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1.
Salt marshes are potentially threatened by sea level rise if sediment supply is unable to balance the rising sea. A rapid sea level rise is one of the pronounced effects of global warming and global sea level is at present rising at an elevated rate of about 3.4 mm y? 1 on average. This increasing rate of sea level rise should make it possible to study the effect of rapidly rising sea level on salt marsh accumulation. However, such an understanding is generally hampered by lack of available data with sufficient precision. Here we present a high-precision dataset based on detailed radiometric measurements of 137Cs in 10 sediment cores retrieved at a natural and unmanaged micro tidal salt marsh. Two distinct 137Cs-peaks were found in all cores, one peak corresponding to the 1963-maximum caused by testing of nuclear weapons in the atmosphere and the other to the Chernobyl accident in 1986. Salt marsh accretion has generally kept pace with sea level rise since 1963 but comparison of the accumulation rates of minerogenic material in the period 1963–1986 and 1986–2003 revealed a slight decrease in accumulation with time in spite of an observed increase in inundation frequency. The observed decrease in sediment deposition is significant and gives reason for concern as it may be the first sign of a sedimentation deficiency which could be threatening this and other salt marshes in the case of a rapidly rising sea level. Our work demonstrates that the assumption of a constant relationship between salt marsh inundation and sediment deposition is not necessarily valid, even for a salt marsh that receives most of its allocthonous sediment from the adjacent sea. The apparent decrease in sediment deposition indicates that the basic assumption of sufficient sediment supply used in contemporary models dealing with salt marsh accretion is most probably not valid in the present case study and it may well be that this is also the case for many other salt marshes, especially if sea level continues to rise rapidly as indicated by some climate change scenarios. 相似文献
2.
Conny Haraldsson Leif G. Anderson Martin Hassellöv Stefan Hulth Kristina Olsson 《Deep Sea Research Part I: Oceanographic Research Papers》1997,44(12):2031-2044
A system for rapid, high precision potentiometric determination of alkalinity in sea water and sediment pore water is presented. Two titration units were used: a 40 ml unit for seawater and a small volume unit for sediment pore water. Titration time was normally less than 10 minutes per sample, including sample exchange. With a 40 ml sample volume, the relative standard deviation of the alkalinity obtained in the laboratory was 0.05% and at sea 0.1 %. The small-volume system (0.5–1.5 ml) gave a precision of 0.07%. Five titration points, in two groups after the second equivalence point, were used to evaluate the equivalence volume. Results from equilibrium calculations and computer simulated alkalinity titrations show that it was possible to use a non-modified Gran function [(V0 +v)*10(E/Z)] and still achieve good accuracy and precision. 相似文献
3.
东印度洋受到印尼贯穿流(Indonesian Throughflow,ITF)等多个大洋流系影响,是太平洋水在低纬度进入印度洋的重要通道,具有显著的生态效应,是金枪鱼的重要渔场之一。为了解上述海域浮游植物群落组成、时空特征及其影响因素,基于2020年1～2月在该海域采集到的浮游植物样品及同步的环境数据,对其种类组成、生态类型、细胞丰度、优势类群等群落组成及其与环境因子关系进行了研究,并与赤道东印度洋浮游植物群落进行了比较。结果表明:研究海域共鉴定浮游植物4门57属268种(含变种、变型),其中,硅藻38属129种,甲藻17属136种,金藻1属2种,蓝藻1属1种;生态类型以热带大洋性种类、大洋暖水种和热带近岸种为主,浮游植物区系属于热带-亚热带生物区系。细胞丰度介于1.28×103～7.84×104 cells/m3之间,平均值为1.55×104 cells/m3。优势种中硅藻占绝大多数,分别为短叉角毛藻(Chaetoceros messanensis)、伏氏海毛藻(Thalas... 相似文献
4.
