Offshore Water Mass Research Articles

Observed Seasonal Evolution of the Antarctic Slope Current System off the Coast of Dronning Maud Land, East Antarctica

AbstractThe access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019–2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite‐derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (a) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (b) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub‐ice‐shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice‐shelf‐ocean interactions in East Antarctica.

Winter storms drive offshore transport and modulate phytoplankton blooms in Northern Taiwan, China

The East China Shelf Sea (ECSS) is subject to high-frequency storms during winter and spring, with these storm processes serving as a significant driving factor for initiating the outward diffusion of materials from the inner shelf. Inner shelf waters tend to be rich in nutrients, thus their horizontal diffusion is crucial to the marine primary productivity of the outer shelf. However, our understanding of the processes that govern the offshore water mass transport under winter storm oscillations and the mechanisms driving their impact on phytoplankton is currently limited. In this study, we used satellite and reanalysis data from 2003 to 2020 to investigate the modulation mechanism of winter offshore currents (WOC) on phytoplankton bloom (PB) stimulated by storms in Northern Taiwan (NTW). The results revealed that at synoptic scales, winter storms result in higher sea surface height (SSH) and potential energy on the inner side of the front. However, during periods of weakened storms (for example, during north wind relaxation or a shift to southerly winds), a strong WOC is produced in the top 30–50 m of the ocean due to continuous SSH adjustments caused by changed pressure gradients and induced by topography. PB occurs in the offshore waters of the front, driven by a continuous nutrient supply and an increase in photosynthetically available radiation (PAR). On an interannual scale, offshore transport is controlled by the storm's duration and the extent of its weakening. As the climate warms and winter winds in NTW have consistently weakened over the past 20 years, lower turbulent kinetic energy (TKE) and a shallower mixed layer depth (MLD) will promote phytoplankton growth. The results suggest that water level fluctuations caused by high-frequency changes in winter storms are strongly linked to the offshore sediment transport from near-shore waters, impacting the material transport and the health of the ecosystem on the continental shelf.

Deep current structure in the Toyama Deep-Sea Channel in the Japan Sea

The flow field in the Toyama Deep-Sea Channel (TDSC) in the Japan Sea was investigated based on mooring observations. An asymmetric current system accompanying offshore and onshore currents over the east- and west-side slopes in the channel, respectively, is suggested. A bottom intensified flow characteristic was observed at the offshore stations in the Yamato Basin. The asymmetric current system in the channel is also suggested by the asymmetric distribution of water characteristics across the TDSC in Toyama Bay; a cold dense water mass with higher dissolved oxygen (DO) and higher transmittance (Tr) was found over the west-side slope of the channel, whereas a water mass with lower DO and lower Tr was distributed over the east-side slope, suggesting a turbidity current from the head of Toyama Bay. The currents facing the shallower depth on their right-hand-side, along with the density distribution in the TDSC, suggest a density current system under the influence of the earth’s rotation. The dissolved oxygen concentration in the TDSC was significantly lower than that in the offshore region of the same temperature range. This suggests that the water mass over the west-side slope in the TDSC is a modified offshore water mass which experienced significant mixing with the low DO water mass over the east-side slope in the TDSC, probably due to strong shear between the offshore and onshore currents in the narrow channel.

