The Effect of Wave-Induced Current and Coastal Structure on Sediment Transport at the Zengwen River Mouth

The mechanisms that control estuarine sediment transport are complicated due to the interaction between riverine flows, tidal currents, waves, and wave-driven currents. In the past decade, severe seabed erosion and shoreline retreat along the sandy coast of western Taiwan have raised concerns regarding the sustainability of coastal structures. In this study, ADCPs(Acoustic Doppler Current Profiler) and turbidity meters were deployed at the mouth of the Zengwen river to obtain the time series and the spatial distribution of flow velocities and turbidity during the base flow and flood conditions. A nearshore circulation model, SHORECIRC, has been adapted into a hybrid finite-difference/finite-volume, TVD (Total Variation Diminishing)-type scheme and coupled with the wave-spectrum model Simulating Waves Nearshore (SWAN). Conventional finite-difference schemes often produce unphysical oscillations when modeling coastal processes with abrupt bathymetric changes at river mouths. In contrast, the TVD-type finite volume scheme allows for robust treatment of discontinuities through the shock-capturing mechanism. The model reproduces water levels, waves, currents observed at the mouth of the Zengwen River reasonably well. The simulated residual sediment transport patterns demonstrate that the transport process at the river mouth is dominated by the interaction of the bathymetry and wave-induced currents when the riverine discharge was kept in reservoirs. The offshore residual transport causes erosion at the northern part of the river mouth, and the onshore residual transport causes accretion in the ebb tidal shoals around the center of the river mouth. The simulated morphological evolution displays significant changes on shallower deltas. The location with significant sea bed changes is consistent with the spot in which severe erosion occurred in recent years. Further analysis of morphological evolution is also discussed to identify the role of coastal structures, for example, the extension of the newly constructed groins near the river mouth.

Large transient capacitive currents in wild-type lysosomal Cl−/H+ antiporter ClC-7 and residual transport activity in the proton glutamate mutant E312A

ClC-7 is a lysosomal 2 Cl−/1 H+ antiporter of the CLC protein family, which comprises Cl− channels and other Cl−/H+ antiporters. Mutations in ClC-7 and its associated β subunit Ostm1 lead to osteopetrosis and lysosomal storage disease in humans and mice. Previous studies on other mammalian CLC transporters showed that mutations of a conserved, intracellularly located glutamate residue, the so-called proton glutamate, abolish steady-state transport activity but increase transient capacitive currents associated with partial reactions of the transport cycle. In contrast, we observed large, transient capacitive currents for the wild-type ClC-7, which depend on external pH and internal, but not external, Cl−. Very similar transient currents were observed for the E312A mutant of the proton glutamate. Interestingly, and unlike in other mammalian CLC transporters investigated so far, the E312A mutation strongly reduces, but does not abolish, stationary transport currents, potentially explaining the intermediate phenotype observed in the E312A mouse line.

Ocean Heat Storage in Response to Changing Ocean Circulation Processes

Ocean heat storage due to local addition of heat (“added”) and due to changes in heat transport (“redistributed”) were quantified in ocean-only 2xCO2 simulations. While added heat storage dominates globally, redistribution makes important regional contributions, especially in the tropics. Heat redistribution is dominated by circulation changes, summarized by the super-residual transport, with only minor effects from changes in vertical mixing. While previous studies emphasized the contribution of redistribution feedback at high latitudes, this study shows that redistribution of heat also accounts for 65% of heat storage at low latitudes and 25% in the midlatitude (35°–50°S) Southern Ocean. Tropical warming results from the interplay between increased stratification and equatorward heat transport by the subtropical gyres, which redistributes heat from the subtropics to lower latitudes. The Atlantic pattern is remarkably distinct from other basins, resulting in larger basin-average heat storage. Added heat storage is evenly distributed throughout midlatitude Southern Ocean and dominates the total storage. However, redistribution stores heat north of the Antarctic Circumpolar Current in the Atlantic and Indian sectors, having an important contribution to the peak of heat storage at 45°S. Southern Ocean redistribution results from intensified heat convergence in the subtropical front and reduced stratification in response to surface heat, freshwater, and momentum flux perturbations. These results highlight that the distribution of ocean heat storage reflects both passive uptake of heat and active redistribution of heat by changes in ocean circulation processes. The redistributed heat transport must therefore be better understood for accurate projection of changes in ocean heat uptake efficiency, ocean heat storage, and thermosteric sea level.

