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We explore the horizontal stirring of a passive tracer field in the vicinity of an isolated, finite amplitude, quasigeostrophic, β-plane eddy. We consider stirring in the presence of a uniform background gradient of tracer concentration as well as cases in which the tracer anomaly is initially contained within the eddy.This paper reports a survey of phenomenology based upon numerical experiments. We explore the sensitivity of results to physical parameters and to various aspects of the numerical simulation.Under the joint effects of β and of non-linearity, the eddy center migrates. Time dependent effects in a radiated wake provide important stirring mechanisms for the background tracer field. An unexpected, persistent result is a tendency to propel a tendril of tracer westward from near the launch latitude of the eddy. In some cases, the westward penetration of the tendril is even further than the migration of the eddy center.Tracer properties characteristics of the launch site of the eddy tend to be captured and carried with the eddy. However, tracer leaks from the eddy, due to both explicit diffusion-like effects and eddy interaction with background flow features, can result in drawing off of secondary tracer patches.We also calculate trajectories of Lagrangian particles launched in and around the eddy. 相似文献
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C. Hillaire-Marcel J. Riser P. Rognon N. Petit-Maire J.C. Rosso I. Soulie-Marche 《Quaternary Research》1983,20(2):145-164
A detailed chronology of hydrological changes that occurred in northeastern Mali during the Holocene is based on approximately 30 14C dates of molluscs which were collected from the lacustrine and paludal deposits of the Ine Sakane sand sea. The presence of cemented paleodunes indicates that the end of the Pleistocene was and arid period. This was followed by an early Holocene lacustrine episode (ca. 9500–6500 yr B.P.) during which numerous lakes occupied depressions formed in the Cretaceous limestones and between the sand ridges. These lakes reflect a significant rise in the water table. Between ca. 6500 and 5500 yr B.P. the lakes dried up, although the water table remained close to the ground surface in several areas. Calcareous concretions formed at the water table fringe during this time, thereby “fossilizing” some of the middle Holocene dunes. A second lacustrine episode is dated between ca. 5500 and 4500 yr B.P.; it corresponds to the establishment of numerous Neolithic settlements in the area. Arid conditions have developed since about 4500 yr B.P. to attain the conditions of the present day. The isotopic composition (18O and 13C) of the fauna reflects highly variable hydrological conditions. Groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen (δ18O ? ?13%.). Evaporation induced an enrichment in 18O; high concentrations characterize some lakes. The 13C content of fossil shells reflect: (1) species ecological requirements, (2) isotopic composition of the total inorganic dissolved carbon (TIDC) in groundwaters, and (3) the lake metabolism. 相似文献
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Hu Dunxin Wang Fan Sprintall Janet Wu Lixin Riser Stephen Cravatte Sophie Gordon Arnold Zhang Linlin Chen Dake Zhou Hui Ando Kentaro Wang Jianing Lee Jae-Hak Hu Shijian Wang Jing Zhang Dongxiao Feng Junqiao Liu Lingling Villanoy Cesar Kaluwin Chalapan Qu Tangdong Ma Yixin 《中国海洋湖沼学报》2020,38(4):906-929
The Western Tropical Pacific(WTP) Ocean holds the largest area of warm water(28℃) in the world ocean referred to as the Western Pacific Warm Pool(WPWP),which modulates the regional and global climate through strong atmospheric convection and its variability.The WTP is unique in terms of its complex 3-D ocean circulation system and intensive multiscale variability,making it crucial in the water and energy cycle of the global ocean.Great advances have been made in understanding the complexity of the WTP ocean circulation and associated climate impact by the international scientific community since the 1960 s through field experiments.In this study,we review the evolving insight to the 3-D structure and multi-scale variability of the ocean circulation in the WTP and their climatic impacts based on in-situ ocean observations in the past decades,with emphasis on the achievements since 2000.The challenges and open que stions remaining are reviewed as well as future plan for international study of the WTP ocean circulation and climate. 相似文献
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Circulation and Mixing of Water Masses of Tatar Strait and the Northwestern Boundary Region of the Japan Sea 总被引：2，自引：0，他引：2
The deep waters of the northern portions of the Japan Sea are examined. It is found that the flow regime south of the southern
Tatar Strait region is generally cyclonic in the upper ocean, with only weak flows present below depths of a few hundred meters.