海草床是三大典型的近海海洋生态系统之一,具有极高的生态服务功能。然而,截至2015年我国近海海草资源分布现状尚不明晰,严重制约了我国海草床保护与修复工作的开展。2015～2021年,笔者通过实地调查,借助船只走航、声呐探测、遥感等技术手段,重点对我国近海海草资源的分布面积、种类及主要威胁进行了全面普查,并据此提出我国海草床管理与可持续利用对策。结果表明,我国近海海域海草床面积共为26 495.69hm2,可划分为:温带海域海草分布区和热带-亚热带海域海草分布区;我国现有海草4科9属16种。其中,温带海域海草床面积为17 095.01 hm2,主要分布在辽宁、河北、天津和山东沿海,分布有2科3属5种,以鳗草(Zosteramarina)和日本鳗草(Z.japonica)为优势种,其中唐山乐亭-曹妃甸海草床面积达9 025.56 hm2,是我国面积最大的海草床;热带-亚热带海域海草床面积为9 400.68 hm2,主要分布在福建、广东、广西和海南沿海,分布有4科8属12种,以泰来草(Thalassia hemprichii)、海菖蒲(Enhalus acoroides... 相似文献
5.
山东荣成临洛北湾夏季大型底栖动物群落生态学初步研究 总被引：1，自引：0，他引：1
利用2010年7月在山东荣成临洛北湾所获得大型底栖动物定量分析资料,研究了夏季该海域海带养殖区和邻近水域大型底栖动物在物种组成、生物量、丰度、优势种以及物种多样性等方面的特征和空间差异,并采用MDS和CLUSTER分析了大型底栖动物的群落结构,以期为该地区以后的科学研究提供基础数据.结果表明,本次调查通过采泥和拖网共采集到大型底栖动物88种,其中采泥得到大型底栖动物51种,拖网采得大型底栖动物45种,各站位的物种多样性差异明显,物种数量从2种到21种.与环境因子的相关性分析显示,各站的物种数和丰度与DO存在明显的负相关.在所有大型底栖动物中,甲壳动物26种,多毛类环节动物24种,软体动物23种,棘皮动物8种,其他类群动物6种(鱼类5种,尾索动物1种).该海域的优势种为多丝独毛虫和短叶索沙蚕.将CLUSTER结果以43%的群落结构相似性来划分,组内的相似性为50%~60%.该海域大型底栖动物的平均丰度为854个/m2,平均生物量为134.73 g/m2,与研究海域附近的历史研究结果相比较,该海域的平均丰度和生物量仍处于较高的水平. 相似文献
6.
Don Maurer 《Marine Ecology》1983,4(3):263-274
Abstract. Animal-animal interactions are recognized as critical in benthic invertebrate recruitment. The hypothesis tested was that benthic recruitment is more successful in low densities of infaunal suspension feeders than in high densities. Densities of young hard clams Mercenaria mercenaria (L.) ranging from 82.5 to 330m-2 were placed in defaunated boxes of sand. The mean number of species, mean number of individuals, mean wet weight biomass, mean species richness and mean dominance index per sample were calculated per density of hard clams from May to October. The experiment did not support the hypothesis. It was concluded that feeding behaviour of dense populations of M. mercenaria did not preclude successful recruitment of other benthic species. 相似文献
7.
桂山岛海域甲藻孢囊的分布与浮游植物休眠体萌发研究 总被引：1，自引：1，他引：0
为了了解珠江口桂山岛海域甲藻孢囊的分布及浮游植物休眠体的萌发状况,以揭示赤潮发生潜势,于2009年1月采集了珠江口桂山岛海域表层沉积物样品,对沉积物中甲藻孢囊的种类和数量进行分析,并对浮游植物休眠体进行了萌发试验。结果表明,桂山岛海域甲藻孢囊有21种,原多甲藻类孢囊在种类数上占优势。甲藻孢囊密度较低,为110~315个/g,平均为202个/g,养殖区密度高于非养殖区。异养型甲藻孢囊百分比含量较高,表明了该海域较高的富营养化程度。活体孢囊密度百分比达61.8%,说明表层沉积物中存在大量未萌发的活性孢囊,为赤潮暴发埋下了隐患。萌发的浮游植物种类数较少,为19属22种。20 d和40 d萌发的浮游植物细胞平均密度分别为490个/g和264个/g。萌发的甲藻优势种为Biecheleriopsis adriatica,其次为锥状斯氏藻(Scrippsiella trochoidea);萌发的硅藻主要以中肋骨条藻(Skeletonema costatum)、旋链角毛藻(Chaetoceros curvistus)和舟形藻(Navicula sp.)占优势。桂山岛海域有毒有害甲藻孢囊的广泛分布以及潜在赤潮种类的大量萌发,表明该海域有较高的赤潮发生风险。 相似文献
8.
