ENSO related variations in biogeochemistry of AA and HA in settling particles along the equatorial Pacific Ocean     

Lallan P. Gupta  Hodaka Kawahata 《Journal of Oceanography》2007,63(4):695-709

Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Niño-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Niño conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Niño were compositionally different from those settling during La Niña condition in the equatorial Pacific.  相似文献   

Spatial and temporal variability in coccolithophore abundance and production of PIC and POC in the NE subarctic Pacific during El Niño (1998), La Niña (1999) and 2000     

M.S. Lipsen  D.W. Crawford  P.J. Harrison 《Progress in Oceanography》2007,75(2):304-325

Seasonal variations in coccolithophore abundance, chlorophyll, nutrients and production of particulate organic and inorganic carbon (POC and PIC) were determined along a coastal to oceanic east-west transect (Line P) culminating at Ocean Station Papa in the northeastern subarctic Pacific between 1998 and 2000. Offshore stations generally exhibited low seasonality in chlorophyll concentrations, with moderate seasonality in POC production. Near shelf stations showed a similar pattern to offshore stations, but were also characterized by sporadic events of higher POC productivity. During the 1998 El Niño, June was characterized by low chlorophyll and POC productivity along the transect, presumably as a result of depleted surface nitrate. In contrast, during the 1999 La Niña, and in 2000, higher POC productivity and surface nitrate occurred along the transect in June. Chlorophyll and POC productivity were similar in late summer in all 3 years. The coccolithophore population was usually numerically dominated by Emiliania huxleyi, particularly in June. Along the transect, abundance of coccolithophores was much higher in June during the 1998 El Niño (mean of 221 cells ml⁻¹) than in the 1999 La Niña (mean of 40 cells ml⁻¹), with their abundance in late summers of both years being very low. Abundances were even higher along the transect in June and the late summer of 2000 with sporadic ‘blooms’ of >1000 cells ml⁻¹ at some stations (cruise averages 395 and 552 cell ml⁻¹, respectively). Production rates of PIC did not consistently correlate with areas of high coccolithophore abundance. PIC production was high (100-250 mg C m⁻² d⁻¹) along the transect during June 1998, and low (1-40 mg C m⁻² d⁻¹) during both winters, June 1999 and during late summers of 1998 and 1999. The year 2000 was more complicated, with high rates of PIC production accompanying high abundance of coccolithophores in late summer, but lower rates of PIC production accompanying high coccolithophore numbers in June. Our data suggest that the abundance of coccolithophores and the production rates of PIC in the subarctic are higher than previously thought. Occasional PIC:POC production ratios of 1 or greater in 1998 and 2000 suggest that coccolithophores in this region could have a significant impact on the efficiency of the biological carbon pump.  相似文献   

Evaluation of a method to reduce uncertainty in wind hindcasts performed with regional atmosphere models     

R. Weisse  F. Feser 《Coastal Engineering》2003,48(4):211-225

For more and more applications in coastal and offshore engineering, numerical simulations of waves and surges are required. An important input parameter for such simulations are wind fields. They represent one of the major sources for uncertainties in wave and surge simulations. Wind fields for such simulations are frequently obtained from numerical hindcasts with regional atmospheric models (RAMs). The skill of these atmospheric hindcasts depends, among others, on the quality of the forcing at the boundaries. Furthermore, results may vary due to uncertainties in the initial conditions. By comparing different existing approaches for forcing a regional atmospheric model, it is shown that the models' sensitivity to uncertainties in the initial conditions may be reduced when a more sophisticated approach is used that has been suggested recently. For a specific, although somewhat brief test period, it is demonstrated that an improved hindcast skill for near surface wind fields is obtained when this approach is adopted. Consequences of the reduced uncertainty in wield fields for the hindcast skill of subsequent wave modelling studies are demonstrated. Recently, this new approach has been used together with a regional atmosphere model to produce a 40-year wind hindcast for the Northeast Atlantic, the North Sea and the Baltic Sea. The hindcast is presently extended to other areas and the wind fields are used to produce 40-year high-resolution hindcasts of waves and surges for various European coastal areas.  相似文献   

Ferromanganese Nodules and their Associated Sediments from the Central Indian Ocean Basin: Rare Earth Element Geochemistry     

J. N. Pattan  Ch. M. Rao  A. A. Migdisov  S. Colley  N. C. Higgs  L. Demidenko 《Marine Georesources & Geotechnology》2001,19(3):155-165

The rare earth element (REE) distribution in nine deep-sea ferromanganese nodules and their associated siliceous sediments from the Central Indian Ocean Basin (CIOB) have been studied to elucidate the REE relationship among them. Total REE concentration varies from 398-928 ppm in the nodules and 137-235 ppm in the associated sediments, suggesting two- to four-fold enrichment in the nodules compared to associated sediments. REE of nodules and their associated sediments show a positive correlation, suggesting REE are supplied from a common source such as seawater. The positive correlation between REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific Ocean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sediment they are carried by P and Mn phases. A similar REE fractionation pattern with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE abundance and their carrier phases.  相似文献   

多金属结核生长过程中元素通量的变化规律     

孙志国  刘季花  姚德  许东禹 《海洋科学进展》1996,(1)

