The distribution of late-Quaternary woody taxa in northern Eurasia: evidence from a new macrofossil database

We present a database of late-Quaternary plant macrofossil records for northern Eurasia (from 23° to 180°E and 46° to 76°N) comprising 281 localities, over 2300 samples and over 13,000 individual records. Samples are individually radiocarbon dated or are assigned ages via age models fitted to sequences of calibrated radiocarbon dates within a section. Tree species characteristic of modern northern forests (e.g. Picea, Larix, tree-Betula) are recorded at least intermittently from prior to the last glacial maximum (LGM), through the LGM and Lateglacial, to the Holocene, and some records locate trees close to the limits of the Scandinavian ice sheet, supporting the hypothesis that some taxa persisted in northern refugia during the last glacial cycle. Northern trees show differing spatio-temporal patterns across Siberia: deciduous trees were widespread in the Lateglacial, with individuals occurring across much of their contemporary ranges, while evergreen conifers expanded northwards to their range limits in the Holocene.     

Forest or no forest: implications of the vegetation record for climatic stability in Western Beringia during Oxygen Isotope Stage 3

Two conflicting stratigraphic schemes describe the Siberian Karginskii interstade (Oxygen Isotope Stage 3 equivalent) as having: 1) relatively stable climate with environments more similar to the full glaciation; or 2) variable climate with landscapes that more closely approximate contemporary ones. New data from continuous lake cores and a nearly continuous section from western Beringia (WB) suggest that both schemes are valid. Herb-dominated communities, possibly with isolated populations of Larix, characterized northern WB with only a slight shift from relatively warm to cool summers during the mid-interstade. In contrast, herb and shrub tundra, steppe, forest-tundra, and modern Larix forest occurred at various times in areas of southern WB, suggesting greater climatic instability. A thermal optimum is evident in the south during the mid-interstade, with modern vegetation in southeastern WB and Larix forest-tundra in the southwest. Variations in Pinus pumila pollen indicate summer warm/winter dry and summer warm/winter wet conditions in southeastern WB. These fluctuations contrast to other areas of WB, where summers and probably winters were consistently arid. Although the interstade presents a unique interval within the Late Pleistocene, paleodata and paleoclimatic models suggest that changes in marine conditions, including sea level, were likely key drivers in the regional climate history.     

Molecular approach to determine contributions of the protist community to particle flux

The importance of key taxonomic groups of eukaryotic phytoplankton as contributors to downward particle flux was evaluated near the European time-series station (ESTOC) in the eastern subtropical North Atlantic in March 2005. For the first time, molecular (cloning and sequencing) techniques were used to compare plankton communities from various depths in the euphotic zone with clone libraries from surface-tethered particle traps. Analyses of 18S rDNA clone libraries revealed compositional differences between the phytoplankton assemblages in the photic zone and those retrieved from shallow particle traps below, suggesting that not all phytoplankton contribute equally to particle flux. Contrary to expectations, our study also showed that it is not diatoms, despite their high abundance in the water column, but rather small phytoplankton taxa that dominated sequences recovered from trap material. We provide here first observational evidence that large taxa with mineral tests may not necessarily contribute more to export production than do smaller taxa even if the former are abundant in the water column.     

A 15 000‐year record of climate change in northern New Mexico,USA, inferred from isotopic and elemental contents of bog sediments

Elemental (C, N, Pb) and isotopic (δ¹³C, δ¹⁵N) measurements of cored sediment from a small bog in northern New Mexico reveal changes in climate during the Late Pleistocene and Holocene. Abrupt increases in Pb concentration and δ¹³C values ca. 14 420 cal. YBP indicate significant runoff to the shallow lake that existed at that time. Weathering and transport of local volcanic rocks resulted in the delivery of Pb‐bearing minerals to the basin, while a ¹³C‐enriched terrestrial vegetation source increased the δ¹³C values of the sedimentary material. Wet conditions developed over a 300 a period and lasted for a few hundred years. The Younger Dryas period (ca. 12 700–11 500 cal. YBP) caused a reduction in terrestrial productivity reflected in decreasing C/N values, δ¹⁵N values consistently greater than 0‰ and low organic content. By contrast, aquatic productivity increased during the second half of this period, evidenced by increasing δ¹³C values at the time of highest abundance of algae. Dry conditions ca. 8 000–6 000 cal. YBP were characterised by low organic carbon content and high Pb concentrations, the latter suggesting enhanced erosion and aeolian transport of volcanic rock. The range in δ¹³C, δ¹⁵N and C/N values in the sedimentary record fall within the range of modern plants, except during the periods of runoff and drought. The sedimentary record provides evidence of natural climate variability in northern New Mexico, including short‐ (multi‐centennial) and long‐(millennial) term episodes during the Late Pleistocene and Holocene. Copyright © 2010 John Wiley & Sons, Ltd.     

Northern hudson bay and foxe basin: Water masses,circulation and productivity

Abstract

Total alkalinity and total carbonate determinations together with salinity and temperature are used to characterize water masses in Foxe Basin, Hudson Bay and Hudson Strait. From these measurements, we are able to infer the amounts of fresh water from river runoff and from sea‐ice meltwater. The average ice cover is estimated to be 1.9 m, and the residence time of river runoff in Hudson Bay is 3—4 years. Estimates of biological productivity were made by “correcting” total carbonate measurements for effects of biological processes, giving a value of 24 gC m a for new production.     

浅海声速剖面自动分类方法研究

海洋中的声速剖面是影响水声设备效能的重要环境因素之一,声速剖面的自动分类和区划对海洋环境的应用意义重大.依据浅海30分方区按月统计声速剖面,通过归一化处理和Akima差值采样,建立了各方区按月归化后声速剖面的分层梯度样本集,并应用多种系统聚类算法分别对分层梯度样本集进行分析;计算各种算法在不同聚类数水平下聚类结果的总的类内离差和,依据总的类内离差和变化曲线拐点对应的聚类数目,结合分类结果确定浅海声速剖面最优聚类数目.对大量历史统计声速剖面数据的分析结果表明,该方法得到的聚类结果与人工经验分类结果吻合较好.     

基于TerraSuite的网络化三维空间信息平台的构建

介绍了基于TerraSuite的三维影像平台,分析了结合TerraSuite与ArcGIS软件实现网络化三维平台的可行性,构建了基于TerraSuite与ArcGIS的网络化三维空间信息平台。     

水声环境仿真及其可视化技术研究

针对水声环境对舰艇声纳探测效能的显著影响以及主要海域海洋环境特点,建立了浅海和深海水声环境仿真模型,实现了对海区水声环境的快速、准确预报。提出了基于3维声场纹理预积分的水声环境体可视化方法,实现了对水下声场的直观表达与多维分析,从而为水声环境的认知、教学训练以及决策支持提供了有效手段。     

水声环境仿真及其可视化技术研究

针对水声环境对舰艇声纳探测效能的显著影响以及主要海域海洋环境特点,建立了浅海和深海水声环境仿真模型,实现了对海区水声环境的快速、准确预报.提出了基于3维声场纹理预积分的水声环境体可视化方法,实现了对水下声场的直观表达与多维分析,从而为水声环境的认知、教学训练以及决策支持提供了有效手段.