A submarine canyon conduit under typhoon conditions off Southern Taiwan     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):223-240

The function of a submarine conduit under typhoon conditions is examined. The study site is the Kao-ping river, shelf, and submarine canyon (KPRSC) system located off southern Taiwan on a wave-dominated microtidal coast. The head of the canyon is located approximately 1 km off the river mouth. Two comprehensive 1-month field experiments were carried out in 2000 and 2002 during the flood season of the river. Both experiments encountered typhoons that generated significant river discharge and wave resuspension events. Particle samples collected in 2000 by sediment-traps were analyzed for coarse fraction by the wet sieving method. Among the coarse fraction, foraminiferal species and their abundance were recorded as a tracer for biogenic particles of marine origin. Stable isotopes of carbon (δ¹³C) of organic particles of sediment-trap samples were analyzed as a tracer for particles of terrestrial origin. All the measured flow and particle concentration records were analyzed by conventional time-series analytical methods. Simultaneously observed records of suspended sediment concentration at the river mouth and the volume concentration of suspended particles near the canyon floor were compared. Instantaneous flux and cumulative transport of suspended particles near the canyon floor were estimated during the deployment period. Results show that Kao-ping Submarine Canyon is a multi-level and process-dependant two-way conduit for particles of terrestrial and marine origins. In general, terrestrial signals are stronger than the marine signals in sediment-trap samples near the head of the canyon. During typhoon events, in the early distal phase of their influence nonlithogenic and biogenic marine sources are enhanced; in the later proximal phase signals of locally generated terrestrial lithogenic sources are enhanced. An episode of momentary downcanyon flushing of suspended particles near the canyon floor is observed during one typhoon occurrence. This flushing suggests nondeposition during the typhoon at the locale of deployment despite increased input of particles to the canyon floor. It also suggests a mechanism by which turbidity currents could be triggered. Yet, this flushing phenomenon is not observed in another typhoon occurrence, suggesting it is not universal in the canyon's response to the typhoon.  相似文献   

Seasonal and annual variations of marine sinking particulate flux during 1993~1996 in the central South China Sea   总被引：1，自引：0，他引：1  

CHEN Ronghu  WIESNER M G  ZHENG Yulong  CHENG Xinrong  JIN Haiyan  ZHAO Qingying  ZHENG Lianfu 《海洋学报(英文版)》2007,26(3):33-43

A total of 67 samples from the upper and lower sediment traps in the central South China Sea were analyzed, which were collected during 1993~1996. It is indicated that the distribution of stable isotope values, surface primary productivity, fluxes of total particulate matter, carbonate, biogenic opal, organic carbon, planktonic foraminiferal species and their total amount exhibit obviously seasonal and annual fluctuations. High values of the fluxes occurred in the prevailing periods of the northeastern and southwestern monsoons, and the low values occurred during the periods between the two monsoons. The fluxes of some planktonic foraminiferal species (Globigerinoides sacculifer, G. ruber, Globigerinita glutinata, Neogloboquadrina dutertrei) and their percentages also exhibit two prominent peaks during the prevailing periods of the northeastern and southwestern monsoons respectively, while those of Globigerina bulloides, Globorotalia menardii and Pulleniatina obliquiloculata only exhibit one peak in the prevailing periods of the northeastern monsoon. In addition, fluxes and percentages of Globigerinoides sacculifer and Globorotalia menardii as well as the fluxes of carbonate and total amount of planktonic foraminifera decrease gradually from 1993 to 1996, and those of Globigerina bulloides, Globigerinita glutinata and biogenic opal increase gradually from 1993 to 1996. The fluxes of carbonate and organic carbon in the upper trap are higher than those in the lower one. The study indicates that the seasonal and annual variations of the sediment fluxes and planktonic foraminiferal species are mainly controlled by the changes of surface primary productivity and hydrological conditions related to the East Asian monsoon. The lower carbonate and organic carbon fluxes in the lower trap are related to the dissolution.  相似文献   

Roles of Continental Shelves and Marginal Seas in the Biogeochemical Cycles of the North Pacific Ocean   总被引：4，自引：0，他引：4  

