Components and Tidal Modulation of the Wave Field in a Semi-Enclosed Shallow Bay

The wave field in coastal bays is comprised of waves generated by far-off storms and waves generated locally by winds inside the bay and regionally outside the bay. The resultant wave field varies spatially and temporally and is expected to control morphologic features, such as beaches in estuaries and bays (BEBs). However, neither the wave field nor the role of waves in shaping BEBs have been well-studied, limiting the efficacy of coastal protection and restoration projects. Here we present observations of the wave field in Tomales Bay, a 20 km long, narrow, semi-enclosed embayment on the wave-dominated coast of Northern California (USA) with a tidal range of 2.5 m. We deployed pressure sensors in front of several beaches along the linear axis of the bay. Low-frequency waves (4 * 10^-2 * 2.5 * 10*^-1 Hz or 4 - 25 s period) dissipated within 4 km of the mouth, delineating the "outer bay" region, where remotely-generated swell and regionally-generated wind waves can dominate. The "inner bay" spectrum, further landward, is dominated by fetch-limited waves generated within the bay with frequency >= 2.5 < 10*-1 Hz. The energy of both ocean waves and locally-generated wind waves across all sites were modulated by the tide, owing to tidal changes in water depth and currents. Wave energies were typically low at low tide and high at high tide. Thus, in addition to fluctuations in winds and the presence of ocean waves, tides exert a strong control on the wave energy spectra at BEBs in mesotidal regions. In general, it is expected that events that can reshape beaches occur during high wind or swell events that occur at high-tide, when waves can reach the beaches with less attenuation. However, no such events were observed during our study and questions remain as to how rarely such wind-tide concurrences occur across the bay.

Numerical Simulation of Tidal Current in Majishan Sea Area of Zhoushan Based on SCHISM

Based on the SCHISM ocean model, this paper constructs a numerical model of the Majishan sea area in Shengsi County, Zhoushan City, and numerically simulates the tidal and tidal current conditions in the sea area. The non-structural triangular elements are used to construct the high-precision nearshore terrain to accurately simulate the tidal and tidal conditions. Yearly measured tidal current data. Have a deeper understanding of the tidal currents in the Majishan sea area of Zhoushan. The results show that the Majishan sea area of Zhoushan belongs to regular shallow sea currents dominated by recurrent currents. In the actual measurement, the speed of the rising and falling tides varies, and the maximum and average flow speeds are both the high tide is greater than the medium tide and the small tide. The tidal changes are mainly controlled by the forward waves of the East China Sea, and the direction of the current is basically the same as the direction of the rising and falling tides.

Advancing the Interpretation of Shallow Water Marine Soundscapes

Soundscapes offer rich descriptions of composite acoustic environments. Characterizing marine soundscapes simply through sound levels results in incomplete descriptions, limits the understanding of unique features, and impedes meaningful comparisons. Sources that contribute to sound level metrics shift in time and space with changes in biological patterns, physical forces, and human activity. The presence of a constant or chronic source is often interwoven with episodic sounds. Further, the presence and intensity of sources can influence other sources, calling for a more integrated approach to characterizing soundscapes. Here, we illustrate this complexity using data from a national-scale effort, the Sanctuary Soundscape Monitoring Project (SanctSound), an initiative designed to support collection of biological, environmental, and human use data to compliment the interpretation of sound level measurements. Using nine examples from this diverse dataset we demonstrate the benefit of integrating source identification and site features to interpret sound levels across a diversity of shallow water marine soundscapes (&lt;150 m). Sound levels from sites in high human use areas reflect the anthropogenic influences on the soundscape, especially when measuring broad frequency bands, whereas sites with relatively low human activity and high sound levels reveal biological features of the soundscape. At sites with large tidal changes, sound levels correlated with the magnitude of tidal flow, and sound levels during high tidal flow periods were similar to sound levels at sites near commercial shipping lanes. At sites in relatively close proximity (&lt;30 km), sound levels diverge because of the presence of different proximate sound contributors and propagation features of the site. A review of emerging methodologies for integrated soundscape analysis, including acoustic scenes, provides a framework for interpreting soundscapes across a variety of conditions. With a global growth in monitoring efforts collecting standardized measurements over widely distributed arrays, more integrated methods are needed to advance the utility of soundscapes in marine resource management.