Mapping Current Fields in a Bay Using a Coast-Fitting Tomographic Inversion

Coast-fitting tomographic inversion that is based on function expansion using three types of normal modes (the Dirichlet, Neumann, and open boundary modes) is proposed to reconstruct current fields from the coastal acoustic tomography (CAT) data. The superiority of the method was validated while using CAT data that were obtained in 2015 in the Dalian Bay. The semidiurnal tidal and residual current fields were accurately reconstructed over the entire model domain surrounded by coasts and open boundaries. The proposed method was effective, particularly around the peripheral regions of the tomography domain and the near-coast regions outside the domain, where accurate results are not expected from the conventional inverse method based on function expansion by Fourier function series with no coast fittings. The error velocity for the semidiurnal tidal currents was 2.2 cm s−1, which was calculated from the root-mean-square-difference between the CAT-observed and inverted range-averaged currents that were obtained along the nine peripheral transmission paths. The error velocity for the residual currents estimated from the 12-h mean net residual transport at the bay mouth was 0.9 cm s−1. The errors were significantly smaller than the amplitude of the tidal and residual currents.

Thickness-Weighted Averaging in Tidal Estuaries and the Vertical Distribution of the Eulerian Residual Transport

This paper presents thickness-weighted averaging (TWA) in generalized vertical coordinates as a unified framework for a variety of existing tidal-averaging concepts in seas and estuaries. Vertical profiles of resulting residual quantities depend on the specific vertical coordinate, which is held fixed during the averaging process. This dependence is demonstrated through the application to one-dimensional analytical tidal flow with sediment transport, to field observations from a tidal channel, and to model results from a two-dimensional estuary. The use of different coordinate systems provides complementary views on the residual dynamics and stresses the importance of a correct interpretation of residual quantities obtained by tidal averaging.

Components of Upper-Ocean Salt Transport by the Gyres and the Meridional Overturning Circulation

The salt transport by the wind-driven gyres and the meridional overturning circulation (MOC) is studied in an idealized-geometry primitive equation ocean model. Two narrow continents, running along meridians, divide the model domain into two basins of different widths connected by a re-entrant channel south of 52.5°S. One of the continents, representing the Americas, is longer than the other, representing Europe/Africa. Two different configurations of the model are used: the “standard” one, in which the short continent is west of the wide basin, and the “exchanged” one, in which the short continent is west of the narrow basin. In both cases, deep water is formed in the basin to the west of the short continent. Most residual transport of the MOC’s upper branch enters this basin by flowing along open streamlines that pass westward south of the short continent before proceeding northward. The meridional salt transport in the upper ocean of the sinking basin is decomposed into two portions: transport along open streamlines and transport by closed streamlines (gyres). In the Northern Hemisphere of the basin in which deep water is formed, the total northward salt transport per unit width along open streamlines is larger in the standard configuration than in the exchanged configuration. This larger salt transport is caused by two factors: a larger northward advection of salt by the interbasin transport and a larger cross-streamline salt transport out of the subpolar gyre. It is concluded that increasing interbasin flow south of Africa would likely bring more salt into the Atlantic Ocean.

Intratidal variability and transport of petroleum aromatic hydrocarbons in an anthropized tropical estuarine system: the Suape estuary (8.4S 35W)

The Suape Estuary encompasses the Suape Industrial Port Complex (SIPC), a major industrial development in Brazil's Northeast region, which, in order to be implanted, caused drastic environmental changes in this system. This study presents the first physical characterization of the Suape estuarine system, focusing on the local hydrodynamics, material transport and its influence on some specific properties. Physical properties were also associated to dissolved dispersed petroleum hydrocarbons (DDPHs). A study was undertaken during a complete semi-diurnal tidal cycle (13 hr), during which water level, water flow, current velocity and direction, water properties (salinity, temperature, suspended particulate matter - SPM -, chlorophyll and dissolved oxygen) were recorded using ADCP and CTD systems. The DDPHs were investigated in surface and bottom waters, by spectrofluorescence, using Carmópolis oil and chrysene as analytical standards. Results showed a well-mixed vertical structure, a semi-diurnal tide regime and a diurnal thermal pattern. There was no statistical difference between DDPH concentrations at surface and bottom, due to the tide acting as an important homogenizer. DDPHs were low and the main contribution seems to be that from SIPC, as the residual transport of DDPHs, chlorophyll and dissolved oxygen, was towards the Massangana estuary. An opposite pattern was observed for salinity and SPM, whose residual transport was towards the lagoon. The results pointed local hydrodynamics as an essential tool for understanding material transport and exchanges among the estuarine segments. A longer time series should be studied in order to obtain more robust conclusions.

