A Late Weichselian stable isotope stratigraphy compared with biostratigraphical data: A case study from southern Sweden

Late Weichselian lake sediments from a site in southern Sweden, were analysed for stable carbon and oxygen isotopes, as well as plant macrofossils and insect remains. By comparison of independent data sets, general climatic changes were demonstrated. Lithological, chemical and stable isotope data reveal two significant climatic oscillations at ca. 12 200–12 000 and ca. 11 000–10 200 yr BP respectively. Continental climatic conditions, indicated by evaporative enrichment of ¹⁸O in lake marl, characterise parts of the early lake history, including the Older Dryas Stadial. Distinct variations of δ¹³C in organic material is discussed in terms of climatically induced changes in lake-water chemistry. Different types of photosynthetic assimilation of dissolved inorganic carbon is proposed as a contributing factor influencing lake marl δ¹³C. The universal application of a positive correlation between lake marl δ¹⁸O and mean annual air temperature is questioned. Quantifications of mean summer and winter temperatures based on beetle analysis show a climatic optimum around 12 000 yr BP, a marked cooling around 11 000 yr BP and a strong amelioration at ca. 10 200 yr BP. These climatic events were accompanied by distinct changes in aquatic vegetation. Plant macrofossil and insect analyses indicate an open vegetation during the entire period studied. Biostratigraphical data reflecting local limnic and terrestrial vegetation and regional climate facilitate the interpretation of stable isotope data.     

Palaeoecology of a late Allerød peat bed at Godøy,western Norway

A peat bed found under solifluction deposits on Godøya island, western Norway, accumulated during a few decades around 11 000 yr BP, at the end of the Allerød period of the Late Weichselian. Palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by Carex nigra. Periodic flooding brought in sand and silt, which decreased as drainage was impeded sufficiently for standing water to develop. The surrounding terrestrial vegetation was dominated by Salix scrub, with some open heath and alpine habitats nearby. Apart from two aquatic species, the 29 insect taxa recorded are characteristic of alpine heaths, plant litter (under Salix scrub) and stream-sides. Their remains, together with the terrestrial plant macrofossils, were washed into the mire from nearby. Because the fossils are locally derived, the environmental reconstructions are of the actual conditions at Godøy at ca. 11 000 yr BP. Palaeotemperature estimates from beetles and plants are in agreement. The coleopteran estimates (Mutual Climatic Range Method) suggest mean July temperatures of 10–13°C, slightly cooler than today (13.5°), and January temperatures between +1 and ?10°C, similar to or much colder than today. Summer temperature estimates from individual plant taxa indicate that temperatures during the Allerød period were similar to today's, but estimates from the reconstructed vegetation and timber-line positions give estimates up to 3.5° cooler. Temperatures fell 2.5–7.5°C at the Younger Dryas. This abrupt and severe cooling initiated the solifluction processes on Godøya that buried the peat. The Godøy peat bed and its contained fossils provide a rare glimpse of Allerød biota and environments at the local (site) scale.     

Martian thermal history,core segregation,and tectonics

A series of calculated thermal histories of Mars is presented, and their possible relation to surface tectonic history is discussed. The models include convective heat transport through an empirical approximation, and heating by radioactivity and core segregation. Initial temperature, T_i, and the timing and duration of core segregation are treated as free parameters. T_i is the main determinant of Martian thermal evolution: as it is varied from 20 to 100% of the present mean temperature, the maximum in surface heat flux moves from very recent to very early in Martian history. For the latter cases, the details of core segregation control the detailed timing of a peak in the thermal flux that exceeded 100 mW/m². It is suggested that the early disruption of cratered terrain crust in the northern hemisphere and subsequent volcanic resurfacing may have been related to core segregation. This would be consistent with a scenario in which an early period of core segregation generated a marked peak in the thermal flux that may have lead to extensivev partial melting and volcanism. This scenario would require Mars to have had an initial mean temperature comparable to the present value.     

Understanding and partitioning future climates for Australian regions from CMIP3 using ocean warming indices

The patterns of large-scale climate change over the 21st century simulated by 23 CMIP3 global climate models are analyzed to provide understanding of the range of projected temperature T and precipitation P changes for Australia published in 2007. Means of change, standardized by the global warming, within each of 11 regions are calculated for each model. Correlations between regions across the 23 models indicate that the changes are rather coherent across much of the mainland. The all-Australian average changes are also well correlated with a pattern of tropical sea surface temperatures. A Pacific-Indian Dipole index, representing this pattern, correlates strongly with Australian P. It also correlates well with variables in Southeast Asia. The global warming itself correlates well with Australian warming. These two indices of large-scale ocean warming are used to partition the 23 models into four representative future climates. For Australia overall, these can be described as much warmer and drier, much warmer, warmer and drier, and warmer. The four climates span much of the range of the earlier Australian projections over most of the continent. Further, they may be reproduced by a downscaling model forced with the SST anomalies. An assessment of the realism of the ocean pattern changes has the potential to reduce the uncertainty of projections, both for Australia and beyond.     

Incorporating a semi-stochastic model of ocean-modulated westerly wind bursts into an ENSO prediction model

Prediction models of the El Niño-Southern Oscillation (ENSO) phenomenon often represent westerly wind bursts (WWBs), a significant player in ENSO dynamics, as stochastic forcing. A recent paper developed an observationally motivated semi-stochastic statistical model that quantifies the dependence of WWBs on large-scale sea-surface temperature. This WWB model is added here to a hybrid coupled model, thus activating a two-way SST-WWB feedback. The WWB model represents both the deterministic and stochastic elements of WWBs and thus is especially appropriate for ensemble ENSO prediction experiments. An ensemble of retrospective forecasts is performed for the years 1979–2002. Overall statistical measures of predictability are neither degraded nor improved relative to the hybrid, coupled general circulation model, perhaps because of the limitations of the hybrid coupled model and the initialization procedure used. While the present work is meant as a proof-of-concept, it is found that the addition of the WWB model does improve the prediction of the onset and the development of the large 1997 warm event, pointing to the potential for ENSO prediction skill improvement using this approach.     

Unique isoprene oxidation products demonstrate chlorine atom chemistry occurs in the Houston,Texas urban area

As part of the 2000 Texas Air Quality Study (TexAQS), we studied the isoprene oxidation process under ambient conditions to discern the presence of chlorine atom (Cl) chemistry in the Houston, Texas urban area. By measuring chloromethylbutenone (CMBO) and an isomer of chloromethylbutenal (CMBA), we clearly observed sixteen episodes of active Cl chemistry during the 24-day experiment. Estimated median Cl concentration during each of these episodes was between the detection limit of ~10² atoms cm⁻³ and 50 _{- 30} ^{+ 70} ×10⁴ 50_{ - 30}^{ + 70} \times {10^4} atoms cm⁻³. Cl concentration during all the episodes averaged 7.6 _{- 2.0} ^{+ 4.7} ×10⁴ 7.6_{ - 2.0}^{ + 4.7} \times {10^4} atoms cm⁻³ and thus amounted to less than 3% of the OH concentration during the same periods. During the episodes, the fraction of oxidation chemistry initiated by Cl ranged from 3–43% and was strongly dependent on the quantity and type of hydrocarbons present in the atmosphere. Because of its intermittent presence and low concentration, Cl is not a broadly influential oxidant in the Houston, Texas urban area.