振冲碎石桩在加固砂性土地基中的应用

本文介绍在杭州市钱江水厂一期工程中，采用振冲碎石桩加固处理砂性土地基，既提高了地基的抗液化能力，又提高了复合地基承载力，取得了良好的效果，并在该水厂建设的后续工程中得到推广应用。     

末次冰消期以来白令海盆的冰筏碎屑事件与古海洋学演变记录

通过对白令海盆中部BR02岩芯高分辨率的颜色、粒度和元素地球化学地层的研究发现:(1)该岩芯较为完整地记录了末次盛冰期结束以来(约16.3 ka BP)的多期冰筏碎屑事件,包括H1、OD、YD和北方2期,其中以H1和YD最为显著,反映了末次冰消期以来该地区海冰/冰山以及区域性冰川的消长变化;(2)BR02岩芯上部17—25 cm段出现富Mn、富Ba的氧化型沉积,说明在全新世高海面时期,白令海与北太平洋、北冰洋之间的水体交换达到极点,白令海环流加强,海盆底层水含氧状况明显改善,并引发海洋生产力增加;(3)CaO、Na2O、Sr、Zr及Na2O/K2O比值的分布说明,海盆冰筏碎屑主要来自富碳酸盐的育空河流域,其次为阿拉斯加半岛和阿留申群岛等火山岩区;岩芯上部Na2O/K2O比值的递增暗示10 ka BP以来与火山物质输运有关的北太平洋入流(阿拉斯加流)可能增加。     

海洋沉积物不同相态中Sr、Nd同位素提取方法研究

海洋沉积物中Fe-Mn氧化物相和残渣态的Sr、Nd同位素组成能够敏感地指示洋流循环及物质来源,但实验室对沉积物中上述相态的Sr和Nd同位素的提取易产生过量或提取不完全,进而影响同位素测定结果的准确性,因此制定有效的提取流程显得非常重要。本文采用不同浓度盐酸羟胺(Hydroxylamine Hydrochloride,HH)与醋酸(Acetic Acid,HAc)混合溶液对中印度洋海盆深海沸石黏土、北极半深海沉积物以及安达曼海近海沉积物的Fe-Mn氧化物相进行提取,残渣态用HNO3-HF高压密闭消解法溶融,测定了各相态的主微量元素含量及Sr、Nd同位素组成,通过分析不同实验条件下得到的Fe-Mn氧化物相与残渣态的稀土元素(REE)配分模式、Al/Nd含量比值及Sr、Nd同位素组成,建立了3种不同成因类型海洋沉积物不同相态的化学提取方法。提取深海沸石黏土中Fe-Mn氧化物相的理想试剂条件为0.25 mol/L HH和15%HAc,北极半深海沉积物和安达曼海近海沉积物的试剂条件为0.5 mol/L HH和15%HAc。该方法可以准确获得沉积物中Fe-Mn氧化物相与残渣态的Sr、Nd同位素组成信息,为古海洋学的研究提供方法支持。     

Plankton of lake Ototoa,a sand‐dune lake in Northern New Zealand

The seasonal cycles of abundance of the phytoplankton and zooplankton in Lake Ototoa, Northland, at 36° 31 S, 174° 14 E, are described. Concentrations of chlorophyll a were low (range 0.04–4.61 mg.m^‐3; mean 0.97 mg.m^‐3), and highest values were in winter. Phytoplankton densities were also low; an oligo‐trophic diatom‐desmid assemblage associated with Botryococcus, Dinobryon, and Svhaerocyslis was found.

The zooplankton was dominated by the calanoid copepod Calamoecia lucasi whose numbers remained fairly constant throughout the year, and the only other copepod found was the cyclopoid Mesocyclops leuckarti which was present in very low numbers. Bosmina meridionalis was the only limnetic cladoceran and was most abundant during autumn and spring. A number of rotifer species were also common.     

Mass stranding of molluscs at Te Waewae bay,southland, New Zealand (note)

A stranding of shellfish on the beach at Te Waewae Bay, Southland, occurred during a period of very cold, stormy weather in September 1970. More than 20 million shellfish were stranded, the majority being Mactra discors Gray. It is suggested that the cause was a combination of Strong inshore winds and low air temperatures, coupled with an increased flow of fresh, cold water across the beach.     

