Upper layer waters and their northward extension from Prydz Bay in summer

In this paper, CTD observational data obtained during the 15th Chinese National Antarctic Research Expedition (CHINARE-15) in the Southern Ocean are used to analyse and study water mass distribution in the Prydz Bay and its adjacent seas. The area, depth, and the thermohaline characteristics are identified for the Prydz Bay summer coastal surface water, the Prydz Bay winter water, the Prydz Bay shelf water, and the circumpolar deep water. Based on the above discussion, the northward extention of the Prydz Bay shelf water are found. Then the thermodynamic and the dynamic characteristics are further discussed, dealing with the inversion layer depth of the water temperature, the locations of the minima of the vertical temperature distribution and the temperature vertical gradient in the water column, the baraclinicity, and the effect of Coriolis deflection force.     

Development of a High-Resolution Coastal Circulation Model for the Ocean Observatory in Lunenburg Bay

An advanced ocean observatory has been established in Lunenburg Bay of Nova Scotia, Canada as part of an interdisciplinary research project of marine environmental prediction. The development of a high-resolution coastal circulation model is one of important components of the observatory. The model horizontal resolution is 60m and the vertical resolution is about 1 m. The coastal circulation model is used to simulate the semi-diurnal tidal circulation and associated nonlinear dynamics with the M2 forcing specified at the model open boundaries. The model is also used to simulate the storm-induced circulation in the bay during Hurricane Juan in September 2003, with the model forcing to be the combination of tides and remotely generated waves specified at the model open boundaries and wind stress applied at the sea surface. The model results demonstrate strong interactions between the local wind stress, tidal forcing, and remotely generated waves during this period. Comparison of model results with the surface elevation and current observations demonstrates that the coastal circulation model has reasonable skills in simulating the tidal and storm-induced circulation in the bay.     

Interannual Variability of Shelf and Slope Circulations in the Northern South China Sea

The northern South China Sea(NSCS) is a dynamically complex region whose shelf and slope currents are driven by different mechanisms. In this study, we used field measurements to identify clear interannual variations in the circulation related to the El Ni?o-Southern Oscillation cycle. To investigate the modulation mechanisms, we used a high-resolution numerical model that covers the shelf and slope regions of the NSCS. The results indicate that the stronger southwestward slope current during La Ni?a and stronger northeastward shelf current during El Ni?o in summer and winter are largely related to changes in wind forcing. The Kuroshio intrusion into the NSCS does not appear to significantly affect the circulation in the southwestern shelf region.     

The upper mixed layer during coastal upwelling events on the northern portugal shelf

The upper mixed layer (UML) depth obtained from temperature is very close to that from density:the maximum is about 15m. This indicates that temperature is a good indicator of mixed layer during measurements. When the surface heat flux is balanced by a cross-shore heat flux, the surface mixed layer depth obtained from the WM model (Weatherly and Martin, 1978),hPRT, is roughly the same as observed. The mixed layer depth calculated from the PWP model (Price, Weller and Pinkel, 1986) is close to the depth obtained from thermistor chain temperature data. The results show that both the WM model and PWP model can provide a good estimate of stratification in the study area during the cruise. The value of log( h/u3) is about 9.5 in the study area, which shows that the study area is strongly stratified in summer. Observations on the northern Portugal shelf reveal high variability in stability, giving rise to semi-diurnal, semi-monthly and diurnal oscillations, and long term variations. The fortnightly oscillatio     

Investigation of wave characteristics in a semi-enclosed bay based on SWAN model validated with buoys and ADP-observed currents

In this study, the simulating waves nearshore(SWAN) model with a locally refined curvilinear grid system was constructed to simulate waves in Jervis Bay and the neighbouring ocean of Australia, with the aim of examining the wave characteristics in an area with special topography and practical importance.This model was verified by field observations from buoys and acoustic Doppler profilers(ADPs). The model precisions were validated for both wind-generated waves and open-ocean swells. We present an approach with which to convert ADP-observed current data from near the bottom into the significant wave height. Our approach is deduced from the Fourier transform technique and the linear wave theory. The results illustrate that the location of the bay entrance is important because it allows the swells in the dominant direction to propagate into the bay despite the narrowness of the bay entrance. The wave period T p is also strongly related to the wave direction in the semi-enclosed bay. The T p is great enough along the entire propagating direction from the bay entrance to the top of the bay, and the largest T p appears along the north-west coast,which is the end tip of the swells' propagation.     

