Bound and mobile soil water isotope ratios are affected by soil texture and mineralogy,whereas extraction method influences their measurement

Questions persist about interpreting isotope ratios of bound and mobile soil water pools, particularly relative to clay content and extraction conditions. Interactions between pools and resulting extracted water isotope composition are presumably related to soil texture, yet few studies have manipulated the bound pool to understand its influence on soil water processes. Using a series of drying and spiking experiments, we effectively labelled bound and mobile water pools in soils with varying clay content. Soils were first vacuum dried to remove residual water, which was then replaced with heavy isotope-enriched water prior to oven drying and spiking with heavy isotope-depleted water. Water was extracted via centrifugation or cryogenic vacuum distillation (at four temperatures) and analysed for oxygen and hydrogen isotope ratios via isotope ratio mass spectrometry. Water from centrifuged samples fell along a mixing line between the two added waters but was more enriched in heavy isotopes than the depleted label, demonstrating that despite oven drying, a residual pool remains and mixes with the mobile water. Soils with higher clay + silt content appeared to have a larger bound pool. Water from vacuum distillation samples have a significant temperature effect, with high temperature extractions yielding progressively more heavy isotope-enriched values, suggesting that Rayleigh fractionation occurred at low temperatures in the vacuum line. By distinctly labelling bound and mobile soil water pools, we detected interactions between the two that were dependent on soil texture. Although neither extraction method appeared to completely extract the combined bound and mobile (total water) pool, centrifugation and high temperature cryogenic vacuum distillations were comparable for both δ²H and δ¹⁸O of soil water isotope ratios.     

Canary in a coal mine: perceptions of climate change risks and response options among Canadian mine operations

A survey documenting how climate change is perceived and responded to by Canadian mine operations was administered to a random sample of practitioners working at mine sites across Canada. Key findings include: (1) Mines are sensitive to climatic hazards; (2) There is concern about climate change among mine practitioners, but the majority have not yet noticed climate change to be affecting operations; (3) Future climate change is expected to have negative impacts for mine operations; (4) Mines are responding to climate change mainly through efforts to reduce greenhouse gas emissions but also through adaptation, although to a lesser degree; and (5) Knowledge of future climate change projections and impacts is limited, potentially constraining understanding of the nature of climate change risks. The survey compliments previous work documenting perceptions among upper level management on climate change in the Canadian mining industry. The results from both surveys are largely consistent, establishing that the mining sector perceives climate change as an emerging risk and is developing response options, but needs to invest more time and resources for adaptation to what are inevitable changes in climate. The results support the need for targeted in-depth research to assess the vulnerability of mining to climate change and to evaluate response options.     

Stable carbon isotopes (δ<Superscript>13</Superscript>C) of total organic carbon and long-chain <Emphasis Type="Italic">n</Emphasis>-alkanes as proxies for climate and environmental change in a sediment core from Lake Petén-Itzá, Guatemala

Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C₃–C₄ terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ¹³C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ¹³C values in total organic carbon, which reflect times of greater proportions of C₄ plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation.     

Personality type differences between Ph.D. climate researchers and the general public: implications for effective communication

Effectively communicating the complexity of climate change to the public is an important goal for the climate change research community, particularly for those of us who receive public funds. The challenge of communicating the science of climate change will be reduced if climate change researchers consider the links between personality types, communication tendencies and learning preferences. Jungian personality type is one of many factors related to an individual’s preferred style of taking in and processing information, i.e., preferred communication style. In this paper, we demonstrate that the Jungian personality type profile of interdisciplinary, early career climate researchers is significantly different from that of the general population in the United States. In particular, Ph.D. climate researchers tend towards Intuition and focus on theories and the “big picture”, while the U.S. general population tends towards Sensing and focuses on concrete examples and experience. There are other differences as well in the way the general public as a group prefers to take in information, make decisions, and deal with the outer world, compared with the average interdisciplinary climate scientist. These differences have important implications for communication between these two groups. We suggest that climate researchers will be more effective in conveying their messages if they are aware of their own personality type and potential differences in preferred learning and communication styles between themselves and the general public (and other specific audiences), and use this knowledge to more effectively target their audience.     

Wind-forced continental shelf waves from a geographical origin

The response of a barotropic coastal ocean on a step-shaped continental shelf to a traveling sinusoidal wind stress forcing is predicted theoretically using a frictional force proportional to the alongshore current velocity. This theory is compared to a small set of observations from the northeast coast of Australia where a sudden widening of the continental shelf provides a geographical origin. The comparison is accomplished by means of frequency response functions relating alongshore wind stress with alongshore velocity. Amplitudes of the response functions are predicted to increase with alongshore distance equatorward and also to decrease with frequency at any location. These predictions are verified by the measurements. Predicted phase lags are generally less than about 30°, with observations agreeing with theory to within about 20°C. In general, the measurements provide reasonable evidence to support the theory of wind-forced continental shelf waves from a geographical origin.     