Environmental drivers of a decline in a coastal zooplankton community

Abstract Major changes in North Atlantic zooplankton communities in recent decades have been linked to climate change but the roles of environmental drivers are often complex. High temporal resolution data is required to disentangle the natural seasonal drivers from additional sources of variability in highly heterogeneous marine systems. Here, physical and plankton abundance data spanning 2003–2017 from a weekly long-term monitoring site on the west coast of Scotland were used to investigate the cause of an increasing decline to approximately -80± 5% in annual average total zooplankton abundance from 2011 to 2017. Generalized additive mixed models (GAMMs), with an autoregressive correlation structure, were used to examine seasonal and inter-annual trends in zooplankton abundance and their relationship with environmental variables. Substantial declines were detected across all dominant taxa, with ∼ 30–70% of the declines in abundance explained by a concurrent negative trend in salinity, alongside the seasonal cycle, with the additional significance of food availability found for some taxa. Temperature was found to drive seasonal variation but not the long-term trends in the zooplankton community. The reduction in salinity had the largest effect on several important taxa. Salinity changes could partly be explained by locally higher freshwater run-off driven by precipitation as well as potential links to changes in offshore water masses. The results highlight that changes in salinity, caused by either freshwater input (expected from climate predictions) or fresher offshore water masses, may adversely impact coastal zooplankton communities and the predators that depend on them.

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.

Community structure of zooplankton in adjacent area of Changjiang Estuary, China in summer 2016.

Based on the data of zooplankton samples from 27 stations in the offshore area of Changjiang Estuary in August 2016, we analyzed the community structure and diversity of zooplankton and examined the relationship between zooplankton community structure and environmental factors. A total of 108 species of zooplankton belonging to 12 groups in six phyla, together with 15 types of pelagic larvae and fish eggs were identified. The main groups were copepods, thaliacea, chaetognaths, cladocladus and medusae, with the average abundance being 273.9, 115.0, 67.1, 63.6 and 61.1 ind·m-3. The most dominant group of zooplankton was copepods (48 species), accounting for 44.4% of the total zooplankton abundance. Medusae ranked second with a total of 12 species, accounting for 11.1% of the total zooplankton abundance. Furthermore, the absolute dominant group was copepods, with the highest contribution to the zooplankton community (20.3%). According to the clustering results of environmental factors, the area could be divided into Changjiang diluted water and offshore water mass. The results of analysis of similarities showed that the difference of zooplankton community between the two regions was significant (the average diffe-rence was 4%), and the contribution to the difference was 20.3%, 18.0%, 14.1%, 13.4%, and 11.8% for copepod, thaliacea, cladocera, chaetognaths, and medusae, respectively.

