Impact of climate variability on an east Australian bay

The climate along the subtropical east coast of Australia is changing significantly. Rainfall has decreased by about 50 mm per decade and temperature increased by about 0.1 °C per decade during the last 50 years. These changes are likely to impact upon episodes of hypersalinity and the persistence of inverse circulations, which are often characteristic features of the coastal zone in the subtropics and are controlled by the balance between evaporation, precipitation, and freshwater discharge. In this study, observations and results from a general ocean circulation model are used to investigate how current climate trends have impacted upon the physical characteristics of the Hervey Bay, Australia. During the last two decades, mean precipitation in Hervey Bay deviates by 13% from the climatology (1941–2000). In the same time, the river discharge is reduced by 23%. In direct consequence, the frequency of hypersaline and inverse conditions has increased. Moreover, the salinity flux out of the bay has increased and the evaporation induced residual circulation has accelerated. Contrary to the drying trend, the occurrence of severe rainfalls, associated with floods, leads to short-term fluctuations in the salinity. These freshwater discharge events are used to estimate a typical response time for the bay.     

Dynamics of hypersaline coastal waters in the Great Barrier Reef

The coastal waters of the Great Barrier Reef (GBR) are hypersaline (salinity ∼37) during the dry season as a result of evaporation greatly exceeding rainfall, of shallow waters, and of the presence of numerous bays along the coast preventing rapid flushing. These hypersaline waters are not flushed out by salinity-driven baroclinic currents because these waters are vertically well-mixed. Instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters. As a result the hypersalinity distribution is 2-D with both cross-shelf and longshore gradients of salinity. The cross-shelf gradients are largely controlled by turbulent diffusion, while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the GBR. Because every bay supplies hypersaline waters, the width of the coastal hypersaline layer increases southwards. Steady state is reached in about 100 days, which is the typical duration of the dry season. The dynamics of the GBR hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems, e.g. in Saloum River Estuary, Laguna San Ignacio, Mission Bay, Tomales Bay, San Diego Bay, Hervey Bay, Shark Bay, Coorong Coast Lagoon, Spencer Gulf, Gulf of California and many others where the salinity gradient is mainly 1-D with a dominant along-channel salinity gradient.     

Effect of Salinity and Currents on Sea Level Variation Along the Indian Coast: A Numerical Study

The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized.     

Effect of Salinity and Currents on Sea Level Variation Along the Indian Coast: A Numerical Study

The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized.     

莱州湾东岸动力地貌对陆海相互作用的响应研究

基于SRTM3_DEM、RS数据分析,结合野外调查和前人研究结果,作者对莱州湾东岸临海冲积-海积小平原的地貌特征及地貌发育进行了研究。研究表明:研究区的海岸地貌结构存在横向上的沙坝-潟湖体系以及纵向上的连岛沙坝-潟湖系统;入海河流下游具有系统性的弯曲特征,其与横向上的沙坝-潟湖体系相对应,是自全新世中期以来海岸带陆海相互作用最显著的河流地貌标志;基于DEM的水文分析显示:研究区西部存在自南而北和自东向西的地势倾斜,王河流域与自东向西的王河下游古河道相对应,现今河道及古河道从DEM中以不同阈值提取的河网得到表达。     

Some hydrological features of Hawke Bay and nearby shelf waters

Temperature and salinity observations were made in Hawke Bay (east coast, North Island) and in the near shore coastal shelf water immediately to’ the south. Water in the bay was cooler and less saline than the shelf water on the open coast to the south. Hydrological analysis confirms that the main inflow is westward along the approximate centre line of the bay.     

