舟山近海海域夏季上升流时空特征及其与风场的关系

利用2002-2013年期间的卫星遥感海表温度(SST)数据分析了舟山海域夏季上升流的时空特征,并结合同时期的海面风场数据探讨了风对该海域夏季上升流的影响。对多年夏季月平均的SST进行经验正交函数(EOF)分解结果表明,7月份前两个模态方差贡献率分别为71.66%、16.55%,8月份前两个模态方差贡献率分别为87.03%和7.30%,并均通过了显著性检验,舟山近海海域的上升流存在较为明显的年际变化。相关分析显示,经向风速和SST异常存在显著的负相关关系,即夏季盛行的西南风有利于上升流的发展。并且,艾克曼(Ekman)体积输运计算结果表明,舟山海域7、8月份风生上升流的量级分别为3.0×10~(-5)m/s和1.5×10~(-5)m/s,7月上升流显著强于8月,这与8月份观测到的海表显著低温异常相关。     

Trends in carbon flux to seabirds in the Peruvian upwelling system: effects of wind and fisheries on population regulation

We hypothesized that change in the annual population size of guano‐producing seabirds (cormorant, Phalacrocorax bougainvillii; booby, Sula variegata; pelican, Pelecanus thagus) is a response to changes in primary and secondary production of the Peruvian upwelling system. We tested this hypothesis by modeling nitrate input through upwelling to the upper layers of the ocean off Peru between 6° and 14°S using data on wind stress and sea surface temperature. The model predicted the amount of carbon fixed by primary production each year from 1925 to 2000, which was then apportioned to the Peruvian anchovy (Engraulis ringens) biomass and ultimately to the seabird population and the anchovy fishery, the largest single‐species fishery on Earth. The model predicted a marked increase in primary production as a consequence of increasing wind stress. It overestimated the anchovy biomass after the collapse of the fishery in 1972, but closely predicted the growth of seabird populations from 1925 to the mid‐1960s, and their decline thereafter, explaining about 94% of the variation in seabird numbers from 1925 to 2000. The model indicates the seabirds consumed 14.4% of the available anchovies and, thus, that seabirds consumed 2.3% of the new production, before the development of the anchovy fishery, and only 2.2% of the available anchovies and 0.3% of the new production after the development of the fishery. The model results clarify the roles that environmental and anthropogenic factors may have had in regulating the guano‐producing seabird populations. It indicates that the growth of seabird populations from 1925 to 1955 was likely a response to increased productivity of the Peruvian upwelling system and that the subsequent drastic decline in seabird abundance was likely due to competition for food with the fishery, which caught ～85% of the anchovies, which otherwise would have been available for the seabirds. This model also shows that an increase in oceanic primary production promotes reproductive success and population growth in higher trophic level organisms.     

Creation of artificial upwelling areas for brown trout, Salmo trutta, spawning in still water bodies

Abstract  Brown trout, Salmo trutta L., spawning sites were constructed by creating areas of artificial upwelling water, 252 ± 37 mL m⁻² min⁻¹ (95% CL), through appropriately sized spawning gravel substrate in 3 m² vessels buried in the bottom of a 150-m² pond. Natural spawning occurred in the vessels during autumn 2001–2004, with hatching and alevin swim up the following spring. In areas of upwelling, egg survival was 85–95%, while no live eggs were observed in areas without upwelling. In areas with upwelling, the maximum density of live eggs at the eyed stage was 570–1510 eggs m⁻². In spring 2004 and 2005, the density of alevins was estimated at 322 (±187) m⁻² and 567 (±217) m⁻², respectively, in areas with upwelling water, compared with 35.2 ± 25.4 m⁻² in areas without upwelling water in 2004.     