Seasonal response of surface wind to SST perturbation in the Northern Hemisphere

The seasonal response of surface wind speed to sea surface temperature(SST)change in the Northern Hemisphere was investigated using 10 years(2002-2011)high-resolution satellite observations and reanalysis data.The results showed that correlation between surface wind speed perturbations and SST perturbations exhibits remarkable seasonal variation,with more positive correlation is stronger in the cold seasons than in the warm seasons.This seasonality in a positive correlation between SST and surface wind speed is attributable primarily to seasonal changes of oceanic and atmospheric background conditions in frontal regions.The mean SST gradient and the prevailing surface winds are strong in winter and weak in summer.Additionally,the eddy-induced response of surface wind speed is stronger in winter than in summer,although the locations and numbers of mesoscale eddies do not show obvious seasonal features.The response of surface wind speed is apparently due to stability and mixing within the marine atmospheric boundary layer(MABL),modulated by SST perturbations.In the cold seasons,the stronger positive(negative)SST perturbations are easier to increase(decrease)the MABL height and trigger(suppress)momentum vertical mixing,contributing to the positive correlation between SST and surface wind speed.In comparison,SST perturbations are relatively weak in the warm seasons,resulting in a weak response of surface wind speed to SST changes.This result holds for each individual region with energetic eddy activity in the Northern Hemisphere.     

Long-term variability of the sharp thermocline in the Yellow and East China Seas

Based on observed temperature data since the 1950s, long-term variability of the summer sharp thermocline in the Yellow Sea Cold Water Mass (YSCWM) and East China Sea Cold Eddy (ECSCE) areas is examined. Relationships between the thermocline and atmospheric and oceanic forcing were investigated using multiyear wind, Kuroshio discharge and air temperature data. Results show that: 1) In the YSCWM area, thermocline strength shows about 4-year and 16-year period oscillations. There is high correlation between summer thermocline strength and local atmospheric temperature in summer and the previous winter; 2) In the ECSCE area, interannual oscillation of thermocline strength with about a 4-year period (stronger in El Ni o years) is strongly correlated with that of local wind stress. A transition from weak to strong thermocline during the mid 1970s is consistent with a 1976/1977 climate shift and Kuroshio volume transport; 3) Long-term changes of the thermocline in both regions are mainly determined by deep layer water, especially on the decadal timescale. However, surface water can modify the thermocline on an interannual timescale in the YSCWM area.     

A water movement study in Lianzhou Bay,Guangxi Province,China

This study investigates the physical conditions (water depth, current speed, salinity, temperature) in Lianzhou Bay, a shallow coastal bay in southern China, during two expeditions in the dry and wet seasons of 2011. Based on these expedition data, basic hydrodynamic parameters like Brunt-Väisälä Frequency, Richardson Number, Rossby radius, and Resonance Period are calculated. The results show that Lianzhou Bay is characterized by comparatively small quantity of freshwater input and weak stratification. Strong tides, which are spatially uniform within the bay, cause turbulent mixing. Residence time of the water is shorter in winter due to a stronger coastal current in that season. Consideration of the water movement may help to reduce the harmful ecological impact of aquaculture waste water discharge.     

