Community structure and nutrition of deep methane-seep macrobenthos from the North Pacific (Aleutian) Margin and the Gulf of Mexico (Florida Escarpment)

Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200–3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep‐water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow‐seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane‐derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 ± 11,618 ind·m⁻²), the lowest in the Florida pogonophoran fields (926 ± 132 ind·m⁻²), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non‐seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (>60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H′) was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non‐seep sediments. Community composition differences between seep and non‐seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep δ¹³C and δ¹⁵N signatures were lighter for seep than non‐seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest δ¹³C values (average of species’ means) were observed at the Florida escarpment (−42.8‰). We estimated that on average animal tissues had up to 55% methane‐derived carbon in Florida mats, 31–44% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9–23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific δ¹³C variation (>30‰) between patch types. Overall we found few characteristic communities or features common to the three deep‐water seeps (>3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.     

黄海西部春季海洋锋及其与渔业的关系

海洋锋是一种海洋学特征。作者根据1960—1981年的资料,用温、盐指标依聚类方法分析研究了该海区的环流结构和水团的混合带,最后定出了海洋锋的位置。本文还描述了春季黄海中的海洋锋的分布及特征,及其与鹰爪虾、鲅鱼、鲐鱼洄游规律和渔场的关系。     

水团相互作用与东海高密水环流的演变

本文利用水文和海流观测资料，从水团相互作用去研究东海高密水及其环流的演变。获得如下一些结果：东海高密水冬季形成于东海中部陆架混合水中，入春以后水团挤压，高密水显得更为突出，入秋后高密水变性，东海中部陆架混合水重新形成；东海高密水核心区可形成气旋环流，从冬到秋经历了一个弱—强—弱的演变过程。海流观测结果证实这个环流是存在的；在东海高密水南侧存在较明显的密度锋，从冬到秋它也经历了一个弱—强—弱的演变过程；水团分析发现，各种与主体分离的混合水从春到夏可在高密水核心周围组合成一个环，从而进一步印证了这个高密水环流的存在     

黄海冷水团上升流对叶绿素垂向分布的影响

利用黄海冷水团物理-生态耦合模式，对冷水团水域叶绿素垂向分布的季节变化进行了数值模拟研究。物理模式为冷水团热动力模型，生态模式主要考虑叶绿素，营养盐和食植浮游动物基本状态变量的耦合方程。研究结果表明，黄海冷水团上升流对叶绿素垂向分布的夏季上层结构具有显著影响。整个夏季，受上升流的影响，叶绿素垂向分布最大值的位置向海面抬升，量值增大，混合层叶绿素的平均浓度增加，与实测资料比较表明，考虑冷水团上升流的影响比不考虑上升流与实测结果符合要好。     

Nature and Distribution of the Deformation Front in the Luzon Arc-Chinese Continental Margin Collision Zone at Taiwan

Marine seismic reflection profiles from offshore SW Taiwan combined with onland geological data are used to investigate the distribution and nature of the deformation front west of Taiwan. Locations of the frontal structure west of Taiwan are generally connected in a linear fashion, although the alignment of frontal structures is offset by strike-slip faults. The deformation front begins from the northern Manila Trench near 21°N and continues northward along the course of the Penghu Submarine Canyon in a nearly N–S direction north of 21°N until it reaches the upper reaches of Penghu Canyon at about 22°15′N. The deformation front then changes direction sharply to the northeast. It connects to the Chungchou thrust fault or the Tainan anticline in the coastal plain and continues northwards along the outer Western Foothills to the northern coast of Taiwan near 25°N. Characteristics of structural style, strain regime, sedimentation and tectonics vary along the trend of the deformation front. Ramp anticlines, diapiric intrusion and incipient thrust faults are commonly associated with the deformation front. Variations in structural style along strike can be related to different stages of oblique collision in Taiwan. The deformation front (collision front) west of Taiwan can be considered as a boundary between contraction in the Taiwan orogen and extension west of the collision zone. The deformation front east of the Tainan Basin and its northward extension along the outer limit of the Western Foothills is the surface trace separating the foreland thrust belt from the nearby foredeep, not a boundary between the Chinese and Taiwan margins. The submarine deformation front off SW Taiwan is the surface trace separating the submerged Taiwan orogenic wedge from the Chinese passive continental margin, not a surface trace of the plate boundary between the Eurasian and Philippine Sea plates.     

Particle flux through the Huanghai Sea cold water mass

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value.     

东海北部区域底层冷水团的形成及其季节变化

本文着重探讨东海北部底层冷水(北部冷水)的形成原因、基本特征和季节变化过程。指出北部冷水系冬季黄海沿岸水南下向东海输送低温水并与外海高盐水混合变性形成的。其位置随季节变化而有明显的移动规律,即先由西向东移,而后向北收缩。大体上可分为四个阶段:冷水舌离岸期,北部冷水半封闭期,北缩消亡期和更新期。文中分析了上述变化的原因,较详细地阐述了黄海沿岸水沿陆架下沉与黑潮次—中层混合水爬升的关系及其对北部冷水的影响。分析了北部冷水与黄海冷水团的关系。     

青岛冷水团强度的变化特征

青岛冷水团盘踞于山东半岛东南部近海的深底层。它是南黄海西部海域中的一个突出而重要的水文现象。青岛冷水团的存在和变动不仅使南黄海西部的环流结构和水文状况趋于复杂，而且还影响山东近海渔场春汛渔期的早晚和鱼群的集散程度(郑东等，1983；张元奎等，1989)。 目前，对青岛冷水团的温、盐特性及其成因早已有研究(郑东等，1983；张启龙等，1996；Zhang et al.，2002)，但有关青岛冷水团的长期变化特征尚未见报道。作者在已有研究结果基础上，利用1959~1995年间的水温资料，对青岛冷水团强度的变化特征进行分析，以期加深对青岛冷水团的认识以及为该海域海洋水产资源的合理开发利用提供科学依据。