Chen-Tung Arthur Chen  Andrey Andreev  Kyung-Ryul Kim  Michiyo Yamamoto 《Journal of Oceanography》2004,60(1):17-44

Most marginal seas in the North Pacific are fed by nutrients supported mainly by upwelling and many are undersaturated with respect to atmospheric CO₂ in the surface water mainly as a result of the biological pump and winter cooling. These seas absorb CO₂ at an average rate of 1.1 ± 0.3 mol C m⁻²yr⁻¹ but release N₂/N₂O at an average rate of 0.07 ± 0.03 mol N m⁻²yr⁻¹. Most of primary production, however, is regenerated on the shelves, and only less than 15% is transported to the open oceans as dissolved and particulate organic carbon (POC) with a small amount of POC deposited in the sediments. It is estimated that seawater in the marginal seas in the North Pacific alone may have taken up 1.6 ± 0.3 Gt (10¹⁵ g) of excess carbon, including 0.21 ± 0.05 Gt for the Bering Sea, 0.18 ± 0.08 Gt for the Okhotsk Sea; 0.31 ± 0.05 Gt for the Japan/East Sea; 0.07 ± 0.02 Gt for the East China and Yellow Seas; 0.80 ± 0.15 Gt for the South China Sea; and 0.015 ± 0.005 Gt for the Gulf of California. More importantly, high latitude marginal seas such as the Bering and Okhotsk Seas may act as conveyer belts in exporting 0.1 ± 0.08 Gt C anthropogenic, excess CO₂ into the North Pacific Intermediate Water per year. The upward migration of calcite and aragonite saturation horizons due to the penetration of excess CO₂ may also make the shelf deposits on the Bering and Okhotsk Seas more susceptible to dissolution, which would then neutralize excess CO₂ in the near future. Further, because most nutrients come from upwelling, increased water consumption on land and damming of major rivers may reduce freshwater output and the buoyancy effect on the shelves. As a result, upwelling, nutrient input and biological productivity may all be reduced in the future. As a final note, the Japan/East Sea has started to show responses to global warming. Warmer surface layer has reduced upwelling of nutrient-rich subsurface water, resulting in a decline of spring phytoplankton biomass. Less bottom water formation because of less winter cooling may lead to the disappearance of the bottom water as early as 2040. Or else, an anoxic condition may form as early as 2200 AD. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

North Pacific Synthesis of the Joint Global Ocean Flux Study: Overview     

Toshiro Saino  Alexander Bychkov  Chen-Tung Arthur Chen  Paul J. Harrison 《Journal of Oceanography》2004,60(1):1-4

This special issue is comprised of 13 papers, including this overview, and focuses on the synthesis of the Joint Global Ocean Flux Study (JGOFS) in the North Pacific which took place from 1997 through 2003. The effort was led by the JGOFS North Pacific Synthesis Group, with the aim of quantifying CO₂ drawdown by physical and biological pumps in the North Pacific by identifying and studying the regional, seasonal to inter-annual variations in the key processes, and understanding their regulating mechanisms. Emphasis was placed on the similarities and differences of the biogeochemical regimes in the eastern and western subarctic Pacific. Effort was also made to address the future research directions which arose from the scientific findings during the North Pacific JGOFS process study. A brief overview of the papers from view points of CO₂ drawdown by physical and biological pumps, spatial variability, and temporal variability from seasonal to decadal scales is made, followed by suggestions for the directions of future research. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Coccolith distribution patterns in South Atlantic and Southern Ocean surface sediments in relation to environmental gradients     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(6):1073-1099

