Renewable energy from the ocean

Growing concern over the threat of global climate change has led to an increased interest in research and development of renewable energy technologies. The ocean provides a vast source of potential energy resources, and as renewable energy technology develops, investment in ocean energy is likely to grow. Research in ocean thermal energy conversion, wave energy, tidal energy, and offshore wind energy has led to promising technologies and in some cases, commercial deployment. These sources have the potential to help alleviate the global climate change threat, but the ocean environment should be protected while these technologies are developed. Renewable energy sources from the ocean may be exploited without harming the marine environment if projects are sited and scaled appropriately and environmental guidelines are followed.     

Measurement of vertical distribution of isoprene in surface seawater, its chemical fate, and its emission from several phytoplankton monocultures

Concurrent measurements of isoprene (2-methyl-1,3-butadiene) in seawater together with atmospheric concentrations in the Gulf Stream off the Florida coast were made. Florida Straits surface water concentrations of isoprene varied between 9.8 and 50.8 pmol 1⁻¹. Surface water isoprene concentrations showed a positive correlation with measured chlorophyll fluorescence, consistent with the biogenic origin of this non-methane hydrocarbon. Depth profiles showed a maximum in isoprene concentration similar to that of biological productivity as indicated by chlorophyll fluorescence. Daytime atmospheric mixing ratios of isoprene were never above 11 parts-per-trillion (pptv) and eight of eleven samples taken were below the ˜ 5 pptv detection limit. Using an estimated value of the Henry's law constant (K_H ˜ 3.1) a supersaturation of surface seawater of 2 to 3 orders of magnitude is estimated.Laboratory grown monocultures of several common phytoplankton species showed production of isoprene. Processes controlling the isoprene concentration in the photic zone of the ocean and the marine boundary layer are discussed. A calculation using a simple time dependent photochemical box model confirmed that isoprene is rapidly consumed by its reaction with the OH radical in the marine atmosphere.     

Uranium(VI) sorption on iron oxides in Hanford Site sediment: Application of a surface complexation model

Sorption of U(VI) on Hanford fine sand (HFS) with varying Fe-oxide (especially ferrihydrite) contents showed that U(VI) sorption increased with the incremental addition of synthetic ferrihydrite into HFS, consistent with ferrihydrite being one of the most reactive U(VI) sorbents present in natural sediments. Surface complexation model (SCM) calculations for U(VI) sorption, using only U(VI) surface-reaction constants obtained from U(VI) sorption data on freshly synthesized ferrihydrite at different pHs, were similar to the measured U(VI) sorption results on pure synthetic ferrihydrite and on HFS with high contents of ferrihydrite (5 wt%) added. However, the SCM prediction using only U(VI) sorption reactions and constants for synthetic ferrihydrite overestimated U(VI) sorption on the natural HFS or HFS with addition of low amounts of added ferrihydrite (1 wt% added). Over-predicted U(VI) sorption was attributed to reduced reactivity of natural ferrihydrite present in Hanford Site sediments, compared to freshly prepared synthetic ferrihydrite. Even though the SCM general composite (GC) approach is considered to be a semi-quantitative estimation technique for contaminant sorption, which requires systematic experimental data on the sorbent–sorbate system being studied to obtain credible SCM parameters, the general composite SCM model was still found to be a useful technique for describing U(VI) sorption on natural sediments. Based on U(VI) batch sorption results, two simple U(VI) monodentate surface species, SO_UO₂HCO₃ and SO_UO₂OH on ferrihydrite and phyllosillicate in HFS, respectively, can be successfully used to describe U(VI) sorption onto Hanford Site sediment contacting varying geochemical solutions.     

Historicizing climate change—engaging new approaches to climate and history

This introduction to a special issue of Climatic Change argues that it is timely and welcome to intensify historical research into climate change and climate as factors of history. This is also already an ongoing trend in many disciplines. The article identifies two main strands in historical work on climate change, both multi-disciplinary: one that looks for it as a driver of historical change in human societies, the other that analyzes the intellectual and scientific roots of the climate system and its changes. In presenting the five papers in this special issue the introduction argues that it is becoming increasingly important to also situate “historicizing climate change” within the history of thought and practice in wider fields, as a matter of intellectual, political, and social history and theory. The five papers all serve as examples of intellectual, political, and social responses to climate-related phenomena and their consequences (ones that have manifested themselves relatively recently and are predominantly attributable to anthropogenic climate change). The historicizing work that these papers perform lies in the analysis of issues that are rising in societies related to climate change in its modern anthropogenic version. The history here is not so much about past climates, although climate change itself is always directly or indirectly present in the story, but rather about history as the social space where encounters take place and where new conditions for humans and societies and their companion species and their life worlds in natures and environments are unfolding and negotiated. With climate change as a growing phenomenon historicizing climate change in this version will become increasingly relevant.     

A Comparison of the International Charters on Geographical Education

This article uses discourse analysis techniques associated with Foucauldian archaeology to examine the two international charters developed by the International Geographical Union Commission on Geographical Education (IGU-CGE), the original one in 1992 and the revised version endorsed in 2016 at the Beijing conference. The examination considers the consultation and development processes before outlining similarities and differences in the messages communicated and how discourses have changed through time. The article concludes with recommendations for the geography education community for the future.     