长江口及邻近海域浮游动物群落结构及季节变化

PDF HTML阅读 XML下载 导出引用 引用提醒 长江口及邻近海域浮游动物群落结构及季节变化 DOI: 10.5846/stxb201507271574 作者: 作者单位: 国家海洋局第二海洋研究所,国家海洋局第二海洋研究所,国家海洋局第二海洋研究所,国家海洋局第二海洋研究所,国家海洋局第二海洋研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国际海域资源调查与开发“十二五”课题（DY125-11-E-03，DY125-14-E-01）；中国海洋公益性项目（201005015）；中国近海海洋综合调查与评价-水体环境调查与研究（908-ST04-I，908-ST04-II） Seasonal variation in zooplankton community structure in the Changjiang Estuary and its adjacent waters Author: Affiliation: Second Institute of Oceanography,State Oceanic Administration,Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China,Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China,Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China,Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根据2006-2007年长江口及其邻近海域（29°30'N-32°30'N，120°00'E-127°30'E）150个站位4个季节的调查资料，对长江口海域浮游动物群落结构、种类组成、优势种及其季节变化进行研究。结果表明，长江口及其邻近海域浮游动物群落物种多样性丰富，四季共鉴定浮游动物460种，隶属7个门，246属，此外，另有54类浮游幼体。其中，桡足类是最优势类群，有193种，占41.96%；端足类为第二优势类群，有51种，占11.09%；水螅水母为第三优势类群，有34种，占7.39%。长江口及其邻近海域浮游动物的物种多样性呈现明显季节变化，其特征为：夏季（317种） > 秋季（309种） > 春季（230种） > 冬季（138种）。中华哲水蚤和百陶带箭虫为长江口及其邻近海域的四季优势种。长江口及其邻近海域浮游动物大体可划分为5种生态类群：近岸低盐类群、广温广盐类群、低温高盐类群、高温广盐类群和高温高盐类群。结合同步调查的水文和水化学数据，进行浮游动物群落丰度与环境因子的相关分析表明：盐度是影响长江口及其邻近海域的浮游动物群落丰度的主要环境因子。 Abstract:Seasonal variation of zooplankton community structure, species composition, and dominant species were determined based on samples collected from 150 stations during four research cruises in the Changjiang Estuary and its adjacent waters (29°30'N-32°30'N,120°00'E-127°30'E). The study was conducted from July to August 2006 (Summer), December 2006 to February 2007 (Winter), April to May 2007 (Spring), and October to December 2007 (Autumn). The mesoscale study areas were positioned from the Changjiang Estuary to the transition area where freshwater from the Changjiang plume and offshore water masses, such as the Kuroshio and its branches, mix with each other. In total, 460 species of zooplankton belonging to 246 genera and 18 groups from seven phyla, together with 54 types of pelagic larvae, were identified in the Changjiang Estuary and its adjacent waters during four seasons. The 18 groups of zooplankton included Hydromedusae, Siphonophora, Scyphomedusae, Ctenophora, Polychaeta, Cladocera, Copepoda, Ostracoda, Isopoda, Mysida, Cumacea, Amphipoda, Euphausiacea, Decapoda, Chaetognatha, Appendicularia, Thaliacea, and pelagic Mollusca. The most dominant group of zooplankton was Copepoda, including 193 species and accounting for 41.96% of the total species. Amphipoda ranked second, with 51 species accounting for 11.09% of the total species. Hydromedusa was the third dominant group of zooplankton with 34 species and accounted for 7.39% of the total species. There was considerable seasonal and spatial variation in the community structure of zooplankton in the Changjiang Estuary and its adjacent waters. More zooplankton species were found in summer (317 species and 43 types of pelagic larvae) and autumn (309 species and 28 types of pelagic larvae) than in spring (230 species and 27 types of pelagic larvae) and winter (138 species and 21 types of pelagic larvae). The number of species increased gradually from the inshore to offshore waters and from north to south, during all seasons. There were seasonal changes in dominant species in the Changjiang Estuary and its adjacent waters:in spring and winter, Calanus sinicus was the most dominant species, but in summer and autumn, the most dominant species was replaced by Centropages dorsispinatus and Subeucalanus subcrassus, respectively. Only Calanus sinicus and Zonosagitta bedoti were dominant in all four seasons. Based on species composition and ecological distribution, the zooplankton community in the Changjiang Estuary and its adjacent waters could be divided into five ecological groups, including the coastal brackish water, eurythermal euryhaline, hypothermal hypersaline, hyperthermal euryhaline, and hyperthermal hypersaline group. The dominant species were distributed primarily in the coastal brackish water group and eurythermal euryhaline group. Furthermore, we measured environmental factors and determined the responses of the zooplankton community to the factors, including temperature, salinity, concentration of suspended matter, and concentration of chlorophyll a. Results of Pearson's correlation analysis revealed that the most important environmental factor influencing changes in zooplankton community structure in the Changjiang Estuary and its adjacent waters was salinity. Furthermore, the Changjiang diluted water introduced a large number of nutrients, which was beneficial to the growth of plankton, but the estuarine turbidity limited the distribution of zooplankton. 参考文献 相似文献 引证文献

