南海海盆海山形态特征的定量化和无监督聚类分析

不同的火山喷发模式形成的海底火山在形态上存在差别,但由于缺乏有效方法,两者之间的关系仍不清晰.创新性地运用机器学习聚类分析法,基于高分辨率多波束水深数据,对南海海盆中的海山地形开展多维的形态参数量化分析,并对其结果进行无监督式聚类研究.结果表明,南海海盆中共发育三类海山：类型Ⅰ,体积大、坡度陡、底盘圆的大型孤立海山;类型Ⅱ,体积大、坡度缓、底盘长的大型线状海山;以及类型Ⅲ,体积小、坡度缓、底盘椭圆的小型海山.类型Ⅰ和Ⅱ位于东部次海盆洋中脊区,类型Ⅰ高耸的海山形态代表了活跃且快速的喷发模式,类型Ⅱ的平缓形态代表了缓慢且喷发物质流动性更强的火山活动,类型Ⅲ沿着转换断层及远离东部次海盆的洋中脊区,代表了缓慢且不强烈的火山活动.本文定量证实了不同构造背景下形成的海山形态具有普遍规律;针对海山形态学建立的聚类分析新方法,可为获得大量岩石学信息之前研究火山喷发模式提供新思路.     

Effect of selection and sequencing of representative wave conditions on process-based predictions of equilibrium embayed beach morphology

In order to decrease the simulation time of morphodynamic models, often-complex wave climates are reduced to a few representative wave conditions (RWC). When applied to embayed beaches, a test of whether a reduced wave climate is representative or not is to see whether it can recreate the observed equilibrium (long-term averaged) bathymetry of the bay. In this study, the wave climate experienced at Milagro Beach, Tarragona, Spain was discretized into ‘average’ and ‘extreme’ RWCs. Process-based morphodynamic simulations were sequenced and merged based on ‘persistent’ and ‘transient’ forcing conditions, the results of which were used to estimate the equilibrium bathymetry of the bay. Results show that the effect of extreme wave events appeared to have less influence on the equilibrium of the bay compared to average conditions of longer overall duration. Additionally, the persistent seasonal variation of the wave climate produces pronounced beach rotation and tends to accumulate sediment at the extremities of the beach, rather than in the central sections. It is, therefore, important to account for directional variability and persistence in the selection and sequencing of representative wave conditions as is it essential for accurately balancing the effects beach rotation events.     

A statistical study of environmental factors controlling concentrations of heavy metals in the burrowing bivalve Scrobicularia plana and the polychaete Nereis diversicolor

Multiple regression analyses indicate that the most important factors controlling Ag, Cd, Co, Cu, Pb and Zn concentrations in the estuarine bivalve Scrobicularia plana and the polychaete Nereis diversicolor are the concentrations of these metals in surface sediments and the partitioning of sediment-bound metals between different sediment constituents. Extraction of the sediments with 1-n HCl provides more information about the bioavailability of the metals than do extractions with five other techniques. Biologically available Cd and Co in solution contribute significantly to Cd and Co concentrations in both Scrobicularia and Nereis. Concentrations of Ag in Scrobicularia are reduced where Cu concentrations in sediments are high. An unexplained increase in concentrations of Cu in Scrobicularia at specific stations in six estuaries suggests that under certain very anoxic conditions the availability of copper may be exceptionally high.     

A preliminary study of the carbon-isotopic content of ambient formic acid and two selected sources: Automobile exhaust and formicine ants

Relatively large quantities (1 mg) of formic acid have been collected from the atmosphere and subjected to carbon-isotopic analysis, as a means of source discrimination. Ambient formic acid was captured on Ca(OH)₂-treated filters using a high-volume sampler. The collection method was not only efficient (>96%), but also appears to have low artifact production.Most of the samples (36 out of 52) were collected over a two-year period at the summit of Mount Lemmon, Arizona, where a strong seasonality in HCOOH mixing ratio was observed (0.2 ppb during winter months to 1.5 ppb in the summer). Other collection sites included the Oregon coast, Colorado Rockies, urban Tucson, and the North Dakota prairie. The carbon-13 content of atmospheric HCOOH was found to be have little variation (–18 to –25), regardless of location or season. This is consistent with a single dominant source of formic acid. The carbon-14 measurements of 6 Mount Lemmon samples showed high levels of modern carbon (93–113% modern).The emissions from formicine ants and automobile combustion were selected as two other potential sources for isotopic analysis. The HCOOH collected from auto exhaust was much more depleted in¹³C than the atmospheric samples, with a ¹³C of –28.0 and –48.6 from a leaded and unleaded automobile, respectively. Formicine ants, on the other hand, ranged from –17.2 to –20.6.     

On aerosol production and enrichment by breaking wind waves

Abstract

A model is presented for the production and enrichment of aerosols. Bubbles distributed in size by fragmentation scavenge particles and transport them to the surface. In the collapse process at the surface the bubble's skin is enveloped into the ejected aerosol leading to significant enrichment. For no mass accumulation at the surface in foam the flux due to scavenging equals that for resuspension leading to an estimate of the enrichment. The model results compare favourably with observations of artificial and wind‐generated enrichment if it is assumed that during the scavenging the bubble's clean and mobile surface during the initial stages collects most of its particle load. Further scavenging by the encrusted bubble surface, while significant, is not as dramatic. Other observations of the wind dependency of the process support the model.