Supercooled water in austral summer in Prydz Bay, Antarctica

Supercooled water with temperatures below freezing point,was identified from hydrographic data obtained by Chinese and Australian expeditions to Prydz Bay,Antarctica,during the austral summer.The study shows that most supercooled waters occurred at depths of 63-271 m in the region north of the Amery Ice Shelf(AIS) front.The maximum supercooling was 0.16°C below the in-situ freezing point.In temperature and salinity ranges of-2.14--1.96°C and 34.39-34.46,respectively,the water was colder and fresher than peripheral shelf water.The supercooled water had less variability in the vertical profiles compared to shelf water.Based on analysis of their thermohaline features and spatial distribution,as well as the circulation pattern in Prydz Bay,we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside of the AIS front.Water emerging from the ice shelf cools to an extremely low temperature(about-2.0°C) by additional cooling from the ice shelf,and becomes buoyant with the addition of melt water from the ice shelf base.When this water flows out of the ice shelf front,its upper boundary is removed,and thus it rises abruptly.Once the temperature of this water reaches below the freezing point,supercooling takes place.In summer,the seasonal pycnocline at-100 m water depth acts as a barrier to upwelling and supercooling.The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar ocean.     

Response of upper ocean currents to typhoons at two ADCP moorings west of the Luzon Strait

We deployed two ADCP mooring systems west of the Luzon Strait in August 2008, and measured the upper ocean currents at high frequency. Two typhoons passed over the moorings during approximately one-month observation period. Using ADCP observations, satellite wind and heat flux measurements, and high-resolution model assimilation products, we studied the response of the upper ocean to typhoons. The first typhoon, Nuri, passed over one of the moorings, resulting in strong Ekman divergence and significant surface cooling. The cooling of surface water lagged the typhoon wind forcing about one day and lasted about five days. The second typhoon, Sinlaku, moved northward east of the Luzon Strait, and did not directly impact currents near the observation regions. Sinlaku increased anomalous surface water transport exchange across the Luzon Strait, which modulated the surface layer current of the Kuroshio.     

Spatial-temporal variation of phytoplankton community structure in Jiaozhou Bay,China

To better understand the spatial-temporal variation in phytoplankton community structure and its controlling factors in Jiaozhou Bay,Qingdao,North China,four seasonal sampling were carried out in 2017.The phytoplankton community structure and various environmental parameters were examined.The phytoplankton community in the bay was composed of mainly diatoms and dinoflagellates,and several other species of Chrysophyta were also observed.Diatoms were the most dominant phytoplankton group throughout the year,except in spring and winter,when Noctiluca scintillans was co-dominant.High Si/N ratios in summer and fall reflect the high dominance of diatoms in the two seasons.Temporally,the phytoplankton cell abundance peaked in summer,due mainly to the high temperatures and nutrient concentrations in summer.Spatially,the phytoplankton cell abundance was higher in the northern part of the bay than in the other parts of the bay in four seasons.The diatom cell abundances show significant positive correlations with the nutrient concentrations,while the dinoflagellate cell abundances show no correlation or a negative correlation with the nutrient concentrations but a significant positive correlation with the stratification index.This discrepancy was mainly due to the different survival strategies between diatoms and dinoflagellates.The Shannon-Wiener diversity index(H')values in the bay ranged from 0.08 to 4.18,which fell in the range reported in historical studies.The distribution pattern of H' values was quite different from that of chlorophyll a,indicating that the phytoplankton community structure might have high biomass with a low diversity index.Compared with historical studies,we believe that the dominant phytoplankton species have been changed in recent years due mainly to the changing environment in the Jiaozhou Bay in recent 30 years.     

Numerical simulation of nutrient and phytoplankton dynamics in Guangxi coastal bays,China

