The process of sedimentation on the surface of a salt marsh

An unditched salt marsh-creek drainage basin (Holland Glade Marsh, Lewes, Delaware) has a sedimentation rate of 0·5 cm year^?1. During normal, storm-free conditions, the creek carries negligible amounts of sand and coarse silt. Of the material in the waters flooding the marsh surface, over 80% disappears from the floodwaters within 12 m of the creek. About one-half of the lost material is theoretically too fine to settle, even if flow were not turbulent; however, sediment found on Spartina stems can account for the loss.The quantity of suspended sediment that does reach the back marsh during these normal tides is inadequate to maintain the marsh surface against local sea level rise. This suspended sediment is also much finer than the deposited sediments. Additionally, remote sections of low marsh, sections flooded by only the highest spring tides, have 15–30 cm of highly inorganic marsh muds.This evidence indicates that normal tidal flooding does not produce sedimentation in Holland Glade. Study of the effects of two severe storms, of a frequency of once per year, suggests that such storms can deposit sufficient sediment to maintain the marsh.The actual deposition of fine-grained sediments (fine silt and clay) appears to result primarily from biological trapping rather than from settling. In addition, this study proposes that the total sedimentation on mature marshes results from a balance between tidal and storm sedimentation. Storms will control sediment supply and movement on micro- and meso-tidal marshes, and will have less influence on macro-tidal marshes.     

兰州风尘沉积的粒度分布模式及其古气候意义

通过对兰州不同气候背景下形成的风尘沉积 1 80个样品详细的粒度分析,建立了该地区风尘沉积的粒度分布基本模式。发现研究区风尘沉积具有以下特征:(1 )沉积物分选差,主要由粒径 >4Φ的颗粒组成,平均6.4Φ (2 )粒级构成为极细砂 2.6 %、粉砂 77.8%、粘土 1 9.6 %,属粉质重亚粘土或典型黄土 (3)频率曲线为单峰、极正偏类型,且具有粗头短促、中间宽大和细尾拉长的特点 (4)短期悬浮颗粒与长期悬浮颗粒大致呈对等配比。这些特征同时也为兰州现代尘暴沉积物所具备,因而可视为该地区风尘沉积的一个基本诊断模式搬运方式。颗粒粒径 <5.5 0Φ的含量指标 (GSP1)和 4.5 0～ 6.5 0Φ的含量指标 (GSP2 )可分别作为冰期-间冰期尺度和冰段-间冰段尺度东亚冬季风演化和沙尘暴强弱程度的基本判据。     

2002年3月21—22日影响韩国的沙尘天气分析

利用气象卫星、天气形势场和NCEP/NCAR再分析资料,分析了2002年3月21—22日影响韩国沙尘天气的原因。结果表明:影响韩国沙尘天气的沙尘主要源地是蒙古国和中国内蒙古地区。沙尘天气发生在地面冷锋后部,高压伸展的前面;19日和20日沙尘暴发生后,沙尘沿着西北风输送,21日早晨影响韩国;PM10最高值达到2 778.2μg/m³,由于西北风较强,沙尘暴发生后很快影响到韩国,但在韩国持续的时间较短。     

Testing the auto‐abrasion hypothesis for dust production using diatomite dune sediments from the Bodélé Depression in Chad

This study examines the role of quartz sand in the production of dust using mixtures of quartz sand from the Sahara and diatomite aggregates from the Bodélé Depression in Chad. An aeolian abrasion chamber is used to reproduce the physical processes of aeolian abrasion and test the hypothesis that the breakdown of saltating diatomite flakes as they collide in saltation, and with the surface, is the most prolific mechanism of dust production (auto‐abrasion). This hypothesis is tested against the competing hypothesis that a hard, higher‐density quartz sand impactor is required to abrade fine‐grained sediments to generate dust. The results show that dust can be produced by a mixture of saltating diatomite and quartz sand particles. However, quartz sand is not required for saltating aggregates to produce dust. Indeed, these results, which used a mixture of very coarse‐grained aggregate (1 to 2 mm diameter) with fine quartz sand, indicate that the addition of quartz sand can decrease dust production. For a very coarse aggregate (1 to 2 mm), a pure diatomite aggregate produced the most dust, although using a coarse‐grained aggregate (0·5 to 1·0 mm) with a mixture of 20% quartz and 80% aggregate was found to produce the most dust overall. The results of this study confirm the auto‐abrasion hypothesis for the breakdown of diatomite particles in the Bodélé Depression, which is the single biggest source of atmospheric mineral dust on Earth.     

2015年3月大气环流和天气分析

2015年3月大气环流主要特征是:北半球极涡呈偶极型分布,位置较常年同期明显偏南,欧亚中高纬环流经向度较小,南支槽平均位置位于70°E附近;同时,西太平洋副热带高压较常年同期明显偏强、位置偏西.3月,全国平均降水量为21.8mm,较常年同期(29.5mm)偏少26.1％.全国平均气温为5.8℃,较常年同期(4.1℃)偏高1.7℃.月内,我国出现5次主要的冷空气过程和5次主要的降水过程.江南等地多阴雨天气,我国东部出现3次轻到中度雾-霾天气,北方出现5次沙尘天气过程.     