In this study, the coccolith compositions of 213 surface sediment samples from the South Atlantic and Southern Ocean were analysed with respect to the environmental parameters of the overlying surface waters. From this data set, the abundance patterns of the main species and their ecological affinities were ascertained. In general, Emiliania huxleyi is the most abundant species of the recent coccolith assemblages in the study region. However, the lower photic zone taxa, composed of Florisphaera profunda and Gladiolithus flabellatus often dominate the assemblages between 20°N and 30°S. If E. huxleyi is excluded, Calcidiscus leptoporus and F. profunda become the most abundant species, each dominating discrete oceanographic regimes. While F. profunda is very abundant in the sediments underneath warmer, stratified surface waters with a deep nutricline, Calcidiscus leptoporus is encountered in high-productivity environments. Furthermore, the results of a canonical correspondence analysis reveal affinities of Gephyrocapsa spp., Helicosphaera spp. and Coccolithus pelagicus for intermediate to higher nutrient conditions in a well-mixed upper water column. In contrast, Gladiolithus flabellatus seems to be associated with high temperatures and salinities under low-nutrient conditions. Based on the relative abundances of Calcidiscus leptoporus, F. profunda, Gladiolithus flabellatus, Helicosphaera spp., Umbilicosphaera foliosa, Umbilicosphaera sibogae and a group of subordinate subtropical species, six surface sediment assemblages have been identified, which reflect the distribution and characteristics of the overlying surface waters. Their distribution appears to be mainly a function of the relative position of the nutricline and thermocline in the overlying photic zone.  相似文献   

Circulation and Brackish Water Dispersal in a Coastal Lagoon of Southwest Taiwan     

Sen Jan  Shenn-Yu Chao  Jia-Jang Hung 《Journal of Oceanography》2001,57(6):647-661

Modest observations and numerical experiments were conducted to investigate circulation and brackish water dispersal in a coastal lagoon southwest of Taiwan. The Chi-Ku Lagoon, partially shielded from the sea by a string of sandbar barriers with two entrances among them, receives modest and episodic runoff from Chi-Ku Stream. Flood and ebb tidal streams entering and leaving the two entrances are found to converge and diverge in a flow stagnation area inside the lagoon. Under weak wind conditions, brackish water is preferentially retained in the flow stagnation area. Besides the observations, scenario runs using a three-dimensional numerical model also indicate strong modulation by monsoon winds. Both summer southwest monsoon and winter northeast monsoon reduce brackish water retention; the latter is found to be more effective. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Summer distribution and geochemical composition of suspended-particulate matter in the east china sea     

Jia-Jang Hung  Chia-Lin Chan  Gong-Ching Gong 《Journal of Oceanography》2007,63(2):189-202

The distribution and geochemical composition of suspended-particulate matter (SPM) in the East China Sea (ECS) were investigated during the summer period of high continental runoff to elucidate SPM sources, distribution and cross-shelf transport. The spatial variability of SPM distribution (0.3–6.5 mg l⁻¹) and geochemical composition (POC, Al, Si, Fe, Mn, Ca, Mg and K) in the ECS was pronounced during summer when the continental fluxes of freshwater and terrestrial materials were highest during the year. Under the influences of Changjiang runoff, Kuroshio intrusion, surface production and bottom resuspension, the distribution generally showed strong gradients decreasing seaward for both biogenic and lithogenic materials. Particulate organic carbon was enriched in surface water (mean ∼18%) due to the influence of biological productivity, and was diluted by resuspended and/or laterally-transported materials in bottom water (mean 9.4%). The abundance of lithogenic elements (Al, Si, Fe, Mn) increased toward the bottom, and the distribution correlations were highly significant. Particulate CaCO₃ distribution provided evidence that the SPM of the bottom water in the northern part of the study area was likely mixed with sediments originally derived from Huanghe. A distinct benthic nepheloid layer (BNL) was present in all seaward transects of the ECS shelf. Sediment resuspension may be caused by tidal fluctuation and other forcing and be regarded as the principal agent in the formation of BNL. This BNL was likely responsible for the transport of biogenic and lithogenic particles across or along the ECS shelf. Total inventories of SPM, POC and PN are 46, 2.8 and 0.4 Tg, respectively, measured over the total area of 0.45 × 10⁶ km² of the ECS shelf. Their mean residence times are about 27, 13 and 11 days, respectively. The inventory of SPM in the water column was higher in the northernmost and southernmost transects and lower in the middle transects, reflecting the influences of terrestrial inputs from Changjiang and/or resuspended materials from Huanghe deposits in the north and perhaps from Minjiang and/or Taiwan’s rivers in the south. The distribution and transport patterns of SPM and geochemical elements strongly indicate that continental sources and cross-shelf transport modulate ECS particulate matter in summer.  相似文献   