The increasing riverine pollutants have resulted in nutrient enrichment and deterioration of water quality in the coastal water of Guangxi Province, China. However, the quantitative relationship between nutrient loads and water quality responses, which is crucial for developing eutrophication control strategies, is not well studied. In this study, the riverine fluxes of nutrients were quantified and integrated with nutrient cycling and phytoplankton dynamics by using box models for Guangxi coastal bays. The model concepts and biogeochemical equations were the same; while most model parameters were specific for each bay. The parameters were calibrated with seasonal observations during 2006–2007, and validated with yearly averaged measurements in 2009. The general features of nutrient and phytoplankton dynamics were reproduced, and the models were proved feasible under a wide range of bay conditions. Dissolved inorganic nitrogen was depleted during the spring algal bloom in Zhenzhu Bay and Fangcheng Bay with relatively less nutrient inputs. Phosphorus concentration was high in spring, which decreased then due to continuous phytoplankton consumption. Chlorophyll-a concentration reached its annual maximum in summer, but was the minimum in winter. Eutrophication was characterized by both an increase in nutrient concentrations and phytoplankton biomass in Lianzhou Bay. Either about 80% reduction of nitrogen or 70% reduction of phosphorus was required to control the algal bloom in Lianzhou Bay. Defects of the models were discussed and suggestions to the environmental protection of Guangxi coastal bays were proposed.     

NUMERICAL STUDY ON THE TIDAL FRONT IN THE WESTERN YELLOW SEA

The formation and evolution of the tidal front in the western Yellow Sea are studied by means of a two-dimensional model in which wind and tide mixing, sun radiation and wind stress, and realistic topography are incorporated. In this numerical study, the schemes employed are stable for time step t= 900 s, so the model can be run for 4 months to simulate the front evolution. The authors examined the effects of mixing and atmospheric forcing on the tidal front under conditions of : mixing and solar heating without wind stress on the sea surface; mixing, solar heating and 50 hours of wind stress; mixing, solar heating and long time periodical wind stress, Results show that (1) the tidal front forms at the beginning of May, and strengthens with the increasing of heat input, (2) the temperature structure in the shallow well-mixed water is dominated by mixing, while in the front and deeper stratified regions, it is controlled by the joint effects of (mainly) mixing and advection, 0) the currents and front all     

Coupled physical-ecological modelling of the central part of Jiaozhou Bay I. Physical modelling

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Pb distribution and translocation in Jiaozhou Bay

The trends of distribution, translocation and seasonal change of heavy metal Pb were studied based on the surface and bottom water sampling in Jiaozhou Bay in 1979, and compared with those in 1990＇s. The results showed that the source of Pb in the bay was from wastewater and sewage in the east of Jiaozhou Bay from ocean vessels. Pb concentration was higher in spring and lower in summer and autumn, and remained stable through sedimentation in the bottom layer. The overall water quality was good in 1970＇s. Compared with the environmental monitoring data of 1995-1999, Pb pollution had become serious. Therefore, more efforts should be made to protect the bay from Pb pollution.     

Simulating the Upper Ocean Circulation on the Belize Shelf： An Application of a Triply Nested-Grid Ocean Circulation Model

We present a three-level nested-grid ocean circulation modeling system for the Belize shelf of the western Caribbean Sea. The nested-grid system has three subcomponents： a coarse-resolution outer model of the western Caribbean Sea; an intermediate-resolution middle model of the southern Mest〉American Barrier Reef System; and a fine-resolution inner model of the Belize shelf. The two-way nesting technique based on the semi-prognostic method is used to exchange information between the three subcomponents. We discuss two applications of the nested-grid system in this study. In the first application we simulate the seasonal mean circulation in the region, with the nested system forced by monthly mean surface fluxes and boundary forcing. The model results reproduce the general circulation features on the western Caribbean Sea and mest〉scale circulation features on the Belize shelf. In the second application, we simulate the storm-induced circulation during Hurricane Mitch in 1998, with the nested-grid system forced by the combination of monthly mean forcing and idealized wind stress associated with the storm. The model results demonstrate that the storm-induced currents transport a large amount of estuarine waters from coastal regions of Honduras and Guatemala to offshore reef atolls.     

