The exposure history of the Apollo 16 site: An assessment based on methane and hydrolysable carbon

Nineteen soils from eight stations at the Apollo 16 landing site have been analyzed for methane and hydrolysable carbon. These results, in conjunction with published data from photogeology, bulk chemistry, rare gases, primordial and cosmogenic radionuclides, and agglutinate abundances have been interpreted in terms of differing contributions from three components-North and South Ray Crater ejecta and Cayley Plains material

High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L13501, doi:10.1029/2009GL037643.Semi-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high-altitude ice fields were detected and identified through use of recently developed analytical tools. Specifically, stir bar sorptive extraction and thermal desorption coupled with gas chromatography/time-of-flight mass spectrometry allowed measurement of multiple biomarkers in small sample volumes (≤30 ml). Among other compounds of interest, several diterpenoids, which suggest inputs from conifers and conifer burning, were identified in post-industrial era and older Holocene ice from the Sajama site in the Bolivian Andes, but not in a glacial period sample, consistent with aridity changes. Differences in biomarker assemblages between sites support the use of these compounds as regionally constrained recorders of vegetation and climate change. This study represents the first application of these analytical techniques to ice core research and the first indication that records of vegetation fires may be reconstructed from diterpenoids in ice.This project was supported in part by NSF-OCE (0402533), and NSF-EAR (0094475)

Stable Isotope and Modelling Evidence for CO2 as a Driver of Glacial-Interglacial Vegetation Shifts in Southern Africa

Atmospheric CO2 concentration is hypothesized to influence vegetation distribution via tree-grass competition, with higher CO2 concentrations favouring trees. The stable carbon isotope (delta C-13) signature of vegetation is influenced by the relative importance of C-4 plants (including most tropical grasses) and C-3 plants (including nearly all trees), and the degree of stomatal closure - a response to aridity in C-3 plants. Compound-specific delta C-13 analyses of leaf-wax biomarkers in sediment cores of an offshore South Atlantic transect are used here as a record of vegetation changes in subequatorial Africa. These data suggest a large increase in C3 relative to C4 plant dominance after the Last Glacial Maximum. Using a process-based biogeography model that explicitly 10 simulates 13 C discrimination, we show that climate change alone cannot explain the observed shift in δ13 C values. The physiological effect of increasing CO2 concentration is decisive, altering the C3/ C4 balance and bringing the simulated and observed δ 13C values into line. It is concluded that CO2 concentration itself was a key agent of tropical vegetation 15 change during the last glacial-interglacial transition. Two additional inferences follow. First, long-term variations in terrestrial δ13 C values are not simply a proxy for regional rainfall as has sometimes been assumed. Such interpretations need to be re-examined. Second, rising CO2 concentration today is likely to be influencing tree-grass competition in a similar way, and thus contributing to the “woody thickening” observed in savannas worldwide. This second inference points to the importance of experiments to determine how vegetation composition in savannas is likely to be influenced by the continuing rise in CO2 concentratio

Developing marker trait associations in the population Chieftan/Barque//Manley/VB9104 using novel techniques

G.L. McMichael, J.K. Eglinton, A.R. Barr and K.J. Chalmer

Boron Toxicity in Barley: Prospects for delivering a yield advantage

J.K. Eglington, R.J. Reid, J.E. Hayes, P. Davies, D. Jha and P. McDonal

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Selective preservation of organic matter in marine environments; processes and impact on the sedimentary record

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 483-511, doi: 10.5194/bg-7-483-2010The present paper is the result of a workshop sponsored by the DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the Alfred Wegener Institute for Polar and Marine Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments. It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, understood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown. To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation. Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation. Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.We acknowledge generous financial support by the DFG Research Center/Cluster of Excellence MARUM “The Ocean in the Earth System”, the International Graduate College EUROPROX and the Alfred Wegener Institute for Polar and Marine Research enabling the realisation of the “Workshop on Selective Preservation of Organic Matter: Processes and Impact on the Fossil Record” which formed the basis of this paper. GJMV acknowledges support by the German Science Foundation (DFG grant VE486/2)

To what extent can online mapping be decolonial? A journey throughout Indigenous cartography in Canada

In this paper, we describe and reflect upon our journey through Indigenous online mapping in Canada. This journey has been planned according to an academic goal: assessing the potential of online cartography for decolonial purposes. To reach this goal, we have followed methodological directions provided by Indigenous scholar Linda Tuhiwai Smith to review 18 Indigenous web-mapping sites across Canada. Supported by a series of ten interviews, this content analysis enabled us to sketch some of the contours of contemporary Indigenous cartography. On one hand, Indigenous communities largely control the data that are shared on these websites. They also partially control the way these data are represented through the mobilization of digital storytelling technologies that are better aligned with Indigenous ways of envisioning relationships to places than conventional maps. On the other hand, they do not have much control over the technological aspects of these projects, for which they remain heavily dependent on non-Indigenous partners. Throughout this journey, we noticed that women’s voices remained marginal in most of these mapping projects, but we also identified evidence supporting the idea that these voices are starting to play a vital role in the on-going effort of decolonizing mapping processes

Fluvial organic carbon composition regulated by seasonal variability in lowland river migration and water discharge

Identifying drivers of seasonal variations in fluvial particulate organic carbon (POC) composition can aid sediment provenance and biogeochemical cycling studies. We evaluate seasonal changes in POC composition in the Río Bermejo, Argentina, a lowland river running ∼1,270 km without tributaries. Weekly POC concentration and isotopic composition from 2016 to 2018 show that during the wet season, increased lateral channel migration generates an influx of 13C-enriched and 14C-enriched floodplain-sourced material, overprinting the 13C-depleted and 14C-depleted headwater signature that is observed during the dry season. These findings demonstrate how channel morphodynamics can drive variability of POC composition in lowland rivers, and may modulate the composition of POC preserved in sedimentary archives