围垦对舟山群岛海域潮流结构及潮能分布影响研究

舟山群岛海域潮能丰富,近年来大面积的围垦工程影响了邻近海域的潮流结构与潮能分布特征。基于FVCOM(finite volume coastal ocean model)三维水动力数值模型,选取1984年、2010年、2019年三个代表年份,探讨围垦工程影响下舟山群岛海域潮流结构与潮能分布的时空变化状况。结果显示:1984年至2010年间围垦面积相对不大,且较为分散,主要改变外海进入杭州湾各通道的潮能分配,对能量耗散的影响较小。2010年至2019年间的围垦工程缩窄了潮汐通道,流速增大使得螺头水道及邻近水道的潮能增加,近底流速增大与较强湍流涡旋的产生,使得围垦工程周边海域能量耗散更为集中。     

Insights of long-term geomorphological evolution of coastal landscapes in hot-spot oceanic islands

The Canary Islands form a volcanic archipelago in which a west–east (W–E) chain of progressively older and less active islands can be observed. In the Canary Islands, unlike most hot-spot archipelagos, certain geodynamic peculiarities have promoted longer periods of island survival, exceeding 20 Myr. This factor makes these islands a suitable context for this work, which aims to analyze extensively the coastal geomorphic structure on islands with different development states. For this, three islands in different volcanic phases were selected: La Palma (1.8 Myr), Gran Canaria (14.5 Myr) and Fuerteventura (22.6 Myr). An ad hoc landform-based hierarchical taxonomy was designed to analyze the coastal geomorphic structure of the three islands. Based on a multi-sourced analysis in geographic information system (GIS) and field recognition, a comprehensive cartographic database was collected using the coastline data-storing (CDS) method as a feature abundance proxy. Three different aspects of the geomorphological structure were compared and related between the islands: (i) composition, (ii) abundance and (iii) diversity. Through their comparison, we attempt to explore geomorphological aspects of coastal evolution over geological spatiotemporal scales. Composition was explored analyzing the distribution of the feature's longshore frequencies (p). Abundance, by metrics of local abundance (N_∩) and whole density (N_U). Diversity, through four indices: normalized richness (S) and Margalef index (M) to estimate richness; Simpson index (D) and Shannon index (H’) to estimate evenness. We identified a systematic transformation in the dominant landform composition and a systematic trend in increasing geomorphological abundance and diversity from younger to older islands. The results show a long-term structural pattern defined by the increase in coastal geomorphic complexity (abundance and diversity) over geological time, as the coasts evolve from predominantly rocky-erosive to increasingly clastic-depositional environments. This long-term geomorphological pattern may be a general aspect of hot-spot island archipelagos, which can bring a new perspective to the knowledge of their coastal evolution. © 2018 John Wiley & Sons, Ltd.     

南海北部东沙海域巨型水下沙丘的分布及特征

本文基于多波束测深和高分辨率多道反射地震数据研究了东沙海域深水巨型水下沙丘的特征.巨型水下沙丘发育在230~830m水深的上陆坡范围内,呈斑块状分布.NW-SE向的近海底流体运动不仅冲蚀地层,形成了三条与水下沙丘间隔分布的冲蚀带,为水下沙丘提供了沉积物来源,同时也为水下沙丘的形成提供了动力源.研究区水下沙丘波长(L)范围55~510m,波高(h)范围1.5~20m,二者呈指数关系分布.沙丘的波长随水深增大而增大,波高则在500~700m水深范围内最大.水下沙丘NE—SW向展布的脊线和几何参数关系是与现今水动力条件相平衡的结果.     

Timing of Cadomian and Variscan tectonothermal activity,La Hague and Alderney,North Armorican Massif: Evidence from 40Ar/39Ar mineral ages

The La Hague region of northwest France exposes Palaeo-Proterozoic Icartian gneisses which were reworked and intruded by calc-alkaline plutonic rocks during the Cadomian Orogeny (about 700–500 Ma). ⁴⁰Ar/³⁹Ar mineral cooling ages have been determined to clarify the timing of the regional metamorphism of orthogneisses and the emplacement of quartz diorite plutons in this region. Metamorphic amphiboles within Icartian gneisses display discordant ⁴⁰Ar/³⁹Ar apparent age spectra interpreted to result from limited Variscan (about 350–300 Ma) overprinting of intracrystalline argon systems which initially cooled through post-metamorphic hornblende closure temperatures during the Cadomian at about 600 Ma. Igneous hornblendes from the weakly foliated Jardeheu and Moulinet quartz diorites record isotope correlation ages of 599 ± 2 and 561 ± 2 Ma, respectively. Igneous hornblende and biotite from foliated quartz diorite on the nearby Channel Island of Alderney record isotope correlation ages of about 560 Ma. The results imply that metamorphic and plutonic events in the La Hague-Alderney region were approximately contemporaneous with those recorded on Guernsey and Sark, which are thus likely to have formed part of the same tectonic block during the Cadomian Orogeny.     