Yoshihisa Shirayama 《Journal of Oceanography》1989,45(1):83-93
I am deeply honored to have been awarded the 1988 Okada Prize of the Oceanographical Society of Japan. The present paper reviews my previous works regarding the ecology of deep-sea meiobenthos in the western Pacific area. The outline cen be summarized as follows:
相似文献
| 1) | On the basis of multivariate analyses, it was found that the rate of the organic-matter flux to the sea bed and the amount of the interstitial space within the sediment are the main factors regulating the abundance of meiofauna in the deep sea. |
| 2) | Two indices were proposed to characterize the vertical distribution of meiofauna in the sediment profile,i.e. their maximum depth in the sediment and the degree of their concentration in the surface layer of the sediment. The index of maximum depth was closely related to the oxygen concentration in the interstitial water. On the other hand, the index of degree of concentration in the surface of the sediment tended to be higher where the supply of food seemed lower. |
| 3) | Some taxonomically important species were found from the axis of the Izu-Ogasawara Trench. They arePliciloricus hadalis, the first species of the newest phylum Loricifera from the Pacific area, from the hadal deep sea and the fine clay sediment, andOccultammina profunda, the first infaunal species of Xenophyophorea, a group of rhizopod Protozoa. |
| 4) | The vertical distribution ofOccultammina profunda coincided well with the unusual distribution of210Pb in the sediment profile. The organisms concentrated as high as 500 dpm g–1 of210Pb in their stercomare and granellare. The steady state model confirmed that the species made the peculiar subsurface peak of210Pb in the sediment. |
| 5) | The depth in the sediment profile where the distinct peak of MnO2 can be seen showed strong correlation with the vertical distribution of meiofauna. This relationship suggests that oxygen concentration in the interstitial water regulates the structure of the characteristic three layers of the calcareous ooze in the deep sea. This idea was proven by the vertical distribution of free oxygen in the sediment calculated on the basis of respiration rate of deep-sea meiofauna measured using the cartesian diver technique. |
| 6) | Radio-isotope techniques used to measure the rates at which particulated organic matter was ingested and dissolved organic matter was absorbed, suggested that deep-sea meiofauna obtained a significant fraction of their energy by absorption. |
| 7) | The work carried out so far has revealed the important role of meiofauna in the benthic ecosystem, and emphasized the necessity for intensive research from various points of views on these microscopic organisms. |
9.
10.
Living on the edge: feeding of subtropical open ocean copepods 总被引：2，自引：0，他引：2
The objective of this study was to provide quantitative information on environmental feeding rates of warm water oceanic epipelagic copepods. We determined clearance rates at 23 °C for various particle size ranges in shipboard studies in the western oligotrophic subtropical Atlantic Ocean for females of the calanoid species Clausocalanus furcatus and Mecynocera clausii. These in situ clearance rates were then applied to the various particle size ranges of environmental particle spectra of auto‐ and heterotrophs at different depths from three stations in the western Atlantic. After calculating the metabolic demands of each of these two copepod species and applying an assimilation efficiency of 90%, we determined that C. furcatus meets its metabolic demands in all six cases, and M. clausii in two of six cases. Clausocalanus furcatus would also meet its energy demands at 25 °C, where it is often found, while M. clausii at 20 °C, where it is regularly found, would cover its metabolic needs in four of six cases. It is hypothesized that these species, and most likely most of the other co‐occurring copepod species, are limited in their abundance by food availability, or, better said, are ‘living on the edge’ in relation to food abundance. 相似文献
11.
