Lichenometric dating of Little Ice Age glacier moraines using explicit demographic models of lichen colonization,growth, and survival

Contemporary variants of the lichenometric dating technique depend upon statistical correlations between surface age and maximum lichen sizes, rather than an understanding of lichen biology. To date three terminal moraines of an Alaskan glacier, we used a new lichenometric technique in which surfaces are dated by comparing lichen population distributions with the predictions of ecological demography models with explicit rules for the biological processes that govern lichen populations: colonization, growth, and survival. These rules were inferred from size–frequency distributions of lichens on calibration surfaces, but could be taken directly from biological studies. Working with two lichen taxa, we used multinomial‐based likelihood functions to compare model predictions with measured lichen populations, using only the thalli in the largest 25% of the size distribution. Joint likelihoods that combine the results of both species estimated moraine ages of ad 1938, 1917, and 1816. Ages predicted by Rhizocarpon alone were older than those of P. pubescens. Predicted ages are geologically plausible, and reveal glacier terminus retreat after a Little Ice Age maximum advance around ad 1816, with accelerated retreat starting in the early to mid twentieth century. Importantly, our technique permits calculation of prediction and model uncertainty. We attribute large confidence intervals for some dates to the use of the biologically variable Rhizocarpon subgenus, small sample sizes, and high inferred lichen mortality. We also suggest the need for improvement in demographic models. A primary advantage of our technique is that a process‐based approach to lichenometry will allow direct incorporation of ongoing advances in lichen biology.     

南极菲尔德斯半岛海鸟与种群分布

2000/2001-2002/2003南极夏季期间,对中国南极长城站所在地乔治王岛菲尔德斯半岛及邻近区海鸟群落组成与种群分布特征进行了观测研究。本文报道了对该地区三次考察期间记录的海鸟共11科25种。其中,有繁殖活动的海鸟12种,优势种有白眉企鹅(Pygoscelispapua)和黄蹼洋海燕(Oceanitesoceanicus),常见种有纹颊企鹅(Pygoscelisantarctica)、巨鹱(Macronectesgiganteus)、花斑鹱(Daptioncapenis)、南极燕鸥(Sternavittata)和灰贼鸥(Catharactaantarctica)等。     

LICHENOMETRIC DATING (LICHENOMETRY) AND THE BIOLOGY OF THE LICHEN GENUS RHIZOCARPON: CHALLENGES AND FUTURE DIRECTIONS

Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates.     

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.     

Using earthquakes to assess lichen growth rates

Botanists make yearly measurements of lichen sizes that describe highly variable radial expansion of young, and old, Rhizocarpon subgenus Rhizocarpon that is a function of thallus size and age. Such non‐uniform growth would negate use of lichens to date geomorphic events, such as landslides and moraines, of the past 1000 years. Fortunately, many crustose lichens tend toward circular shapes, which can be achieved only when overall uniform radial growth prevails. Largest lichen measurements on rockfall blocks that accumulate incrementally as hillslope talus in earthquake‐prone California plot as distinct peaks in frequency distributions. Rockfall surface‐exposure times are known to the day for historical earthquakes and to the year where mass movements damage trees. Lichenometry consistently dates regionally synchronous rockfall events with an accuracy and precision of ±5 years. Only historical records and tree‐ring dating of earthquakes are better. The four crustose lichens used here have constant long‐term growth rates, ranging from 9.5 to 23.1 mm per century. Growth rates do not vary with altitude or climate in a 900 km long mountainous study region in California, USA. Linear growth regressions, when projected to the present, constrain estimates of colonization time and possible styles of initial lichen growth.     

