Coastal Upwelling Off the China Coasts

Upwelling is an important oceanographic phenomenon that brings cooler and nutrient-rich water upward to the surface, facilitating the growth of phytoplankton and other primary producers, which results in high levels of primary productivity and hence fishery production. This chapter presents a review of recent studies on six major upwelling regions along the China coasts, with a focus on the eastern and southeastern coasts of mainland China, based on in situ measurements, satellite observations and numerical simulations. These upwelling regions result primarily from the summer monsoon winds, though other mechanisms, such as river discharge, baroclinicity, topography, tides, and the presence of mean current, may also be in play. In this review, their impacts on local biogeochemical processes are briefly summarized. Also discussed are their possible responses to the globally changing climate

Variabilité interannuelle et intrasaisonnière de l'Upwelling du Sud Vietnam : le rôle du forçage atmosphérique haute fréquence, de la dynamique océanique hauturière et côtière et de la variabilité intrinsèque océanique

L'Upwelling du Sud Vietnam (SVU) se développe en été au large de la côte vietnamienne (mer de Chine du Sud, SCS) sous l'influence des vents de mousson du sud-ouest. Une configuration haute résolution (1 km à la côte) du modèle SYMPHONIE a été développée pour étudier le fonctionnement, la variabilité et l'influence du SVU. Une simulation a d'abord été réalisée sur la période 2009-2018. Le réalisme de cette simulation en termes de représentation de la dynamique océanique et des masses d'eau, des échelles journalière à interannuelle, et côtière à régionale, a été évalué en détail par comparaison avec les données satellitaires disponibles et quatre jeux d'observations in-situ. Cette simulation a ensuite été utilisée pour examiner la variabilité interannuelle du SVU sur ses principales zones de développement : les zones côtières sud (BoxSC) et nord (BoxNC), et la zone offshore (BoxOF). Pour BoxSC et BoxOF, nos résultats confirment que l'intensité moyenne estivale du vent dans la région et de la circulation induite pilotent au premier ordre cette variabilité . Ils révèlent de plus qu'elle est modulée par l'organisation spatiale et temporelle des structures océaniques de méso-échelle et du forçage atmosphérique de haute fréquence. Pour BoxNC, la variabilité interannuelle de l'upwelling est principalement déterminée par la circulation côtière et les structures de méso-échelle : des conditions de vent estivales similaires peuvent être associées à des intensités d'upwelling très contrastées, et vice versa, en fonction de la circulation dans la zone. Nous avons ensuite réalisé un ensemble de 10 simulations jumelles avec des conditions initiales perturbées pour examiner les mécanismes impliqués dans la variabilité journalière à intrasaisonnière de l'upwelling. Cet ensemble révèle le rôle de la chronologie quotidienne à intrasaisonnière du vent, mais aussi la forte influence de la variabilité intrinsèque de l'océan (OIV), liée à l'influence de la circulation côtière et de mésoéchelle.The South Vietnam Upwelling (SVU) develops off the Vietnamese coast (South China Sea, SCS) under the influence of southwest summer monsoon winds. A high resolution configuration (1 km at the coast) of the SYMPHONIE model was developed to study the functioning, variability and influence of the SVU. A simulation was first performed over the period 2009-2018. The realism of the simulation in terms of representation of ocean dynamics and water masses, from daily to interannual, and coastal to regional scales, was assessed in detail by comparison with available satellite data and four sets of in-situ observations. The interannual variability of the SVU is examined over its main areas of development: the southern (BoxSC) and northern (BoxNC) coasts, and the offshore area (BoxOF). For BoxSC and BoxOF, our results confirm the driving role of the summer regional mean wind and induced circulation. They moreover reveal that the spatial and temporal organization of mesoscale ocean structures and high frequency atmospheric forcing modulate this interannual variability. For BoxNC, the upwelling interannual variability is mainly determined by coastal circulation and mesoscale structures: similar summer wind conditions can be associated with very contrasting upwelling intensities, and vice versa, depending on the circulation in the BoxNC area. We then perform an ensemble of 10 twin simulations with perturbed initial conditions to examine the mechanisms involved in the daily to intraseasonal variability of upwelling. This ensemble reveals the role of the daily to intraseasonal chronology of wind forcing, but also the strong influence of Ocean Intrinsic Variability (OIV), related to the influence of coastal and mesoscale circulation

Progress of regional oceanography study associated with western boundary current in the South China Sea

Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection in the WBC based on satellite images, cross-continental shelf exchange in the WBC, eddy-current interaction, interannual variability of the WBC, air-sea interaction, the SCS throughflow (SCSTF), among others. The WBC in the SCS is strong, and its structure, variability and dynamic processes on seasonal and interannual time scales are yet to be fully understood. In this paper, we summarize progresses on the variability of the WBC, eddy-current interaction, air-sea interaction, and the SCSTF achieved in the past few years. Firstly, using the drifting buoy observations, we point out that the WBC becomes stronger and narrower after it reaches the central Vietnam coast. The pos-sible mechanisms influencing the ocean circulation in the northern SCS are discussed, and the dynamic mechanisms that induce the countercurrent in the region of northern branch of WBC in winter are also studied quantitatively using momentum balance. The geostropic component of the WBC was diagnosed using the ship observation along 18°N, and we found that the WBC changed significantly on interannual time scale. Secondly, using the ship observations, two anti-cyclonic eddies in the winter of 2003/2004 in the northern SCS, and three anti-cyclonic eddies in the summer of 2007 along 18°N were studied. The results show that the two anti-cyclonic eddies can propagate southwestward along the continental shelf at the speed of first Rossby wave (~0.1 m s1) in winter, and the interaction between the three anti-cyclonic eddies in summer and the WBC in the SCS is preliminarily revealed. Eddies on the continental shelf of northern SCS propagated southeastward with a maximum speed of 0.09 m s-1, and those to the east of Vietnam coast had the largest kinetic energy, both of which imply strong interaction between eddy activity and WBC in the SCS. Thirdly, strong intraseasonal variability (ISV) of sea surface temperature (SST) near the WBC regions was found, and the ISV signal of SST in winter weakens the ISV signal of latent heat flux by 20%. Fourthly, the long-term change of SCSTF volume transport and its connection with the ocean circulation in the Pacific were discussed

Response of Coastal Upwelling East of Hainan Island in the South China Sea to Sudden Impact and Long-Term Variability of Atmospheric Forcing

The wind-driven coastal upwelling east of Hainan Island (UEH) in the northwestern South China Sea (SCS) is sensitive to the multi-scale variability of atmospheric forcing. This chapter focuses on two ends of time scales of atmospheric forcing: very short-time or sudden impact, i.e., typhoon passages; and long-term variability associated with El Niño events. The response of the sea surface temperature (SST) associated with the UEH to typhoon passages was investigated based on concurrent satellite SST and wind products. The long-term variability and response of the UEH to super El Niño events were analyzed based on recent 30 years of satellite data. The results show that the UEH has significant responses to atmospheric forcing. Meanwhile, the ocean circulation also plays an important role in modulation of the coastal upwelling

Phytoplankton Biomass Dynamics in the Strait of Malacca within the Period of the SeaWiFS Full Mission: Seasonal Cycles, Interannual Variations and Decadal-Scale Trends

Seasonal cycles, interannual variations and decadal trends of Sea-viewing Wide Field-of-view Sensor (SeaWiFS)-retrieved chlorophyll-a concentration (Chl-a) in the Strait of Malacca (SM) were investigated with reconstructed, cloud-free SeaWiFS Chl-a during the period of the SeaWiFS full mission (September 1997 to December 2010). Pixel-based non-parametric correlations of SeaWiFS Chl-a on environmental variables were used to identify the probable causes of the observed spatio-temporal variations of SeaWiFS Chl-a in northern, middle and southern regions of the SM. Chl-a was high (low) during the northeast (southwest) monsoon. The principal causes of the seasonality were wind-driven vertical mixing in the northern region and wind-driven coastal upwelling and possibly river discharges in the middle region. Among the three regions, the southern region showed the largest interannual variations of Chl-a. These variations were associated with the El Nino/Southern Oscillation (ENSO) and river runoff. Interannual variations of Chl-a in the middle and northern regions were more responsive to the Indian Ocean Dipole and ENSO, respectively, with atmospheric deposition being the most important driver. The most significant decadal-scale trend of increasing Chl-a was in the southern region; the trend was moderate in the middle region. This increasing trend was probably caused by environmental changes unrelated to the variables investigated in this study

U.S.-GLOBEC: NEP Phase IIIb-CGOA: A synthesis of climate-forced variability on mesoscale structure in the CGOA with direct comparisons to the CCS

