Calibration of cosmogenic noble gas production based on ³⁶Cl-³⁶Ar ages. Part 2. The ⁸¹Kr-Kr dating technique

We calibrated the ⁸¹Kr-Kr dating system for ordinary chondrites of different sizes using independent shielding-corrected ³⁶Cl-³⁶Ar ages. Krypton concentrations and isotopic compositions were measured in bulk samples from 14 ordinary chondrites of high petrologic type and the cosmogenic Kr component was obtained by subtracting trapped Kr from phase Q. The thus-determined average cosmogenic ⁷⁸Kr/⁸³Kr, ⁸⁰Kr/⁸³Kr, ⁸²Kr/⁸³Kr, and ⁸4Kr/⁸³Kr ratiC(Lavielle and Marti 1988; Wieler 2002). The cosmogenic ⁷⁸Kr/⁸³Kr ratio is correlated with the cosmogenic 22Ne/21Ne ratio, confirming that ⁷⁸Kr/⁸³Kr is a reliable shielding indicator. Previously, ⁸¹Kr-Kr ages have been determined by assuming the cosmogenic production rate of ⁸¹Kr, P(⁸¹Kr)c, to be 0.95 times the average of the cosmogenic production rates of ⁸⁰Kr and ⁸²Kr; the factor Y = 0.95 therefore accounts for the unequal production of the various Kr isotopes (Marti 1967a). However, Y should be regarded as an empirical adjustment. For samples whose ⁸⁰Kr and ⁸²Kr concentrations may be affected by neutron-capture reactions, the shielding-dependent cosmogenic (⁷⁸Kr/⁸³Kr)c ratio has been used instead to calculate P(⁸¹Kr)/P(⁸³Kr), as for some lunar samples, this ratio has been shown to linearly increase with (⁷⁸Kr/⁸³Kr)c (Marti and Lugmair 1971). However, the ⁸¹Kr-Kr ages of our samples calculated with these methods are on average ~30% higher than their ³⁶Cl-³⁶Ar ages, indicating that most if not all the ⁸¹Kr-Kr ages determined so far are significantly too high. We therefore re-evaluated both methods to determine P(⁸¹Kr)c/P(⁸³Kr)c. Our new Y value of 0.70 ± 0.04 is more than 25% lower than the value of 0.95 used so far. Furthermore, together with literature data, our data indicate that for chondrites, P(⁸¹Kr)c/P(⁸³Kr)c is rather constant at 0.43 ± 0.02, at least for the shielding range covered by our samples ([⁷⁸Kr/⁸³Kr]c = 0.119–0.185; [22Ne/21Ne]c = 1.083–1.144), in contrast to the observations on lunar samples. As expected considering the method used, ⁸¹Kr-Kr ages calculated either directly with this new P(⁸¹Kr)c/P(⁸³Kr)c value or with our new Y value both agree with the corresponding ³⁶Cl-³⁶Ar ages. However, the average deviation of 2% indicates the accuracy of both new ⁸¹Kr-Kr dating methods and the precision of the new dating systems of ~10% is demonstrated by the low scatter in the data. Consequently, this study indicates that the ⁸¹Kr-Kr ages published so far are up to 30% too high.

On the theory of high and low pressure areas: The significance of divergence in pressure areas

This is the edited and translated version of the article by Richard Scherhag “Zur Theorie der Hoch- und Tiefdruckgebiete. Die Bedeutung der Divergenz in Druckfeldern” (On the theory of high and low pressure areas: The significance of divergence in pressure areas), which was published in Meteorologische Zeitschrift 51, 129–138.

Is dating violence associated with substance use and sexual risk behaviors among urban, minority, middle school youth

Background. One in 4 adolescents reports some form of dating violence each year. Dating violence among high school adolescents has been linked with several morbidity issues. However, the association between dating violence and sexual risk and/or substance use among young adolescents has rarely been studied.^ Methods. Research hypotheses were tested using a secondary data analysis from a HIV, STI, pregnancy prevention intervention study for urban middle school students.^ Results. At baseline, 21% of youth reported experiencing physical ADV victimization, 48.2% reported non-physical victimization, and 52.6% report any victimization. After adjusting for race/ethnicity, gender, and age ever having sex, alcohol use, and illicit drug use were significantly associated with several forms of ADV.^ Conclusions. Dating violence appears to be associated with early initiation of sexual behavior, as well as alcohol and drug use. Few interventions address ADV among middle school youth. Early interventions that prevent dating violence are needed. ^

The Need for School-Based Teen Dating Violence Prevention

Schools have several competing demands, and often suffer from inefficient access to needed resources. Thus, the addition of any program into an already overtaxed school system must be met with convincing evidence that 1) a need or problem exists and is relevant to the education of students, 2) the problem is amenable to change, and 3) addressing the problem is in the best interest of educators and students. The purpose of the present paper is to present a case for inclusion of teen dating violence prevention programs in middle and high schools. We also discuss a recent survey of 219 employees of a suburban school district in southeast Texas. Specifically, we examined their perceived need for and appropriateness of a school-based dating violence prevention program. The anonymous internet-based survey revealed that a majority of participants believed that teen dating violence was a problem, 19% reported having observed an instance of teen dating violence, and 82% believed school to be an appropriate outlet for the implementation of a dating violence prevention program.

