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1.
A. Anil Kumar V. Purnachandra Rao S.K. Patil Pratima M. Kessarkar M. Thamban 《Marine Geology》2005,220(1-4):59-82
Rock-magnetic measurements along with grain size, acid-insoluble residue (AIR), organic carbon (OC), CaCO3 and δ18O of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of India. Magnetic susceptibility (MS) values in the surficial sediments reflect the land-derived input and, in general, are the highest in terrigenous sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed by the sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin.
The down-core variations in mineral magnetic parameters reveal that the glacial sediments off the Indus are characterized by low MS values/S-ratios associated with high AIR-content, low OC/CaCO3 contents and relatively high δ18O values, while those off SW India are characterized by low MS values/high S-ratio% associated with low AIR content, and relatively high OC, CaCO3 and δ18O values. Conversely, the Early Holocene sediments of all cores are characterized by high MS values/S-ratio% associated with high AIR content, low OC, CaCO3 contents and gradually decreased δ18O values. These results imply that during the Last Glacial Maximum (LGM), the cores off northwestern India received abundant continental supply leading to the predominance of eolian/fluvial sedimentation. In the SW region the influence of hinterland flux is less evident during this period, but convective mixing associated with the NE monsoon resulted in increased productivity. During the early Holocene intense SW monsoon conditions resulted in high precipitation on land, which in turn contributed increased AIR content/MS values in the continental margin sediments. A shallow water core off Kochi further suggests that the intense SW monsoon conditions prevailed until about 5 ka. The late Holocene organic-rich sediments of the SW margin of India were, however, subjected to early diagenesis at different intervals in the cores. Therefore, caution is needed when interpreting regional climatic change from down-core changes in sediment magnetic properties. 相似文献
2.
珊瑚中的δ18O含量可以高精度地记录热带海洋中的气候变率及气候变化信息, 从而弥补器测观测时间长度有限的缺陷, 为反演过去长期的气候状况提供了可能。热带印度洋的气候模态通过海气相互作用影响周边区域甚至全球的气候, 具有重要的研究意义。本文对比分析了1880—1999年间热带印度洋4个站点(肯尼亚、坦桑尼亚、塞舌尔、明打威)的珊瑚δ18O数据, 研究了其对热带印度洋气候的反演情况。结果显示, 珊瑚δ18O对海表温度(sea surface temperature, SST)的长期变化趋势反演良好, 珊瑚δ18O与局地SST在季节循环中保持一致, 且在低温季节对SST的变化更为敏感。此外, 4个站点的珊瑚δ18O对印度洋海盆模态(Indian Ocean Basin Mode, IOBM)和印度洋偶极子模态(Indian Ocean Dipple Mode, IODM)有一定的表征能力, 并且δ18O记录的热带印度洋年际变率受年代际变率调制。本文的研究结果表明, 珊瑚δ18O数据对于了解古气候时期热带印度洋气候变率具有重要的指示意义, 但同时也需要综合考虑不同站点的信息来完整地反映印度洋在历史时期的气候变化情况。 相似文献
3.
东沙海域是南海北部一个重要的天然气水合物成藏区, 其陆坡广泛发育滑塌构造。文章对采自东沙陆坡中部973-4柱样和下部平坦区973-5柱样开展了沉积学粒度、底栖有孔虫种属特征和稳定同位素等的综合分析。研究结果表明: 两个柱样中底栖有孔虫的δ13C在末次冰期均出现明显负偏现象, 同时δ18O增高, 指示该时期东沙海域存在持续的天然气水合物分解事件; 末次冰消期以来, δ13C负偏现象逐渐消失, δ18O值降低, 可能是由于海平面上升阻止了天然气水合物分解。973-4柱样仅在末次盛冰期对应层位440~600cm段存在明显的滑塌沉积, 且该层段对应的特征底栖有孔虫Uvigerina spp.和Bulimina spp.的数量突增, 推测该区的海底滑塌可能是由于末次盛冰期海平面大幅度下降引起天然气水合物大量分解诱发所致; 973-5柱样同样记录到了海底滑塌现象, 但其滑塌沉积晚于973-4柱样的滑塌时间, 且其规模较小。 相似文献
4.