A variety of extreme climate events occurred during the period of US GLOBEC monitoring and process studies in the NEP (1997-2004). These provide an unprecedented opportunity to examine a range of climate variability experienced by the coastal Gulf of Alaska (CGOA). By relating these climate events to regional physical and biological observations, using multiple and diverse data sources (GLOBEC observations, historical data sets and reanalyses, satellites, models), we can determine how these events affect mesoscale ocean variability in the CGOA and its related target populations (the primary goal of the NEP program). We can then directly compare these responses to those evident in the California Current System (CCS). There are two overarching goals for this project. 1) Characterize the linkages between basin-scale variability indicative of climate events and local CGOA changes in mesoscale variability that impact ecosystem pattern, structure and productivity. 2) Compare the linkages between basin-scale and local structure in the coastal Gulf of Alaska (CGOA) with those evident in the CCS, contrasting differing ecosystem responses to the same climate signals. The emphasis is on synthesis of physical circulation, upper ocean structure, nutrients and lower (planktonic) trophic levels to develop metrics based on multiple data sets spanning a wide spectrum of space and time scales. A funded GLOBEC-NEP Phase IIIa proposal to the same PIs to carry out similar analyses in the California Current System provides significant leverage, both financially and intellectually. This team of investigators represents expertise in diverse aspects of climate mesoscale interactions and data analysis. They will use correlative methods to characterize mesoscale variability in the CGOA and the concurrent basin-scale conditions during Field Program years, and then extend these comparisons back in time where possible. They will build on these correlational linkages between basin-scale and mesoscale patterns, examining the mechanisms behind these linkages from three points of view: i) comparing interannual and decadal scales of climate variability, ii) identifying and comparing different shelf regions of climate response in the CGOA, and iii) examining changes in seasonal signals. They will then compare and contrast signals observed in the CCS to those in the CGOA. BROADER IMPACTS: This project will contribute to the legacy of the GLOBEC NEP program in the form of analyses (papers), data sets, and indices for monitoring, assessing, and managing marine resources in the CGOA. By integrating and analyzing multiple data sets, the investigators will provide robust indicators of the response of the CGOA shelf to climate change, a useful tool for resource assessment and management. Improvement of ecosystem management strategies for the Alaskan shelf directly affects a large socio-economic sector of the US west coast. Two graduate students are funded under our CCS and CGOA efforts. Some of the satellite and survey data sets will also be incorporated into curriculum material that is under development within the OSU SMILE program. These materials are used in twelve Oregon high school districts with large proportions of students from groups traditionally under-represented in university science and mathematics departments. They are available for use in schools elsewhere

Global perspectives on observing ocean boundary current systems

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Todd, R. E., Chavez, F. P., Clayton, S., Cravatte, S., Goes, M., Greco, M., Ling, X., Sprintall, J., Zilberman, N., V., Archer, M., Aristegui, J., Balmaseda, M., Bane, J. M., Baringer, M. O., Barth, J. A., Beal, L. M., Brandt, P., Calil, P. H. R., Campos, E., Centurioni, L. R., Chidichimo, M. P., Cirano, M., Cronin, M. F., Curchitser, E. N., Davis, R. E., Dengler, M., deYoung, B., Dong, S., Escribano, R., Fassbender, A. J., Fawcett, S. E., Feng, M., Goni, G. J., Gray, A. R., Gutierrez, D., Hebert, D., Hummels, R., Ito, S., Krug, M., Lacan, F., Laurindo, L., Lazar, A., Lee, C. M., Lengaigne, M., Levine, N. M., Middleton, J., Montes, I., Muglia, M., Nagai, T., Palevsky, H., I., Palter, J. B., Phillips, H. E., Piola, A., Plueddemann, A. J., Qiu, B., Rodrigues, R. R., Roughan, M., Rudnick, D. L., Rykaczewski, R. R., Saraceno, M., Seim, H., Sen Gupta, A., Shannon, L., Sloyan, B. M., Sutton, A. J., Thompson, L., van der Plas, A. K., Volkov, D., Wilkin, J., Zhang, D., & Zhang, L. Global perspectives on observing ocean boundary current systems. Frontiers in Marine Science, 6, (2010); 423, doi: 10.3389/fmars.2019.00423.Ocean boundary current systems are key components of the climate system, are home to highly productive ecosystems, and have numerous societal impacts. Establishment of a global network of boundary current observing systems is a critical part of ongoing development of the Global Ocean Observing System. The characteristics of boundary current systems are reviewed, focusing on scientific and societal motivations for sustained observing. Techniques currently used to observe boundary current systems are reviewed, followed by a census of the current state of boundary current observing systems globally. The next steps in the development of boundary current observing systems are considered, leading to several specific recommendations.RT was supported by The Andrew W. Mellon Foundation Endowed Fund for Innovative Research at WHOI. FC was supported by the David and Lucile Packard Foundation. MGo was funded by NSF and NOAA/AOML. XL was funded by China’s National Key Research and Development Projects (2016YFA0601803), the National Natural Science Foundation of China (41490641, 41521091, and U1606402), and the Qingdao National Laboratory for Marine Science and Technology (2017ASKJ01). JS was supported by NOAA’s Global Ocean Monitoring and Observing Program (Award NA15OAR4320071). DZ was partially funded by the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063. BS was supported by IMOS and CSIRO’s Decadal Climate Forecasting Project. We gratefully acknowledge the wide range of funding sources from many nations that have enabled the observations and analyses reviewed here