长江口南支、北支、北港及口外水域浮游动物群聚相似性

PDF HTML阅读 XML下载 导出引用 引用提醒 长江口南支、北支、北港及口外水域浮游动物群聚相似性 DOI: 10.5846/stxb201503190530 作者: 作者单位: 中国水产科学院东海水产研究所农业部海洋与河口渔业重点开放实验室;上海海洋大学海洋学院,中国水产科学院东海水产研究所,中国水产科学院东海水产研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41176131）；海洋公益性行业科研专项经费项目（201305027） Similarity analysis of zooplankton assemblages among different zones in the Yangtze River estuary Author: Affiliation: Ministry of Agriculture Key and Open Laboratory of Marine and Estuary Fisheries;College of Marine Sciences,Shanghai Ocean University,Ministry of Agriculture Key and Open Laboratory of Marine and Estuary Fisheries,Ministry of Agriculture Key and Open Laboratory of Marine and Estuary Fisheries Fund Project: The foundation was financially supported by the project of National Natural Science foundation(41176131) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:依据2009-2010年春、秋季在长江口南支、北支、北港以及口外水域的海洋综合调查资料，基于聚类、排序等多元分析方法，对长江口不同水域的浮游动物群聚进行相似性分析。春季，长江口水域的浮游动物群聚在40%相似性程度上可以明显分为口外和口内两组，分别记为Ⅰ、Ⅱ组。位于口外水域的I组受外海水团和长江径流的影响，浮游动物以近海种、沿岸种和河口种为主，如中华哲水蚤（Calanus sinicus，35.30ind/m3）、真刺唇角水蚤（Labidocera euchaeta，34.59 ind/m3）、虫肢歪水蚤（Tortanus vermiculus，42.46 ind/m3）。位于长江口内的Ⅱ组可以进一步分为Ⅱ-1、Ⅱ-2和Ⅱ-3三个组。受长江径流的影响，口内水域的的浮游动物群聚以河口种为主，主要优势种为中华华哲水蚤（Sinocalanus sinensis）。秋季，长江口水域可明显分为Ⅲ、Ⅳ、Ⅴ、Ⅵ 4个组，由于外海势力和长江径流都增大，导致不同水域的水环境差异更大，浮游动物群聚的差异也相对增大。其中，Ⅲ组（北港水域）以河口种为主，主要种类为虫肢歪水蚤，丰度为3.08个/m3；Ⅳ组（北支水域）因受长江径流影响较小，盐度较高，以沿岸种为主，主要种类为针刺拟哲水蚤（Euconchoecia aculeata），丰度为4.97个/m3；Ⅴ组（口外水域）受外海水团和台湾暖流的影响，以外海种和近海种为主，外海种主要有亚强次真哲水蚤（Subeucalanus subcrassus）等，近海种主要有中华哲水蚤等；受长江径流的强烈影响，Ⅵ组（南支水域）以淡水种为主，主要种类为汤匙华哲水蚤（Sinocalanus dorrii），其优势度高达0.93，是该水域的关键种。可以看出，盐度和水团是导致长江口浮游动物群聚在不同水域产生差异的主要因素。 Abstract:Similarity analyses were performed on zooplankton communities in the South Branch (SB), North Branch (NB), North Channel (NC), and offshore area (OS) of the Yangtze River estuary based on the survey conducted during spring and autumn from 2009 to 2010. According to the results of the hierarchical cluster analysis and non-metric multidimensional scaling. The zooplankton species occurring in this estuary in spring can be divided into two communities:I and Ⅱ.. Community I in OS is significantly different from community Ⅱ. Community I was dominated by offshore zooplankton species, e.g., Calanus sinicus (density of 35.30 ind/m3), which may be due to the effect of water masses. Few estuarine and coastal species were also observed during this period. As a result of the Yangtze River runoff, community Ⅱ was dominated by estuarine species; this community can be further divided into community Ⅱ-1 (NC), Ⅱ-2 (NB), and Ⅱ-3 (SB). Sinocalanus sinensis was the most dominant species across these subcommunities, present at varying densities. The differences in estuarine communities were mainly caused by the adaption of S. sinensis to freshwater environment. In autumn, the communities of the Yangtze River could be distinctly divided into four clusters:Ⅲ, Ⅳ, Ⅴ, and Ⅵ. Owing to the stronger runoff and the offshore water mass, there were considerable differences from the dominant species which led to form the different communities. Estuarine species prevailed in community Ⅲ (NC), with Tortanus vermiculus observed as the dominant species (3.08 ind/m3). Due to the small impact of the Yangtze River Runoff and with a high salinity in the waters of NB, community Ⅳ was mainly composed of coastal species. Furthermore, owing to the effects of offshoe currents and water mass, community Ⅴ (OS) was dominated by offshore species such as Calanus sinicus and marine species such as Subeucalanus subcrassus and Sagitta enflata. As a result of the stronger runoff of the Changjiang River, freshwater species dominate community Ⅵ (SB). Sinocalanus dorrii was the key species of community Ⅵ, with a high dominance(0.93). Thus, salinity and water masses were considered key factors to cause differences in zooplankton communities in the Yangtze River Estuary, and the differences between the offshore area and the estuarine areas were larger than those in the estuarine areas. 参考文献 相似文献 引证文献