冷水珊瑚也称为深水珊瑚, 在生物多样性、生态资源和科研价值等方面具有重要意义。文章对采自南海北部冷泉区的冷水珊瑚骨骼碎屑进行测定, 鉴定出冷水珊瑚2个种(Crispatotrochus sp.1和Crispatotrochus sp.2), 以及4个属[Balanophyllia (Balanophyllia)、Balanophyllia (Eupsammia)、Lochmaeotrochus和Enallopsammia]。测定的冷水珊瑚的δ13C为-7.36‰~-1.15‰, δ18O为-1.38‰~3.67‰, 与全球冷水珊瑚碳氧同位素组成相似, 但明显不同于南海暖水珊瑚、冷泉碳酸盐岩及低温热液成因碳酸盐岩的碳氧同位素组成。 相似文献
5.
High-resolution benthic oxygen isotope and XRF (Fe and Ca) records from Site 1085 drilled in the Mid-Cape basin (ODP Leg 175) are used to investigate global climate changes during the Late Miocene in relation to Messinian geological events. The cyclic fluctuations of the time series at Site 1085 enable us to establish a reliable chronology for the time interval 7.3–4.7 Ma. Spectral analysis of the δ18O record indicates that the 41-kyr period of orbital obliquity dominates the Late Miocene record. A global climate record was extracted from the oxygen isotopic composition of benthic foraminifera. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The time interval 7.3–6.25 Ma characterized by low-amplitude δ18O variations is followed by a period marked by maximum in the δ18O values (6.25–5.57 Ma). At about 5.56 Ma, a rapid decrease in δ18O values is documented that may reflect a warming of deep-water temperature associated with a global warming period. Comparison between the timing of the oceanic isotope events and the chronology of the Mediterranean Salinity Crisis suggest that global eustatic processes were not essential in the Mediterranean Salinity Crisis history. From our data, we infer that the global warmth documented in the Early/mid-Pliocene probably started during the Late Miocene (at 5.55 Ma). At the same time, the onset of evaporite deposition in the central basin of the Mediterranean Sea took place. Sharp changes in the sedimentation rates, mainly driven by terrigenous input at this site, are observed during the Messinian Stage. 相似文献
6.
南海北部琼东南盆地海底存在着巨型麻坑, 现有研究多认为其形成主要与海底流体渗漏有关。目前对琼东南盆地深海沉积物地球化学特征及麻坑区的生物地球化学过程等尚不清楚。文章选取南海北部琼东南盆地C14、C19两个站位岩心样品, 进行了总硫(TS)、总碳(TC)、总有机碳(TOC)、铬还原性硫化物(CRS)及其δ34SCRS值测试, 并结合总氮/总碳(TN/TOC)比值和已发表的孔隙水中SO42-浓度等进行了地球化学特征分析。研究表明: C14站位以3.91m bsf (below seafloor)为界, 上下分别存在有机质参与的硫酸盐还原反应(OSR)和甲烷厌氧氧化作用(AOM)驱动的硫酸盐还原反应(SR); 3.91m bsf以上的部位沉积物的TS、TC含量均低于3.91m bsf以下部位, 且沉积物孔隙水中SO42-浓度由3.91m bsf以上的缓慢凹型减少变成3.91m bsf以下的线性减少, 说明该处成为沉积物中地球化学特征分界的明显标志; 在3.91m bsf以下, 受到甲烷渗漏的影响。C19站位沉积物中TS与TC含量由浅到深逐渐增加, 但与TN/TOC比值变化呈现几乎相反趋势, 即整个岩心以OSR为主, 并呈现出有机质早期成岩阶段的沉积现象。C14和C19两个站位柱状沉积物的δ34SCRS值变化范围分别为-50.2‰~-46.9‰和-50.1‰~-42.0‰ (V-CDT标准), 均显示出了较为偏负的硫同位素值, 表明研究区主要的生物化学过程是在相对开放体系下硫酸盐还原作用的结果, 综合说明该研究区麻坑的甲烷流体已经喷发, 目前可能处于衰退期, 甚至已经不活跃, 该结果与前人的认识基本一致。 相似文献
7.