Hypoxia-based habitat compression of tropical pelagic fishes

Large areas of cold hypoxic water occur as distinct strata in the eastern tropical Pacific (ETP) and Atlantic oceans as a result of high productivity initiated by intense nutrient upwelling. We show that this stratum restricts the depth distribution of tropical pelagic marlins, sailfish, and tunas by compressing the acceptable physical habitat into a narrow surface layer. This layer extends downward to a variable boundary defined by a shallow thermocline, often at 25 m, above a barrier of cold hypoxic water. The depth distributions of marlin and sailfish monitored with electronic tags and average dissolved oxygen (DO) and temperature profiles show that this cold hypoxic environment constitutes a lower habitat boundary in the ETP, but not in the western North Atlantic (WNA), where DO is not limiting. Eastern Pacific and eastern Atlantic sailfish are larger than those in WNA, where the hypoxic zone is much deeper or absent. Larger sizes may reflect enhanced foraging opportunities afforded by the closer proximity of predator and prey in compressed habitat, as well as by the higher productivity. The shallow band of acceptable habitat restricts these fishes to a very narrow surface layer and makes them more vulnerable to over‐exploitation by surface gears. Predictably, the long‐term landings of tropical pelagic tunas from areas of habitat compression have been far greater than in surrounding areas. Many tropical pelagic species in the Atlantic Ocean are currently either fully exploited or overfished and their future status could be quite sensitive to increased fishing pressures, particularly in areas of habitat compression.     

Biophysical dynamics of western transition zones: a preliminary synthesis

The nature of the western portions of the biogeographic temperate or transition zones in the North Pacific and North Atlantic is reviewed. The physical transport of nutrients and biomass into them from the Kuroshio and Gulf Stream as well as from the poleward sides are estimated. The conclusion is that the upwelling in the two western boundary currents makes the largest contribution to the nutrient and biomass fluxes into these transition zones. A conservative estimate of the amount of upwelled fluid is derived from absolute velocity sections in the Gulf Stream. The estimate suggests that upwelling into the euphotic zone exceeds 2 × 10⁶ m³ s^–1. This implies that upwelling in these western boundary currents matches or exceeds that in eastern boundary currents such as the California Current. The two western boundary regimes have very different poleward situations. The Oyashio extension flows parallel to the Kuroshio and is a deep current. The North Atlantic Shelf Front flow is to the west where it is ultimately entrained into the edge of the Gulf Stream. There does not seem to be any tendency for this to occur in the Kuroshio. Despite these differences in the northern and western boundaries, the two transition zones are similar with large amplitude meanders, anticyclonic rings and streamers dominating their physical structure. The physical features responsible for the transfer of materials from the boundary current extensions into the transition zones are similar in both systems. Ring formation contributes only ? 10% of the transfer, while ring‐induced streamers contribute 30%. The rest of the transport is contributed by branching of the boundary current front. Both currents have well developed secondary fronts consisting of subtropical surface water pulled into the transition zone. Biologically, the upwelling in both western boundary currents leads to a biomass maximum along the boundary in both secondary producers (copepods) and in small pelagic fish. In the Kuroshio, the latter are the Japanese sardine, Sardinops melanostictus, that spawn in the Kuroshio and then enter the transition zone for the summer and fall months. In the Gulf Stream, the dominate species are menhaden, Brevoortia tyrannus and B. smithi. These species make use of the coastal environments of North America and although the adults spawn in the Gulf Stream, they are not thought to play a major role in the Slope Water, transition zone. The similar differences in the use of the Kuroshio and the Gulf Stream ecosystems occurs in the behaviour of bluefin tuna, squid and other large pelagics. The Gulf Stream system also lacks an equivalent to Pacific saury, Cololabis saira. The biology therefore is at least subtly different, with saury and sardines being replaced by mid‐water fish in the North Atlantic. A fuller comparison of the biology with quantitative methods in both systems should be encouraged.     

The global distribution of wind-induced upwelling

The global distribution of wind-induced upwelling at the base of the surface Ekman layer has been computed from the COADS monthly wind stress from 1950 to 1988. In contrast to previous studies where the Ekman transport equations became invalid near the Equator, this paper computed upwelling right to the equator by incorporating friction in the surface transport equations. Comparing the seasonal changes in the equatorial upwelling between the Atlantic and the Pacific, we found that the Atlantic had the larger magnitude change while the Pacific had the larger latitudinal shift. The anomalous wind-induced upwelling/downwelling associated with El Niño were computed over several latitudinal bands in the Pacific by compositing the data from six El Nino events. By plotting the July zonally averaged upwelling anomalies in the Pacific in a latitude-time contour plot, we found northward phase propagation at about 3.5° latitude per decade in the low latitudes, a feature not found in the January upwelling. Long-term upwelling trends were computed and their potential influence on fisheries are discussed.     

