磨刀门河口在20世纪60至70年代的演变模拟与动力地貌过程分析

使用长周期动力地貌模型(long-term morphodynamic model),再现了磨刀门河口1964—1977年的演变过程,并从水动力、地形演变规律以及人类活动等角度系统分析了长周期地貌演变过程。模拟结果显示在1964—1977年磨刀门河口鹤州至交杯沙浅滩和上沟快速淤积,13a的平均淤积厚度均在40cm以上,与之相反,横洲水道杧州至大井角段和上沟东部深槽冲刷明显。磨刀门河口演变季节性特征明显。在洪季浅滩淤积,深槽冲刷;在枯季滩槽都处于淤积状态。演变过程中各种基岩岛屿使动力结构和演变规律呈现多元化,同时人类活动对整个区域的演变起到了重要的作用。     

Reconstruction of sea surface dimethylsulfide in the North Pacific during 1970s to 2000s

We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R² = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year^− 1 in the subpolar region, and 0.01 ± 0.001 nM year^− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m^− 2 year^− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.     

Ecological characteristics of Walleye pollock eggs and larvae in the southeastern Bering Sea during the late 1970s

Walleye pollock (Theragra chalcogramma) is an ecologically and economically important groundfish in the eastern Bering Sea. Its population size fluctuates widely, driving and being driven by changes in other components of the ecosystem. It is becoming apparent that dramatic shifts in climate occur on a decadal scale, and these “regime shifts” strongly affect the biota. This paper examines quantitative collections of planktonic eggs and larvae of pollock from the southeastern Bering Sea during 1976–1979. Mortality, advection, and growth rates were estimated, and compared among the years encompassing the 1970s’ regime shift. These data indicate that pollock spawning starts in late February over the basin north of Bogoslof Island. Over the shelf, most spawning occurs north of Unimak Island near the 100 m isobath in early or mid April. Pollock eggs are advected to the northwest from the main spawning area at 5–10 cm/sec. Larvae are found over the basin north of Bogoslof Island in April, and over the shelf between Unimak Island and the Priblof Islands in May. Compared to 1977, the spawning period appeared to be later in 1976 (a cold year) and earlier in 1978 (a warm year) in the study area. At the lower temperatures in 1976, egg duration would be longer and thus egg mortality would operate over a longer period than in the other years. Mean larval growth appeared to be lower in 1976 than in 1977 and 1979. Estimated egg mortality rate in 1977 was 0.6 in April and 0.3 in early May.     

The IOD signal in the upper-ocean Indonesian Throughflow since the mid-1970s

On the basis of simple ocean data assimilation (SODA) reanalysis product, the interannual variability of upper-ocean Indonesian Throughflow (ITF) volume transport since the mid 1970s is examed. The wavelet analysis shows a second prominent interannual oscillation with a period of about 2~4 a. To reveal any relationship between this band-scale oscillation of upper-ocean ITF and the Indian Ocean dipole (IOD), the correlation and wavelet analyses are used. The correlation coefficient between the upper-ocean ITF and the IOD reaches -0.40 with upper-ocean ITF lagging an IOD index by eight months. The wavelet power spectrum of upper-ocean ITF shows similar structure to that of the IOD index. And the evolution of IOD is reproduced by lagged correlation between the upper-ocean ITF and the sea surface temperature anomaly (SSTA) over the Indian Ocean. It suggests that the 2~4 a band-scale oscillation of upper-ocean ITF is related uniquely to the IOD over the tropical Indian Ocean.     

Relationship between transitional variation of summer sea surface temperature in the northwestern Pacific and ocean events during the 1960s

INTRODUCTIONIt has been pointed out in recent years by Yan et al. (1990 a, b) through analyses of timeand space variations in the different elements in the summer of the Northern Hemisphere during1951 ~ 1980 that climate jump generally occurred in the summer of the Northern Hemisphere during the 1960s, in which geopotential height on 500 hPa in the Northern Hemisphere, the nearsurface air temperature and the SST of the northwestern Pacific appeared in the early of the1960's (Fig. 1).T…     