2013年5月、8月和11月调查了象山港大黄鱼网箱养殖区及附近沉积物中总有机氮(TON)、总有机碳(TOC)和总磷(TP)含量,并采用实验室模拟法研究了底泥耗氧率(SOCs)和沉积物-水界面营养盐(NH+4、NO-2+NO-3和PO3-4)通量。结果表明:养殖区(YZ)沉积物中的TON和TP含量显著高于距离养殖区50 m(F1)和100 m(F2)的区域(P<0.05)。底泥释放NH+4到上覆水中,但是从上覆水中吸收NO-2+NO-3和PO3-4。沉积物-水界面营养盐通量表现出明显的季节性变化,在8月,NH+4及PO3-4的释放量达到最大值。上覆水中NH+4、NO-2+NO-3和PO3-4的质量浓度随着沉积物-水界面营养盐通量的变化而变化。研究表明,象山港大黄鱼养殖活动对养殖区底泥造成了一定污染,且通过影响沉积物-水界面营养盐通量影响上覆水中营养盐分布,最终给整个养殖系统造成生态负担。 相似文献
8.
Richard W. Murray Beth A. Christensen James L. Kalbas Kelly A. Kryc 《Marine Geology》2002,180(1-4):133-150
We have analyzed 33 Pliocene bulk sediment samples from Ocean Drilling Program Site 1085 in the Cape Basin, located offshore of western Africa in the Angola–Benguela Current system, for 17 major and trace elements, and interpreted their associations and temporal variations in the context of an allied data set of CaCO3, opal, and Corg. We base our interpretations on elemental ratios, accumulation rates, inter-element correlations, and several multi-element statistical techniques. On the basis of qualitative assessment of downhole changes in the distributions of P and Ba, utilized as proxies of export production, we conclude that highs in bulk and biogenic accumulation that occur at 3.2 Ma, 3.0 Ma, 2.4 Ma, and 2.25 Ma were caused by increases in export production as well as terrigenous flux, and record a greater sequestering of organic matter during these time periods. Studies of refractory elements and other indicator proxies (SiO2, Al2O3, TiO2, Fe2O3, MgO, V, Cr, Sr, and Zr) strongly suggest that the terrigenous component of the bulk sediment is composed of two compositional end-members, one being ‘basaltic’ in composition and the other similar to an ‘average shale’. The basaltic end-member comprises approximately 10–15% of the total bulk sediment and its presence is consistent with the local geology of source material in the drainage basin of the nearby Orange River. The increase in bulk accumulation at 2.4 Ma appears to reflect a greater relative increase in basaltic input than the relative increase in shale-type input. Although studies such as this cannot precisely identify the transport mechanisms of the different terrigenous components, these results are most consistent with variations in sea level (and associated changes in shelf geometry and fluvial input) being responsible for the changing depositional conditions along the Angolan Margin during this time period. 相似文献
9.
台风因其特殊的物理结构, 带来的降雨有别于一般的暴雨事件, 其降水稳定同位素组成与一般的大气降水事件也有较大的差异。本文根据2018年第22号台风“山竹”登陆前后广州、东莞两地气象资料和每小时间隔的降水样品收集, 分析了此次台风在两地的降水稳定同位素变化特征及其影响因素。台风“山竹”影响期间, 广州降水δ18O值变化范围为-5.7‰~-19.2‰, 变化幅度达13.5‰, 其平均值为-15.5‰; 东莞降水δ18O值变化范围为-7.3‰~-20.0‰, 变化幅度达12.7‰, 平均值为-14.8‰; 两地降水δ18O值均呈现为3个阶段倒U型的变化特征。受到蒸发作用的影响, 两地台风前端和尾端的降水氧同位素值相对偏正, 其中广州为-5.7‰~-9.3‰, 东莞为-7.3‰~-8.1‰。两地台风中端的降水稳定同位素值极端偏负, δ18O值变化范围分别为-16.0‰~-19.2‰(广州)和-13.0‰~-20.0‰(东莞), 是该地区迄今为止已报道的最为偏负的降水δ18O值。分析认为, 在厄尔尼诺状态下生成的远源台风“山竹”强度增强, 其内部具有更强的对流和水汽循环过程, 导致降水δ18O值极端偏负。 相似文献
10.