The Håkon Mosby Mud Volcano (HMMV) is a methane seep that is densely populated by the bacteria Beggiatoa spp. as well as by tubeworms of the Family Siboglinidae. Analyses of samples from seven stations located in five different habitats (bare sediments, bacterial mats, siboglinid fields, sediments with small patches of siboglinids and areas of ‘normal’ sea floor) revealed differences in the density and species‐level diversity of nematode communities. Total densities increased from stations inside the mud volcano and on its rim towards the ‘normal’ areas outside the volcano. Nematode species diversity was similar in samples from the siboglinid fields and the bare HMMV sediments. However, the sediment with patches of siboglinids collected outside the volcano was characterised by a diverse nematode community comprising 47 species, whereas the control sediments without siboglinids yielded only 27 species. The nematode assemblage at the bacterial mat site included only two identified species, Halomonhystera disjuncta and Sabatieria ornata, with H. disjuncta being strongly dominant. Terschellingia distlamphida, S. ornata and Aponema ninae dominated nematode communities at the siboglinid fields and in bare HMMV sediments. Species dominating at stations inside the caldera were found in comparable low densities in the sediment with siboglinid patches collected outside the volcano, but were missing in the background samples, where species of Endeolophos, Acantholaimus and Desmoscolex were dominant. Species diversity generally decreased with sediment depth. A subsurface‐dwelling nematode community was observed in the siboglinid fields and the bare sediments. Background sediments showed a sharp decline with 18–20 species at 0–2 cm versus three species at 3–5 cm sediment depth. The trophic composition of the nematode fauna at the HMMV showed a prevalence of deposit feeders at almost all stations, whereas background sediments exhibited a uniform distribution of non‐selective and selective deposit feeders and epistrate feeders. The high percentage of deposit feeders inside the mud volcano could be related to the grain‐size distribution and the significantly higher bacterial biomass compared to the control sediments. 相似文献
12.
深圳海域弧菌种类组成、数量分布及其与环境因子的关系研究 总被引：2，自引：0，他引：2
研究了深圳海域2008年4月、9月的水体弧菌数量、种类组成及其分布,探讨了弧菌总数及各优势类群的数量分布与环境因子间的相关关系。结果表明:弧菌总数分布具有季节性,东部海域春季(4月)的弧菌数量高于秋季(9月)的,其均值分别为1.50×104,8.89×102CFU/cm3;在西部海域秋季的略高于春季的,其均值分别为5.09×102,2.66×102CFU/cm3;弧菌数量最高值出现在大亚湾(4.40×104CFU/cm3)。弧菌的优势类群具有季节性分布特征:春季特有的优势类群有Vibrio gigantis类似种和V.splendidus类似种,秋季特有的优势类群有V.natriegens类似种;V.alginolyticus类似种是两个季节共有的优势类群,其数量春季高于秋季的。弧菌种类、数量与海水温度、盐度及细菌总数、Chl-a等环境因子有一定的相关性,其中盐度为弧菌种类及数量分布的主要影响因子。 相似文献
13.
To explore the spatial pattern of macrobenthic communities and their response to environmental factors in the Prydz Bay,samples were collected using a 0.25-m2 box corer at 10 stations from November 2012 to April 2013.A total of 50 species of macrobenthos belonging to 8 phyla and 33 families were identified,of which polychaetes(e.g.,Maldane sarsi)and sponges(e.g.,Halichondria sp.and Leucosolenia sp.)were the most prominent groups.The macrobenthos in study area were categorized into five functional groups based on the feeding type,and the detritivorous group represented by polychaetes showed the highest average abundance,while the planktophagous group represented by sponges showed the highest average biomass.Macrobenthos abundance(0–592 ind./m2)and biomass(0–1155.5 g/m2)in the Prydz Bay were relatively lower than those of other Antarctic shelf soft-bottom waters,although the compositions of the dominant species and functional feeding groups were similar.The results of the Spearman rank correlation analysis indicated that the average biomass of the macrobenthos and the biomass of the planktophagous group in the study area were negatively correlated with the water depth,sediment grain size and silt percentage.However,these variables were clearly not strong determinants of macrobenthos assemblage structure.Many factors not measured in the study,e.g.,sediment organic matter and iceberg interference,have probably influenced the spatial distribution of macrobenthic community structure in the Prydz Bay. 相似文献
14.
根据2021年渔业资源调查数据构建了含有23个功能组的舟山海域生态系统Ecopath模型,分析了当前舟山海域生态系统总体特征并估算了褐菖鲉在舟山海域的生态容量。结果表明:舟山海域生态系统营养级范围为1.000 (浮游植物和有机碎屑)～4.277 ( 鳐类),石首鱼科、虾类和 鳐类为舟山海域生态系统中的关键种。碎屑食物链和牧食食物链是舟山海域生态系统主要的食物链。碎屑和浮游植物对食物网的贡献率分别为61.32%和38.69%。始于浮游植物和碎屑的营养传递效率分别是9.34%和10.50%,系统总营养传递效率是9.82%。总初级生产量/总呼吸量为2.26,系统连接指数为0.372,系统杂食性指数为0.222。生态系统总体特征反映了舟山海域生态系统的成熟状态较低,生态系统处于不稳定阶段,容易受到外界环境变化的影响。根据模型估算,当褐菖鲉生物量增加至8.6倍时,褐菖鲉达到生态容量0.007 95 t/km2,此时生态系统仍保持平衡,且生态系统总体特征基本稳定。因此,褐菖鲉在舟山海域尚有较大增殖潜力。 相似文献
15.