Life Cycle of Edible Jellyfish Acromitus hardenbergi Stiasny, 1934 (Scyphozoa: Rhizostomeae) Inhabiting a Brackish-Water Environment

The edible jellyfish Acromitus hardenbergi Stiasny, 1934 is harvested throughout the year at the mouth of the Perak River, Malaysia. Although this species is an important fishery resource in the local area, limited biological studies have been carried out on it. The aim of the present study was to elucidate the life cycle of this unique brackish-water jellyfish in order to conserve the species and develop sustainable jellyfish fisheries. Mature medusae were collected at the mouth of the Perak River. Embryonic and larval development after fertilization was completed within 24 h until the planula stage and within 48 h until the polyp stage. Primary polyps had a long stalk with a small stolon at the base of the calyx. Fully developed polyps were bowl-or goblet-shaped but became an elongated stalk under starved conditions. Asexual reproduction was accomplished only by means of budding, and no podocysts were produced. Strobilation was mono-disc type. These characteristics may be adaptations to the dynamic environmental conditions in the estuary of the Perak River, where salinity fluctuates widely due to strong inflows of highly turbid freshwater coupled with tidal changes. This study suggests that polyps of A. hardenbergi expand their population not by podocysts, but by budding as quickly as possible and forming one large ephyra by mono-disc strobilation without the residuum, because the polyp cannot remain for a long time at its settlement place in the sediment-rich environment with drastic salinity change.

Trends in tidal range around the U.S. and potential implications for flooding occurrence

&lt;p&gt;Many locations in the U.S. have experienced large trends in their tidal range since the 19&lt;sup&gt;th&lt;/sup&gt; century, often in response to altered coastal and estuarine morphology. &amp;#160;Such tidal changes may enhance the vulnerability of an area towards flooding. In this contribution, &gt;1000 estimates of tidal range from around the contiguous United States are digitized from the published tide tables of 1899 and compared to the tide table of 2020. Our approach enables much greater spatial coverage than previous studies. Tidal range has more than doubled in many regions due to anthropogenic development, including Miami, the Saint Johns River, and the Connecticut River. Important changes are noted in other tidal rivers, including the Sacramento, Savannah, and James Rivers. On average, gauges located inland experienced the largest changes in tidal range, followed by estuary stations; coastal stations showed the least variability. Amplified tidal range increases the prevalence of minor (nuisance) flooding.&amp;#160; As shown by case studies of San Francisco, Wilmington (North Carolina) and Miami (Florida), the prevalence of minor (nuisance) flooding events has greatly increased due to tidal evolution. In locations without historical time-series, we infer the changed flooding using a statistical model that estimates changes to tidal constituents based on the observed change in tidal range and known constituent ratios. &amp;#160;Results show that tidal change may be a previously underappreciated factor in the increasing prevalence of nuisance flooding in cities like Miami and Jacksonville, Florida, where long time series of data back to the 19&lt;sup&gt;th&lt;/sup&gt; century are not available.&amp;#160; Understanding the reasons for tidal change may provide planners and engineers with new tools to adapt to climate change effects like sea-level rise.&lt;/p&gt;

Evolving tides aggravate nuisance flooding along the U.S. coastline

Nuisance flooding (NF) is defined as minor, nondestructive flooding that causes substantial, accumulating socioeconomic impacts to coastal communities. While sea-level rise is the main driver for the observed increase in NF events in the United States, we show here that secular changes in tides also contribute. An analysis of 40 tidal gauge records from U.S. coasts finds that, at 18 locations, NF increased due to tidal amplification, while decreases in tidal range suppressed NF at 11 locations. Estuaries show the largest changes in NF attributable to tide changes, and these can often be traced to anthropogenic alterations. Limited long-term measurements from estuaries suggest that the effects of evolving tides are more widespread than the locations considered here. The total number of NF days caused by tidal changes has increased at an exponential rate since 1950, adding ~27% to the total number of NF events observed in 2019 across locations with tidal amplification.

Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern U.K. and northern France

ABSTRACT The influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces. Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana Ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos Ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10°) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shoreface sandstones was modulated by tidal changes in water depth. The upper, upward-fining part of each sandstone tongue typically comprises an erosionally based bioclastic lag overlain by subtidal lower-shoreface deposits, and constitutes an upward-deepening succession developed during transgression. Regressive–transgressive sandstone tongues fringe the northeastern margin of the basin, which was exposed to an energetic wave climate driven by westerly and southwesterly winds with a fetch of 200–600 km. The high tidal range interpreted from the shoreface sandstone tongues is attributed to resonant amplification in a broad (150–200 km), shallow (18–33 m) embayment as the tidal wave propagated from the Tethys Ocean into the adjacent intracratonic Laurasian Seaway, of which the Weald Basin was a part.