Climate Variability and Oceanographic Settings Associated with Interannual Variability in the Initiation of Dinophysis acuminata Blooms

In 2012, there were exceptional blooms of D. acuminata in early spring in what appeared to be a mesoscale event affecting Western Iberia and the Bay of Biscay. The objective of this work was to identify common climatic patterns to explain the observed anomalies in two important aquaculture sites, the Galician Rías Baixas (NW Spain) and Arcachon Bay (SW France). Here, we examine climate variability through physical-biological couplings, Sea Surface Temperature (SST) anomalies and time of initiation of the upwelling season and its intensity over several decades. In 2012, the mesoscale features common to the two sites were positive anomalies in SST and unusual wind patterns. These led to an atypical predominance of upwelling in winter in the Galician Rías, and increased haline stratification associated with a southward advection of the Gironde plume in Arcachon Bay. Both scenarios promoted an early phytoplankton growth season and increased stability that enhanced D. acuminata growth. Therefore, a common climate anomaly caused exceptional blooms of D. acuminata in two distant regions through different triggering mechanisms. These results increase our capability to predict intense diarrhetic shellfish poisoning outbreaks in the early spring from observations in the preceding winter.     

Nonlocal wind-driven fjord–coast advection and its potential effect on plankton and fish recruitment

The Bergen Ocean Model (BOM), a three-dimensional physical coastal ocean model, was used for a numerical simulation experiment to investigate short-term effects of wind-generated coastal upwelling and downwelling on the dynamics of adjacent large outer and smaller inner fjords. The effect of the real alongshore wind regime on advection for an idealized fjord topography, resembling Masfjorden, western Norway, is used as an example. This modelling exercise is a supplement to, and its predictions support, the various hypotheses investigated in ecosystem simulation studies of the Masfjorden. The model predicts that coastal winds from the north cause upwelling and transport the upper water layer out from the fjords. Winds from the south cause downwelling and transport the upper water layer into the fjords. The transport is rapid and ≈50% of the upper water layer may be replaced within 1–2 days. Implications of these physical processes for the dispersal and retention of planktonic organisms and the early life stages of fish are discussed. If strong southerly winds occur frequently, this will transport planktonic organisms into the fjord and may increase the carrying capacity for planktivorous fish. In contrast, frequent strong northerly winds may reduce the abundance of planktonic organisms, including the early life stages of marine fish, and thus possibly reduce recruitment to fjord fish populations. Frequent shifts between southerly and northerly winds would cause an exchange of early life stages between neighbouring fjords and thus enhance genetic exchange.     

A model‐based meso‐zooplankton production index and its relation to the ocean survival of juvenile coho (Oncorhynchus kisutch)

The ocean survival of coho salmon (Oncorhynchus kisutch) off the Pacific Northwest coast has been related to oceanographic conditions regulating lower trophic level production during their first year at sea. Coastal upwelling is recognized as the primary driver of seasonal plankton production but as a single index upwelling intensity has been an inconsistent predictor of coho salmon survival. Our goal was to develop a model of upwelling‐driven meso‐zooplankton production for the Oregon shelf ecosystem that was more immediately linked to the feeding conditions experienced by juvenile salmon than a purely physical index. The model consisted of a medium‐complexity plankton model linked to a simple one‐dimensional, cross‐shelf upwelling model. The plankton model described the dynamics of nitrate, ammonium, small and large phytoplankton, meso‐zooplankton (copepods), and detritus. The model was run from 1996 to 2007 and evaluated on an interannual scale against time‐series observations of copepod biomass. The model’s ability to capture observed interannual variability improved substantially when the copepod community size distribution was taken into account each season. The meso‐zooplankton production index was significantly correlated with the ocean survival of hatchery coho salmon from the Oregon production area, although the coastal upwelling index that drove the model was not itself correlated with survival. Meso‐zooplankton production within the summer quarter (July–September) was more strongly correlated with coho survival than was meso‐zooplankton production in the spring quarter (April–June).