Biogeochemical and ecological impacts of boundary currents in the Indian Ocean

Monsoon forcing and the unique geomorphology of the Indian Ocean basin result in complex boundary currents, which are unique in many respects. In the northern Indian Ocean, several boundary current systems reverse seasonally. For example, upwelling coincident with northward-flowing currents along the coast of Oman during the Southwest Monsoon gives rise to high productivity which also alters nutrient stoichiometry and therefore, the species composition of the resulting phytoplankton blooms. During the Northeast Monsoon most of the northern Indian Ocean boundary currents reverse and favor downwelling. Higher trophic level species have evolved behavioral responses to these seasonally changing conditions. Examples from the western Arabian Sea include vertical feeding migrations of a copepod (Calanoides carinatus) and the reproductive cycle of a large pelagic fish (Scomberomorus commerson). The impacts of these seasonal current reversals and changes in upwelling and downwelling circulations are also manifested in West Indian coastal waters, where they influence dissolved oxygen concentrations and have been implicated in massive fish kills. The winds and boundary currents reverse seasonally in the Bay of Bengal, though the associated changes in upwelling and productivity are less pronounced. Nonetheless, their effects are observed on the East Indian shelf as, for example, seasonal changes in copepod abundance and zooplankton community structure. In contrast, south of Sri Lanka seasonal reversals in the boundary currents are associated with dramatic changes in the intensity of coastal upwelling, chlorophyll concentration, and catch per unit effort of fishes. Off the coast of Java, monsoon-driven changes in the currents and upwelling strongly impact chlorophyll concentrations, seasonal vertical migrations of zooplankton, and sardine catch in Bali Strait. In the southern hemisphere the Leeuwin is a downwelling-favorable current that flows southward along western Australia, though local wind forcing can lead to transient near shore current reversals and localized coastal upwelling. The poleward direction of this eastern boundary current is unique. Due to its high kinetic energy the Leeuwin Current sheds anomalous, relatively high chlorophyll, warm-core, downwelling eddies that transport coastal diatom communities westward into open ocean waters. Variations in the Leeuwin transport and eddy generation impact many higher trophic level species including the recruitment and fate of rock lobster (Panulirus cygnus) larvae. In contrast, the transport of the Agulhas Current is very large, with sources derived from the Mozambique Channel, the East Madagascar Current and the southwest Indian Ocean sub-gyre. Dynamically, the Agulhas Current is upwelling favorable; however, the spatial distribution of prominent surface manifestations of upwelling is controlled by local wind and topographic forcing. Meanders and eddies in the Agulhas Current propagate alongshore and interact with seasonal changes in the winds and topographic features. These give rise to seasonally variable localized upwelling and downwelling circulations with commensurate changes in primary production and higher trophic level responses. Due to the strong influence of the Agulhas Current, many neritic fish species in southeast Africa coastal waters have evolved highly selective behaviors and reproductive patterns for successful retention of planktonic eggs and larvae. For example, part of the Southern African sardine (Sardinops sagax) stock undergoes a remarkable northward migration enhanced by transient cyclonic eddies in the shoreward boundary of the Agulhas Current. There is evidence from the paleoceanographic record that these currents and their biogeochemical and ecological impacts have changed significantly over glacial to interglacial timescales. These changes are explored as a means of providing insight into the potential impacts of climate change in the Indian Ocean