Isotopic and noble gas study of Chalk groundwater in the London Basin, England

The chemical and isotopic composition of groundwater from 52 sites in the London (U.K.) area was determined as part of a project aimed at assessing the spatial variation in the age of Chalk groundwater, and in determining the relationship between fracture and matrix groundwater in this dual porosity system.Systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes. These processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation-reduction reactions, gypsum dissolution and saline intrusion. As a result of the above processes, Chalk groundwater follows an evolutionary path from Ca bicarbonate type to Na bicarbonate type.The age of Chalk groundwater was modelled using¹⁴C, δ¹³C,³H, δ²H and δ¹⁸0. There is a general increase in the groundwater age in a downgradient direction with the oldest water found in N central areas of the basin. Groundwater in the unconfined zones and in areas S of the Greenwich fault is almost entirely of unevolved, modem composition. Carbon-14 modelling suggests that Chalk groundwater in the S basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old. The presence of³H in concentrations of up to 7 TU in groundwater which yields ages of several 1000 a, however, indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer. Results of palaeorecharge temperature determinations using δ²H, δ¹⁸0 and noble gas analytical results suggest that significant Devensian recharge did indeed occur in the aquifer.A model of the development of the Chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system. The upper 50 m of the aquifer was flushed with fresh water during the 2–3 × 10⁶ a of the Quaternary and therefore meteoric water largely replaced the Tertiary and Cretaceous marine water that previously saturated the system. Most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high. Although fracture flow dominates the flow regime, diffusion from the matrix into the fracture porosity controls the chemistry of Chalk groundwater.     

Comparative Hydrodynamics during Events along a Barrier Island: Explanation for Overwash

A fairly undeveloped barrier island along the mid-Atlantic coast, Onslow Beach, was exposed to two differing, yet sequential meteorological events in the fall of 2008. The response of the barrier island differed significantly enough to warrant investigation into the causes of aberrant overwash locations. Tropical Storm Hanna generated high significant wave heights for a short period of time and caused overwash events along the southern portion of Onslow Beach. The Nor’easter and subsequent wind shift after TS Hanna generated significant wave heights that were lower than during TS Hanna, yet more locations of overwash were recorded along the beach. Data from NOAA wave buoys and a nearshore deployed AWAC were analyzed to understand the underlying physics behind the recorded differences in barrier island response. These data were also used to validate a coupled hydrodynamic (ADCIRC) and waves (SWAN) model to investigate the alongshore variability. Low frequency variability, on the order of days, and tidal timing of shoreward high significant wave heights contributed to the recorded variability.     

The synergistic effect of calcium on organic carbon sequestration to ferrihydrite

Sequestration of organic carbon (OC) in environmental systems is critical to mitigating climate change. Organo-mineral associations, especially those with iron (Fe) oxides, drive the chemistry of OC sequestration and stability in soils. Short-range-ordered Fe oxides, such as ferrihydrite, demonstrate a high affinity for OC in binary systems. Calcium commonly co-associates with OC and Fe oxides in soils, though the bonding mechanism (e.g., cation bridging) and implications of the co-association for OC sequestration remain unresolved. We explored the effect of calcium (Ca²⁺) on the sorption of dissolved OC to 2-line ferrihydrite. Sorption experiments were conducted between leaf litter-extractable OC and ferrihydrite at pH 4 to 9 with different initial C/Fe molar ratios and Ca²⁺ concentrations. The extent of OC sorption to ferrihydrite in the presence of Ca²⁺ increased across all tested pH values, especially at pH ≥ 7. Sorbed OC concentration at pH 9 increased from 8.72 ± 0.16 to 13.3 ± 0.20 mmol OC g^?1 ferrihydrite between treatments of no added Ca²⁺ and 30 mM Ca²⁺ addition. Batch experiments were paired with spectroscopic studies to probe the speciation of sorbed OC and elucidate the sorption mechanism. ATR-FTIR spectroscopy analysis revealed that carboxylic functional moieties were the primary sorbed OC species that were preferentially bound to ferrihydrite and suggested an increase in Fe-carboxylate ligand exchange in the presence of Ca at pH 9. Results from batch to spectroscopic experiments provide significant evidence for the enhancement of dissolved OC sequestration to 2-line ferrihydrite and suggest the formation of Fe–Ca-OC ternary complexes. Findings of this research will inform modeling of environmental C cycling and have the potential to influence strategies for managing land to minimize OM stabilization.     

Probable Neolithic footprints preserved in inter-tidal peat at Kenfig, South Wales (UK)

Holocene footprints have been reported from several locations around the UK coast preserved within inter-tidal sediments. These sediments are normally fine-grained silts, sands and clays. Here we report potential human footprints preserved in the lower of two inter-tidal peat units exposed on the foreshore at Kenfig in South Wales. The lower peat layer pre-dates 3810 ± 40 BP and its maximum age is constrained by two dates, one of 4930 ± 50 BP and another of 5110 ± 50 BP. The prints may have formed at any point within this time interval. Both peat units formed in a salt marsh, or fen environment, as indicated by the analysis of both diatoms and pollen and have been tentatively assigned to the middle Wentlooge Formation within the Holocene lithostratigraphy established for the Severn Estuary Holocene sequence. The footprints were digitised using an optical laser scanner and are compared to other Holocene human footprints exposed on the Sefton Coast in North West England. In comparison the Kenfig prints have poor anatomical form which may be the result of both the substrate and post-depositional modification. The paper demonstrates the value of using optical laser scanning in the data capture and analysis of transitory archaeological and geological trace evidence.