Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cold Climate”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed2001

A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles.

To understand better the link between atmospheric CO2 concentrations and climate over geological time, records of past CO2 are reconstructed from geochemical proxies. Although these records have provided us with a broad picture of CO2 variation throughout the Phanerozoic eon (the past 544 Myr), inconsistencies and gaps remain that still need to be resolved. Here I present a continuous 300-Myr record of stomatal abundance from fossil leaves of four genera of plants that are closely related to the present-day Ginkgo tree. Using the known relationship between leaf stomatal abundance and growing season CO2 concentrations, I reconstruct past atmospheric CO2 concentrations. For the past 300 Myr, only two intervals of low CO2 (<1,000 p.p.m.v.) are inferred, both of which coincide with known ice ages in Neogene (1-8 Myr) and early Permian (275-290 Myr) times. But for most of the Mesozoic era (65-250 Myr), CO2 levels were high (1,000-2,000 p.p.m.v.), with transient excursions to even higher CO2 (>2,000 p.p.m.v.) concentrations. These results are consistent with some reconstructions of past CO2 (refs 1, 2) and palaeotemperature records, but suggest that CO2 reconstructions based on carbon isotope proxies may be compromised by episodic outbursts of isotopically light methane. These results support the role of water vapour, methane and CO2 in greenhouse climate warming over the past 300 Myr.

Atmosphere↗
PubMed1997

Impact of light regimes on productivity patterns of benthic microbial mats in an antarctic lake: a modeling study.

Filamentous cyanobacteria often dominate benthic microbial communities of antarctic lakes and usually exhibit saturation of photosynthesis at light intensities approximately 100 microEinst m-2 s-1. Incident light regimes are controlled by ice and snow accumulations overlaying water columns during much of the year. Thus, light availability to microbial mats is often below saturation intensity and is strongly influenced by modest changes in climatic factors. A model of net primary production for benthic mat communities of the subantarctic Sombre Lake, Signy Island, was developed (1) to evaluate depth-specific productivities of mat communities, (2) to test the relative importances of model parameters to mat production, and (3) to explore the potential impacts of climate change on mat production as manifested through changes in light regime. Simulated rates of net primary production corresponded to observations on a daily basis (approximately 1-4 micrograms C fixed mg-1 ash-free DW of mat d-1) but were an order of magnitude lower than estimates of net annual production based on field measurements (< or = 3 vs. 11-45 g C m-2 yr-1, respectively). Close examination suggested that the simulated values were more plausible. A detailed sensitivity analysis of model behavior revealed that variations in the time of ice and snow melt in spring accounted for 40-60% of the total variation in model behavior, emphasizing the importance of climatic factors to net primary production of mat communities and the sensitivity of mat production to climate change.

Antarctic Regions↗
PubMed2004

Detecting interregionally diversifying natural selection on modern human cranial form by using matched molecular and morphometric data.

This comparison of morphological and neutral genetic variation in 10 human populations was designed to test a neutral hypothesis of cranial evolution in living and recent humans and to explain deviations from neutrality where detected. Overall, among-population differences in extant Homo sapiens cranial morphology are proportional to among-population differences in neutral molecular characteristics. For most of the populations studied, cranial morphology varies among regions in a manner consistent with neutral expectations. Removal of the effects of shared population history and structure by using the partial Mantel's test, however, does not remove the correlation between some aspects of cranial morphology and a measure of coldness of climate. The excess differentiation is most apparent in those population comparisons that involve a Siberian population living in an extremely cold environment. This finding suggests the action of natural selection, associated with regional variation in temperature, leading to among-population differentiation in excess of neutral expectations for some cranial dimensions. Those dimensions reflect the breadth of the skull, cranial vault size and shape, and aspects of nasal morphology. Although morphology for most of the world appears to vary among populations in accordance with neutral expectations in the context of population structure and history, morphology of the Siberian population appears to have undergone adaptation by natural selection.