A Modeling Study on Hypoxia Formation in the Bottom Water of the Youngsan River Estuary, Korea

Cho, C.-W.; Song, Y.-S.; Kim, C.-K.; Kim, T.-I.; Han, J.-S.; Woo, S.-B.; An, S., and Choi, T., 2015. A modeling study on hypoxia formation in the bottom water of the Youngsan River estuary, Korea.Hypoxia negatively affects marine environment and organisms and is an important indicator of estuarine water quality. We conducted a field survey and a three-dimensional particle transport modeling study to investigate summer hypoxia formation in the bottom water of the Youngsan River estuary (YRE). The field survey showed that dissolved oxygen (DO) decreased upstream and toward the bottom. The lowest DO, at 4.4 mg L−1, occurred in the bottom water in front of the estuary dam. We found persistent two-layer estuarine circulation driven by freshwater discharge, which is the main mechanism for delivering offshore water mass upstream. Applying the total oxygen consumption rate (0.50 mg L−1 d−1) observed in the estuary, the offshore water mass entering the estuary loses as much as 4.4 mg L−1 of oxygen during the average travel time (8.8 days) from the mouth of the estuary to the dam. These findings indicate that bottom hypoxia can be formed in front of the estuary dam in summer if offshore water mass with relatively low DO (<8.4 mg L−1) enters the estuary. For the sound management of water quality in the YRE, therefore, we recommend improving the quality of the offshore water entering the YRE and also decreasing oxygen demand by reducing nutrient loading from the YRE dam.

Nutrients and water masses in the Gulf of Maine–Georges Bank region: Variability and importance to blooms of the toxic dinoflagellate Alexandrium fundyense

We report here the results of ten oceanographic survey cruises carried out in the Gulf of Maine–Georges Bank region of the Northwest Atlantic during the late spring to summer period in 2007, 2008 and 2010, for which we examine and characterize relationships among dissolved inorganic nutrient fields, water mass dynamics and cell densities of the toxic dinoflagellate Alexandrium fundyense. Nutrients are supplied to continental shelf waters of the Gulf of Maine–Georges Bank region by inflows of deep offshore water masses; once in the Gulf they are transported with the residual circulation and mix with surface waters, both in the Gulf and on the Bank. Those fluxes of offshore water masses and their nutrient loads are the major source of nutrients for phytoplankton production in the region, including annual blooms of A. fundyense in the Gulf and on Georges Bank. This much is already known. We suggest here that the locations and magnitude of A. fundyense blooms are controlled in part by variable nutrient fluxes to the interior Gulf of Maine from offshore, and, those interior Gulf of Maine waters are, in turn, the main nutrient source to Georges Bank, which are brought onto the Bank by tidal pumping on the Northern Flank. We present evidence that nitrate is the initial form of nitrogenous nutrient for A. fundyense blooms, but it is quickly depleted to limiting concentrations of less than 0.5µM, at which time continued growth and maintenance of the population is likely fueled by recycled ammonium. We also show that phosphate may be the limiting nutrient over much of Georges Bank in summer, allowing recycled ammonium concentrations to increase. Our temperature–salinity analyses reveal spatial and temporal (seasonal and interannual) variability in the relative proportions of two deep source waters that enter the Gulf of Maine at depth through the Northeast Channel: Warm Slope Water (WSW) and Labrador Slope Water (LSW). Those two source waters are known to vary in their nutrient loads, with nitrate concentrations about 50% higher in WSW than LSW, for example, and as such the proportions of these two water masses to one another are important determinants of the overall nutrient loads in the interior Gulf. In addition to these deep slope water fluxes, we show evidence here of episodic fluxes of relatively fresh and low-nutrient shelf waters from the Nova Scotian Shelf, which enter the Gulf in pulses at depths between the surface and approximately 150m, displacing deep slope waters, and consequently they significantly dilute the Gulf's interior waters, reducing nutrient concentrations and, in turn, affect the magnitude of A. fundyense blooms.