Sedimentological interpretation of an Ediacaran delta: Bonney Sandstone,South Australia

The type section of the late Ediacaran (ca 565 Ma) Bonney Sandstone in South Australia provides an opportunity to interpret a succession of Precambrian clastic sediments using physical sedimentary structures, lithologies and stacking patterns. Facies models, sequence stratigraphic analysis, and process-based architectural classification of depositional elements were used to interpret depositional environments for a series of disconformity-bounded intervals. This study is the first detailed published work on the Bonney Sandstone, and provides additional context for other Wilpena Group sediments, including the overlying Rawnsley Quartzite and its early metazoan fossils. Results show that the ～300 m-thick section studied here shows a progressive change from shallow marine to fluvially dominated sediments, having been deposited in storm-dominated shelf and lower shoreface environments, lower in the section, and consisting primarily of stacked channel sands, in a proximal deltaic environment near the top. Based on the degree of influence of wave, tidal or fluvial depositional processes, shallow marine sediments can be classified into beach, mouth bar, delta lobe and channel depositional elements, which can be used to assist in predicting sandbody geometries when only limited information is available. Sediments are contained within a hierarchical series of regressive, coarsening-upward sequences, which are in turn part of a larger basin-scale sequence that likely reflects normal regression and filling of accommodation throughout a highstand systems tract. Paleogeographic reconstructions suggest the area was part of a fluvially dominated clastic shoreline; this is consistent with previous reconstructions that indicate the area was on the western edge of the basin adjacent to the landward Gawler Craton. This research fills in a knowledge gap in the depositional history of a prominent unit in the Adelaide Rift Complex and is a case study in the interpretation of ancient deposits that are limited in extent or lacking diagnostic features.     

Robust tracking of multiple objects in sector-scan sonar imagesequences using optical flow motion estimation

The fast update rate and good performance of new generation electronic sector scanning sonars is now allowing practicable use of temporal information for signal processing tasks such as object classification and motion estimation. Problems remain, however, as objects change appearance, merge, maneuver, move in and out of the field of view, and split due to poor segmentation. This paper presents an approach to the segmentation, two-dimensional motion estimation, and subsequent tracking of multiple objects in sequences of sector scan sonar images. Applications such as ROV obstacle avoidance, visual servoing, and underwater surveillance are relevant. Initially, static and moving objects are distinguished in the sonar image sequence using frequency-domain filtering. Optical flow calculations are then performed on moving objects with significant size to obtain magnitude and direction motion estimates. Matches of these motion estimates, and the future positions they predict, are then used as a basis for identifying corresponding objects in adjacent scans. To enhance robustness, a tracking tree is constructed storing multiple possible correspondences and cumulative confidence values obtained from successive compatibility measures. Deferred decision making is then employed to enable best estimates of object tracks to be updated as subsequent scans produce new information. The method is shown to work well, with good tracking performance when objects merge, split, and change shape. The optical flow is demonstrated to give position prediction errors of between 10 and 50 cm (1%-5% of scan range), with no violation of smoothness assumptions using sample rates between 4 and 1 frames/s     

Hillslope run‐off thresholds with shrink–swell clay soils

Irrigation experiments on 12 instrumented field plots were used to assess the impact of dynamic soil crack networks on infiltration and run‐off. During applications of intensity similar to a heavy rainstorm, water was seen being preferentially delivered within the soil profile. However, run‐off was not observed until soil water content of the profile reached field capacity, and the apertures of surface‐connected cracks had closed >60%. Electrical resistivity measurements suggested that subsurface cracks persisted and enhanced lateral transport, even in wet conditions. Likewise, single‐ring infiltration measurements taken before and after irrigation indicated that infiltration remained an important component of the water budget at high soil water content values, despite apparent surface sealing. Overall, although the wetting and sealing of the soil profile showed considerable complexity, an emergent property at the hillslope scale was observed: all of the plots demonstrated a strikingly similar threshold run‐off response to the cumulative precipitation amount. Copyright © 2014 John Wiley & Sons, Ltd.     

Hillslope groundwater discharges provide localized stream ecosystem buffers from regional per- and polyfluoroalkyl substances contamination

Emerging groundwater contaminants such as per- and polyfluoroalkyl substances (PFAS) may impact surface-water quality and groundwater-dependent ecosystems of gaining streams. Although complex near-surface hydrogeology of stream corridors challenges sampling efforts, recent advances in heat tracing of discharge zones enable efficient and informed data collection. For this study, we used a combination of streambed temperature push-probe and thermal infrared methods to guide a discharge-zone-oriented sample collection along approximately 6 km of a coastal trout stream on Cape Cod, MA. Eight surface-water locations and discharging groundwater from 24 streambed and bank seepages were analysed for dissolved oxygen (DO), specific conductance, stable water isotopes, and a range of PFAS compounds, which are contaminants of emerging concern in aquatic environments. The results indicate a complex system of groundwater discharge source flowpaths, where the sum of concentrations of six PFAS compounds (corresponding to the U.S. Environmental Protection Agency third Unregulated Contaminant Monitoring Rule “UCMR 3”) showed a median concentration of 52 ± 331 (SD) ng/L with two higher outliers and three discharges with PFAS concentrations below the quantification limit. Higher PFAS concentration was related (− 0.66 Spearman rank, p < .001) to discharging groundwater that showed an evaporative signature (deuterium excess), indicating flow through at least one upgradient kettle lake. Therefore, more regional groundwater flowpaths originating from outside the local river corridor tended to show higher PFAS concentrations as evaluated at their respective discharge zones. Conversely, PFAS concentrations were typically low at discharges that did not indicate evaporation and were adjacent to steep hillslopes and, therefore, were classified as locally recharged groundwater. Previous research at this stream found that the native brook trout spawn at discharge points of groundwater recharged on local hillslopes, likely in response to generally higher levels of DO. Our study shows that by targeting high oxygen discharges the trout may thereby be avoiding emerging contaminants such as PFAS in groundwater recharged farther from the stream.