采用气相色谱-质谱技术对南极半岛东北海域海底表层沉积物的总有机碳、有机质碳同位素(δ13 Corg)和生物标志化合物等进行了测试分析。研究区表层沉积物总有机碳TOC平均值高于现代深海沉积物中的平均含量。δ13 Corg的变化说明该海域有机碳来源呈海洋水生生物来源和陆源混合的特征。正构烷烃的峰型分布、主峰碳、饱和烃轻重比C-21/C+22和(C21+C22)/(C28+C29)、甾烷组合和藿烷组合证实研究区西部表层沉积物有机质来源以陆源高等植物为主,其陆源可能来自于附近的南极半岛和南舍得兰群岛;研究区东部表层沉积物有机质来源偏以海源为主,且以低等浮游生物、藻类及细菌生物等海源输入为主。碳优势指数(Carbon preference index,CPI)、奇偶优势指数(Odd-even Predominance,OEP)和甾烷C29ααα20S/(20S+20R)比值显示研究区D1-7站位和D5-9沉积物有机质演化程度较高,D5-2和D2-4站位的有机质演化程度低,其他站位介于中间状态。饱和烃中姥鲛烷、植烷及其比值(Pr/Ph)等组合显示研究区西部以氧化-弱还原的沉积环境为主,其可能是受高温低盐别林斯高晋海水流和附近火山喷发的影响所致;研究区东部以还原—强还原沉积环境为主,可能是受低温高盐的威德尔底层水(WSBW)和威德尔海深层水(WSDW)影响所致。 相似文献
11.
南海东沙群岛东北部海洋IV号地区GC16站重力柱状沉积物中的有机碳、总氮,以及自生碳酸盐岩矿物的无机碳同位素组成分析结果表明,甲烷流体活动区硫酸盐甲烷转换带(SMTZ—sulfate methane transition zone)是重要的生物地球化学界面,该带内沉积物中有机碳、氮与无机碳同位素组成变化明显。GC16站SMTZ上界面以下的沉积物中有机碳、氮同位素组成分别比其上的沉积物负偏1.4‰PDB和0.93‰,反映该带内甲烷缺氧氧化作用(AOM—anaerobic oxidation of methane)与氨氧化作用发育。无机碳同位素组成表明SMTZ界面之下沉积物中的自生碳酸盐岩矿物为以微生物为媒介的甲烷驱动成因,地质历史时期(至柱状沉积物底部沉积时期)曾发生过2次较强烈的CH4流体活动;目前该区甲烷流体活动较弱,甲烷流体影响深度与SMTZ上界面一致,未能到达海底。 相似文献
12.
海洋暖池的发展、变化及其效应与沉积环境有密切关系。文章对北部湾暖池主要水域进行表层沉积物取样, 测试鉴定其粒度、化学元素、微体古生物化石, 并对数据进行分析比较。结果表明: 研究区物源来自陆区上陆壳风化, 在水动力作用下粒度组成分异明显, 平均粒径为1.1Φ~6.9Φ (Φ=-log2d, d为直径, 单位: mm)。常量元素以SiO2占优, 其平均质量分数最高达到66.61%, 其次为Al2O3; 微量元素的质量分数平均为9.05~297.00μg•g-1, 稀土元素的平均质量分数为0.34~69.43μg•g-1, 化学蚀变指数(CIA)平均为47.33, 轻重稀土元素分馏比为7.46~10.07。古生物多样性指数(H°)为0~2.52。在海湾尺度下化学要素分布的空间异质性显著。在研究区西部, 大部分化学元素质量分数高, 沉积物颗粒最细, 稀土元素分馏显著, CIA较高, 物质来源多样, 古生产力较高; 而东部则几乎表现相反, 以砂质沉积物为主, 除了CaO、MnO、Sr较高之外, 大部分元素质量分数低且稀土元素分馏弱, CIA低下, 古生产力偏低, 显示出物源有限和海洋自生碳酸盐沉积的可能性。浮游类有孔虫以表层暖水种占优, 硅藻为热带和亚热带种, 属种内在结构显示出暖水、高盐等特征。该暖池兼具一定的独立性和开放性, 对生物活动、生物多样性乃至碳酸盐沉积等具有维护作用。 相似文献
13.