Automatic detection of coastal plumes using Landsat TM/ETM+ images

Riverine fresh water outflows create coastal plumes that are distinguished from surrounding sea water by their specific spectral signature. Coastal waters are unique ecosystems, and they are very important in terms of living resources and oceanographic processes. River plumes and coastal turbid waters have important effects on coastal marine ecosystems, and they also influence marine life cycles, sediment distribution, and pollution. Remote sensing and digital image-processing techniques provide an effective tool to detect and monitor these plume zones over large areas. The primary goal of this study was automatic detection and monitoring of coastal plume zones using multispectral Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM+) imagery. For that purpose, the proposed algorithm exploits spectral features of the multispectral images by using feature extraction and decision-making steps. The procedure has two main stages: (1) some pre-processing operations were applied to the images in order to extract the plume core reflectance values with maximum turbidity and offshore water mass reflectance values; (2) a k-means algorithm was applied with initial seed values of reflectance computed from the pre-processing stage to classify coastal plume zones. Spatial pattern and variability of optical characteristics of coastal plume zones were then defined following the results of the classification process. The algorithm was automatically applied in three different regions with three multispectral Landsat images acquired on different dates, and yielded a very high classification accuracy in detecting coastal plume zones.

Observed and modeled bio-optical, bioluminescent, and physical properties during a coastal upwelling event in Monterey Bay, California

[1] During spring and summer time, coastal upwelling influences circulation and ecosystem dynamics of the Monterey Bay, California, which is recognized as a National Marine Sanctuary. Observations of physical, bio-optical properties (including bioluminescence) together with results from dynamical biochemical and bioluminescence models are used to interpret the development of the upwelling event during August 2003 in Monterey Bay, California. Observations and the biochemical model show the development of a phytoplankton bloom in the southern portion of Monterey Bay. Model results show an increase of nutrients in the southern portion of the bay, where nutrient-rich water masses are brought in by the southward flow and cyclonic circulation inside the bay. This increase in nutrients together with the sluggish circulation in the southern portion of the bay provides favorable conditions for phytoplankton growth. Our observations and models suggest that with the development of upwelling the offshore water masses with the subsurface layer of bioluminescent zooplankton were replaced by water masses advected from the northern coast of the bay with a relatively high presence of mostly nonbioluminescent phytoplankton. Inshore observations from autonomous underwater vehicles (AUVs) show consistent coincidence of chlorophyll, backscatter, and bioluminescence maxima during upwelling development. Offshore AUV observations (taken at the entrance to the bay) show a deeper bioluminescence maximum below the surface layers of high chlorophyll and backscatter values during the earlier stages of upwelling development. Later, the observed deep offshore bioluminescence maximum disappeared and became a shallower and much weaker signal, coinciding with high chlorophyll and backscatter values offshore. Based on the biochemical and bioluminescence models, a methodology for estimating the nighttime water-leaving radiance due to stimulated bioluminescence is demonstrated and evaluated.