Seasonal variation of the barrier layer in the PN section

In this paper, we use the conductivity-temperature-depth (CTD) observation data and a three-dimensional ocean model in a seasonally-varying forcing field to study the barrier layer (BL) in the PN section in the East China Sea (ECS). The BL can be found along the PN section with obviously seasonal variability. In winter, spring and autumn, the BL occurs around the slope where the cold shelf water meets with the warm Kuroshio water. In summer, the BL can also be found in the shelf area near salinity front of the Changjiang (Yangtze) River Dilution Water (YRDW). Seasonal variations of BL in the PN section are caused by local hydrological characteristics and seasonal variations of atmospheric forcing. Strong vertical convection caused by sea surface cooling thickens the BL in winter and spring in the slope area. Due to the large discharge of Changjiang River in summer, the BL occurs extensively in the shelf region where the fresh YRDW and the salty bottom water meet and form a strong halocline above the seasonal thermocline. The formation mechanism of BL in the PN section can be explained by the vertical shear of different water masses, which is called the advection mechanism. The interannual variation of BL in summer is greatly affected by the YRDW. In the larger YRDW year (such as 1998), a shallow but much thicker BL existed on the shelf area. Supported by National Basic Research Program of China (973 Program, No. 2005CB422303 and 2007CB411804), the Key Project of the International Science and Technology Cooperation Program of China (No. 2006DFB21250), the “111 Project” of the Ministry of Education (No. B07036), the Program for New Century Excellent Talents in University, China (No. NECT-07-0781)     

Formation of well-mixed warm water column in central Bohai Sea during summer: Role of high-frequency atmospheric forcing

The influence of high-frequency atmospheric forcing on the formation of a well-mixed summer warm water column in the central Bohai Sea is investigated comparing model simulations driven by daily surface forcing and those using monthly forcing data. In the absence of high-frequency atmospheric forcing, numerical simulations have repeatedly failed to reproduce this vertically uniform column of warm water measured over the past 35 years. However, high-frequency surface forcing is found to strongly influence the structure and distribution of the well-mixed warm water column, and simulations are in good agreement with observations. Results show that high frequency forcing enhances vertical mixing over the central bank, intensifies downward heat transport, and homogenizes the water column to form the Bohai central warm column. Evidence presented shows that high frequency forcing plays a dominant role in the formation of the well-mixed warm water column in summer, even without the effects of tidal and surface wave mixing. The present study thus provides a practical and rational way of further improving the performance of oceanic simulations in the Bohai Sea and can be used to adjust parameterization schemes of ocean models.     

Climatology and seasonal variability of satellite-derived chlorophyll a around the Shandong Peninsula

The chlorophyll a(Chl a) is an important indicator of marine ecosystems. The spatiotemporal variation of the Chl a greatly aff ects the mariculture and marine ranching in coastal waters of the Shandong Peninsula. In the current study, the climatology and seasonal variability of surface Chl-a concentration around the Shandong Peninsula are investigated based on 16 years(December 2002–November 2018) of satellite observations. The results indicate that the annual mean Chl-a concentration is greater in the Bohai Sea than in the Yellow Sea and decreases from coastal waters to off shore waters. The highest Chl-a concentrations are found in Laizhou Bay(4.2–8.0 mg/m 3), Haizhou Bay(4.2–5.9 mg/m 3) and the northeast coast of the Shandong Peninsula(4.4–5.0 mg/m 3), resulting from the combined eff ects of the intense riverine input and long residence time caused by the concave shape of the coastline. The seasonal Chl-a concentration shows a signifi cant spatial variation. The Chl-a concentrations in these three subregions generally exhibit an annual maximum in August/September, due to the combined eff ects of sea surface temperature, river discharge and sea surface wind. In the southeast coast region, however, the Chl-a concentration is lowest throughout the year and reaches a maximum in February with a minimum in July, forced by the seasonal evolution of the Yellow Sea Cold Water and monsoon winds. The interannual Chl-a concentration trends vary among regions and seasons. There are signifi cant increasing trends over a large area around Haizhou Bay from winter to summer, which are mainly caused by the rising sea surface temperature and eutrophication. In other coastal areas, the Chl-a concentration shows decreasing trends, which are clearest in summer and induced by the weakening land rainfall. This study highlights the diff erences in the Chl-a dynamics among regions around the Shandong Peninsula and is helpful for further studies of coupled physical-ecological-human interactions at multiple scales.