Photographic observations of the brittle starOphiura sarsi were conducted at a depth of approximately 280 m in the Pacific Ocean off tsuchi, northeastern Japan. Bottom photographs showed that this ophiuroid occurred in high densities, uniformly covering the sea floor and that other megafauna was rare. The mean density and biomass of ophiuroids in the dense bed were estimated to be 373 m–2 and 124 g m–2, respectively. Ophiuroids comprised 99% of all megabenthic organisms in terms of number of individuals, and megafaunal assemblage of the dense bed showed very low species diversity.O. sarsi exhibited a regular spatial pattern avoiding contact with conspecific neighbors. This regular spatial pattern was disrupted by certain other organisms, around which halo-like, bare areas were observed. The size and shape of these halo-like areas varied and were apparently related to the body size and/or motility of the organisms. In the present observation areaO. sarsi covered 96% of the sea bottom, and the remaining 4% was occupied by other organisms and their halo-like bare areas. 相似文献
16.
Holothuria arguinensis is a potential species for sea cucumber aquaculture in Europe. In a first experiment, feeding rate (FR), growth, absorption efficiency (AE) and survival of adults (135.01?±?10.87?g eviscerated weight) were assessed under sediment tank conditions. In a second experiment, the feasibility to use sea bream (Sparus aurata) biodeposits as a food source was studied for adults (168.69?±?14.59?g eviscerated weight). Individuals in the first experiment showed an increase of weight (specific growth rate (SGR)?=?0.2% d?1), positive FRs and mean value of AE close to 80% with a mean organic matter content of 90.07?±?11.5?mg/g in the offered sediment. Sea cucumbers fed with fish biodeposits showed a reduction of weight (SGR??1), low FRs and negative values of AE. The influence of low salinity and temperature during experiments should be considered to explain these results. Indeed, sea cucumbers can be affected by a decrease of these parameters during winter months resulting in a period of inactivity. 相似文献
17.
为改善热带珊瑚岛礁型海洋牧场的珊瑚礁生境,实现生物资源的养护和渔业资源的产出功能,在对海参等高值经济种开展底播增殖前,科学评估其生态容量是防止引发海洋牧场生态风险的重要保证。运用生态系统模型法评估了三亚蜈支洲岛热带珊瑚岛礁海洋牧场花刺参(Stichopus monotuberculatus)的底播增殖容量。根据2020~2021年蜈支洲岛海洋牧场近岛区渔业资源调查与环境因子数据,运用Ecopath with Ecosim 6.6软件构建了该海域的生态系统营养通道模型。研究表明:生态系统各功能组营养级范围介于1~3.52,系统的食物网结构以牧食食物链为主,总能流中有43%的能量来源于碎屑功能组,其在系统总能流中有重要地位。系统的总平均能量传递效率为9.353%,略低于林德曼能量传递效率(10%)。总初级生产量/总呼吸量为3.726,总初级生产量/总生物量为28.834,系统连接指数为0.256,杂食性指数为0.120,系统Finn''s循环指数和平均路径长度分别为2.485%和2.379,表明近岛区生态系统食物网结构较为简单,且系统稳定性和成熟度偏低,易受外界干扰。根据模型评估的花刺参增殖生态容量为110.21 t/km2,是现存量的206 倍,有较大增殖空间,并且达到生态容量后碎屑组的能量再循环利用效率将显著增加,营养级结构能得到进一步优化,系统稳定性及成熟度将有所提高。基于研究结果,可适当采捕与花刺参生态位相近的生物,同时增殖放流其他处于不同营养层次的经济种,从而减少种间竞争,有效利用系统冗余能量,进而扩大花刺参的生态容量,实现海洋牧场的健康可持续发展。 相似文献
18.