THE ENVIRONMENTAL EVENTS ON KING GEORGE ISLAND SINCE THE LAST GLACIATION

The extension of ice sheet on King George Island during the last glaciation was an environment event since the last glaciation. At that time South Shedlands Islands were a large unified island and the ice mass on King George Island might come from the Antarctic Peninsula. The model of ice retreat and ice advance events in the Holocene show that the ice sheet was separated into three small ice caps and then dispeared gradually. At present the retreating velocity of glacier is about 1.3m each year. After the retreat of ice sheet the isostatic compensation appeared in the crust there, and then 5-6 steps of the uplifted marine terraces have been developed along the coast. The uplift rate of the crust may be 6-10mm/a.     

Lichenometric dating in southeast Iceland: the size–frequency approach

Abstract The age of recent deposits can be determined using an intrinsic characteristic of the lichen ‘population’ growing on their surface. This paper presents a calibrated dating curve based on the gradient of the size‐frequency distribution of yellow‐green Rhizocarpon lichens. The dating potential of this new curve is tested on surfaces of known age in southeast Iceland. This particular size—frequency technique is also compared with the more traditional largest‐lichen approach. The results are very encouraging and suggest that the gradient can be used as an age indicator, at least on deposits formed within the last c. 150 years – and probably within the last c. 400 years – in the maritime subpolar climate of southeast Iceland. Using both lichenometric techniques, revised dates for moraines on two glacier forelands are presented which shed new light on the exact timing of the Little Ice Age glacier maximum in Iceland.     

ESTABLISHING LICHENOMETRIC AGES FOR NINETEENTH- AND TWENTIETH-CENTURY GLACIER FLUCTUATIONS ON SOUTH GEORGIA (SOUTH ATLANTIC)

Glaciers in small mountain cirques on South Georgia respond rapidly and sensitively to changes in South Atlantic climate. The timing and rate of their deglaciation can be used to examine the impact that nineteenth- and twentieth-century climate change has had on the glacial dynamics and terrestrial ecosystems of South Georgia. As part of a reconnaissance study in Prince Olav Harbour (POH), South Georgia, we measured the size of lichens ( Rhizocarpon Ram. em Th. Fr. subgenus. Rhizocarpon group) on ice-free moraine ridges around two small mountain cirques. Our aims were twofold: first, to provide age estimates for lichen colonization, and hence, deglaciation of the moraine ridges, and second, to examine the potential of applying lichenometry more widely to provide deglacial age constraints on South Georgia. In the absence of lichen age-size (dating) curves for South Georgia, we use long-term Rhizocarpon lichen growth-rates from recent studies on sub-Antarctic Islands and the western Antarctic Peninsula to calculate likely age estimates. These data suggest ice retreat from the two outermost moraines occurred between the end of the 'Little Ice Age' (post c. 1870) and the early twentieth century on South Georgia. Lichen colonization of the innermost moraines is probably related to glacier retreat during the second half of the twentieth century, which has been linked to a well-defined warming trend since c. 1950. Patterns of possible nineteenth- and twentieth-century glacial retreat identified in POH need to be tested further by establishing species- and site-specific lichen age-size (dating) curves for South Georgia, and by applying lichenometry to other mountain cirques across South Georgia.     

人类活动对南极乔治王岛菲尔德斯半岛环境的影响

人类活动对南极环境的影响主要表现为全球性人类活动的影响和南极局地人类活动的影响两方面。本文在对南极乔治王岛菲尔德斯半岛环境进行调查和采样分析的基础上,明确了南极环境中存在源于北半球中高纬地区人类核活动产生的人工放射性同位素１３７Ｃｓ：土壤表层（０～５ｃｍ）、苔藓活体层、枝状地衣、壳状地衣体中１３７Ｃｓ比活度分别为６．０～１４．８、２５．１、２９．０和５８．１Ｂｑ／ｋｇ;而中国北方地区土壤表层（０～１０ｃｍ）、壳状地衣体中１３７Ｃｓ比活度分别为６．４～３７．３和２９４．０～３１２．０Ｂｑ／ｋｇ,可见这类全球陆地表面广泛分布的壳状地衣是监测人工放射性核素长期扩散影响极为敏感的信息载体。南极科学考察活动对局地生态系统和地表冻融过程有一定程度的干扰,南极生物体（特别是地衣体）和水体是对人类活动影响极为敏感的环境信息载体,考察站区周围的生物体和水体中Ｃｒ、Ｃｕ、Ｎｉ、Ｐｂ、Ｚｎ等污染物含量明显偏高。菲尔德斯半岛作为南极科学考察站最为密集的地区之一,其环境与陆地生态系统受人类活动影响较为明显,故加强本区环境和生物保护工作已成为当前南极环境科学研究的重要方面     