2006-2012年青岛市空气质量与气象条件的关系

利用2006-2012年青岛市SO₂、NO₂及PM₁₀的监测资料,统计分析3种污染物时空分布特征及污染物平均浓度与气象要素的关系,并分析污染日气象条件变化特征。结果表明：2006-2012年青岛市年平均污染日数为23-33 d;青岛市空气污染主要出现在冬、春两季,主要污染物为PM₁₀。青岛中度以上污染为PM₁₀污染,大多由浮尘天气引起。污染物浓度与云量、降水量和气温呈负相关,与气压呈正相关。冬季大雾易造成空气污染加重,而4-6月海雾则使空气质量提高。弱的地面天气形势和接地逆温层结的存在及持续的烟、霾天气易导致青岛空气污染。     

Identifying regional dust transport pathways: ­application of kinematic trajectory modelling to a trans‐Tasman case

A kinematic trajectory model is used to investigate potential pathways of dust transport from Australia to New Zealand. Historically, these have been assumed to follow rather direct west–east trajectories spanning 2 to 3 days, often resulting in red snow events in the Southern Alps of New Zealand. However, results from the present study which examined the route taken by air parcels originating in southern Australia during dust storms on 24 and 25 May 1994, indicate that trans‐Tasman dust transport trajectories are more diverse than previously thought, and display considerable variation during single events. These more divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the Tasman Sea, and may account for the deposition of Australian dust on sub‐Antarctic islands located well south of the Australian continent. Copyright © 2000 John Wiley & Sons, Ltd.     

The variation characteristics and effect factors of surface ozone concentration in the Taklimakan Desert hinterland

Based on automatic continuous surface ozone concentration observation data from June 10, 2010 to March 20, 2012 in the Taklimakan Desert hinterland, combined with corresponding meteorological data, the temporal, seasonal and daily variation characteristics of surface ozone concentrations under different weather conditions were analyzed. At the same time, the main fac- tors affecting ozone variation are discussed. Results show that： （1） Daily variation of ozone concentration was characterized by one obvious peak, with gentle changes during the night and dramatic changes during the day. The lowest concentration was at 09：00 and the highest was at 18：00. Compared to urban areas, there was a slight time delay. （2） Ozone concentration variation had a weekend effect phenomenon. Weekly variation of ozone concentration decreased from Monday to Wednesday with the lowest in Wednesday, and increased after Thursday with the highest in Sunday. （3） The highest monthly average concentration was 89.6 I.tg/m3 in June 2010, and the lowest was 32.0 ~g/m3 in January 2012. Ozone concentration reduced month by month from June to December in 2010. （4） Ozone concentration in spring and summer was higher than in autumn and winter. The variation trend agreed with those in other large and medium-sized cities. （5） Under four different types of weather, daily ozone concentration var- ied most dramatically in sunny days, followed by slight variation in rain days, and varied gently in cloudy days. Ozone concentra- tion varied inconspicuously before a sandstorm appearance, and dropped rapidly at the onset of a sandstorm. （6） Daily variation of radiation was also characterized by a single peak, and the variation was significantly earlier than ozone concentration variation. Sun radiation intensity had a direct influence on the photochemical reaction speed, leading to variation of ozone concentration. （7） Daily average ozone concentration in dust weather was higher than in slight rain and clear days. The variation of near surface ozone concentration could also be affected by meteorological factors such as relative humidity, wind speed, wind direction and sunshine hours. Thus, numerous factors working together led to ozone pollution.     

Impact of dust aerosol on glacial-interglacial climate

The temperature anomaly and dust concentrations recorded from central Antarctic ice core records display a strong negative correlation. The dust concentration recorded from an ice core in central Antarctica is 50-70 times higher during glacial periods than interglacial periods. This study investigated the impact of dust aerosol on glacial-interglacial climate, using a zonal energy balance model and dust concentration data from an Antarctica ice core. Two important effects of dust, the direct radiative effect and dust-albedo feedback, were considered. On the one hand, the direct radiative effect of dust significantly cooled the climate during the glacial period, with cooling during the last glacial maximum being as much as 2.05℃ in Antarctica. On the other hand, dust deposition onto the ice decreased the surface albedo over Antarctica, leading to increased absorption of solar radiation, inducing a positive feedback that warmed the region by as much as about 0.9℃ during the glacial period. However, cooling by the direct dust effect was found to be the controlling effect for the glacial climate and may be the major influence on the strong negative correlation between temperature and dust concentration during glacial periods.     

Particle-size analysis of aeolian dusts,soils and sediments in very small quantities using a Coulter Multisizer

The Coulter Multisizer has clearly defined strengths and weaknesses as a particle-sizing instrument. It is easier to operate than its Coulter predecessors, though less so than several of its competitors. The Multisizer is best suited to handle very small samples with a narrow particle-size range, such as aeolian dusts and other sediments available only in small quantities. For such samples, Multisizer analysis times are short, resolution is very high (256 size classes) and reproducibility is good. The Multisizer is less well suited to soils and other samples available in large quantities and with a broad particle-size range. For soil particle-size analyses a composite method is proposed involving: Multisizer (2–75 μm), Pipette (<2 μm) and Sieve (>75 μm). © 1997 John Wiley & Sons, Ltd.