Spatial organization of food webs along habitat gradients at deep-sea hydrothermal vents on Axial Volcano,Northeast Pacific     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(4):726-739

Deep-sea hydrothermal vents are characterized by steep spatial gradients and high temporal variability in habitat conditions. This leads to the organization of species distribution along spatial habitat gradients, which may constrain food resource utilization and food web structure. We conducted a stable-isotope-based study to test the hypothesis that food resource utilization is constrained by spatial habitat variability at diffuse hydrothermal vents on Axial Volcano, Northeast Pacific. Our study included the ten most biomass-prominent species and considered the temporal change in food web structure at recently created vent sites during three consecutive years. We related species average stable isotopic composition to their position between the center and the periphery of vent sites, using previously published data. Species spread widely along the δ¹³C axis, and showed a small variability in δ¹⁵N. This indicates that most species partition food resources between isotopically different carbon sources, and that they are not organized along predator–prey trophic chains. Particulate organic matter (POM) stable isotopic composition from a concomitant study corresponds to the signature of the expected diet for most organisms. Species average δ¹³C was significantly correlated to their relative position between the center and the periphery of vent sites. We relate this spatial variability in species isotopic composition to variability in the isotopic signature of both dissolved inorganic carbon (DIC) and POM. This spatial isotopic signal of consumers reveals the spatial structuring of food (POM) production and its consumption by the fauna. Accrual of species during the development of diffuse sites increased the inter-specific spread in δ¹³C, but did not increase the range in δ¹⁵N. Our results show that the spatial organization of species distribution results in a fragmented food web where species partition POM food resources according to their position in space. Shaping of species distribution by habitat gradients therefore constrains food web structure and the occurrence of predator–prey and competitive interactions.  相似文献   

Speciation of volatile arsenic at geothermal features in Yellowstone National Park   总被引：1，自引：0，他引：1  

Britta Planer-Friedrich  Corinne Lehr  Jörg Matschullat  Darrell Kirk Nordstrom 《Geochimica et cosmochimica acta》2006,70(10):2480-2491

Geothermal features in the Yellowstone National Park contain up to several milligram per liter of aqueous arsenic. Part of this arsenic is volatilized and released into the atmosphere. Total volatile arsenic concentrations of 0.5-200 mg/m³ at the surface of the hot springs were found to exceed the previously assumed nanogram per cubic meter range of background concentrations by orders of magnitude. Speciation of the volatile arsenic was performed using solid-phase micro-extraction fibers with analysis by GC-MS. The arsenic species most frequently identified in the samples is (CH₃)₂AsCl, followed by (CH₃)₃As, (CH₃)₂AsSCH₃, and CH₃AsCl₂ in decreasing order of frequency. This report contains the first documented occurrence of chloro- and thioarsines in a natural environment. Toxicity, mobility, and degradation products are unknown.  相似文献   

Paleoclimatological and paleoenvironmental records since 4 000 a B. P. in sediments of alpine lakes in Taiwan     

Jiann-Yuh Lou  Chen-Tung Arthur Chen 《中国科学D辑(英文版)》1997,40(4):424-431

The 3 310-m-high Chia-min Lake records the climatic history since 4 ka B. P. in Taiwan. The warm/wet period before 2.2 ka B.P. seemed to correspond to the later part of the Holocene Megathermal, and the cold/dry period during 0–2.2 ka B. P. corresponded to the Katathermal. Before the termination of the Megathermal, an especially warm and humid segment (2.2–2.4 ka B. P.) emerged. The paleoclimatic records from Yuen-yang and Chi-tsai Lakes support the notion that the Megathermal in Taiwan terminated during 2—2.3 ka B. P. A warm segment (820–1 320 AD) in the Katathermal could be considered the Medieval Warm Period. The climate turned cold and dry after 1 320 AD and this indicated the onset of the Little Ice Age. These paleoclimatic variations are also in good agreement with those recorded in Great Ghost Lake.  相似文献