Building an Evidence-Based Approach to Address Dating Violence Prevention

Purpose: To discuss the approach and recommendations related to the adoption of school based curriculum for violence prevention. Findings: Preliminary assessments suggest that middle and high school youth experience a variety of forms of violence in social and dating relationships. Such experiences have negative academic, behavioral and emotional consequences. Conclusions: The authors have clearly illuminated the need for addressing the phenomenon of dating violence. The field could benefit from more robust evidenced-based investigations that substantiate that interventions have an impact beyond attitudinal changes toward the behavior. Such academic endeavors will provide a platform to validate the inclusion of such information in a school based curriculum as act as a call for action for broad based interventions.

(Supplement Table S2) Results of 230Th/U-dating

We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk material samples of another coral show younger ages and lower (230Th/238U) ratios than the corresponding theca wall samples. This coral also contains a considerable amount of 232Th. The application of the available open-system models developed to account for post-depositional diagenetic effects in corals shows that none of the models can successfully be applied to the Bonaire corals. The most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set. Comparison of the theca wall and bulk material data enables us to obtain information about the open-system processes that affected the corals. The corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary (detrital) phase. The most likely source of the detrital material is carbonate sand. The higher (230Th/232Th) ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk Earth (230Th/232Th) ratio and that the threshold for the commonly applied 232Th reliability criterion would be much lower than the generally used value of 1 ng g^-1. The coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process. A potential scenario is a combination of detrital contamination and U addition by secondary pore infillings. Our results show that the dense theca wall material of D. strigosa is generally less affected by post-depositional open-system behaviour and better suited for 230Th/U-dating than the bulk material. This is also obvious from the fact that all ages of theca wall material reflect a Last Interglacial origin (~125 ka), whereas the bulk material samples are either substantially older or younger. However, for some corals, the 230Th/U-ages and activity ratios of the bulk material and the theca wall samples are similar. This shows that strictly reliable 230Th/U-ages can also be obtained from bulk material samples of exceptionally well-preserved corals. However, the bulk material samples more frequently show elevated activity ratios and ages than the corresponding theca wall samples. Our findings should be generally applicable to brain corals (Mussidae) that are found in tropical oceans worldwide and may enable reliable 230Th/U-dating of fossil corals with similar skeletal architecture, even if their bulk skeleton is altered by diagenesis. The 230Th/U-ages we consider reliable (120-130 ka), along with a recently published age of 118 ka, provide the first comprehensive dating of the elevated lower reef terrace at Bonaire (118-130 ka), which is in agreement in timing and duration with other Last Interglacial records.

Radiocarbon dating, sedimentation rate, granulometry and organic carbon content of ODP Leg 182 sites

This data report presents sedimentological (grain size) and geochemical (X-ray diffraction, total organic carbon, accelerator mass spectrometry radiocarbon, and percent carbonate) information obtained from the western transect (Sites 1132, 1130, and 1134) and the eastern transect (Sites 1129, 1131, and 1127) in the Great Australian Bight during Leg 182. The purpose is to quantify changing rates of sediment accumulation and changes in sediment type from the late Pleistocene and Holocene, in order to relate these changes to the well-known sea level curve that exists for this time frame. Ultimately, these data can be used to more effectively interpret lithologic variations deeper in the Pleistocene succession, which most likely represent orbitally forced sea level events.

A multi-proxy investigation of sediment core GeoB7165-1 and AMS 14C dating points from sediment cores off Conceptión (~ 36°S)

A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36°S off central-south Chile (GeoB 7165-1, 36°33'S, 73°40'W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30°-41°S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling. Marine productivity augmented rather abruptly at 13-14 ka, well after the oceanographic changes.We suggest that the late deglacial increase in paleoproductivity off central-south Chile reflects the onset of an active upwelling system bringing nutrient-rich, oxygen-poor Equatorial SubsurfaceWater to the euphotic zone, and a relatively higher nutrient load of the Antarctic Circumpolar Current. During the Last Glacial Maximum, when the Southern Westerlies were located further north, productivity off central-south Chile, in contrast to off northern Chile, was reduced due to direct onshore-blowing winds that prevented coastal upwelling and export production.