为了解大亚湾西南海域食物网的营养结构特征, 本研究于2020年1月份使用底拖网采集了该海域的渔业生物, 并分析了35种主要渔业生物的碳氮稳定同位素值。根据δ13C和δ15N值, 计算出该海域食物网6种营养结构的生态指标和主要渔业生物的营养级, 并绘制了连续营养谱。本次调查渔业生物主要为鱼类和虾蟹类, 鱼类的δ13C和δ15N值范围分别为-17.63‰ ~ -14.85‰和12.92‰~15.46‰, 平均值分别为-16.47‰和13.80‰; 虾蟹类的δ13C和δ15N值范围分别为-17.67‰ ~ -15.51‰和11.05‰~12.62‰, 平均值分别为-16.30‰和11.85‰。根据δ15N值, 用相加模型(trophic position by the additive model, TPA)和缩比模型(trophic position by the scaled model, TPS)分别计算了主要渔业生物的营养级, 结果显示两个模型计算的结果无显著性差异(P>0.1), 呈现鱼类平均营养级>虾蟹类的趋势。本研究发现大亚湾西南海域食物网初始食物来源较为单一, 存在食物链营养层级较少和长度不足, 食物网营养级多样性较低和营养结构冗余程度高的现象。与30多年前相比, 大亚湾近年高营养级生物量减少, 食物网结构由复杂趋向简单化, 生态系统稳定性较差。本研究结果不仅为了解大亚湾食物网结构组成提供了基础资料, 也为保护大亚湾渔业资源, 维持生态系统结构的稳定性提供参考依据。 相似文献
14.
Stable isotope evidence for a marine origin of ophicalcites from the north-central Apennines (Italy) 总被引：1，自引：0，他引：1
Carbon and oxygen isotope ratios of 59 samples of Mesozoic ophicalcites from the north-central Apennines were measured. Strontium content and isotope ratios were only determined for selected samples.
The data obtained (−4.1 ≤ δ 13C ≤ + 3.0; 16.5 ≤ δ 18O ≤ 30.1; 0.7076 ≤ 87Sr/86Sr ≤ 0.7086; 60 ≤ Sr ppm ≤ 1140) suggest that the carbonate cement of the Apennines ophicalcites had a marine origin.
The 18O/16O values of most of the carbonates studied, however, indicate that the rocks have interacted with hydrothermal fluids, dominantly represented by sea water. In particular, the rocks from the northern section of the Apennines apparently reequilibrated their δ 18O content at higher temperature than those from the central zone.
Strontium isotope ratios, close to the Cretaceous—Cenozoic ocean water values, are well in agreement with such a kind of sea water/ophicalcites interaction, even if the carbonate cement formed earlier during the Jurassic period. 相似文献
15.
颗粒物粒径分布(Particle Size Distribution, PSD)代表了颗粒物浓度与颗粒物粒径之间的关系, 影响着海洋生态环境和水体光学特性等。文章基于2016年夏季航次调查的生物光学剖面数据, 研究了南海海盆海域PSD的分布特征。研究发现, 幂律函数可以较好地拟合南海海盆区域的PSD, 对数空间中的实测的PSD与模拟的PSD平均决定系数高达0.95。PSD斜率(ξ)的分布范围为[1.27, 7.65], 均值为3.93±0.56。南海海盆区域表层水体的ξ均值与全球大洋表层水体的ξ均值相近, 但高于海湾等表层水体的ξ均值。ξ能较好地表征颗粒物平均粒径DA的大小, 两者存在明显负相关关系, 即ξ值越高, DA越小; 反之, DA越大。通过分析T1断面的生物光学剖面数据及总体平均的PSD剖面数据, 发现PSD剖面分布特征如下: 1)表层水体的ξ值相对较高, 且DA值相对较低, 推测可能是由于微微型藻类为主导颗粒物所致; 2) ξ值极小值层出现在次表层叶绿素浓度极大值层(Subsurface Chlorophyll Maximum Layer, SCML)中, 并伴随DA极大值层的出现, 其原因可能是SCML中的大粒径浮游植物占比显著增加; 3)弱光层中的ξ值较SCML中的高, 但略低于表层的ξ值, 而DA则位于表层与SCML的DA之间, 这可能与浮游植物及其碎屑的絮凝、分解、沉降等过程相关。PSD特征影响着海水的固有光学特性, 分析发现: 由于SCML中的叶绿素浓度增加, 颗粒物散射系数(bp(532))和颗粒物后向散射系数(bbp(532))也相应呈现显著增加的趋势。弱光层中的平均bp(532)与平均bbp(532)最小。ξ与颗粒物衰减光谱斜率之间呈高分散性, Boss 等(2001b) 的模型适合用于粗略估算区域性的ξ分布范围及均值。 相似文献
16.
