The geological record of a mid-Holocene marine storm in southwestern Spain

Integrated analysis of a 50-m long sedimentary core collected in the central part of the Odiel estuary (SW Atlantic coast of Spain) allows delineation of the main paleoenvironmental changes that occurred in this area during the Holocene. Eight sedimentary facies were deposited in the last ca. 9000 years BP, confirming a transgressive-regressive cycle that involves the transition from fluvial to salt marsh deposits with intermediate marine tidal deposits. A storm event is detected at ca. 5705 ¹⁴C years BP (mean calibrated age) with distinct lithostratigraphical, textural, geochemical, and palaeontological features.     

南海永暑礁晚全新世微型腹足类——仁螺目,古腹足目,盘足目

南海南沙群岛永暑礁南永3井揭示了1 680年以来礁泻湖的沉积变化。沉积柱样主要由沉积遗壳组成,其中腹足类是最主要的类型之一。对该井88个样品分析共发现了159个种类和一些难以归入属种的胎壳,大多数种类为该海区首次记录的类型,有四个种是新发现的种类,即Astraea armata sp .nov .,Munditiella flammea sp .nov .,Serpulorbis spiralis sp .nov .,Cerithiopsis bellatulus sp .nov .,主要的优势种包括Acteocina coarctata , Ac-teocinaexilis , Alvania sp .,Boschitestella eloiseae , Cerithidium fusca , Cerithiopsis ingens , Cerithium( Therici-um) elegantulum, Circumstella biconcave , Clathrofenella reticulata , Diniatys dentifer , Granulina cotamago , Lophocochlias minutissi mus , Merelina wanawana , Omalogyra cf .atomus, Ondina elachisinoides , Orbitestella bermudezi , Orbitestella decorata , Plesiotrochus acutangulus , Retusa ( Ventomnestia) bizonata, Ringicula durodai ,Ringicula columnifera , Ringicula niinoi , Scissurella coronata , Tricoliavariabilis , Turbonilla eupellucida。这些种类个体非常微小,大多数小于2 mm。绝大多数种类为典型的热带海区分子,它们具有广泛的地理分布。本文按Okutani(2000)分类系统进行了分类,主要描述了仁螺目,古腹足目和盘足目共40个种的形态特征、地理分布和生态习性,包括2个新种,绝大多数种类系南沙群岛海区首次记录。     

Significance of <Emphasis Type="Italic">Halimeda</Emphasis> bioherms to the global carbonate budget based on a geological sediment budget for the Northern Great Barrier Reef,Australia

Since the correlation between carbon dioxide (CO₂) levels and global temperatures was established in the ice core records, quantifying the components of the global carbon cycle has become a priority with a view to constraining models of the climate system. The marine carbonate budget is still not adequately constrained and the quantitative significance of the calcareous green alga Halimeda still remains particularly poorly understood. Previously, it has been suggested that Halimeda bioherms on the shelf of the Great Barrier Reef may contain a volume of carbonate equal to or greater than that contained within the shelf edge coral reefs. This study uses published datasets to test this hypothesis in the Northern Great Barrier Reef (NGBR) province. It is estimated that Halimeda bioherms on the outer shelf of the NGBR contain at least as much (and up to four times more) CaCO₃ sediment as the adjacent ribbon reef facies. Globally, if these findings are even only partially applicable, the contribution of shallow water carbonate sediments to the global carbon budget based on coral reefs alone is currently substantially underestimated.     

Vegetation history of Lago Battaglia (eastern Gargano coast,Apulia, Italy) during the middle-late Holocene

A pollen and charcoal record from Gargano (southern Italy) provides new information on the vegetation history and environmental change in southern Italy during the middle to late Holocene. The chronological framework is provided by six AMS radiocarbon dates carried out on plant macroremains. Pollen diagrams record a Mediterranean vegetation along the coastland and a stable mixed oak forest at higher elevations between ca. 5900 and 4200 cal b.p. A sharp and dramatic fall of tree pollen concentrations and a change in fire frequencies occurred from approximately 4200 cal b.p. suggesting a climate change towards drier conditions. This event is coherent with regional and extra-regional palaeoclimatic records that suggest that a mid-Holocene dry period was experienced in southern Italy, southern Spain, and perhaps further afield. Human impact on vegetation seems to have occurred since about 2700 cal b.p.     

Changes in forest cover in China during the Holocene

Pollen map data at 2000-year intervals are used to reconstruct changes in Holocene forest cover in China north of the Yangtze River. In almost all regions, the early Holocene from 10 ka b.p. to 6 ka b.p. is characterised by an increase in forest cover although there was a reversal to lower forest cover at 8 ka b.p. in the eastern monsoon regions. A maximum of forest cover was reached at 6 ka b.p. in all regions except for Northeast China where forest cover peaked in the late Holocene. All regions except for Northeast China experienced a marked decline in forest cover after 6 ka b.p. Since 6 ka b.p., forest cover has decreased by about 92% in the middle and lower reaches of the Yellow River, 64% in the easternmost part of the Qinghai-Tibet Plateau and 37% between the Yangtze River and the Huaihe River. In contrast, forest cover in Northeast China increased significantly from 6 ka b.p., but has declined between 2 ka b.p. and the present. Changes in forest cover prior to 6 ka b.p. were probably caused by climate, but the evident drop in forest cover since that time in most regions may have been induced predominantly by human activities.     

