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1.
Effects of cold eddy on phytoplankton production and assemblages in Luzon strait bordering the South China Sea 总被引：6，自引：0，他引：6
Yuh-Ling Lee Chen Houng-Yung Chen I. -I. Lin Ming-An Lee Jeng Chang 《Journal of Oceanography》2007,63(4):671-683
The biochemical effects of a cold-core eddy that was shed from the Kuroshio Current at the Luzon Strait bordering the South
China Sea (SCS) were studied in late spring, a relatively unproductive season in the SCS. The extent of the eddy was determined
by time-series images of SeaWiFS ocean color, AVHRR sea surface temperature, and TOPEX/Jason-1 sea surface height anomaly.
Nutrient budgets, nitrate-based new production, primary production, and phytoplankton assemblages were compared between the
eddy and its surrounding Kuroshio and SCS waters. The enhanced productivity in the eddy was comparable to wintertime productivity
in the SCS basin, which is supported by upwelled subsurface nitrate under the prevailing Northeastern Monsoon. There were
more Synechococcus, pico-eucaryotes, and diatoms, but less Trichodesmium in the surface water inside the eddy than outside. Prochlorococcus and Richelia intracellularis showed no spatial differences. Water column-integrated primary production (IPP) inside the eddy was 2–3 times that outside
the eddy in the SCS (1.09 vs. 0.59 g C m−2d−1), as was nitrate-based new production (INP) (0.67 vs. 0.25 g C m−2d−1). INP in the eddy was 6 times that in the Kuroshio (0.12 g C m−2d−1). IPP and INP in the eddy were higher than the maximum production values ever measured in the SCS basin. Surface chlorophyll
a concentration (0.40 mg m−3) in the eddy equaled the maximum concentration registered for the SCS basin and was higher than the wintertime average (0.29
± 0.04 mg m−3). INP was 3.5 times as great and IPP was doubled in the eddy compared to the wintertime SCS basin. As cold core eddies form
intermittently all year round as the Kuroshio invades the SCS, their effects on phytoplankton productivity and assemblages
are likely to have important influences on the biogeochemical cycle of the region. 相似文献
2.
Variations in the abundance and distribution of pelagic tuna populations have been associated with large-scale climate indices such as the Southern Oscillation Index in the Pacific Ocean and the North Atlantic Oscillation in the Atlantic Ocean. Similarly to the Pacific and Atlantic, variability in the distribution and catch rates of tuna species have also been observed in association with the Indian Ocean Dipole (IOD), a basin-scale pattern of sea surface and subsurface temperatures that affect climate in the Indian Ocean. The environmental processes associated with the IOD that drive variability in tuna populations, however, are largely unexplored. To better understand these processes, we investigated longline catch rates of yellowfin tuna and their distributions in the western Indian Ocean in relation to IOD events, sea surface water temperatures (SST) and estimates of net primary productivity (NPP). Catch per unit effort (CPUE) was observed to be negatively correlated to the IOD with a periodicity centred around 4 years. During positive IOD events, SSTs were relatively higher, NPP was lower, CPUE decreased and catch distributions were restricted to the northern and western margins of the western Indian Ocean. During negative IOD events, lower SSTs and higher NPP were associated with increasing CPUE, particularly in the Arabian Sea and seas surrounding Madagascar, and catches expanded into central regions of the western Indian Ocean. These findings provide preliminary insights into some of the key environmental features driving the distribution of yellowfin tuna in the western Indian Ocean and associated variability in fisheries catches. 相似文献
3.
Jian-Wei Li Paulo Vasconcelos Wei Zhang Xiao-Dong Deng Nurdan Duzgoren-Aydin Dai-Rong Yan Jian-Qiang Zhang Ming-An Hu 《Mineralium Deposita》2007,42(4):361-383
Supergene Mn-oxide deposits are widely distributed in Guangxi, Guangdong, Yunnan, and Hunan Provinces, South China, accounting
for 18% of the total Mn reserves in the country. Direct dating of supergene Mn enrichment, however, is lacking. In this paper,
we present high-resolution 40Ar/39Ar ages of Mn oxides from the Xinrong Mn deposit, western Guangdong, to place numerical constraints on the timing and duration
of supergene Mn enrichment. A total of ten cryptomelane samples, spanning a vertical extent of 67 m, were dated using the
40Ar/39Ar laser incremental heating technique, with seven samples yielding well-defined plateau or pseudo-plateau ages ranging from
23.48 ± 0.91 to 2.06 ± 0.05 Ma (2σ). One sample yields a staircase spectrum that does not reach a plateau; the spectrum, however, indicates the presence of
two or more generations of Mn oxides in the sample, whose ages are best estimated at 22.34 ± 0.31 and 10.2 ± 0.86 Ma, respectively.