Effects of mixing on resolved and unresolved scales on stratospheric age of air

Mean age of air (AoA) is a widely used metric to describe the transport along the Brewer-Dobson circulation. We seek to untangle the effects of different processes on the simulation of AoA, using the chemistry-climate model EMAC and the Lagrangian chemistry transport model CLaMS. Here, the effects of residual transport and two-way mixing on AoA are calculated. To do so, we calculate the residual circulation transit time (RCTT). The difference of AoA and RCTT is defined as aging by mixing. However, as diffusion is also included in this difference, we further use a method to directly calculate aging by mixing on resolved scales. Comparing these two methods of calculating aging by mixing allows for separating the effect of unresolved aging by mixing (which we term "aging by diffusion" in the following) in EMAC and CLaMS. We find that diffusion impacts AoA by making air older, but its contribution plays a minor role (order of 10 %) in all simulations. However, due to the different advection schemes of the two models, aging by diffusion has a larger effect on AoA and mixing efficiency in EMAC, compared to CLaMS. Regarding the trends in AoA, in CLaMS the AoA trend is negative throughout the stratosphere except in the northern hemisphere middle stratosphere, consistent with observations. This slight positive trend is neither reproduced in a free-running nor in a nudged simulation with EMAC – in both simulations the AoA trend is negative throughout the stratosphere. Trends in AoA are mainly driven by the contributions of RCTT and aging by mixing, whereas the contribution of aging by diffusion plays a minor role.

The circulation of the lower Capibaribe Estuary (Brazil) and its implications for the transport of scalars

The Capibaribe Estuary is a water body that crosses the Recife Metropolitan Area (RMA), one of the largest population centers in Brazil, and causes large pollutant loads and poor water quality. The fresh water inflow of wastewater from the RMA can account for three times the volume of the river discharge during the low discharge period. This article assesses the hydrodynamics and potential transport of particulate and dissolved scalars in this estuary. A field experiment was conducted to record the water level, current velocity, salinity, temperature and suspended particulate matter (SPM) contents during a full semi-diurnal tidal cycle. This experiment was performed during low river discharge and spring tide conditions. The estuary showed a partially mixed circulation pattern. The residual transport of water and salt were up estuary, while the SPM residual transport was down estuary. The former were understood as the effect of the residual circulation around the islands, while the latter was interpreted as a morphological factor inducing greater resuspension during the ebb, despite the symmetrical ebb and flood currents. This mechanism may transport SPM to the inner shelf, even under tide-dominated conditions when the opposite would be expected.

Residual circulation and freshwater transport in the Dutch Wadden Sea: a numerical modelling study

The Dutch Wadden Sea is a region of intertidal flats located between the chain of Wadden Islands and the Dutch mainland. We present numerical model results on the tidal prisms and residual flows through the tidal inlets and across one of the main watersheds. The model also provides insight into the pathways of fresh water originating from the two sluices at the Afsluitdijk (enclosure dike) through the use of passive tracers. All these results are obtained from three-dimensional numerical simulations carried out with the General Estuarine Transport Model (GETM), at a horizontal resolution of 200 m and with terrain-following vertical coordinates with 30 layers. We concentrate on the years 2009–2010, for which we impose meteorological forcing, freshwater discharge, and boundary conditions for tidal forcing and storm surges. Results from the model show an excellent agreement with various observational data sets for sea surface height, temperature, salinity and transport through the Texel Inlet. The simulations show that although tides are responsible for a characteristic pattern of residual transport through the inlets, the wind imposes a large variability on its magnitude and can even invert its direction during strong southwesterly winds. Even though these events are sporadic, they play an important role in the flushing of the Dutch Wadden Sea, as they strongly diminish the flushing time of fresh water. In addition, wind can force a residual transport across the Terschelling watershed of the same order, if not larger, than through any of the main tidal inlets, despite the fact that its tidal prism is much smaller than any of those of the inlets. For the pathways of fresh water, the Terschelling watershed turns out to be more important than was previously thought, while the opposite holds for the Vlie Inlet.