长江口及其邻近海区环流和温、盐结构动力学研究Ⅱ.环流的基本特征

利用POM模型,以研究海区的海面风应力、温度和盐度资料作为海面边界条件,以与外海界面处的温度和盐度资料作为侧向液边界条件,并考虑长江径流、台湾暖流和东海沿岸流的影响,对长江口及其邻近海区各季节的三维斜压环流和温、盐结构进行了数值模拟。环流的数值结果表明,冬季和秋季研究海区的水平环流主要由长江径流、东海沿岸流、台湾暖流、杭州湾环流和沿岸流与台湾暖流之间的气旋和反气旋涡构成;东海沿岸流与长江径流顺岸南下,随着自北往南岸界地形坡度的增大,其流幅变窄,流速增强;台湾暖流沿陡坡及其外缘蜿蜒北上,随着自南往北水深的变浅,其流幅由宽变窄继而又由窄变宽,流速却一直由强变弱。冬季和秋季海区纬度断面垂直环流的总趋势由近岸向外海流动,海底地形变化缓慢区离岸流产生波动,海底地形变化显著的陡坡区离岸流产生剧烈振荡而生成强升降流。春季和夏季研究海区的水平环流主要由长江径流与东海沿岸流汇合流、台湾暖流、杭州湾环流、舟山群岛附近及长江径流和东海沿岸流汇合流与台湾暖流之间的气旋和反气旋涡构成;长江径流和台湾暖流平行北上并在长江口以北产生顺时针偏转。由海区水平环流特征和变化趋势证实,春季长江冲淡水已开始向东北偏转,夏季冲淡水的偏转程度、伸展距离和扩展范围都更甚于春季;春季在长江口近岸存在弱上升流,夏季长江口外的陡坡区出现下降流,而长江口以北和以南的陡坡区出现上升流。     

The hydrodynamics and salinity regime of a coastal lagoon – The Coorong,Australia – Seasonal to multi-decadal timescales

The Coorong is a choked coastal lagoon in South Australia that forms part of the terminal lake system at the end of the River Murray, Australia’s major river. It is an inverse estuary with a constricted channel connection to the sea at one end and extends parallel to the coast for more than 100 km away from this inlet. The present paper considers the physical dynamics of the Coorong, particularly its ecologically important salinity and water level regimes, and how these respond to connectedness with the ocean, barrage flows and meteorological conditions. The approach combines hydrodynamic modelling with measurements and considers temporal variation in the system ranging from seasonal to multi-decadal timescales.     

苏北沿岸水的去向与淡水来源估算

本文基于2006—2007年春、夏、秋、冬季CTD观测的盐度资料分析了苏北沿岸水盐度的季节变化特征,并利用冬、夏季盐度场变化估算了苏北沿岸水的淡水来源。结果表明:冬季苏北沿岸水在东北季风的驱动下顺岸南下,在离开苏北浅滩后转向东南进入东海;夏季低盐的苏北沿岸水分多支向北、向东流出沿岸区,后者汇入南黄海夏季冷水团环流中。估算结果表明苏北沿岸水的淡水来源主要是苏北沿岸的入海径流水,约占总量的65%,次之是降水/蒸发量通量和长江冲淡水沿江苏沿岸的北向扩展。     

Hypersalinity,flushing and transient salt-wedges in a tidal gulf—an inverse estuary

Because of high evaporation and low rainfall, gulfs and embayments in the arid coastal regions of Australia are endowed with highly saline water masses, with salinities ranging from oceanic values at their mouths to values as high as 60 at their heads. This presents the case of an ‘inverse estuary’. In Gulf St Vincent of South Australia, an example of such an inverse estuary, the salinity at the head ranges from ∼39 in winter to ∼42 in summer in sympathy with the seasonal changes of the local excess of evaporation over precipitation. The salient characteristics of temperature, salinity and density distributions in the Gulf are here described. Despite a seasonal reversal of spatial temperature gradients, the salinity gradient maintains the same sign and is strong enough to control a persistent density gradient from mouth to head. In parallel with the case of estuaries, a flushing time for salt is defined and estimated for the northern regions of the Gulf.Although the water mass was initially assumed to be vertically well-mixed because of tidally induced turbulence, the present observations reveal the striking feature that at neap tides the horizontal density-gradient forces a salt-wedge from the north, below the fresher water in the south.     

Trapping of fine sediment in a semi-enclosed bay, Palau, Micronesia

Airai Bay, Palau, is a small (3 km²), semi-enclosed, mangrove-fringed, meso-tidal, coral lagoon on the southeast coast of Palau. It drains a small catchment area (26 km²) of highly erodible soils in an area with high annual rainfall (3.7 m). River floods are short-lived and the sediment load is very large, with suspended fine sediment concentration exceeding 1500 mg l⁻¹. The resulting river plume is about 2 m thick. The brackish water residence time is about 7 days; during this period the plume remains a distinct surface feature even after river runoff has ceased. About 98% of the riverine fine sediment settles in Airai Bay, of which about 15–30% is deposited in the mangroves during river floods. This mud remains trapped in Airai Bay because the bay is protected from ocean swells and the tidal currents and locally generated wind waves are too small to resuspend the mud in quantity. The mud is smothering coral reefs, creating a phase shift from coral to fleshy algae dominance, and is even changing habitats by creating mud banks. The persistence of Airai Bay marine resources may not be possible without improved soil erosion control in the river catchment.     