南极考察站废弃物对贼鸥食性的影响

对南极乔治王岛菲尔德斯半岛贼鸥的食性生态进行观测与研究 ,结果表明 ,本区贼鸥的食物结构中 ,自然生态类食物百分组成 ,棕贼鸥 (C .s.lonnbergi)占 63.4% ,灰贼鸥 (C .maccormic ki)占 77.8%。同期 ,取自考察站的人类废弃物中垃圾食物的百分组成分别为 36.6%和 2 2 .3%。贼鸥食性对考察站废弃物有一定的依赖性 ,与本区环境质量下降 ,尤其考察站对废弃物的疏于管理有着直接的关系。由此表明 ,强化南极考察人员环境意识 ,建立封闭式废弃物管理系统 ,对保护南极环境有重要意义     

南极乔治王岛柯林斯冰帽小冰穹冰芯中火山喷出物的首次鉴定

对采自南极乔治王岛柯林斯冰帽小冰穹顶冰芯40～50m深度处黑色沉积物样品进行了内部结构和外部形态的观察和分析。偏光显微镜下光性鉴定表明该样品具有显著的火山喷出物指征性结构。经EPM—810Q型电子探针分析发现了样品较强的火山喷出物形貌方面的指征,全元素定性分析验征了偏光显微镜下观察到的几种特定矿物组成。这是首次在柯林斯冰帽冰芯中发现并得到鉴定的火山喷出物。     

SPATIAL AND TEMPORAL PATTERNS OF TALUS ACTIVITY – A LICHENOMETRIC APPROACH IN THE STUBAIER ALPS,AUSTRIA

Lichenometric measurements using Rhizocarpon ssp. were carried out on 20 talus slopes in the cirques of the Finstertal valley (Austria) at an elevation of 2300–3000 m a.s.l. The aim was to assess activity patterns on selected slopes and between the slopes of the study area, to find evidence of rockfall pulses in the last centuries and to calculate rockwall retreat rates. A calibration curve was derived from five sites of known age and adapted to the prevailing size of talus boulders. We measured the five largest lichens on more than 300 boulders and the percentage coverage of Rhizocarpon‐free clasts on more than 1000 test fields. Most of the investigated talus cones are characterized by moderate rockfall supply, with the apex being more active than the talus foot and moderate redistribution by avalanche and debris flows. Considerably enhanced activity was found under rockwalls influenced by permafrost, particularly on the north faces at an elevation of >2600 m a.s.l. At currently moderately active sites, boulder falls seem to have been slightly more frequent in the late nineteenth and first half of the twentieth century. In positions where permafrost is expected in the rockwalls, a weak maximum in the late nineteenth century and highly active present‐day conditions were found, the latter being assigned to current permafrost melt. Rockwall retreat rates derived from lichen coverage are between 400 and 1500 mm/ka which is in good concurrence with talus volume assessments, but higher than the rates derived from direct rockfall measurements. The rates derived from lichen coverage have to be taken with caution as the effects of debris redistribution are hard to quantify.     