Palynology and radiocarbon dating on sediment profile PG1756 from Lake Billyakh, NE Siberia, Russia

In this study a radiocarbon-dated pollen record from Lake Billyakh (65°17'N, 126°47'E; 340 m a.s.l.) in the Verkhoyansk Mountains was used to reconstruct vegetation and climate change since about 15 kyr BP (1 kyr=1000 cal. yr). The pollen record and pollen-based biome reconstruction suggest that open cool steppe and grass and sedge tundra communities with Poaceae, Cyperaceae, Artemisia, Chenopodiaceae, Caryophyllaceae and Selaginella rupestris dominated the area from 15 to 13.5 kyr BP. On the other hand, the constant presence of Larix pollen in quantities comparable to today's values points to the constant presence of boreal deciduous conifer trees in the regional vegetation during the last glaciation. A major spread of shrub tundra communities, including birch (Betula sect. Nanae), alder (Duschekia fruticosa) and willow (Salix) species, is dated to 13.5-12.7 kyr BP, indicating a noticeable increase in precipitation toward the end of the last glaciation, particularly during the Allerød Interstadial. Between 12.7 and 11.4 kyr BP pollen percentages of herbaceous taxa rapidly increased, whereas shrub taxa percentages decreased, suggesting strengthening of the steppe communities associated with the relatively cold and dry Younger Dryas Stadial. However, the pollen data in hand indicate that Younger Dryas climate was less severe than the climate during the earlier interval from 15 to 13.5 kyr BP. The onset of the Holocene is marked in the pollen record by the highest values of shrub and lowest values of herbaceous taxa, suggesting a return of warmer and wetter conditions after 11.4 kyr BP. Percentages of tree taxa increase gradually and reach maximum values after 7 kyr BP, reflecting the spread of boreal cold deciduous and taiga forests in the region. An interval between 7 and 2 kyr BP is noticeable for the highest percentages of Scots spine (Pinus subgen. Diploxylon), spruce (Picea) and fir (Abies) pollen, indicating mid-Holocene spread of boreal forest communities in response to climate amelioration and degradation of the permafrost layer.

Radiocarbon dating of mollusk shells from southern Kara Sea sediments

Riverine water and sediment discharge to the Arctic Ocean is among the most important parameters influencing Arctic climate. It is clear that the evaluation of Arctic paleoclimate requires information on the paleodischarge of major rivers entering the sedimentation basin. Presently, the water discharge of the Ob River accounts for about 12% of the total input of river water into the Arctic Ocean. During the investigation of the Kara Sea in the framework of the Russian-German SIRRO Project, the history of Yenisei discharge received much attention in a number of publications. This paper presents the results of lithological and geochemical investigations with application to the Holocene discharge of the Ob River. Qualitative (SiO2, Al2O3, K2O, and some modules) and quantitative (sedimentation rates and absolute masses of sedimentary material) parameters were used to characterize the history of the Ob sediment discharge. It was shown that the investigated paleochannels of the Ob were initiated at the Pleistocene-Holocene boundary, and during the first half of the Holocene, the river discharge decreased irregularly with decreasing age of sediments. The observed maxima are in fairly good agreement with the data for the Yenisei. We proposed a hypothesis on the influence of glacioisostatic movements in the marginal region of the former Kara ice sheet of late Valdai age on the cessation of marine-fluvial glaciation in the paleochannels of Ob and Yenisei in the periphery of the Ob-Yenisei shoal.

Pollen record and dating of a sediment profile from Ahlequellmoor in Germany

A pollen diagram from the Ahlequellmoor in the Solling area shows the history of vegetation and settlement over the last 7,800 years. In the early Atlantic period mixed deciduous forest with mainly Tilia together with Ulmus and Quercus grew in the area. In the late Atlantic period Quercus became most abundant. Fagus spread in the Sub-boreal period at about 2700 B.C. Since ca. 900 B.C. the Solling was covered by beech forests with some oak. In prehistoric times woodland grazing is indicated. Only in Medieval times are two settlements in the vicinity of the Ahlequellmoor reflected in the pollen diagram. The earlier one is dated to about A.D. 750-1020, and may be connected with the former Monastery of Hethis, which is thought to have existed close to the fen from A.D. 815 to 822. The second Medieval settlement dates to the 11th-12th century. The large-scale woodland destruction of late Medieval and modern times is not clearly visible. The silvicultural measures of the last 200 years are reflected by increasing values of spruce and grassland taxa.