Hydrogen isotope ratios of leaf wax n-alkanes in grasses are insensitive to transpiration

We analyzed hydrogen isotope ratios of high-molecular weight n-alkanes (δD_l) and oxygen isotope ratios of α-cellulose (δ¹⁸O_C) for C₃ and C₄ grasses grown in the field and in controlled-environment growth chambers. The relatively firm understanding of ¹⁸O-enrichment in leaf water and α-cellulose was used to elucidate fractionation patterns of δD_l signatures. In the different relative humidity environments of the growth chambers, we observed clear and predictable effects of leaf-water enrichment on δ¹⁸O_C values. Using a Craig-Gordon model, we demonstrate that leaf water in the growth chamber grasses should have experienced significant D-enriched due to transpiration. Nonetheless, we found no effect of transpirational D-enrichment on the δD_l values. In field samples, we saw clear evidence of enrichment (correlating with relative humidity of the field sites) in both δ¹⁸O_C and δD_l. These seemingly contrasting results could be explained if leaf waxes are synthesized in an environment that is isotopically similar to water entering plant roots due to either temporal or spatial isolation from evaporatively enriched leaf waters. For grasses in the controlled environment, there was no enrichment of source water, whereas enrichment of grass source water via evaporation from soils and/or stems was likely for grass samples grown in the field.Based on these results, evaporation from soils and/or stems appears to affect δD_l, but transpiration from leaves does not. Further evidence for this conclusion is found in modeling expected net evapotranspirational enrichment. A Craig-Gordon model applied to each of the field sites yields leaf water oxygen isotope ratios that can be used to accurately predict the observed δ¹⁸O_C values. In contrast, the calculated leaf water hydrogen isotope ratios are more enriched than what is required to predict observed δD_l values. These calculations lend support to the conclusion that while δ¹⁸O_C reflects both soil evaporation and transpiration, δD_l appears to only record evaporation from soils and/or stems. Therefore, the δD of n-alkanes can likely be used to reconstruct the δD of water entering a leaf, supporting the soil-enrichment model of Smith and Freeman (2006). In both the field and controlled studies, we found significant photosynthetic pathway effects on n-alkane δD suggesting that biochemical pathways or plant phylogeny have a greater effect on leaf wax δD than leaf-water enrichment in grasses.     

Clues from Current High CO2 Environments on the Effects of Ocean Acidification on CaCO3 Preservation

Acidification of surface seawater owing to anthropogenic activities has raised serious concerns on its consequences for marine calcifying organisms and ecosystems. To acquire knowledge concerning the future consequences of ocean acidification (OA), researchers have relied on incubation experiments with organisms exposed to future seawater conditions, numerical models, evidence from the geological record, and recently, observations from aquatic environments exposed to naturally high CO₂ and low pH, e.g., owing to volcanic CO₂ vents, upwelling, and groundwater input. In the present study, we briefly evaluate the distribution of dissolved CO₂–carbonic acid parameters at (1) two locations in the Pacific and the Atlantic Ocean as a function of depth, (2) a mangrove environment in Bermuda, (3) a seasonally stratified body of water in a semi-enclosed sound in Bermuda, and (4) in temporarily isolated tide pools in Southern California. We demonstrate that current in situ conditions of seawater pCO₂, pH, and CaCO₃ saturation state (Ω) in these environments are similar or even exceed the anticipated changes to these parameters in the open ocean over the next century as a result of OA. The observed differences between the Pacific and Atlantic Oceans with respect to seawater CO₂–carbonic acid chemistry, preservation of CaCO₃ minerals, and the occurrence and distribution of deep-sea marine calcifiers, support the hypothesized negative effects of OA on the production and preservation of CaCO₃ in surface seawater. Clues provided from shallow near-shore environments in Bermuda and Southern California support these predictions, but also highlight that many marine calcifiers already experience relatively high seawater pCO₂ and low pH conditions.     

High resolution absorption cross-section measurements of ozone at 195 K in the wavelength region 240–350 nm

Cross-sections of the Hartley-Huggins bands of 03 at the temperature 195 K have been obtained from photoabsorption measurements at column densities in the range 2 × 10¹⁷?1 × 10²¹ cm^?2 throughout the wavelength region 240–350 nm with a 6.65 m photoelectric scanning spectrometer equipped with a 2400 lines mm^?1 grating and operated at an instrumental width (FWHM) of 0.003 nm. The assumptions made in putting the measured relative cross-sections on an absolute basis are discussed. Fine structure in the cross-section observed in the Huggins bands is illustrated in the region 323–327 nm where shallow features of width 0.01–0.02 nm occur superposed on a stronger apparent continuum exhibiting broader wavy structure.     

Monitoring changes of ice streams using time series of satellite-altimetry-based digital terrain models

The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world’s oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometerresolution with meteraccuracy. Geostaristical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a limeseries analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/iceshelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem.     

Riverine dominance of a nearshore marine demersal food web: evidence from stable isotope and C/N ratio analysis

The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.     

Piltdown Man's ‘Treasure Map’

The ‘Maresfield Map’ is a map that purports to show features pertinent to the old iron industry in the Sussex Weald of southern England in 1724. It first appeared in a journal published by the Sussex Archaeological Society in early 1913, at roughly the same time as the formal publication by the Geological Society of London of papers introducing the discovery of the ‘remains’ of what became known as ‘Piltdown Man’ to the world. Piltdown Man was eventually revealed as fraudulent in 1953, followed by the Maresfield Map in 1974. Experiments in replication now show that the Maresfield Map is a sort of ‘treasure map’ (in a negative sense), which points fairly accurately to the supposed find‐spot of Piltdown Man, along with a coded accusation against Charles Dawson. The map's compiler is thought to have been L.F. Salzmann, the editor of the journal in which the map appeared. As such, the map represents the only such denunciation to have been published in the open literature in Dawson's lifetime, albeit a cryptic one. Mr Salzmann's possible motives are explored.