用温盐资料研究夏季南海水通过琼州海峡进入北部湾的特征

夏季琼州海峡水交换向来存在两种观点:一种认为在西南风作用下,琼州海峡水交换从西向东;另一种观点则和上述相反。我们通过琼州海峡东部水域温盐分布和沿岸海洋站同步观测资料的对比发现,夏季北部湾的涠州岛盐度变化规律和琼州海峡东部、琼州海峡中部变化规律一致。由此证明,夏季南海水通过琼州海峡进入北部湾的事实。北海略受影响。而远离琼州海峡的龙门和白龙尾两站,则更多反映夏季陆地水文规律。由此证明,夏季南海水通过琼州海峡进入北部湾的事实。     

2002年夏季粤东外海的海洋状况

本文利用2002年7月22日至8月2日对粤东外海进行的水文观测资料，分析了调查海区的水温、盐度和跃层的分布状况，并对粤东沿岸的上升冷水、海洋锋等海洋现象进行了探讨．结果表明，整个粤东沿岸都存在着下层冷水的涌升现象，该现象在大亚湾外海附近和广东总来外海附近尤为明显，从而导致粤东沿岸水等温线非常密集，产生上升流锋．上升流锋随着深度的增加有向外海扩展的趋势．此外，在台湾浅潍的南部，陆架的坡析处和东沙群岛的东例以及西南部海战似乎也有下层冷水涌升的迹象．东沙群岛的北侧和西部海战有暖水中心存在，该暖水中心可能是离岸的表层水离异一定距离后发生下沉所致．珠江口的东例出现高温低盐水，其低盐水舌向东伸展，可达大亚湾口外海，等盐度线非常密集，是一个非常强的冲淡水羽状锋。     

辽东湾两侧砂质海岸侵蚀灾害与防治

自20世纪60年代至90年代，由于多种原因，辽东湾东西两侧的初始沙质海岸侵蚀范围逐年扩大，侵蚀不断加剧，给当人民的生产和生活带来严重危害。由多年监测资料发现，侵蚀严重的熊岳岸线以2～4m／a的速率而大幅度后退，特别严重的地区最大后退达10km；辽西绥中某些岸段平均每年后退1～2m。20世纪90年代后期，由于一些海域管理措施的出台和相应的海岸防护工程的建设，海岸侵蚀逐渐减弱。通过现场调查和多年监测，分析了辽东湾东西两侧砂质海岸侵蚀的特点，认为海岸组成物质松散与海岸动力作用强烈是本区现代海岸侵蚀的基本条件，人为活动是关键因素，并提出了海岸侵蚀灾害的防治对策。     

2004-2009年黄河口近岸海域低盐区面积的变化趋势研究

近年来黄河人海淡水量显著降低,而且年内分布极其不均匀,河口区的盐度场发生了重大变化.准确了解河口近岸海域的低盐区面积及其变化趋势,对于河口生态系统的研究极为重要.本文通过对2004-2009年丰、枯水期黄河口近岸海域低盐区面积大小的分析,建立了低盐区面积与黄河径流量的关系.结果表明,2004-2009年丰、枯水期低盐区面积与月径流量均呈现较好的线性关系,增加单位平方千米盐度小于27的低盐区面积需要增加的月径流量约为0.046亿m3;若要维持紧邻河口的3号方区海域的平均盐度小于27,月径流量应保持在50亿m3以上.此外,年内黄河口近岸海域低盐区面积的较大值主要集中在6～11月份,均高于370km2,而4、5月份的低盐区面积却不足200 km2,春季生态补水刻不容缓.     