我国典型潮间带底栖硅藻群落空间分布特征 总被引：2，自引：0，他引：2
底栖硅藻是河口、泥质海滩生态系统的重要生物类群,其数量与分布变化直接或间接地影响到多种海洋生物的饵料供给、海鸟的生存与迁徙。通过对我国从南到北14个典型潮间带表层沉积物中底栖硅藻的分析,共鉴定出硅藻153种,其物种多样性（Shannon-Weaver 指数范围:1.61~4.39）与生物量（范围:0.09×103 ~ 10×103个/g,干质量）在空间上存在显著差异;聚类分析与相似性分析检验（r=0.738,P=0.1%< 0.01）表明,14个调查区域的硅藻群落在空间上可分为4个大的组合,分别对应着渤、黄、东、南海4个区域,吻合了我国近海浮游植物的地理分布特征。与环境因素的相关性分析表明,底栖硅藻群落的物种多样性与生物量受沉积物类型与盐度的影响显著,泥质区域更有利于硅藻的保存,而生物多样性在泥砂质低盐区域相对较高。此外,底栖硅藻生物量与表层沉积物中TOC含量表现出显著正相关性;δ13C数值的空间变化范围为-25‰~-20‰,指示了有机质陆海混合的特征,其中,涧河河口、黄河口、大沽河口、苏北浅滩区域,δ13C数值明显偏正,表明底栖硅藻可能是这些区域沉积物中有机碳的重要贡献者。 相似文献
17.
南海自新生代以来发育了大量的碳酸盐岩台地和生物礁, 并普遍发生白云岩化作用, 具有广阔的油气勘探前景。文章通过开展岩相学观察、矿物学分析、常微量元素和碳氧同位素分析, 同时结合Fe组分及Fe同位素地球化学分析, 对南沙群岛南科1井白云岩的发育特征和成岩环境进行了系统研究。结果表明: 南科1井上中新统—下更新统白云岩主要形成于近地表环境中, 溶蚀孔隙发育, 残余结构明显。白云岩层中发育有多个与暴露成因有关的界面, 未发现石膏层的存在。同时, 白云岩普遍具有低Fe、Mn和Sr的特征以及与现代海水相似的REE分布模式, δ13C和δ18O多为正值, 但不存在相关性。整体来看, 白云岩可能形成于轻微蒸发海水的渗透回流作用, 还受到了与古气候变冷有关的海平面下降的控制。此外, 南科1井岩芯中多个层位发育铁白云石, 并且集中分布在暴露面附近。Fe组分和Fe同位素组成结果显示, 白云岩中Fe主要来源于海水中碳酸盐的沉淀, 成岩过程中基本不存在额外的陆源或热液来源的Fe混入。铁白云石主要形成于低温和浅埋藏环境中, 大气淡水对生物骨架、生物碎屑以及自生碳酸盐矿物的淋滤-溶解作用为其提供了重要的物质来源。作为生物礁体暴露地表期间的产物, 铁白云石的发育层位可能指示着低海平面时期。 相似文献
18.
Distinctive light–dark color cycles in sediment beneath the Benguela Current Upwelling System indicate repetitive alternations in sediment delivery and deposition. Geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid-Pleistocene intervals from ODP Sites 1082 and 1084. Concentrations of total organic carbon (TOC) vary between 3.5 and 17.1%. Concentrations of CaCO3 vary inversely to TOC and Al, which suggests that both carbonate dissolution and terrigenous dilution contribute to the light–dark cycles. Opal concentrations are independent of both TOC and CaCO3, therefore eliminating diatom production and lateral transport of shelf material as causes of the light–dark cycles. δ13Corg and δ15Ntot values do not vary across light–dark sediment intervals, implying that the extent of relative nutrient utilization did not change. The stable δ15Ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the TOC-rich layers. Parallel changes in concentrations of indicator trace elements and TOC imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen. Cu, Ni, and Zn are enriched in the darker sediment as a consequence of greater organic matter delivery. Redox-sensitive metals vary due to loss (Mn and Ba) or enrichment (Mo) under reducing conditions created by TOC oxidation. Organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution, sulfate reduction and the concentration of metals. Thus, export production is considered ultimately responsible for the generation of the color cycles. 相似文献
19.
