Latitudinal distribution of mesozooplankton in the off-equatorial northeastern Pacific before and after the 1998/99 La Niña event

Factors affecting mesozooplankton distributions in the northeastern tropical Pacific Ocean were investigated using data obtained along a meridian line (5 degrees -12 degrees N, 131.5 degrees W) in the summers of 1998, 1999, and 2003. The survey periods corresponded to a sharp transition between the 1997-1998 El Ni?o and 1998-1999 La Ni?a events, the 1999 La Ni?a event, and near-normal conditions after the moderate 2002-2003 El Ni?o in the equatorial Pacific. A strong upwelling in the divergence zone from 10.5 degrees to 11 degrees N caused a shoaling of the thermocline depth (approximately 30 m), resulting in increases in nitrate and phytoplankton chlorophyll a (chl-a) concentrations, and, in turn, mesozooplankton abundance during the La Ni?a in 1999. In contrast, in 1998, remnants of El Ni?o characteristics, deeper thermocline depth (60-150 m) and warm surface water (>28 degrees C), led to low concentrations of nitrate, chl-a and low mesozooplankton abundance, except in the convergence zone around 7 degrees N. The thermocline depth and nitrate concentration obtained during the near-normal period in 2003 corresponded to intermediate values as compared to those obtained during El Ni?o and La Ni?a conditions. Interannual changes in the position and strength of ecotones, such as divergence and convergence zones, affected mesozooplankton community structure and cyclopoid-to-calanoid ratios along the 131.5 degrees W meridian line. The clustering pattern of the mesozooplankton community was mostly characterized by calanoid (mainly Clausocalanus sp.) and cyclopoid (mainly Oncaea sp.) copepods, accounting for most of the observed differences among groups during the study period. Cyclopoids and calanoids were more abundant in 1999 than in 1998 or 2003, with a sharp increase to the north, while they were less abundant to the north in 1998 and 2003. The cyclopoid-to-calanoid ratio peaked in the convergence zone in 1998 and the divergence zones in 1999 and 2003, apparently due to the strength and location of the ecotones. Principal component analysis (PCA) with environmental factors and dominant mesozooplankton groups showed that dominant groups were affected by nitrate and chl-a concentrations in 1998, by sigma-t (water density), nitrate and chl-a concentrations in 1999, and by sigma-t, salinity and chl-a concentration (except siphonophores) in 2003. Latitudinal distribution of thermocline depth before and after the 1998/99 La Ni?a event showed a distinct interannual difference. The abundance of mesozooplankton in the divergence zone in 1999 was distinctively higher than abundances found in the convergence and divergence zones in 1998 and 2003, which resulted from the shallow thermocline depth due to an intensified upwelling during the strong 1998-1999 La Ni?a event.     

复杂磁异常的定量解释方法

本文利用解析函数的罗朗展开式对复杂磁异常进行分解,并指出,分解异常的方法亦能同时用于解决山区的地形校正问题,最后探讨了确定复杂磁异常的延深、倾角和截面积的定量计算方法,并举出某铁矿区的勘探实例来阐明上述方法在磁测资料定量解释中的实际应用。     

Rogoznica Lake(Croatia),a Unique Euxinic Seawater System on the Adriatic Coast

正1 Introduction Rogoznica Lake is a typical example of euxinic saline lake,situated on the eastern Adriatic coast(43o32’N15o58’E).It is a karstic depression filled with seawater,     

河南许昌地区航磁数据处理结果的研究

前言七五年1:5万航磁测量,在本区测得面积近二千平方公里的低缓磁异常区。航磁异常主要集中在苏桥.泉店一带。地表为厚层黄土复盖。以往地质研究程度很差,在找铁历史上是一个空白点。为了对这一地区航磁异常迅速进行评价,提供优先开展地面物探和钻探验证工作的地区,我们选取了北至玉皇庙—长葛一线,南至禹县—许昌范围内的1296平方公里的1:5万航磁资料,在电子计算机上进行数据处理工作。通过数据处理,对该区内C1至C20航磁异常加以分类,作出评价,提供了地质上有用的资料。     

底辟作用作为有效花岗岩类运移机理

在缺乏构造迁移情况下,解释地壳中部深成岩体的侵位和上升过程中最使人感兴趣的机理就是底辟作用。不过本文认为这种底辟作用机理的关键问题所在还存在重要分歧。构造研究趋向性的结果就是花岗岩底辟为了上升必须受到充分结晶作用,而机械模式的结果却总结出相矛盾的结论,因为在这种模式中岩浆的上升、岩浆必是重要流体,以达到对流循环的目的。的确,与底辟作用有关的热量逃逸是如此之多以致使整体岩浆上升受到明显限制。这些大不相同观点的出现似乎是反映火山岩上升/侵位在整体上看来具有不同岩相。