Large-scale Climate Oscillations Research Articles

Incongruence among morphological species circumscriptions and two molecular datasets in Sarmentypnum (Bryophyta: Calliergonaceae)

AbstractRelationships among species in Sarmentypnum, and Warnstorfia, are investigated based on the nuclear ITS and the chloroplast markers trnL–trnF, rpl16, and tRNA–Gly of up to 237 specimens. Six specimens in which morphology agrees with ITS sequences have chloroplast markers belonging to other species, whereas in two specimens morphology agrees with the chloroplast markers but have ITS sequences belonging to other species. Although hybridization has been recorded in Sarmentypnum, such incongruence could also be a result of other processes, including rapid morphological differentiation and incomplete lineage sorting. ITS and the chloroplast markers partly agree with the morphological species, although some of the latter appear to be polyphyletic or paraphyletic. Sarmentypnum exannulatum consists of two to three haplotype groups that are connected to S. sarmentosum, but not with each other. Sarmentypnum sarmentosum haplotypes are connected with haplotypes of most other species and may have played a central role in the genus' diversification. The trnL–trnF spacer inversion shows patterns congruent with other chloroplast information; it is therefore clearly informative. The incongruence among mainly non–coding molecular datasets and partial disagreement with morphological species could possibly be attributable to the special history of the boreal to arctic environments where Sarmentypnum is predominantly found. The species must be young in terms of number of generations and have experienced large–scale climatic oscillations during the Pleistocene. Incomplete lineage sorting in combination with rapid morphological evolution that is not reflected in the non–coding markers and an unknown frequency of hybridization most likely explains the observed incongruence.

A Holocene peat record in the central South Atlantic: an archive of precipitation changes

Peat deposits from the littoral part of the wetland 2nd Pond on Nightingale Island in the central South Atlantic have been analysed to investigate the Holocene climate development on the island and to test a hypothesis about regionally persistent humidity variations. A variety of proxies were analysed – total carbon and nitrogen, biogenic silica, diatoms, amount of organic matter, macrofossils and magnetic susceptibility – and together with the lithology they are interpreted as a record reflecting changes in humidity/precipitation. Early Holocene (10,000–8500 cal. BP) was possibly significantly drier than today, probably caused by a southerly displacement of the Southern Hemisphere Westerlies (SHW) during the Antarctic climate optimum. From 8500 cal. BP and onwards, the climate became generally more humid and surface run-off increased due to higher precipitation, possibly as an effect of increased influence from the SHW as it moved north. During this generally humid period, our data disclose a distinct pattern of recurrent centennial- to millennial-long events of increased precipitation and the results corroborate the only other study in the region with a similar humidity record. The events might represent large-scale climate oscillations in the Southern Hemisphere, such as latitudinal shifts of the SHW, but may also be related to changes in sea surface temperatures.

Cold conditions in Antarctica during the Little Ice Age — Implications for abrupt climate change mechanisms

The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000 yrs. It has been suggested that the LIA might be the most recent of the Dansgaard–Oeschger events, which are better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~ 2 °C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods.

The response of African land surface phenology to large scale climate oscillations

Variations in agricultural production due to rainfall and temperature fluctuations are a primary cause of food insecurity on the African continent. Analysis of changes in phenology can provide quantitative information on the effect of climate variability on growing seasons in agricultural regions. Using a robust statistical methodology, we describe the relationship between phenology metrics derived from the 26year AVHRR NDVI record and the North Atlantic Oscillation index (NAO), the Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO), and the Multivariate ENSO Index (MEI). We map the most significant positive and negative correlation for the four climate indices in Eastern, Western and Southern Africa between two phenological metrics and the climate indices. Our objective is to provide evidence of whether climate variability captured in the four indices has had a significant impact on the vegetative productivity of Africa during the past quarter century. We found that the start of season and cumulative NDVI were significantly affected by large scale variations in climate. The particular climate index and the timing showing highest correlation depended heavily on the region examined. In Western Africa the cumulative NDVI correlates with PDO in September–November. In Eastern Africa the start of the June–October season strongly correlates with PDO in March–May, while the PDO in December–February correlates with the start of the February–June season. The cumulative NDVI over this last season relates to the MEI of March–May. For Southern Africa, high correlations exist between SOS and NAO of September–November, and cumulative NDVI and MEI of March–May. The research shows that climate indices can be used to anticipate late start and variable vigor in the growing season of sensitive agricultural regions in Africa.

Long-term solar activity variations as a stimulator of abrupt climate change

Analysis of solar forcing of climate on long time scales has shown that it is necessaryto take into consideration the influence of long-term solar cyclicity, such as 200 and 2300–2400-year cycles, on climate. Even in the relatively warm climate of the last 10,000 years, atendency to climate cooling at deep minima of long-term solar cyclicity is observed. Alongwith this, a long-term solar forcing of climate manifests itself not only as an external factordue the influence of solar irradiance variations on the atmosphere-ocean system, but alsoas a stimulator of internal processes in the climatic system, which, in turn, can lead toabrupt climate change. Large-scale abrupt climate oscillations – warmings and subsequentcoolings (Dansgaard-Oeschger cycles) – have been revealed in cores of Greenland ice forthe interval 60,000–10,000 years BP. They are attributed to the ice-rafting events in theNorth Atlantic. A comparative analysis of the development of Dansgaard-Oeschger eventsand solar activity variations (variations in the

Influence of climate variation on seasonal precipitation in the Colorado River Basin

This study analyzed the influence of large-scale climate pattern on precipitation in the Colorado River Basin. Large-scale climatic oscillations, like ENSO, PDO, NAO, and the global warming trend are associated with regional hydrologic variation. Ten types of climate indices were gathered and analyzed to investigate their influence on seasonal precipitation variation in the basin based on a linear correlation analysis and an influence index analysis. The influence index was developed in this study to measure the effect of climate variation on the seasonal precipitation in the basin. The statistical evidence achieved in this study confirms that the Colorado River Basin is subjected to the phase of climate variation. The strength of the seasonal response of precipitation to the climate variation varies in different localities in the basin. The methods of analysis used in this study were proposed in the hope that progress in understanding and modeling dynamic climatic systems can result in developing a valuable long-term forecasting model for water resources management.