本文主要研究太平洋ＣＣ区多金属结核ＣＣＡ３３，ＣＣＢ２９，ＣＣＣ５０，ＣＣＣ１４生长过程中锰、铁、镍、铜的通量（ＦＭｎ），ＦＦｅ，ＦＮｉ，ＦＣｕ）的变化规律．研究表明：１．结核生长过程中Ｍｎ，Ｆｅ，Ｎｉ和Ｃｕ的通量都是波动性的；２．ＦＭｎ与ＦＦｅ，ＦＮｉ，ＦＣｕ均呈正相关性；３．结核的元素通量与结核的成因类型和生长阶段密切相关，并记录了海底缺氧事件；４．结核的元素通量存在区域性差异，是沉积环境不同的反映。  相似文献   

Energetics of the Tsunami of 26 December 2004 in the Indian Ocean: A Brief Review     

N. Nirupama  T. S. Murty  I. Nistor  A. D. Rao 《Marine Geodesy》2006,29(1):39-47

The energetics of the most destructive tsunami in historical time, and that of the under ocean earthquake that triggered this tsunami of 26 December 2004 in the Indian Ocean have been briefly reviewed. This latest tsunami has several other unique characteristics besides being one of the worst natural disasters in human history. It is the first truly global tsunami after modern seismographic and sea level monitoring networks have been put in place. It was the first tsunami on record detected by a satellite, even though at present, global satellite coverage of the oceans for real time tsunami detection is not adequate. Finally, the energy associated with the tsunami and the earthquake that triggered it is so large that speculation has been made about the normal modes of oscillation of the earth, that were triggered by the earthquake as well as some suggestions, that some of the earth's rotational characteristics may have temporarily changed to a discernible degree. Here, we briefly review the energetics of the tsunami and the earthquake that triggered it.  相似文献   

Rare earth elements-rich phase and enriching mechanism in sediments from CC area, the Pacific Ocean   总被引：1，自引：0，他引：1  

Meng Xianwei  Chen Zhihu  Wang Xiangqin  Liu Na 《海洋学报(英文版)》2001,20(2):209-214

Compared to North American shale composition (NASC),REE contents of sediments from the CC area in the Pacific Ocean are obviously high except that cerium has equal content to that of NASC.Three-valence rare earth elements were completely enriched in phosphate-phase and cerium in iron-phase.Rare earth elements in the sediments were originally derived from seawater.During lithigenic and minerogenic processes of metalliferous nodules,three-valence rare earth elements in sediments mobilized and incorporated into sediments as authigenous biogenic-apatite,while cerium had change from Ce³⁺ to Ce⁴⁺ and directly precipitated from seawater and entered metalliferous nodules and caused Ceanomalies in REE pattern in sediments.  相似文献   

High resolution velocity analysis of ocean bottom seismometer data by theτ-p method     

Masanao Shinohara  Naoshi Hirata  Narumi Takahashi 《Marine Geophysical Researches》1994,16(3):185-199

A method of high resolution seismic velocity analysis for ocean bottom seismometer (OBS) records is applied to the study of the shallow oceanic crust, especially sedimentary and basement layers. This method is based on the direct-p mapping and the-sum inversion. We use data obtained from a 1989 airgun-OBS experiment in the northern Yamato Basin, Japan Sea and derive P- and S-wave velocity functions that can be compared with the seismic reflection profiles. Using split-spread profile records, we obtain interface dips and true interval velocities from the OBS data. These results show good agreement with the reflection profile records, the acoustic velocities of core samples, and sonic log profiles. We also present a method for estimating errors in the derived velocity functions by calculating covariance of the derived layers' thicknesses. The estimated depth errors are about 150 m at shallow depths, which is close to the seismic wavelength used. The high resolution of this method relies on accurate determination of shot positions by GPS, spatially dense seismic observations, and the use of unsaturated reflected waves arriving after the direct water wave that are observed on low-gain component records.  相似文献   

南极沿海冷水环境中低分子挥发性脂肪酸的初步研究     

杨和福 《海洋与湖沼》1992,23(6):599-605

于1988年5月—1989年2月,对东南极Vestfold丘陵地区沿海海域水体中的低分子挥发性脂肪酸的连续测定表明,该海域海水中的低分子挥发性脂肪酸主要以甲酸、乙酸、丙酸和丙烯酸为主,其含量明显呈季节性变化。变化范围分别为:甲酸0.4—7.0μmol/L;乙酸0.1—40.0μmol/L;丙酸0.7—128.0μmol/L和丙烯酸0.001—0.393μmol/L,最高浓度出现在夏季。通过对浮游植物的观察和二甲基硫的测定,揭示低分子挥发性脂肪酸主要来自微生物作用,其中丙烯酸直接来源于棕囊藻(Phaeocystis pouchetii)细胞繁殖生长过程中的代谢作用。  相似文献   

海台及其性质的初步分析   总被引：6，自引：0，他引：6  

张抗 《海洋地质与第四纪地质》1991,11(1):1-13

本文对海台及其性质作了初步分析,它具有相对平静或非线性的磁场,一般为无震区,其地壳明显厚于大洋盆地,并具洋陆地壳间的某种过渡性.  相似文献