南印度洋SST在20世纪60年代的年代际转变及其相关气候变化过程

The change of sea surface temperature(SST) in the southern Indian Ocean(SIO) during the recent six decades has been analyzed based on oceanic reanalysis and model, as well as atmospheric data. The results show that a thermal regime shift in SIO during the 1960 s, which is not caught enough attentions, has been of equal magnitude to the linear warming since 1970. Empirical Orthogonal Function(EOF) analyses reveal that a thermal shift is combined with atmospheric changes such as the weakening of westerly during the period of 1960–1967. Inner dynamic connections can be defined that when the westerly winds turn weak, the anticyclonic wind circulation between westerly winds and the trade winds decreases, which further reduces the SST to a negative peak in this period. It is noted that the shifts in the 1960 s are also evident for Southern Hemisphere. For example, subtropical high and the entire westerly winds belt at high latitudes both change dramatically in the 1960 s. This large-scaled process maybe link to the change of southern annular mode(SAM).     

全球变暖背景下最近40年太平洋海温变化数值模拟

用Non-Boussinesq POP模式和1960—1999年NCEP的1 000 hPa大气温度和风场资料,模拟了最近40 a太平洋海温的变化,通过与实际观测结果比较,得出模拟结果是可信的,并且得到了一些有意义的结果:在海面,太平洋最大的增温发生在赤道中东太平洋,即Niño1-Niño4区内,最大的降温在中纬度南北太平洋中部,除了北半球太平洋西岸40°N附近为降温外,在北半球太平洋沿岸基本上为升温,但太平洋东海岸的升温幅度要远大于西海岸;在太平洋0~483 m深度垂直方向,除了赤道中太平洋区域海温的变化在海面为上升,在169 m处为下降,在483 m处又转为上升外,其他区域海温的变化在垂直方向基本上为线性变化。在全球增暖的背景下,虽然El Niño现象在20世纪90年代以后表现出增强的趋势,但是反映在赤道表面以下的次表层西太平洋暖池中的异常暖中心,在由西向东移动过程中其强度却是减弱的。     

Comparison of the response of Atlantic cod (Gadus morhua) in the high-latitude regions of the North Atlantic during the warm periods of the 1920s–1960s and the 1990s–2000s

Concern about future anthropogenic warming has lead to demands for information on what might happen to fish and fisheries under various climate-change scenarios. One suggestion has been to use past events as a proxy for what will happen in the future. In this paper a comparison between the responses of Atlantic cod (Gadus morhua) to two major warm periods in the North Atlantic during the 20th century is carried out to determine how reliable the past might be as a predictor of the future. The first warm period began during the 1920s, remained relatively warm through the 1960s, and was limited primarily to the northern regions (>60°N). The second warm period, which again covered the northern regions but also extended farther south (30°N), began in the 1990s and has continued into the present century. During the earlier warm period, the most northern of the cod stocks (West Greenland, Icelandic, and Northeast Arctic cod in the Barents Sea) increased in abundance, individual growth was high, recruitment was strong, and their distribution spread northward. Available plankton data suggest that these cod responses were driven by bottom-up processes. Fishing pressure increased during this period of high cod abundance and the northern cod stocks began to decline, as early as the 1950s in the Barents Sea but during the 1960s elsewhere. Individual growth declined as temperatures cooled and the cod distributions retracted southward. During the warming in the 1990s, the spawning stock biomass of cod in the Barents Sea again increased, recruitment rose, and the stock spread northward, but the individual growth did not improve significantly. Cod off West Greenland also have shown signs of improving recruitment and increasing biomass, albeit they are still very low in comparison to the earlier warming period. The abundance of Icelandic cod, on the other hand, has remained low through the recent warm period and spawning stock biomass and total biomass are at levels near the lowest on record. The different responses of cod to the two warm events, in particular the reduced cod production during the recent warm period, are attributed to the effects of intense fishing pressure and possibly related ecosystem changes. The implications of the results of the comparisons on the development of cod scenarios under future climate change are addressed.     