Structure of a mudflat diatom community in the Avon‐Heathcote Estuary,New Zealand

Parameters of community structure (species composition and relative abundance, number of taxa, diversity, evenness, and cell density) were measured for a mudflat diatom community in the Avon‐Heathcote estuary, New Zealand. Fifty three diatom species were identified: 25 taxa (species and varieties) are new New Zealand records. The Shannon‐Wiener information index (H') was 3.46, indicating high diversity. Evenness (J') ranged from 0.57–0.67. The association between the biomass of the pulmonate gastropod, Amphibola crenata, and benthic diatom community structure was studied using large open enclosures (4.0 m²) to manipulate snail biomass. Community structure was compared at 0, 5 (natural biomass), and 10 g A. crenata dry weight per m. A similarity index (SIMI=0.88–0.95), as well as H’ and J’ indicated close similarity between the diatom assemblages within all enclosures, but number of taxa increased from 33 to 49 with increasing snail biomass. Cell densities were significantly lower at high snail biomass (6088 valves per mm²) compared to enclosures with no snails (10 110 valves per mm ). A. crenata had a higher ratio of diatom fragments to whole diatom valves in its faeces (2.42) than in its crop (0.55), indicating that it is capable of fragmenting diatoms.     

The flux of floating macrodetritus in the North inlet estuarine ecosystem

An estimate of floating macrodetritus flux in a salt marsh-dominated estuarine ecosystem indicates that this material is exported regularly. However, the amount of macrodetrital material exported is small, less than 1% of the net marsh primary productivity. The export of floating macrodetritus is seasonal with maximum values in summer.     

Were glacial iceberg surges in the North Atlantic triggered by climatic warming?

High-resolution physical, mineralogical, sedimentological and micropalaeontological studies were carried out on North Atlantic cores from the Reykjanes Ridge at 59°N and from the region southwest of the Faeroe Islands. All core sites are situated along the pathway of Iceland-Scotland Overflow Water (ISOW) and the various parameters measured display similar features. Previously identified carbonate oscillations [Keigwin and Jones (1994) J. Geophys. Res., 99, 12397-12410] in the time span back to the Marine Isotope Stage 5-4 transition and Late Glacial lithic events [Bond and Lotti (1995) Science, 267, 1005-1010], such as the Heinrich ice-rafting events, are all represented in the core records. Long-term trends and higher-frequency changes in ISOW intensity were reconstructed on the basis of various independent proxy records. The long-term trends in circulation match theoretical orbitally forced insolation changes. Our observed links between ice-rafted detritus (IRD) input, variations in sea surface temperature (SST) and circulation at greater depth point to the need to re-examine the origin of IRD events. We suggest that these events may have been triggered by enhanced, partly sub-surface, heat transport to the north. Enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves, leading to increased iceberg discharge and ice sheet destabilization. This discharge resulted in lower SST’s and a lower temperature over Greenland. Thus, as shown by our records, this scenario implies a temporary de-coupling of surface processes and circulation at greater depth. A key feature is the occurrence of a saw-tooth pattern in the marine data, which is similar to the Greenland ice core records. Moreover, the ‘warming’ theory of IRD events would explain the observed ‘out-of-phase’ relationship between the Greenland and Antarctic ice core records and also the rapid establishment of higher temperatures over Greenland immediately after the cold phases (stadials) of the Dansgaard-Oeschger cycles.     

The Detritic Compartment in a Posidonia oceanica Meadow: Litter Features, Decomposition Rates, and Mineral Stocks

Abstract. The ecosystem associated to the Mediterranean seagrass Posidonia oceanica shows a clear distinction in two subcompartments regarding turnover time: aboveground and belowground. Aboveground parts (leaves) are highly dynamic, and most of the leaf material is decomposed or exported in less than one year, representing a net loss of nutrients. In contrast, belowground biomass (roots and rhizomes) has a turnover time of the order of centuries, with a consequent accumulation of organic matter in the sediment. The accumulation rates for the single elements rank in the order C > N > P. This ecosystem may be considered as a sink for biogenic elements.