 pH units associated to this tidal transport was 6 times larger than the annual acidification trend observed in the area. A frequency/time analysis of the HF signal revealed the presence of a day/night cycle in the tidal signal. The diel biological cycle accounted for 9% of the annual pCO 2 amplitude during spring phytoplankton blooms. The duration and intensity of the biologically productive periods, characterized by large inter-annual variability, were the main drivers of pCO 2 dynamics. HF monitoring enabled us to accurately constrain, for the first-time, annual estimates of air-sea CO 2 exchanges in the nearshore tidally-influenced waters of the sWEC, which were a weak source to the atmosphere at 0.51 mol CO 2 m −2 yr −1. This estimate, combined with previous studies, provided a full latitudinal representation of the WEC (from 48 • 75 N to 50 • 25 N) over multiple years for air-sea CO 2 fluxes in contrasted coastal ecosystems. The latitudinal comparison showed a clear gradient from a weak source of CO 2 in the tidal mixing region toward sinks of CO 2 in the stratified region with a seasonal thermal front separating these hydrographical provinces. In view of the fact that several continental shelf regions have been reported to have switched from sources to sinks of CO 2 in the last century, weak CO 2 sources in such tidal mixing areas could potentially become sinks of atmospheric CO 2 in coming decades.

Persistent Hydrodynamic Cues Elicit Orientation-Specific Behavioral Sensitivities and Kinematic Responses in Dispersed Crab Larvae

The estuarine mud crab Panopeus herbstii navigates a complex, but structured, hydrodynamic environment throughout its life history. The effects of hydrodynamic cues associated with turbulent flows on larval behavior are relatively well understood in the context of selective tidal stream transport (STST) phenomena during the dispersed (pelagic) larval stages preceding benthic settlement. In contrast, the potential relevance of hydrodynamic cues associated with spatiotemporally persistent flow features, which are typical of estuarine regions of enhanced productivity such as fronts and clines, remains much less certain. To investigate the behavioral relevance of persistent hydrodynamic cues, larval assays were conducted in a flume system that uses a laminar slot jet to produce steady fluid shear layers. Further, to ascertain whether or not the spatial orientation of the shear layers relative to gravity significantly affected larval behavior, assays were conducted in upwelling, downwelling, and horizontal shear flows, corresponding to the direction of the bulk flow produced by the jet. The flow was quantified using particle image velocimetry (PIV) and tuned to produce ecologically-relevant hydrodynamic conditions for larval assays. Changes in larval swimming kinematics show a distinct response to shear flows in all orientations relative to no-flow conditions, and the macro effect of these changes is to enhance depth-keeping and induce area-restricted search behaviors. Furthermore, the specifics of larval behavioral responses depend on the directional orientation of the shear flow, and the statistical properties of the strength of the hydrodynamic cue (vorticity) eliciting these responses are also shown to be shear flow orientation-specific. Orientation-specific hydrodynamic sensitivity and behavioral response strategies in the presence of persistent hydrodynamic cues may enable larvae to effectively forage and sample to locate and exploit nearby resource patches, while also inducing dispersal trajectories towards favorable benthic settlement habitats through depth regulation and effective STST. In this regard, hydrodynamic cues associated with spatiotemporally persistent flow features are likely fundamental drivers of decapod crab larvae behavior and may act as another mechanism of larval patchiness by directly impacting finescale population distributions and resultant dispersal trajectories.

Assessing the Dynamics of Dissolved Organic Matter (DOM) in the Coastal Environments Dominated by Mangroves, Indian Sundarbans

Tidal transport from coastal wetlands (“outwelling”) together with riverine fluxes provide most important sources of terrigenous organic matter (OM) to the ocean. The flux of dissolved organic carbon (DOC) from the mangrove swamps accounts for 10% of the terrestrial DOC flux to the coastal water. This study examines the sources, distribution, and export of dissolved OM at inter-annual, seasonal and diurnal basis along the estuaries located at the Sundarbans, world’s largest deltaic mangrove and heritage site. Sampling was carried out from riverine (Hooghly) and mangrove-dominated tidal estuaries (Saptamukhi, Thakuran, Matla) covering all three seasons (pre-monsoon, monsoon and post-monsoon) during 2012-2017. DOC varied at a broad range from 109 to 462 µM (n = 146) with higher concentration observed in the Hooghly (383±120 µM, n = 35) than the mangrove estuaries (246±82 to 266±120 µM, n = 111). Nonconservative mixing of DOC along the salinity gradient attested to mangrove input, particularly in the polyhaline waters. Upper and mid estuarine zones of the mangrove estuaries showed slightly higher DOC concentration (270±92 µM, n = 84, salinity range 18-25) than the mouth (250±85 µM, n = 27, salinity range 26-27) because of the dilution with marine waters having low DOC concentration and shorter water residence time downstream. Seasonally, higher DOC concentration during the post-monsoon might be linked to higher litterfall promoting leaching of organic compounds to the water. In that connection, colored dissolved organic matter (CDOM) could be the by-product of mangrove litter leaching, and its absorption coefficient (at 350 nm) exhibited non conservative mixing pattern at wide ranges from 2.5 to 7.6 m-1 (n = 40). CDOM enrichment was observed in the surface water during the low tide when outwelling maximized. Overall, central and eastern part of the Indian Sundarbans showed enrichment of more terrigenous type CDOM (evident from optical proxies e.g. S275-295 and SUVA254) than the western part, probably due to greater mangrove productivity in the eastern side. Flux estimates of DOM resulted in higher yield and export of mangrove-derived DOC but lower export of CDOM to the Bay of Bengal as compared to their riverine transport.