Morphological evolution of a large sand bar in the Qiantang River Estuary of China since the 1960s

A large sand bar develops in the inner Qiantang River Estuary, China. It is a unique sedimentary system,elongating landwards by about 130 km. Based on long-term series of bathymetric data in each April, July, and November since the 1960 s, this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP) implemented in the last decades. The results show that three timescales, namely the seasonal, interannual a...     

The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).     

The seasonal growth of ice in the Antarctic

Composite pictures of the areal extent of Antarctic sea ice derived from satellite photographs, show that the growth and the rate of growth of the pack ice compare favorably to the values previously estimated on other bases. Anomalous growth patterns are found in the Weddell Sea. Possible causes of this anomaly include surface and subsurface advection of ice crystals. The rate of retrogradation of the pack ice is found to exceed the rate of progradation.     

The seasonal succession of zooplankton in the Southern Ocean south of Australia,part I: The seasonal ice zone

Between November 2001 and March 2002 an Australian/Japanese collaborative study completed six passes of a transect line in the Seasonal-Ice Zone (south of 62°S) along 140°E. Zooplankton samples were collected with a NORPAC net on 22–28 November, and a Continuous Plankton Recorder on 10–15 January, 11–12 February, 19–22 February, 25–26 February, and 10–11 March. Zooplankton densities were lowest on 22–28 November (ave=61 individuals (ind) m⁻³), when almost the entire transect was covered by sea ice. By 10–15 January sea surface temperature had increased by ∼2 °C across the transect line, and the study area was ice-free. Total zooplankton abundance had increased to maximum levels for the season (ave=1301 ind m⁻³; max=1979 ind m⁻³), dominated by a “Peak Community” comprising Oithona similis, Ctenocalanus citer, Clausocalanus laticeps, foraminiferans, Limacina spp., appendicularians, Rhincalanus gigas and large calanoid copepodites (C1–3). Total densities declined on each subsequent transect, returning to an average of 169 ind m⁻³ on 10–11 March. The seasonal density decline was due to the decline in densities of “Peak Community” taxa, but coincided with the rise of Euphausia superba larvae into the surface waters, increased densities of Salpa thompsoni, and an increased contribution of C4 to adult stages to the populations of Calanoides acutus, Calanus propinquus and Calanus simillimus. The seasonal community succession appeared to be influenced by the low sea ice extent and southward projection of the ACC in this region. The relatively warm ACC waters, together with low krill biomass, favoured high densities of small grazers during the January/February bloom conditions. The persistence of relatively warm surface waters in March and the seasonal decrease in chlorophyll a biomass provided favorable conditions for salps, which were able to penetrate south of the Southern Boundary.     

North Pacific Tropical Water: its climatology and temporal changes associated with the climate regime shift in the 1970s

North Pacific Tropical Water (NPTW) is characterized as a subsurface salinity maximum flowing in the North Equatorial Current and is the main source of salt for the North Pacific. We briefly describe the climatological features of its formation and circulation, and then examine temporal changes in its properties associated with the climate regime shift in the 1970s. We use a variety of data, which include the repeat hydrographic sections along 130°E, 137°E, 144°E and 155°E meridians, the hydrographic data from the Hawaii Ocean Time-series, the World Ocean Atlas 1994, and available gridded data of wind stress and evaporation. The classical idea that NPTW originates from the zone of the highest sea surface salinity at 20°–30°N centered around the international date line and spreads along the isopycnal geostrophic flow patterns is confirmed. Further, it is shown that the meridional extent of NPTW along 137°E is from 10°N to 23°N on average and the highest salinity core lies at about 15°N and 24.0σ_θ, and that the portion of NPTW north (south) of about 15°N originates from the formation region west (east) of the date line. NPTW in the 137°E section changed remarkably associated with the mid-1970s regime shift. North of 15°N NPTW increased both in its salinity and thickness while to the south of 15°N only its salinity increased and its thickness remained unchanged. The westward geostrophic velocity is increased significantly in both the southern and northern parts of NPTW. The northern thickening and speedup and the southern speedup increased NPTW transport across 137°E. The changes in the thermohaline forcing such as evaporation and Ekman salt convergence in the NPTW formation region possibly contributed to the increases in salinity in the southern part of NPTW, but not to that of the northern part. On the other hand, the increased Ekman pumping accounts for the increase of the NPTW inventory and transport at 137°E. The increased salinity of NPTW at 137°E, especially its northern portion, was presumably caused by an increase in its formation rate rather than changes in the sea surface salinity in its formation region; the thicker the NPTW layer is, the saltier is the core that tends to survive the mixing processes.     