Impact of Estuarine Outflow on Coastal Upwelling

A two-dimensional numerical model is developed facilitating the locationwise study of coastal upwelling. The coastal rigid boundary in the model is replaced with an open boundary to understand the dynamical response of the coastal ocean in the presence of an estuary. The model is applied to the east coast of India in a plane perpendicular to the coast of Kakinada where the Godavari river joins the Bay of Bengal. The model is driven, starting from a state of rest, by the combined effect of the wind stress forcing and the freshwater discharge from the estuary. Two numerical experiments were conducted to study the effect of the variation in the freshwater discharge on upwelling. It is found that the freshwater discharge from the Godavari estuary suppresses the upwelling off Kakinada.     

Impact of Estuarine Outflow on Coastal Upwelling

A two-dimensional numerical model is developed facilitating the locationwise study of coastal upwelling. The coastal rigid boundary in the model is replaced with an open boundary to understand the dynamical response of the coastal ocean in the presence of an estuary. The model is applied to the east coast of India in a plane perpendicular to the coast of Kakinada where the Godavari river joins the Bay of Bengal. The model is driven, starting from a state of rest, by the combined effect of the wind stress forcing and the freshwater discharge from the estuary. Two numerical experiments were conducted to study the effect of the variation in the freshwater discharge on upwelling. It is found that the freshwater discharge from the Godavari estuary suppresses the upwelling off Kakinada.     

胶州湾湿地动态变化的遥感分析及质量评价

通过对1988、1997、2002和2005年4个时相Landsat卫星遥感数据的解译,得到了各年份胶州湾湿地的变化情况,由此建立了海岸湿地质量定量评价体系。分析结果表明:随着环胶州湾沿岸城市化进程的加快,近20年来胶州湾湿地退化状况日渐严重。初期阶段,自然湿地不断被人工湿地占据,后期又出现湿地向非湿地类型的转化。针对胶州湾湿地的现状,从湿地保护与城市、社会、经济统一协调发展的角度出发,提出了缓和人与自然的矛盾、保护胶州湾湿地的建议。     

Dry Season Salinity Changes in Arid Estuaries Fringed by Mangroves and Saltflats

Mangrove swamps and hypersaline saltflats fringe many estuaries in dry tropical climates, especially in Northern Australia. For most of the year these estuaries receive zero riverine freshwater input and thus, after the wet season, a steady increase in salinity occurs. In some locations the estuary becomes fully inverse, i.e. the salinity increases monotonically from the mouth to the head. In other locations, a salinity maximum zone separates the sea from low salinity water that persists at the head of the estuary throughout the dry season. Field data from five estuaries indicate that in short estuaries where a large area of saltflats and mangroves extends over the whole length of the estuary, the estuary becomes completely inverse with salinity rising to 55 within a couple of months. The evaporation and evapotranspiration over the saltflats and mangroves cause this rapid increase in salinity. Longer estuaries where a large area of salt flat exists only close to the mouth do not become completely hypersaline for the whole length of the estuary by the end of the dry season. A salinity-maximum is generated close to the river mouth but salinities of less than 10 persist in the upper reaches of the estuary until the end of the dry season, even though the estuary does not receive any further freshwater input. A simple analytical expression is presented that reproduces the changes in salinities in the estuaries studied. This model can be used to predict the formation of hypersaline conditions in other mangrove and saltflat fringed estuaries where freshwater flow is negligible.     

Spatiotemporal variations of the δ18O–salinity relation in the northern Indian Ocean

A new data set of oxygen isotopic composition (δ¹⁸O) and salinity (S) of surface and sub-surface waters of the northern Indian Ocean, collected during the period 1987–2009, is presented. While the results are consistent with positive P?E (excess of precipitation over evaporation) over the Bay of Bengal and negative P?E over the eastern Arabian Sea, a significant spatiotemporal variability in the slope (also intercept) of the δ¹⁸O–S relation is observed in the Bay; the temporal variability is difficult to discern in the Arabian Sea. The slope and intercept are positively and negatively correlated, respectively, with the annual rainfall over India, a rough measure of river runoff. Both the slope and intercept appear to be sensitive to rainfall; the slope (intercept) is higher (lower) during years of stronger monsoon. The observed variability in the δ¹⁸O–S relation implies that caution needs to be exercised in paleosalinity estimations, especially from the Bay of Bengal, based on δ¹⁸O of marine organisms.