Speciation of trace metals in sediments of a tropical estuary

Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment.     

Infiltration at the Tai rain forest (Ivory Coast): Measurements and modelling

Infiltration experiments have been performed at three sites along a well-known catena under virgin tropical rain forest using a portable sprinkling infiltrometer. Experimentally determined infiltration curves are presented. Infiltration curves are also simulated on the basis of the Mein-Larson equation. The parameters for this model have been obtained from the infiltration curves (saturated conductivity) and simple soil moisture determinations (fillable porosity). The agreement between experimentally determined and modelled infiltration is reasonable, provided (a) saturated conductivity as derived from the experimental data is corrected, (b) a storage parameter, also derived from the experimental data, is added to the Mein-Larson model, and (c) the decline in soil porosity with depth is either small or occurs abruptly at shallow depth. Comparison of observed infiltration rates with rainfall intensity shows that Horton Overland Flow has to occur naturally at least on the middle and lower section of the catena. Despite the fact that most parameters can be estimated in principle from basic soil data, it remains advisable to obtain sprinkling infiltrometer field measurements, because of soil variability due to dynamic surface conditions, macroporosity, air entrapment, and irregularity of the wetting front.     

Coastal geomorphic evolution at the Denglou Cape, the Leizhou Peninsula

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23,000 yr of vegetation history of the Upper Lerma, a tropical high-altitude basin in Central Mexico

Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 ¹⁴C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 ¹⁴C yr B.P. and the Tres Cruces Tephra of 8500 ¹⁴C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 ¹⁴C yr B.P. to ca. 11,600 ¹⁴C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 ¹⁴C yr B.P., and at ca. 12,600 ¹⁴C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 ¹⁴C yr B.P. After 10,000 ¹⁴C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 ¹⁴C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 ¹⁴C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles.     

The mesoscale convection life cycle: Building block or prototype for large-scale tropical waves?

A cumulonimbus cloud may ascend and spawn its anvil cloud, precipitation, and downdrafts within an hour or so. This paper inquires why a similar progression of events (life cycle) is observed for tropical weather fluctuations with time scales of hours, days, and even weeks. Regressions using point data illustrate the characteristic unit of rain production: the mesoscale convective system (MCS), covering tens of kilometers and lasting several hours, with embedded convective rain cells. Meanwhile, averages over larger spatial areas indicate a self-similar progression from shallow to deep convection to stratiform anvils on many time scales.Synthetic data exercises indicate that simple superpositions of fixed-structure MCS life cycles (the Building Block hypothesis) cannot explain why longer period life cycles are similar. Rather, it appears that an MCS may be a small analogue or prototype of larger scale waves. Multiscale structure is hypothesized to occur via a Stretched Building Block conceptual model, in which the widths (durations) of zones of shallow, deep, and stratiform anvil clouds in MCSs are modulated by larger scale waves.Temperature (T) and humidity (q) data are examined and fed into an entraining plume model, in an attempt to elucidate their relative roles in these large-scale convection zone variations. T profile variations, with wavelengths shorter than troposphere depth, appear important for high-frequency ( 2–5-day period) convectively coupled waves, as density directly links convection (via buoyancy) and large-scale wave dynamics (via restoring force). Still, the associated q anomalies are several times greater than adiabatic, suggesting a strong amplification by shallow convective feedbacks. For lower frequency (intraseasonal) variability, q anomalies are considerably larger compared to T, and may be dominant.     