Influences of microtidal regime and eutrophication on estuarine zooplankton

This study describes the ecology of mesozooplankton in the shallows of the large central basin area of the Swan-Canning Estuary on the microtidal lower west coast of Australia during the mid-1980s when, as in most other south-western Australian estuaries, it was mesotrophic. As the vast majority of species reproduce within the estuary and there is a lack of a net upstream flow of bottom water during each tidal cycle to facilitate selective tidal transport, the populations of those species are considered autochthonous. Species restricted to the estuary accounted for 63% of the total number of species and 83% of abundance. Contributions by tychoplankton to total number of species (68%) and individuals (59%) exceeded the corresponding values of 18 and 39% for holoplankton and 14 and 2% for meroplankton. Low meroplankton values result from a paucity of benthic macroinvertebrate species with planktotrophic development. Comparisons with data for the shallow basin areas of the nearby highly eutrophic Peel-Harvey Estuary were used to indicate how mesozooplankton in the microtidal estuaries respond to excessive nutrient enrichment. The mean number of species in the Swan-Canning was essentially the same as in the Peel-Harvey, whereas concentrations were only half, reflecting the lower productivity of the former estuary. However, concentrations of the four most abundant species in the Swan-Canning, the amphipod Grandidierella propendatata, the calanoids Gladioferens imparipes and Acartia cf. clausi and a harpacticoid species, exceeded those of these species in the Peel-Harvey by between 1.6 and 11.7 times. Greater concentrations in the Swan-Canning were attributable to this mesotrophic system not undergoing the reduction in oxygen concentrations and/or environmental degradation, to which these species are susceptible. In contrast, concentrations of the amphipods Corophium minor and Tethygenia elanora and large nematodes, which are tolerant of degraded environmental conditions, were greater in the Peel-Harvey. Holoplankton made a far greater contribution in the Swan-Canning than Peel-Harvey, due to substantial numbers of copepods that benefit from good environmental conditions. Mesozooplankton composition in both estuaries underwent cyclical changes during the year due to time-staggered differences in seasonal concentrations of various species. Cyclical changes and variations in composition were more closely related to measured environmental variables in the Swan-Canning than Peel-Harvey estuaries. The concentrations of many species were greater at night than during the day presumably reflecting a nycthemeral response and/or low nocturnal oxygen concentrations at the bottom of the water column.

The diurnal transport of atmospheric water vapor during major dust storms on Mars based on the Mars Climate Database, version 5.3

In recent studies of the Martian atmosphere, strong diurnal variation in the dust was discovered in the southern hemisphere during major dust storms, which provides strong evidence that the commonly recognized meridional transport process is driven by thermal tides. This process, when coupled with deep convection, could be an important part of the short-term atmospheric dynamics of water escape. However, the potential of this process to alter the horizontal distribution of moist air has not been systematically investigated. In this work, we conducted pre-research on the horizontal transport of water vapor associated with the migrating diurnal tide (DW1) at 50 Pa in the upper troposphere during major dust storms based on the Mars Climate Database (MCD) 5.3, a state-of-the-art database for Martian atmospheric research that has been validated as simulating the relevant short-period atmospheric dynamics well. We found westward-propagating diurnal patterns in the global water vapor front during nearly all the major dust storms from Martian years (MYs) 24 to 32. Statistical and correlation analyses showed that the diurnal transport of water vapor during global and A-season regional dust storms is dominated by the DW1. The effect of the tidal transport of water vapor varies with the types of dust storms in different seasons. During regional dust storms, the tidal transport induces only limited diurnal motion of the water vapor. However, the horizontal tidal wind tends to increase the abundance of daytime water vapor at mid- to low latitudes during the MY 28 southern summer global dust storm while decreasing it during the MY 25 southern spring global dust storm. The tidal transport process during these two global dust storms can induce opposite effects on water escape.