The Japan Sea appears to be remarkably well-mixed below depths of a few hundred meters, both horizontally and vertically.
Based on chlorofluorocarbon measurements, it is concluded that the deep waters of the Japan Sea have been only weakly ventilated
in recent decades. Results from a simple box model suggest two possible scenarios for the ventilation of the Japan Sea since
the 1930s. In the first scenario, deep ventilation of the Japan Sea was relatively weak, but constant, from the 1930s to the
present, with a deep-water residence time of approximately 500 years. In the second scenario, ventilation was relatively vigorous
through the mid-1960s, with a deep-water residence time of approximately 100 years; after the mid-1960s, the ventilation of
the deep waters stopped. The model results are consistent with the idea that presently the ventilation of the deep water of
the Japan Sea is weak or nonexistent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Kalle Olli Christian Wexels Riser Paul Wassmann Tatjana Ratkova Elena Arashkevich Anna Pasternak 《Progress in Oceanography》2001,51(2-4)
Lagrangian experiments with short-term, drifting sediment traps were conducted during a cruise on RRS Charles Darwin to the NW coast of Spain to study the vertical flux and composition of settling biogenic matter. The cruise was split into two legs corresponding to (i) a period of increased production following an upwelling event on the continental shelf (3–10 August 1998) and (ii) an evolution of a cold water filament originating from the upwelled water off the shelf (14–19 August). The export of particulate organic carbon (POC) from the upper layer (0–60m) on the shelf was 90–240mgC.m−2.d−1 and off the shelf was 60–180mgC.m−2.d−1. Off shelf the POC flux at 200m was 50–60mg.m−2.d−1. A modest sedimentation of diatoms (15–30mgC.m−2.d−1) after the upwelling was associated with increased vertical flux of chlorophyll a (1.8–2.1mg.m−2.d−1) and a decrease of the POC:PON molar ratio of the settled material from 9 to 6.4. Most of the pico-, nano-, and microplankton in the settled material were flagellates; diatoms were significant during the on shelf and dinoflagellates during the off shelf leg. Off shelf, the exponential attenuation of POC flux indicated a strong retention capacity of the plankton community between 40 and 75m. POC:PON ratio of the settled particulate matter decreased with depth and the relative portion of flagellates increased, suggesting a novel, flagellate and aggregate mediated particulate flux in these waters. Export of POC from the euphotic layer comprised 14–26% of the integrated primary production per day during the on shelf leg and 25–42% during the off shelf leg, which characterises the importance of sedimentation in the organic carbon budget of these waters. 相似文献
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Production, retention and export of zooplankton faecal pellets on and off the Iberian shelf, north-west Spain 总被引：1，自引：0，他引：1
Christian Wexels Riser Paul Wassmann Kalle Olli Elena Arashkevich 《Progress in Oceanography》2001,51(2-4)
Vertical distribution of faecal pellets (FP), their sedimentation and the production rates of FP by mesozooplankton were studied during a cruise on and off the Iberian shelf in August 1998. The cruise was divided into two legs, each of them a short-term Lagrangian drift experiment. FP were collected with water bottles, with drifting sediment traps and during experiments carried out onboard the ship. The pellets were enumerated and their biovolumes and carbon contents (FPC) were calculated.The standing stock of FP in the upper 50 m was on average three times higher during the first on-shelf experiment than during the second off-shelf experiment. There were large diurnal variations, but no clear pattern emerged between day and night sampling. The vertical export of FPC from the upper, productive layer was on average one order of magnitude greater on the shelf (range 6–160 mg.m−2.d−1) compared to the off-shelf experiment (range 1–30 mg.m−2.d−1). FPC sedimentation explained 20% of the total POC export from the euphotic layer on the shelf, but <5% off the shelf. FP sedimentation was dominated by medium-sized cylindrical pellets (40–60 μm in diameter), but larger cylindrical pellets (60–100 μm in diameter) also played an important role. The smaller FP size fractions were never of any significance, in spite of the high abundance of smaller calanoid and cyclopoid copepods. The community production of FPs by mesozooplankton were calculated for the off shelf stations, and the average retention potential of FP in the upper 200 m was estimated to be 98%. Thus retention processes are clearly important for cross-shelf advection of FPs, their injection into the deep ocean and in the regulation of pelagic benthic coupling. 相似文献
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