A review of phytoplankton ecology in estuarine and coastal waters around Ireland

A review of the distribution of phytoplankton in coastal, shelf and estuarine waters around Ireland was undertaken to consolidate our understanding of the ecology of these organisms in the region. In broad terms, the review has highlighted the relative importance of vertical water column stability and horizontal transport processes in influencing the abundance and composition of phytoplankton. In coastal waters, the seasonal stabilization and de-stabilization of the water column accounts for most of the natural variation in both phytoplankton species composition and biomass. Much of the remaining natural variability can be explained by the interaction of phytoplankton with a number of oceanographic features and processes such as the presence of tidal and thermohaline fronts, wind and topographically associated coastal upwelling, advection landward of offshore water masses and the flow of coastal and oceanic currents. In estuarine waters, the scenario is somewhat reversed, and although seasonality is important in broad terms, the structure of phytoplankton populations is determined more by local factors operating over much smaller time-scales in the order of days and weeks. The interplay of these factors, such as the periodic rise and fall of the tide and episodic changes in river flow, creates a broad range of conditions that result in greater variation in phytoplankton biomass, while at the same time selecting for a reduced number of species that are adapted to survive in this highly changeable environment.

Pre-Bloom Phytoplankton in the Surface Waters of the Celtic Sea and Some Adjacent Waters

Pre-Bloom Phytoplankton in the Surface Waters of the Celtic Sea and Some Adjacent Waters

Hydrography of the Labrador Sea during Active Convection

The hydrographic structure of the Labrador Sea during wintertime convection is described. The cruise, part of the Deep Convection Experiment, took place in February‐March 1997 amidst an extended period of strong forcing in an otherwise moderate winter. Because the water column was preconditioned by previous strong winters, the limited forcing was enough to cause convection to approximately 1500 m. The change in heat storage along a transbasin section, relative to an occupation done the previous October, gives an average heat loss that is consistent with calibrated National Centers for Environmental Prediction surface heat fluxes over that time period (; 200 Wm 22). Deep overturning was observed both seaward of the western continental slope (which was expected), as well as within the western boundary current itself—something that had not been directly observed previously. These two geographical regions, separated by roughly the 3000-m isobath, produce separate water mass products. The offshore water mass is the familiar cold/fresh/dense classical Labrador Sea Water (LSW). The boundary current water mass is a somewhat warmer, saltier, lighter vintage of classical LSW (though in the far field it would be difficult to distinguish these products). The offshore product was formed within the cyclonic recirculating gyre measured by Lavender et al. in a region that is limited to the north, most likely by an eddy flux of buoyant water from the eastern boundary current. The velocity measurements taken during the cruise provide a transport estimate of the boundary current ‘‘throughput’’ and offshore ‘‘recirculation.’’ Finally, the overall trends in stratification of the observed mixed layers are described.

Atmospheric and Oceanic Forcings on the Spring Coastal Thermal Environment in the Kuroshio/Oyashio Frontal Region

Satellite infrared images and coastal meteorological and oceanographic data are used to investigate the influence of weather and offshore conditions on spring thermal environment around the Sendai Bay in the Kuroshio/Oyashio frontal region. Sea surface temperature (SST) anomaly represents a high annual variation and a high correlation with those of the duration of sunshine and air temperature. The multiple regression analysis of SST with five-explanatory variables (weather variation components) provides a good correlation between the predicted value and in situ SST. Temporal behaviors of coastal SST and salinity show that water mass of the bay is closely connected with the advection of the Kuroshio/Oyashio. Analyses of SST images represent well the properties and durability of the Kuroshio/Oyashio interaction in the same year, and the low SST fluctuation at the inner area of the Sendai Bay and coastal area of the Oyashio flowing path. Empirical orthogonal function (EOF) analyses of monthly-averaged infrared images describe a spatial and temporal variability, which is consistent with in situ measurements. The first modes of the temporal variance, 91.6% (April) and 95.7% (May), show spatially varying offshore water-mass in the presence of the Kuroshio/Oyashio current.