研究了深圳海域2008年4月、9月的水体弧菌数量、种类组成及其分布,探讨了弧菌总数及各优势类群的数量分布与环境因子间的相关关系。结果表明:弧菌总数分布具有季节性,东部海域春季(4月)的弧菌数量高于秋季(9月)的,其均值分别为1.50×104 ,8.89×102 CFU/cm3;在西部海域秋季的略高于春季的,其均值分别为5.09×102,2.66×102 CFU/cm3;弧菌数量最高值出现在大亚湾(4.40×104 CFU/cm3)。弧菌的优势类群具有季节性分布特征:春季特有的优势类群有Vibrio gigantis类似种和V. splendidus类似种,秋季特有的优势类群有V. natriegens类似种;V. alginolyticus类似种是两个季节共有的优势类群,其数量春季高于秋季的。弧菌种类、数量与海水温度、盐度及细菌总数、Chl-a等环境因子有一定的相关性,其中盐度为弧菌种类及数量分布的主要影响因子。 相似文献
19.
为了解舟山附近海域大型底栖动物群落组成特点及其与环境因子的内在关联,在2019~2020年对舟山附近海域12个站位的大型底栖动物及环境因子进行了调查研究。采用丰度、生物量、相对重要性指数(IRI)、Cluster聚类以及PCoA分析和Pearson相关性分析等方法对该海域的大型底栖动物群落组成、主要影响环境因子进行了分析。结果表明,两个航次共在舟山海域采集到大型底栖动物56种,其中多毛类动物28种,甲壳动物8种,软体动物7种,棘皮动物6种,刺胞动物3种、纽形动物2种,星虫动物和脊索动物各1种;两年平均丰度和生物量分别为36.32ind./m2和5.59g/m2,纽虫(Nemertea)是丰度的最大贡献者,而星虫爱氏海葵(Edwardsia sipunculoides)和棘刺锚参(Protankyra bidentata)则是生物量的最大贡献者;2020年大型底栖动物的总物种数、丰富度指数和多样性指数高于2019年,且两年舟山海域大型底栖动物的总物种数、丰富度指数和多样性指数均高于舟山邻近海域。与舟山海域大型底栖动物群落最相关的环境因子是水深、底层水盐度和硝态氮(NO3),这三个环境因子彼此相关性显著,随着盐度的增加,水深逐渐增加而硝酸氮含量则显著降低,群落物种数、丰度和丰富度则显著增加。通过对舟山附近海域大型底栖动物群落组成特点及其与环境因子的内在关联的研究,有望为东海近岸海域大型底栖动物群落的演替规律研究提供基础数据和科学依据。 相似文献
20.
J. Gómez-Enri M. A. Srokosz C. P. Gommenginger P. G. Challenor M. P. Milagro-Pérez 《Marine Geodesy》2013,36(3):217-233
An adequate conceptual definition of the geoid is essential for the unambiguous combination of satellite tracking data, satellite al‐timetry, and surface gravity measurements to obtain sea surface topography. The factors influencing the selection of a particular level surface of the earth's gravity field include the purpose(s) for which the geoid is to be used at the 5‐cm level, and the types of data to be used in achieving these objectives. The principal reasons for high precision determinations of the shape of the geoid are: the determination of sea surface topography for applications in oceanography; and the unification of leveling datums with a resolution equivalent to that of first order geodetic leveling. A conceptual definition of the geoid acceptable to oceanographers would be: The geoid for a selected epoch of measurement is that level surface of the earth's gravity field in relation to which the average non‐tidal (or quasi‐stationary) sea surface topography is zero as sampled globally in ocean regions. In the geodetic context, it would be convenient, though not essential, to modify this definition in such a way that the global sea surface topography had zero mean as sampled for evaluations of the geodetic boundary value problem. In either case, a basis exists for unifying all leveling datums serving areas in excess of 106 km2, using either gravity anomaly data for the regions or precise determinations of position at first order bench marks. Unfavorable signal‐to‐noise ratios can pose problems when dealing with datums serving smaller areas. Elevation and gravity data banks must be correctly referenced to leveling datums prior to use in sea surface topography determinations. A recent attempt to upgrade the Australian gravity anomaly data bank indicates that all current data banks of this type are inadequate for the task. It is unlikely that time variations in the radial position of the geoid as conceptually defined above, will exceed ±5 cm per century, provided the rate of earth expansion was less than 1 part in 1010 yr‐l and there is no dramatic change in the present rate of secular change in Mean Sea Level. 相似文献