Non-synchronous records of Holocene aeolian sand deposition and landscape stability at adjacent lake-side sites in the Falkland Islands,South Atlantic: a caution

Lithostratigraphical interpretation and ¹⁴C dating of adjacent lake-side sedimentary sequences at the Sulivan House lakes, West Falkland, indicate between-site non-synchronous records of Holocene aeolian sand deposition and landscape stability. It is inferred that the sands are associated with deflation of exposed sandy shorelines at times of lower lake levels, whereas stability phases are characterised by peat formation and/or organic matter incorporation into sand horizons at times of ‘normal’ lake levels. The data imply that a cautious approach to interpretation of lake-side sediments may be warranted if the purpose is to use lake-level changes and aeolian — non-aeolian interbeds as proxy indicators of regional climatic signals. © 1998 John Wiley & Sons, Ltd.     

Sedimentary fabric characterized by X-ray tomography: A case-study from tsunami deposits on the Marquesas Islands,French Polynesia

X-ray tomography is used to analyse the grain size and sedimentary fabric of two tsunami deposits in the Marquesas Islands (French Polynesia, Pacific Ocean) which are particularly exposed to trans-Pacific tsunamis. One site is located on the southern coast of Nuku Hiva Island (Hooumi) and the other one is on the southern coast of Hiva Oa Island (Tahauku). Results are compared with other techniques such as two-dimensional image analysis on bulk samples (particle analyser) and anisotropy of magnetic susceptibility. The sedimentary fabric is characterized through three-dimensional stacks of horizontal slices (following a vertical step of 2·5 mm along the cores), while grain-size distribution is estimated from two-dimensional vertical slices (following a step of 2 mm). Four types of fabric are distinguished: (a) moderate to high angle (15 to 75°); (b) bimodal low-angle (<15°); (c) low to high angle with at least two different orientations; and (d) dispersed fabric. The fabric geometry in a tsunami deposit is not only controlled by the characteristics of the flow itself (current strength, flow regime, etc.) but also sediment concentration, deposition rate and grain-size distribution. There is a notable correlation between unimodal high-angle fabric – type (a) – and finely-skewed grain-size distribution. The two tsunami deposits studied represent two different scenarios of inundation. As demonstrated here, X-ray tomography is an essential method for characterizing past tsunamis from their deposits. The method can be applied to many other types of sediments and sedimentary rocks.     

全球变化下中国南海诸岛珊瑚礁热压力临时避难所研究

选取第五次耦合模式比较计划（CMIP5）模式中较适宜于南海海表面温度（SST）模拟的加拿大地球系统模式(CanESM2),并获取其在IPCC RCP2.6、RCP4.5和RCP8.5温室气体排放情景下模拟的2006-2100年南海SST数据。基于南海诸岛珊瑚礁和线性回归方法分析了RCPs情景下的珊瑚礁区夏季SST上升趋势,并基于热周指数(DHW, Degree Heating Weeks)及年白化时间指数分析了RCPs情景下的南海诸岛珊瑚礁热压力临时避难所,主要得出以下结论：① RCPs情景下,明显变暖的珊瑚礁海域均为南沙群岛;② 年白化时间不晚于全球珊瑚礁平均年白化时间的珊瑚礁像元占南海诸岛总珊瑚礁像元的比例,在RCP2.6、RCP4.5和RCP8.5情景下分别为17%、29%和42%,均分布在南沙群岛;③ RCPs情景下,较高纬度的西沙群岛、中沙群岛和南沙群岛北部为未来南海诸岛珊瑚礁热压力临时避难所。     

Linked turbidite–debrite resulting from recent Sahara Slide headwall reactivation

The northwest African margin has been affected by numerous large-scale landslides during the late Quaternary. This study focuses on a recent collapse of the Sahara Slide headwall and characterises the resulting flow deposit. Core and seismic data from the base of the upper headwall reveal the presence of blocky slide debris, comprising heavily deformed hemipelagic slope sediments. The blocky slide debris spilled over a lower headwall 60 km downslope and formed a thick transparent debris flow unit. Cores recovered 200–250 km farther downslope contain a surficial turbidite that is interpreted to be linked to the headwall collapse event based on timing and composition. One core located approximately 200 km from the headwall scar (C13) contains debrite encased in turbidite. The debrite comprises sheared and contorted hemipelagic mudstone clasts similar as those seen in the vicinity of the Sahara Slide headwall, and lacks matrix. This debrite pinches out laterally within 25 km of C13, whereas the accompanying turbidite can be correlated across 700 km of the northwest African margin. The linked turbidite–debrite bed is interpreted to have formed through recent failure of the steep Sahara Slide headwall that either 1) generated both a debris flow and a turbidity current almost simultaneously, or 2) generated a debris flow which with entrainment of water and progressive dilution led to formation of an accompanying turbidity current.     

浙江南麂列岛海域氮、磷营养盐季节动态及其环境影响因子分析

利用南麂海域4个站位2006年4月至2007年3月的连续调查资料,研究了该海域氮、磷营养盐的季节变化特征及其影响因素.南麂海域的无机氮主要由硝酸盐构成,平均占有比例77%.氮、磷营养盐的季节性变化显著,并且两者呈现同步的上升或下降的趋势.PO4-P 与 NO3-N 的相关性显著 ( r = 0.665 ).NO3-N 与水温、pH、盐度等多项因子之间均具有显著的相关性,其中与水温的相关性最为密切 ( r = 0.798 ).