菲律宾海温跃层的区域性特征及其季节性变化

由于<海洋调查规范>规定的中国近海温跃层计算标准不适用于菲律宾海,本文通过统计分析得出了更合理的计算标准,并应用WOA01数据集对菲律宾海的温跃层进行了计算,得到了主温跃层和季节性跃层特征值的区域性分布和季节性变化.菲律宾海温跃层结构可分为热带型、亚热带型和温带型三个区域类型以及冬季和夏季两种季节性模态,总结了各种类型的典型剖面结构和特征值.应用Argo数据对WOA01数据的计算结果进行了验证,给出了各类型温跃层特征值的误差量级.     

Changes in the epibenthos of Saldanha Bay,South Africa,between the 1960s and 2001: an analysis based on dredge samples

Saldanha Bay, which lies on the south-west coast of South Africa, has undergone major development over the past 30 years, including breakwater and harbour construction, harbour extension, dredging, mining, fishing, fish processing and mussel culture. This study examines whether the benthic macrofaunal communities in the bay have been altered over this period. Twelve stations that had been sampled in the 1960s, prior to harbour construction, were re-sampled in 2001 (40 years later) with a surface dredge. Species abundances were coded from 1 (present) to 5 (abundant) to make the two sets of samples comparable. The benthic communities before harbour development were significantly different from those in 2001 (ANOSIM, p < 0.001). Increases in the abundances of the whelk Nassarius speciosus and the crab Hymenosoma orbiculare were mainly responsible for these differences. Two main benthic communities were recognised in the 1960s and, at that stage, covered large extents of the bay, whereas in 2001 the communities were divided into distinct 'Small Bay' and 'Big Bay' groups, reflecting the division of the bay into two areas by the development of a harbour wall. Although natural fluctuations may account for some of these changes, it is more likely that the considerable anthropogenic activities within Saldanha Bay, which are known to have altered physical conditions, have led to the changes observed in the benthic communities.     

The regime shift of the 1920s and 1930s in the North Atlantic

During the 1920s and 1930s, there was a dramatic warming of the northern North Atlantic Ocean. Warmer-than-normal sea temperatures, reduced sea ice conditions and enhanced Atlantic inflow in northern regions continued through to the 1950s and 1960s, with the timing of the decline to colder temperatures varying with location. Ecosystem changes associated with the warm period included a general northward movement of fish. Boreal species of fish such as cod, haddock and herring expanded farther north while colder-water species such as capelin and polar cod retreated northward. The maximum recorded movement involved cod, which spread approximately 1200 km northward along West Greenland. Migration patterns of “warmer water” species also changed with earlier arrivals and later departures. New spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased. Some southern species of fish that were unknown in northern areas prior to the warming event became occasional, and in some cases, frequent visitors. Higher recruitment and growth led to increased biomass of important commercial species such as cod and herring in many regions of the northern North Atlantic. Benthos associated with Atlantic waters spread northward off Western Svalbard and eastward into the eastern Barents Sea. Based on increased phytoplankton and zooplankton production in several areas, it is argued that bottom-up processes were the primary cause of these changes. The warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the North Atlantic in the 20th century.     

南大洋凯尔盖朗海台区的流场结构及季节变化

利用冰-海耦合等密面模式模拟了南大洋凯尔盖朗海台区的环流及其季节变化.对模拟结果的分析表明,该海区的南极绕极流具有非常显着的条带状分布和非纬向性特征.南极绕极流流经凯尔盖朗海台时,在海台的南部、中部和北部表现出不同的形式,其南部的一个分支贴近南极大陆,与西向的陆坡流之间有强的相互作用.海台以北的南极绕极流的变化以年周期为主,海台以南的变化以半年周期为主,其时间变化规律与这里的风应力的变化规律是一致的.