Climate Variability and the Energetic Pathways of Evolution: The Origin of Endothermy in Mammals and Birds

Large-scale climate oscillations in earth's history have influenced the directions of evolution, last but not least, through mass extinction events. This analysis tries to identify some unifying forces behind the course of evolution that favored an increase in organismic complexity and performance, paralleled by an increase in energy turnover, and finally led to endothermy. The analysis builds on the recent concept of oxygen-limited thermal tolerance and on the hypothesis that unifying principles exist in the temperature-dependent biochemical design of the eukaryotic cell in animals. The comparison of extant water-breathing and air-breathing animal species from various climates provides a cause-and-effect understanding of the trade-offs and constraints in thermal adaptation and their energetic consequences. It is hypothesized that the high costs of functional adaptation to fluctuating temperatures, especially in the cold (cold eurythermy), cause an increase in energy turnover and, at the same time, mobility and agility. These costs are associated with elevated mitochondrial capacities at minimized levels of activation enthalpies for proton leakage. Cold eurythermy is seen as a precondition for the survival of evolutionary crises elicited by repeated cooling events during extreme climate fluctuations. The costs of cold eurythermy appear as the single most important reason why metazoan evolution led to life forms with high energy turnover. They also explain why dinosaurs were able to live in subpolar climates. Finally, they give insight into the pathways, benefits, and trade-offs involved in the evolution of constant, elevated body temperature maintained by endothermy. Eurythermy, which encompasses cold tolerance, is thus hypothesized to be the "missing link" between ectothermy and endothermy. Body temperatures between 32 degrees and 42 degrees C in mammals and birds then result from trade-offs between the limiting capacities of ventilation and circulation and the evolutionary trend to maximize performance at the warm end of the thermal tolerance window.

Lake-Level fluctuations at Le Locle, Swiss Jura, from the Younger Dryas to the Mid-Holocene: A high-resolution record of climate oscillations during the final deglaciation

On the basis of a high-resolution (10 cm / 110 years) lacustrine sequence from Le Locle, Swiss Jura, a fine-scale pattern of palaeohydrological changes is reconstructed for the late Younger Dryas (YD) and the early to mid-Holocene period. The late YD is characterized by a general trend of a fall in lake level and a large climatic instability. The early to mid-Holocene period shows a quasi-cyclic pattern of lake-level fluctuations. Large drops in lake level occurred at ca. 11 600-10 200 cal. BP and ca. 8 900-7 700 cal. BP. Each was interrupted by a short-term rise in lake-level and followed by a longer phase of high lake level respectively at ca. 10 200-8 900 cal. BP and ca. 7 700-6 600 cal. BP. The high lake-level periods at le Locle appear to be in phase with cold spells reconstructed in central Europe, in eastern North America and in the Greenland ice-sheet, or with cooling events and salinity anomalies recorded in the North Atlantic zone. They also coincide with rising residual Δ14C values. These data and the Lateglacial oxygen-isotope GISP2 record suggest three successive quasi-cycles of climatic and environmental changes showing strong similarities in their internal structure. These cycles suggest that large-scale climate oscillations developing from the Bølling warming to the mid-Holocene could have been associated with changes in ocean ventilation probably induced by three deglaciation steps. Finally, as a working hypothesis, a re-exami- nation of the YD event is proposed from a Holocene point of view.

Decadal‐scale variability in long‐range atmospheric transport to the Summit of the Greenland Ice Sheet

Ice cores extracted from the Summit of the Greenland Ice Sheet date to >110 kyr b.p. and reveal fluctuations in chemical and physical characteristics on time scales ranging from days to millenia. Long‐range atmospheric transport patterns contribute substantially to variability in both airborne and snow‐deposited chemical species, and are thus one of the most important considerations in assessing climate variability preserved in polar ice cores. Here we present new evidence of decadal‐scale climate variability through an analysis of 44 years of modeled, 10‐day air trajectories arriving daily at Summit, Greenland. Trajectory residence times over specific upwind regions reveal interannual oscillations with periods of 4–14 years, and are correlated with three climate teleconnection indices. Our results suggest that the observed link between upstream source regions and the phases of large‐scale climate oscillations may be exploited to further understand paleoclimatic oscillations.

Origin and Mechanism of Large-Scale Climatic Oscillations

Numerical experiments with a simplified thermodynamic model of the glacier-ocean-atmosphere global system have been performed. Characteristic regimes of the system are auto-oscillations with periods varying between 20,000 and 80,000 years. The longer climatic waves are generated by the influence of variations of the earth's orbital parameters. Computed changes of glacial area, temperature, sea level, and other climate characteristics have values within expected ranges. The transition from a relatively warm epoch (when continental ice sheets are absent) to conditions characteristic of the Pleistocene is modeled. The calculated curves show how weak temperature fluctuations have been followed by large-scale oscillations.