南方涛动、热带海温与西北太平洋副高的联系

本文应用统计方法,首先探讨南方涛动指数与西北太平洋副热带高压的联系,然后分析赤道和热带太平洋区域海温对南方涛动的响应情况,同时分析南方涛动响应区域的海温与当时及滞后的西北太平洋副热带高压的联系,从中探讨南方涛动、厄尔尼诺海温异常及西北太平洋副热带高压之间的一种可能的相互作用机制。     

165°E赤道太平洋溶解氧垂直分布异常分析

根据1986—1990中美热带西太平洋海气相互作用8个航次合作综合调查资料，分析了1987年10月赤道中西太平洋165°E（10°N－6°S）次表层水形成溶解氧最大值的原因。1986－1987年E1Nino衰退时期，该海域赤道附近在E1Nino强盛时期下沉的次表层水开始回升，短时期内形成了类似于中、高纬度海域的理化环境，使浮游生物在混合层内聚集生长，最终导致溶解氧含量在次表层出现最大值和过饱和含量。     

The Sunda Shelf—A Submerged Amazon Basin?

A crucial and debatable issue in paleoclimatology is the change of terrestrial vegetation and the role of its carbon storage in glacial cycles. In the modern world, the Amazon Basin hosts the largest tropical rainforest and plays a major role of carbon sink, but during the glacial times another large tropical rainforest must have formed in the then emerged Sunda Shelf, SE Asia, and significantly changed the global carbon cycling. Accordingly, ocean drilling expeditions to the Sunda Shelf are being proposed in order to investigate the sea level changes, evolution of river network, vegetation and carbon storage, as well as biogeography of the tropical region over the last millions of years.     

Seismic and stratigraphic evidence for reef expansion and onset of aridity on the Northwest Shelf of Australia during the Pleistocene

Modern reef (the Great Barrier Reef and Ryukyu Reef) distribution in the Indo-Pacific region is strongly controlled by warm currents (East Australian and Kuroshio Currents) that radiate from the Indo-Pacific Warm Pool. The modern distribution of reefs (south of 15°S) on the Western Australian shelf is related to the presence of the warm Leeuwin Current. However, the age of the reefs south of 15°S, and hence their temporal relationship to the Leeuwin Current, has been largely unknown. Seismic and subsurface stratigraphic data show that reef growth and expansion on the Northwest Shelf of Australia began in the Middle Pleistocene (∼0.5 Ma). The oldest ooids in the region are approximately synchronous with reef growth. We suggest a two stage process for the spread of reefs to higher latitudes on the Western Australian coast; first an increase in Leeuwin Current activity at approximately 1 Ma brought warm waters and a tropical biota to the region; and second, increased aridity after ∼0.6 Ma led to a decline in clastic input and increased alkalinity, triggering ooid formation and reef expansion to higher latitudes associated with the switch to higher amplitude glacio-eustatic cycles at the end of the Middle Pleistocene Transition. The timing and mechanisms for reef expansion south along the Western Australian coast has implications for the origin of the Eastern Australian Middle Pleistocene Great Barrier Reef, the New Caledonia Barrier Reef and Japanese Ryukyu Reef systems.     

台湾地形对台风Meranti(1010)经过海峡地区时迅速增强的影响研究

台风在趋近大陆过程中强度一般衰减, 但Meranti(1010)北上进入台湾海峡过程中却迅速加强, 且在登陆福建时达到最强。采用中国气象局台风资料、NCEP GFS 0.5°×0.5°再分析资料及台湾雷达资料, 结合中尺度数值模式WRF(The Weather Research and Forecasting Model)开展台湾地形敏感性试验, 研究Meranti进入台湾海峡过程中的结构变化及迅速加强机理。结果表明:台湾地形是Meranti迅速加强的一个重要影响因子。Meranti北上过程中, 一方面通过台湾岛地形分流作用及其背风坡效应在台湾海峡内诱生中尺度涡旋, 形成正负相间的涡度分布, 激发出与台风相关的扰动波列。地形强迫抬升及扰动波列可加强垂直运动和积云对流, 有利于台风对流发展。另一方面, 台湾地形还通过改变环境气流使台风高空辐散场加强, 环境风垂直切变减小, 形成有利于台风发展的环流背景。比较不同高度台湾地形试验中台风动能收支发现, 台湾地形激发的扰动波列和积云对流增强了次网格尺度系统与台风间能量的交换, 成为Meranti登陆前迅速加强的主要动能源。