The remaining two samples gave meaningless or uninterpretable results due to significant 39Ar recoil and contamination by old phases. The 40Ar/39Ar data thus reveal a protracted history of weathering and supergene Mn enrichment that started at least in the end of the
Oligocene or beginning of Miocene and extending into the latest Pliocene. Staircase-apparent age spectra, resulting from banded
or botryoidal samples, yield an average growth rate of Mn oxides at 0.6–0.7 × 10−3 mm kyr−1. The values indicate that a 1-mm grain of Mn oxides may host minerals precipitated during a time span of ca. 1.5 m.y., and
accumulation of Mn oxides to form economic deposits under weathering environments may take millions of years. The distribution
of weathering ages shows that the oldest Mn oxides occur on the top of the profile, whereas the youngest minerals are found
at the bottom, suggesting downward propagation of weathering fronts. However, two samples located at the intermediate depths
of the profile yield ages comparable with those occurring at the highest elevations. Such a complexity of age distribution
is interpreted in terms of preferential penetration of Mn-rich weathering solutions along more permeable fault zones, or as
a result of multi stages of dissolution and re-precipitation of Mn oxides. A synthesis of geochronological and geological
data suggests that formation of the Xinrong deposit was a consequence of a combination of favorable lithological, climatic,
and structural conditions. Because the climatic and structural conditions are similar among the provinces of South China during
the Cenozoic, the geochronological results obtained at Xinrong may also have implications for the timing of supergene Mn enrichment
throughout South China. 相似文献
4.
庐枞盆地浅表地壳速度成像与隐伏矿靶区预测 总被引：4，自引：2，他引：2
利用反射地震初至波可以精确反演地壳速度结构和构造信息.对庐枞盆地采集的高分辨地震数据,运用初至波层析成像方法,反演得到了该区1200 m以上的浅表地壳速度结构信息.找矿信息总是同地球化学异常联系紧密,对采集于炮孔深处的岩屑、泥砂样品进行了地球化学分析,发现了多处显著的金属元素异常.对五条测线的速度成像结果及其映射的地下岩性结构和炮孔地球化学分析结果进行了相关性对比分析.结果显示,庐枞盆地的沉积岩、火山岩和侵入岩具有不同的速度范围,侵入岩具有高波速特征,地球化学信息高异常往往出现在高速侵入岩体的上方;精细的速度信息蕴含着丰富的浅表地壳结构变化特征,与庐枞矿集区已知的地质、岩体、构造和矿体分布存在着良好的对应关系.速度成像结果可以准确刻画地下隐伏侵入岩体的空间分布形态,结合地球化学分析异常和重磁探测等信息,预测隐伏矿床,提供深部找矿靶区. 相似文献
5.
基于重力异常分离方法寻找深部隐伏铁矿 ——以安徽泥河铁矿为例 总被引：5，自引：4，他引：1
重力异常是地下不同规模、不同形态和不同埋深的不均匀地质体的综合响应,重力勘探主要通过从重力异常中提取感兴趣的局部异常,以便探测深部结构,寻找隐伏矿床.为探讨重力异常分离原则并检验方法效果,本文从各方法原理入手,加上模型试验以及在安徽省泥河矿区深部隐伏铁矿的探寻实践检验,阐明:趋势分析法是整体拟合不同于最小二乘圆滑的局部拟合,由于是多项式拟合区域场,趋势分析法不适宜范围大、地质情况复杂的测区;插值切割法以计算点场值与四点圆周平均值的插值运算为切割算子,通过连续切割,得到重力异常的切割区域场和局部场,插值切割法对于小测区单个异常的分离效果较好,切割次数选择1到2次即可;匹配滤波法通过分析实测异常功率谱曲线、选择合适的滤波段、建造适宜的低通和带通滤波器进行滤波,从而提取不同波数成分的异常场,匹配滤波更适合垂向叠加的异常分离;解析延拓是根据一个面上的一组位场数据确定另一个不同高度面上位场值,应用中要把握延拓高度;垂向二阶导数法可以起到突出浅源异常,区分水平叠加异常,确定异常体的边界,消除或削弱背景场的作用.通过安徽泥河铁矿重力异常分离实验,发现三阶趋势分析、向上延拓以及插值切割法能很好地分离出矿体异常和背景场,同时发现在泥河矿区东南部和东北部还存在剩余重力异常,可为泥河铁矿扩大规模提供新的线索. 相似文献
6.