Data Interpretation, Statistical↗
PubMed2002

Reference values of body mass at. birth among native northern population of Russia.

Infants with body mass at birth deviating from the mean values exhibit higher level of mortality. The absence of the expressed phenotype deviations refers to the preservation and heredity of the most adopted genotypes (reference values). The newborns out of the adaptive norm are morbidity-prone. The reference value for body mass at birth was studied in the indegenous populations of the Kola Peninsula, Siberia, Far East and the Urals. By our data the Arctic Saami and the Far East Nanais show the reference values more distinct from other. Lasting (many-centuries-long) adaptation to specific environmental conditions leads to development of a special phenotype complex. The Saami and Nanais are the most representative populations of the arctic and the monsoon climate zones. Accordingly, the parameters of reference values of their newborns are significantly different from the characteristics of the infants of the moderate climate zone.

Anthropometry↗
PubMed2006

Life at the edge: an experimental study of a poleward range boundary.

Experimental studies of biogeographic processes are important, but rarely attempted because of the logistical challenges of research at large spatial scales. I used a series of large-scale transplant experiments to investigate the mechanisms controlling species abundance near a poleward range boundary. The intertidal limpet Collisella scabra experiences a 100-fold decline in abundance over the northernmost 300 km of its range. Temperature and food supply both strongly influenced individual survival, growth, and maturation. Regression analysis also revealed significant interactions among these conditions: the effect of one could not be predicted without knowing the level of the other. But these relationships could not explain geographic abundance patterns. Instead, individual limpets were highly successful at sites with relatively low abundance. These results suggest that, even though temperature is important to the success of individual C. scabra populations, the primary effect of warming temperatures under climate change may not be a shift in geographic distribution.

Animals↗
PubMed2004

Surviving the ice: Northern refugia and postglacial colonization.

The contemporary distribution of biological diversity cannot be understood without knowledge of how organisms responded to the geological and climatic history of Earth. In particular, Quaternary expansions and contractions of glacial ice sheets are thought to have played an important role in shaping the distribution of biodiversity among current populations in the north-temperate region. In the central U.S., fossil and palynological data provide support for the maintenance of a large southeastern refuge during the last glacial maximum, and many temperate organisms are believed to have responded to glacial expansion by shifting their ranges to southern refugia and recolonizing northward to track the receding ice sheets. Thus, organisms are assumed to track favorable climates, and species ranges are expected to have shifted significantly. Here we present data from a deciduous forest vertebrate, the eastern chipmunk (Tamias striatus) in the central U.S., indicating the maintenance of multiple refugial sources as well as a southward expansion from a northern refugium. These results challenge the view that, during glacial maxima, organisms must have migrated south out of their ranges to track favorable climates.

Animal Migration↗
PubMed2004

Mountain biodiversity patterns at low and high latitudes.

This paper presents an overview of mountain biodiversity at a multitude of scales in space, time, and function. Even though species richness is usually the focal component in nature conservation, genetic diversity within species is equally important. The small-scale distribution of species in the tropical Andes, as exemplified by the plant genera Calceolaria and Bartsia, contrasts against the situation in high-latitude mountains, e.g., the Scandes, where species have wide ranges and many are circumpolar. Recent studies on alpine plants based on molecular methods show that the intraspecific genetic diversity tends to increase with latitude, a situation brought about by the glaciation history with repeated contraction-expansion episodes of species' distributions. In tropical mountains, species distributions are geographically much narrower, often as a result of relatively recent, local speciation. Thus, whereas species richness in mountains decreases from the Equator towards the poles, genetic diversity shows the opposite trend. Finally, a comparison of ecosystem diversity in low- and high-latitude mountain ranges (tropical Andes vs. Scandes) shows that the landscapes differ profoundly with regard to timberline ecotones, snow distribution, and climate variables, and are subject to widely different impacts of global change

Altitude↗