Prorocentrum donghaiense is one of the most common red tide causative dinoflagellates in the Changjiang （Yangtze） River Estuary and the adjacent area of the East China Sea. It causes large-scale blooms in late spring and early summer that lead to widespread ecologic and economic damage. A means for distinguish- ing dinoflagellate blooms from diatom （Skeletonema costatum） blooms is desired. On the basis of measure- ments of remote sensing refectance [Rrs（λ）] and inherent optical parameters, the potential of using a mul- tispectral approach is assessed for discriminating the algal blooms due to P. donghaiense from those due to S. costatum. The behavior of two reflectance ratios [R1 = Rrs（560）/Rrs（532） and Re = Rrs（708）/Rrs（665）], suggests that differentiation of P. donghaiense blooms from diatom bloom types is possible from the current band setup of ocean color sensors. It is found that there are two reflectance ratio regimes that indicate a bloom is dominated by P. donghaiense; （1） R1 〉 1.55 and R2 〈 1.0 or （2） R1 〉 1.75 and R2 ≥ 1.0. Various sensitivity analyses are conducted to investigate the effects of the variation in varying levels of chlorophyll concentration and colored dissolved organic matter （CDOM） as well as changes in the backscattering ratio （bbp/bp） on the efficacy of this muitispectral approach. Results indicate that the intensity and inherent op- tical properties of the algal species explain much of the behavior of the two ratios. Although backscattering influences the amplitude of Rrs（λ）, especially in the 530 and 560 nm bands, the discrimination between P. donghaiense and diatoms is not significantly affected by the variation of bbp/bp. Since aCDOM （440） in coastal areas of the ECS is typically lower than 1.0 m-1 in most situations, the presence of CDOM does not interfere with this discrimination, even as SCDOM varies from 0.01 to 0.026 nm-1. Despite all of these effects, the dis- crimination of P. donghaiense blooms from diatom blooms based on multispectral measurements of Rrs（λ） is feasible. 相似文献
20.
An array of four sediment trap moorings recorded the particulate flux across the Antarctic Circumpolar Current (ACC) at 170 °W, between November 1996 and January 1998, as part of the US JGOFS-Antarctic Environment and Southern Ocean Process Study (AESOPS) program. The trap locations represent sampling within the Polar Frontal Zone, the Antarctic Polar Front, the Antarctic Zone and the Southern Antarctic Zone. Here we report observations from 1000 m below the sea-surface compared to seafloor and surface water distributions. Sub-sample splits from each trap were obtained and total diatom flux and species composition were determined. The diatom fluxes were quantified using both a dilution and a ‘spike’ method to allow for the rapid repeatability of measurements. Diatom flux was found to be highly seasonal across the ACC particularly at higher latitudes. Marine snow aggregates of intact diatom cells and chains were the major components of the biogenic flux. Siliceous particle size was noted to decrease with increasing latitude, which could be aligned with a shift of the diatom assemblage to small-size species/sea-ice affiliated species. A ‘double-structured’ diatom flux was recorded at the location of the Antarctic Polar Front trap, with a shift in the diatom assemblage from larger to smaller diatoms in the second flux episode. The sediment trap assemblage shows deviations from the surface water assemblage, while surface sediment samples indicate that significant dissolution occurs after 1000 m and at the sediment–water interface. Estimation of diatom biovolumes across the ACC shows that large diatoms have the potential to greatly impact biogenic fluxes to the ocean interior despite their low fluxes. Small species of the genus Fragilariopsis could potentially export as much Corg as Fragilariopsis kerguelensis near the retreating ice edge. However, their low abundance in the surface sediments also suggests that these diatoms are a shallow export species. 相似文献