Typhoons can cause substantial sea surface cooling (typically 2–4 °C), which is usually biased to the right side of the storm track. Under influence of the complex bathymetry of the southern Taiwan Strait (TS), two types of sea surface temperature (SST) response, cooling and warming, each associated with a different type of typhoon track were identified using satellite and mooring observations. When a typhoon moved westward (or northwestward) and passed through the TS (track A), the SST cooling in the TS was biased toward the left of the storm track. Numerical model results indicated that in track A, strong wind stress accelerates the flow east of the Taiwan Banks and drove the bottom flow to uplift due to the topography. Moreover, both wind stress and wind stress curl enhanced the Luzon loop. After the typhoon passed, the mean circulation was modified around strong cooling in the southern TS, causing more South China Sea surface water to be distributed to the Kuroshio region. However, when a typhoon moved westward (or northwestward) and passed south of the TS, SST warming was induced in the southern TS (track B). The model results indicated that when the typhoon passed to the south of the TS, the typhoon-induced horizontal divergent flow travelled to the north, where it encountered the shallower shelf of the TS that was confined to the water, causing warm water transported into this area to accumulate and downwelling to occur. This can be regarded as redistributing the heat content in the shelf area. After the typhoon, the thickened mixed layer resulting from downwelling prevented the formation of near-inertial waves and reduced the vertical mixing. 相似文献
7.
Kuo-Wei Lan Ming-An Lee Chang Ik Zhang Pei-Yuan Wang Long-Jing Wu Kuo-Tien Lee 《Climatic change》2014,126(1-2):189-202
Grey mullet (Mugil cephalus L.) is one of the most important commercial species of fish in the coastal fisheries of Taiwan. In this study, we analyzed the long-term (1967–2009) records of grey mullet catch per unit effort (CPUE) in the Taiwan Strait (TS) to investigate the influences of climatic indices on the annual catch of grey mullet at multiple timescales. A wavelet analysis revealed that variations in climatic indices, namely the Pacific Decadal Oscillation (PDO), the Oceanic Niño Index, and sea surface temperatures (SSTs) might have affected the abundance and migration behavior of grey mullet in the TS in winter. The CPUE of grey mullet showed significant high correspondence with the annual PDO index (R 2?=0.82, p?<0.01). The results suggested that the PDO affects the migration of grey mullet, but that increases in SSTs are a more important influence on the decreased catches of grey mullet after 1980. Mean SSTs increased 1.01 °C at the Chang-Yuen Rise in the TS from 1984 to 2009. The 20 °C isotherms in the TS in the winter also shifted from 23–24°N in 1958–1978 to north of 25°N after 1998. The fishing grounds of grey mullet also shifted to the north following changes in the 20 °C isotherm in the TS. 相似文献
8.
为研究AMT数据的"死频带"畸变特征及其校正方法,在长江中下游地区,利用凤凰MTU-5A仪器,系统观测了音频电磁场的"死频带"数据.对不同季节、不同时段的AMT"死频带"数据进行了分析.提出AMT"死频带"频率域畸变数据的Rhoplus校正方法,给出了该方法的适用条件、关键技术与评价方案,并提供了大量实测数据论证其应用效果.观测实验表明:在"死频带"内天然音频电磁场信号强度极低,正交电磁场分量相干度极低;造成了阻抗视电阻率、相位及相位张量等数据的畸变;畸变范围可达10k~100Hz,以5~1kHz频段最为明显;并且数据畸变程度与观测时段密切相关,在长江中下游地区为秋冬季畸变强夏季弱,日间畸变强夜间弱.处理实例表明:Rhoplus校正方法可以有效地处理AMT"死频带"内畸变的视电阻率、相位数据,相干度阈值与人机交互相结合的处理策略快速客观,所得结果曲线光滑连续,数据与实测未畸变数据基本一致. 相似文献
9.
Tuvia Turkeltaub Matthew. J. Ascott Daren C. Gooddy Xiaoxu Jia Ming-An Shao Andrew Binley 《水文研究》2020,34(15):3347-3357
Extensive nitrogen loads at the soil surface exceed plant uptake and soil biochemical capacity, and therefore lead to nitrogen accumulation in the deep vadose zone. Studies have shown that stored nitrogen in the vadose zone can eventually reach the water table and affect the quality of groundwater resources. Recently, global scale models have been implemented to quantify nitrate storage and nitrate travel time in the vadose zone. These global models are simplistic and relatively easy to implement and therefore facilitate analysis of the considered transport processes at a regional scale with no further requirements. However, the suitability of applying these models at a regional scale has not been tested. Here, we evaluate, for the first time, the performance and utility of global scale models at the regional scale. Applied to the Loess Plateau of China, we compare estimates of groundwater recharge and nitrate storage derived from global scale models with results from a regional scale approach utilizing the Richards and advection-dispersion equations. The estimated nitrate storage was compared to nitrate observations collected in the deep vadose zone (>50 m) at five sites across the Loess Plateau. Although both models predict similar spatial patterns of nitrate storage, the recharge fluxes were three times smaller and the nitrate storage was two times higher compared with the regional model. The results suggest that global scale models are a potentially useful screening tool, but require refinement for local scale applications. 相似文献
10.