Predicting small‐mammal responses to climatic warming: autecology,geographic range,and the Holocene fossil record

Forecasting how species will respond to climatic change requires knowledge of past community dynamics. Here we use time‐series data from the small‐mammal fossil records of two caves in the Great Basin of the American West to evaluate how contrasting and variable local paleoclimates have shaped small‐mammal abundance dynamics over the last ～7500 years of climatic change. We then predict how species and communities will respond to future scenarios of increased warming and aridity coupled with continued spread of an invasive annual grass (Bromus tectorum). We find that most community‐level responses to climatic change occur in the mammalian abundance structure at both sites; the dominance of the community by individuals from species with a southern geographic affinity increases with climatic warming. This suggests that responses occurred in situ rather than by the immigration of new taxa over this time interval. Despite predictability at the community‐scale, species‐level relationships between abundance and climate are variable and are not necessarily explained by a species' geographic affinity. Species present at both sites, however, exhibit remarkably similar responses to climate at each site, indicating that species autecology (specifically dietary functional group) is important in determining response to climatic warming. Regression‐tree analyses show remarkable concordance between the two cave faunas and highlight the importance of a granivorous dietary strategy in this desert ecosystem. Under projections of increased temperature and decreased precipitation over the next 50 years, our results indicate that granivores should thrive as communities become more dominated by individuals with a southern geographic affinity. Granivores, however, are negatively impacted by the invasion of cheatgrass. The last century of anthropogenic impacts has thus placed granivores at a greater risk of extinction than predicted under climate‐only scenarios.     

Viola rupestris: molecular analyses to elucidate postglacial migration in Western Europe

Aim Our aim was to elucidate the postglacial migration of Viola rupestris F.W. Schmidt, with its two subspecies, rupestris and relicta Jalas, in Europe, using molecular methods. Location Norway, Sweden, Finland, England, the Netherlands, France and Switzerland. Methods Isoenzymes were analysed from 49 populations of Viola rupestris s.lat. Based on former experience of variation in the taxon, the following were included: aspartate aminotransferase, leucine/aminopeptidase, and phosphoglucomutase, yielding a total of nine interpretable and six variable (putative) loci. Results Six multilocus phenotypes were revealed (A–F). Phenotype A (only one individual) is restricted to northern Norway, B is shared by all populations in northern Norway and an isolated population on the west coast of southern Norway (Møre). Phenotype B comes close to C, co‐occurring with D in England, the latter also occurring in southern France. Phenotypes E and F occur in the rest of Europe. Main conclusions Viola rupestris ssp. relicta Jalas, previously known only from northern Scandinavia (northern unicentric), was discovered on the west coast of southern Norway (Møre), making the taxon ‘bicentric’. Populations are connected through a putative migration route from the Grands Causses in southern France (Massif Central) via England and western Norway to northern Scandinavia. The Grands Causses might represent a glacial refugium.     

Effects of Mesolithic hunter-gatherers on local vegetation in a non-uniform glacio-isostatic land uplift area, northern Sweden

The oldest early Mesolithic settlements found so far (i.e. 8600 b.p.) in the interior of northern Sweden, in the province of Norrbotten, have been discovered through the application of a model simulating glacio-isostatic land uplift. The objective of this study was to investigate, through pollen and charred particle analyses, vegetation composition and the influence of man on vegetation and fire pattern in the vicinity of two of these early settlements. Early Holocene vegetation was characterised by Betula, Hippophaë and Salix-species, but no initial impact by hunter-gatherers on vegetation was detected. Subsequently Betula and Pinus became dominant but abrupt changes in the tree layer followed, Poaceae, Hippophaë and Salix-species increased, and Humulus occurred. These changes, which were synchronous with dates of archaeological findings at the settlements, indicated local vegetation changes caused by man. The relationship between these changes and fire was, however, subtle. Eventually Pinus forests became dominant and human impact on vegetation became less apparent. It is concluded that the impact of early Mesolithic hunter-gatherers on vegetation was detectable, but that their effect on fire pattern was difficult to evaluate. Further, we show that the glacio-isostatic land uplift must be considered in the search for Mesolithic settlements in areas previously covered by the Weichselian Ice, and that the process has influenced the biological archives through re-deposition of material.     

Elevational gradients during the Late-Glacial/Holocene vegetational transition in southern Bulgaria

The Late Glacial and early-Holocene vegetational history of a newly dated pollen and macrofossil diagram from Besbog, a cirque lake at 2250 m just above the forest limit in the Pirin Mountains of southwestern Bulgaria, is compared with a newly dated pollen diagram for the mire Shiroka Polyana at 1400 m in the conifer forest of the nearby Rhodope Mountains in order to investigate the chronology of major changes in the vegetation at different elevations. In the Lake Besbog record the non-arboreal pollen assemblage of the Late Glacial changed abruptly to that of Betula, Quercus and other deciduous types. The date for this change is about 11.6 ka cal b.p. The Quercus assemblage may be composed of pollen blown from intermediate elevations, to which deciduous forest had expanded because of higher summer temperatures related to high summer insolation. At Shiroka Polyana (1400 m) in the modern conifer belt, a similar change did not occur until about 8.8 ka cal b.p. The persistence of the dry steppe or steppe forest in the early Holocene at this lower site can also be attributed to high summer insolation. Thus as atmospheric temperature increased at the end of the Late Glacial, deciduous forests expanded first at intermediate elevations in the Pirin Mountains and only later in the Rhodope Mountains at lower elevations as summer insolation decreased.