高空西风带环流演变综合图及其功用

本文先略述苏联与我国过去对大气环流的研究状况,及其重要性.过去研究环流偏差的问题,常以月平均高空图及地面图对准平均图的偏差状况来讨论,如苏联坡戈香(Х.П.Погосян)也是如此^**.但月平均图对该月的详细环流演变过程不能表示出来.本文设计用一种环流综合图,以求表示长时期中(月或季)高空西风带内环流演变的具体情况.采用七种符号,来表示逐日各经线上环流系统的性质及气流的运动.并把西风带分为南北两部分来处理,北带从北纬50°到65°,南带从北纬35°到50°.这样在一个月内逐日西风带环流的演变,就可以在同一张图上表示出来.     

Jurassic lagoon: salt or soup?

The 140-million-year-old Solnhofen lithographic limestone of Bavaria, famous for the remarkable preservation of the earliest bird, Archaeopteryx, is one of the most acclaimed fossil horizons on Earth. Understandably, interest has focused on the more glamorous fossil finds from these rocks; the most common macrofossil, a small sea lily, has been neglected. However, this unprepossessing animal is a key player in the Solnhofen story .     

HEIMDALL'S STONES AT VITEMÖLLA IN SE SWEDEN AND THE CHRONOLOGY AND STRATIGRAPHY OF THE SURROUNDINGS

Heimdall's Stones at Vitemölla is an archaeological monument of stones arranged in circles and where sightlines can be identified of the sunrise and sunset at winter and summer solstices and spring and autumn equinoxes. Therefore, this stone monument is likely to have served as an archaeoastronomic observatory. It is founded in a fossil land surface now covered by half a metre of eolian sand. In order to date this sand drift, sediment coring was performed in the nearby Sandefloen bog. Seven levels were subjected to AMS C14 dating. The first sand drift, correlated with the sand drift covering Heimdall's Stones, was dated at 500–600 cal. bc . Consequently, the observatory has to date back to the Bronze Age, fitting well with its Sun cult and with the rock carvings recorded on the individual stones. At the seashore 500 m east of the observatory and the bog, we were able to reconstruct the sea-level changes. In conclusion, we combine the recorded sea-level changes with the C14-dated bog stratigraphy and the observed stratigraphy at Heimdall's Stones (covering an area of 500×500 m) into one unified picture. The chronostratigraphic position of Heimdall's Stones agrees well with the dating of the Kivik grave. The Vitemölla area is likely to have been an important cultural centre in the Bronze Age.     

LATE QUATERNARY MORAINES ALONG THE SEKHOKONG RANGE, EASTERN LESOTHO: CONTRASTING THE GEOMORPHIC HISTORY OF NORTH- AND SOUTH-FACING SLOPES

Considerable Quaternary environmental reconstruction for the high Drakensberg is based on geomorphological and sedimentological work undertaken along the northern aspects of the Sekhokong mountain range of eastern Lesotho. Given that no previous investigations have focused on the southern aspects, this paper documents the observed geomorphology and provides a more complete palaeo-environmental picture for this range. Data on the morphology, sedimentology and micromorphology for two linear debris ridges are presented. It is demonstrated that the two ridges are most likely moraines originating from a small niche glacier. The combined use of macro- and micro-scale sedimentology is proven to be an essential tool in ascribing a glacial process origin for the landforms, given the complex depositional history they have undergone. AMS ages obtained from the deposits (14 700 cal. yrs bp and 19 350 cal. yrs bp ) places these in the time-scale of the Last Glacial Maximum. The study demonstrates rather contrasting aspect-controlled palaegeomorphological environments along the Sekhokong range, which is also reflected in the dissimilar contemporary biophysical micro-environments. It is suggested that the south-facing slopes were dominated by glacial processes during the Last Glacial Maximum (LGM), as is evident from the moraines, while the proposition for previously described north-facing glacial cirques is rejected based on the absence of erosional/depositional evidence and greater insolation received on these warmerequator-facing slopes. Rather, we propose that the observed north-facing hollows are a product of a multitude of geomorphic processes spanning several tens to hundreds of thousands of years.     

LICHENOMETRIC DATING: A COMMENTARY, IN THE LIGHT OF SOME RECENT STATISTICAL STUDIES

This commentary article discusses the relative merits of new mathematical approaches to lichenometry. It highlights their strong reliance on complex statistics; their user unfriendliness; and their occasional mistreatment of existing lichenometric techniques. The article proposes that the success of lichenometric dating over the past 50 years has stemmed from its relative simplicity, transparency, and general field applicability. It concludes that any new techniques which ignore these principles are likely to be unjustified, unsuitable to the user community and inappropriate for the subject matter. Furthermore, the article raises a more general philosophical question: can statistical complexity and high precision in a ‘geobotanical’ dating technique, fraught with high degrees of environmental variability and inbuilt uncertainty, ever be scientifically valid?     

USE OF BOMB-14C TO INVESTIGATE THE GROWTH AND CARBON TURNOVER RATES OF A CRUSTOSE LICHEN

The reliability of lichenometric dating is dependent on a good understanding of lichen growth rates. The growth rate of lichens can be determined from direct measurement of growing lichens or indirect methods by measuring lichens growing on surfaces of known age, although there are limitations to both approaches. Radiocarbon (¹⁴C) analysis has previously been used in only a handful of studies to determine lichen growth rates of two species from a small area of North America. These studies have produced mixed results; a small amount of carbon turnover appears to occur in one of the species ( Caloplaca spp.) previously investigated introducing uncertainty in the growth rate, while much higher carbon cycling occurred in another ( Rhizocarpon geographicum ), making the ¹⁴C approach unsuitable for estimating growth rates in the species most commonly used in lichenometric dating. We investigated the use of bomb-¹⁴C analysis to determine the growth rate of a different crustose species ( Pertusaria pseudocorallina ) common to Northern Europe. ¹⁴C-based growth rates were considerably higher than growth rates of morphologically similar species based on direct measurement made at locations nearby and elsewhere in the UK. This observation strongly suggests that a degree of carbon turnover probably occurs in Pertusaria pseudocorallina , and that bomb-¹⁴C analysis alone cannot be used to determine lichen age or absolute growth rates in this lichen species.     

LICHENOMETRY ON ADELAIDE ISLAND, ANTARCTIC PENINSULA: SIZE-FREQUENCY STUDIES, GROWTH RATES AND SNOWPATCHES

This paper presents new lichenometric population data from the Antarctic Peninsula (67°S), and describes a new approach to lichen growth-rate calibration in locations where dated surfaces are extremely rare. We use historical aerial photography and field surveys to identify sites of former perennial snowpatches where lichen populations now exist. As an independent check on lichen mortality by snowkill, and the timing of snow patch disappearance, we use a positive-degree day (PDD) approach based on monthly climate data from Rothera Research Station. We find that maximum growth rates for lichens <40 mm in diameter on Adelaide Island are around 0.8 mm/yr. Furthermore, we propose that our combined methodology may be more widely applicable to the Polar Regions where the construction of lichenometric dating (age-size) curves remains a problem.