南极乔治王岛环境质量现状调查

本文以１９９２／１９９３年度中国第九次南极考察期间对南极乔治王岛的表土、地衣、苔藓等样品的分析资料为基础，研究探讨了８种无机重金属元素、５种有机污染物的浓度水平。其结果表明，重金属在三种环境样品中的含量分布存在着明显的差异；地衣、苔藓两种植物呈现对不同重金属元素的不同富集能力；∑６６６、∑ＤＤＴ和ＰＣＢｓ及油的沾污亦很明显。本文还对污染物质的来源、南极环境样品历次调查分析的结果以及世界部分地区的背景水平进行了讨论和比较     

A REVIEW OF LICHENOMETRIC DATING OF GLACIAL MORAINES IN ALASKA

In Alaska, lichenometry continues to be an important technique for dating late Holocene moraines. Research completed during the 1970s through the early 1990s developed lichen dating curves for five regions in the Arctic and subarctic mountain ranges beyond altitudinal and latitudinal treelines. Although these dating curves are still in use across Alaska, little progress has been made in the past decade in updating or extending them or in developing new curves. Comparison of results from recent moraine-dating studies based on these five lichen dating curves with tree-ring based glacier histories from southern Alaska shows generally good agreement, albeit with greater scatter in the lichen-based ages. Cosmogenic surface-exposure dating of Holocene moraines has the potential to test some of the assumptions of the lichenometric technique and to facilitate the development of a new set of improved lichen dating curves for Alaska.     

南极半岛西北海域表层沉积物~(14)C年龄测定及其年代误差问题的探讨

本文报道了应用~(14)C年龄测定法对南极半岛西北海域所采集的12个表层沉积物样品~(14)C年龄测定结果,以及在乔治王岛采集的2个现代碳样品~(14)C比度测定结果。这些结果表明,该海区大气CO_2中~(14)C比度与海水中的~(14)C比度存在一定的差异,作者对这种差异所造成的沉积物年龄偏老现象进行了初步的讨论,认为南极半岛西北海域表层沉积物的~(14)C年龄比真实年龄至少要老456年(该值仅反映海洋贮存库效应的表观年龄,没有作由于原子弹爆炸使大气中~(14)C比度增加而造成~(14)C年龄偏低的校正)。     

乔治王岛菲尔德斯半岛早第三纪植物群及其环境意义

南极乔治王岛菲尔德斯半岛化石山植物群的发现是研究该地区新生代地质历史的一件大事。通过层位对比、化石特征、植物群组合面貌的研究,认为该植物层的时代为始新世末期至渐新世早、中期,当时为温暖偏干的温带或亚热带疏林环境。     

南极苔藓小气候的初步研究

198 9年 2月 1— 1 0日 ,对南极乔治王岛菲尔德斯半岛长城站附近的苔藓小气候进行了初步考察、观测和分析 ,并与长城站相应时间的常规记录进行了比较 ,初步揭示了南极地区苔藓小气候方面值得引起注意的某些特征。     

南极乔治王岛三种藓类的染色体观察

本文报道了南极乔治王岛３种藓类植物染色体的研究结果：１．钩枝镰刀藓［Ｄｒｅｐａｎｏｃｌａｄｕｓｕｎｃｉｎａｔｕｓ（Ｈｅｄｗ）Ｗａｖｒｓｔ．］的染色体数为１４；２．［Ｃｈｏｒｉｓｏｄｏｎｔｉｕｍａｃｉｐｈｙｌｕｍｇ（Ｈｏｏｋ．）ｅｔＷｉｌｓＢｒｏｔｈ．］的染色体数为１０；３．高山拟金发藓［Ｐｏｌｙｔｒｉｃｈａｓｔｒｕｍａｌｐｉｎｕｍ（Ｈｅｄｗ．）Ｇ．Ｓｍ．］的染色体数为７。     

南极长城站及附近岛屿南极发草的形态特征与分布

南极发草是本研究地区常见的种子植物，作为南极极少的维管束植物成员之一，它在南极陆地生态系统中有着特殊的作用。本文对南极发草的分类特征和分布进行了描述，并讨论了环境变化可能影响植被发展的问题。     

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.