From littoral to pelaglab comparing the distribution of phytoplankton and dilated protozoa along a transect

The seasonal dynamics of phytoplankton and ciliates were examined at several stations from littoral to pelagial over 2 years. Special interest lay on the evaluation of the interchange between the littoral and pelagic community. The phytoplankton succession showed recurrent features at all stations along the transect. In the annual mean total phytoplankton biomass decreased from littoral towards midlake. The algal assemblage of the littoral waterbody was strongly influenced by detached phytobenthos species, mostly pennate diatoms, which diminished rapidly after the slope. ailoro phytes and cyanophytes also decreased along the transect. Cryptophytes and dinophytes showed different distribution gradients. Species of the same class could reveal countercurrent distribution pat terns. The mean annual diversity index reached highest values nearshore. The ciliated protozoa also revealed recurrent species succession at all stations. However, they exhibited far less prominent gradients along the transect. Among the numerically most important representatives were Oligo tnchidae in the annual mean which reached similar abundances at all stations, whereas Prostomatidae increased towards the pelagial. A further conspicuous difference between phytoplankton and ciliates was the fact that benthic ciliate species could only seldom be found in the littoral water samples. Nearshore and offshore water masses and the organisms therein were in a continuous mutual exchange. Thus a per se littoral water body does not exist in this part of Lake Constance.

Water mass structure and boundaries in the Mackenzie shelf estuary

The Mackenzie shelf is a broad, estuarine region bordering the southeastern Beaufort Sea in the Arctic Ocean. Its fields of temperature and salinity result from the modification of offshore water masses by river inflow, ice melting and freezing, solar insolation, and air‐sea exchange. We here relate water masses resident on the Mackenzie shelf to the large‐scale oceanography of the Arctic mediterranean. The summertime exchange between the shelf and open ocean is largely confined to waters lying above the main halocline (S&lt;32.3 psu), thus excluding underlying offshore waters from the nutrient maximum layer (S ≈ 33.1 psu) and Atlantic layer (S&gt;34.2 psu). Cross‐shelf property distributions show that individual water masses maintain their structural identity (i.e., core properties and buoyancy frequency) as they move across the shelf and participate in the estuarine circulation. Shelf waters are strongly influenced by river inflow; however, the concept of a single “plume” issuing from the incoming river and forming a strictly two‐layered structure over uniform shelf water is misleading, since a variety of temperature, salinity, and turbidity fronts co‐exist on the shelf at any given time.

Formation of water masses and fronts due to density-induced current system

Several numerical experiments were carried out on the formation of water masses and their fronts such as observed in the Kii Channel in winter. Such water masses and fronts may caused by density-induced current system. The phenomenon is assumed to take place in the vertical two-dimensional plane not involving the effect of the earth's rotation. The linear momentum equation and the diffusion-advection equations of salinity and temperature are integrated with respect to time under a vertically hydrostatic condition. The result is that two rolls which correspond to the onshore water mass and the offshore water mass are formed with an accompanying front between them. The apparent diffusion coefficient reaches a relatively great amount inside the water masses and drops down to the eddy diffusivity level at the front. The dependence of the synoptic distributions of the temperature and salinity on several parameters is also examined. Finally another experiment is carried out involving the effect of the earth's rotation, which results in a rather different distribution pattern from that of the non-rotating model.

Circulation observations in the Louisiana bight using LANDSAT imagery

A method for quantifying the turbidity of offshore water masses using LANDSAT imagery is discussed and the results of a laboratory experiment correlating radiance with concentrations of suspended Mississippi River sediment are presented. The results of the experiment are used to plot suspended sediment contours on eight LANDSAT images of the Louisiana Bight. These contours are observed to depend on the speed and direction of the wind as well as the amount of fresh water discharged by the Mississippi River. The presence of a clockwise circulation in the bight is also indicated by the contours.