R. M. Dunk

A reevaluation of the oceanic uranium budget for the Holocene

We present a new assessment of the pre-anthropogenic U budget for the Holocene ocean. We find that the gross input of U to the ocean lies in the range 53±17 Mmol/year, where the dominant source is river runoff (42.0±14.5 Mmol/year) and the direct discharge of groundwater could represent a significant additional input (9.3±8.7 Mmol/year). The soluble U flux associated with the aeolian input of crustal dust is minor (1.8±1.1 Mmol/year), falling well within the errors associated with the riverine flux. Removal of U to the organic rich sediments of salt marshes and mangrove swamps during river–sea mixing may significantly modify the riverine flux, such that the net U input is reduced to 42±18 Mmol/year. Evaluation of the U isotope budget demonstrates that the limits we have established on the U input flux are reasonable and suggests that direct groundwater discharge may play a significant role in maintaining the oceanic excess of 234U. The total sink of U from the ocean lies in the range 48±14 Mmol/year. We find that three major processes control the magnitude of this flux: (1) removal to oxygen-depleted sediments (26.9±12.2 Mmol/year); (2) incorporation into biogenic carbonate (13.3±5.6 Mmol/year); and (3) crustal sequestration during hydrothermal alteration and seafloor weathering (5.7±3.3 Mmol/year). The removal of U to opaline silica (0.6±0.3 Mmol/year) and hydrogenous phases (1.4±0.8 Mmol/year) is minimal, falling well within the errors associated with the other sinks. That the input and output fluxes balance within the calculated errors implies that U may be in steady state in the Holocene ocean. In this case, the input and output fluxes lie in the range 34–60 Mmol/year, giving an oceanic U residence time of 3.2–5.6×105 years. However, given the large uncertainties, a significant imbalance between the Holocene input and output fluxes cannot be ruled out. The constancy of the ancient seawater U concentration implies that the U budget is in steady state over the time period of a glacial–interglacial climate cycle (∼105 year). A Holocene flux imbalance must, therefore, be offset by an opposing flux imbalance during glacial periods or at the interglacial–glacial transition. We suggest that the storage of U in the coastal zone and shallow water carbonates during interglacial periods and the release of that U at or following the interglacial–glacial transition could be sufficient to affect the short-term stability of the U budget. Providing tighter constraints on U fluxes in the Holocene ocean is a prerequisite to understanding the U budget on the time scale of a glacial–interglacial climate cycle and using this element as a valuable palaeoceanographic proxy.

In situ Raman analyses of deep-sea hydrothermal and cold seep systems (Gorda Ridge and Hydrate Ridge)

The Deep Ocean Raman In Situ Spectrometer (DORISS) instrument was deployed at the Sea Cliff Hydrothermal Field and Hydrate Ridge in July 2004. The first in situ Raman spectra of hydrothermal minerals, fluids, and bacterial mats were obtained. These spectra were analyzed and compared to laboratory Raman measurements of standards and samples collected from the site. Spectra of vent fluid (∼294°C at the orifice) at ∼2700 m depth were collected with noncontact and immersion sampling optics. Compared to spectra of ambient (∼2°C) seawater, the vent fluid spectra show changes in the intensity and positions of the water O-H stretch bands due to the elevated temperature. The sulfate band observed in seawater spectra is reduced in vent fluid spectra as sulfate is removed from vent fluid in the subseafloor. Additional components of hydrothermal fluid are present in concentrations too low to be detected with the current Raman system. A precision underwater positioner (PUP) was used to focus the laser spot on opaque samples such as minerals and bacterial mats. Spectra were obtained of anhydrite from actively venting chimneys, and of barite deposits in hydrothermal crusts. Laboratory analysis of rock samples collected in the vent field also detected the presence of gypsum. Spectra of bacterial mats revealed the presence of elemental sulfur (S8) and the carotenoid beta-carotene. Challenges encountered include strong fluorescence from minerals and organics and insufficient sensitivity of the instrument. The next generation DORISS instrument addresses some of these challenges and holds great potential for use in deep-sea vent environments.

Tracing low-temperature fluid flow on ridge flanks with sedimentary uranium distribution

The uranium content of sediments and pore fluids along a ridge axis to ridge flank transect perpendicular to the southern East?Pacific Rise is used to assess the impact of low?temperature fluid flow on U distribution. Two distinct regions are identified: (1) a young crustal site (0.36 Ma crust) where significant solid phase U enrichments occur and (2) the ridge flank (1.9–4.6 Ma crust) with uniform U association with hydrothermal Fe oxide phases in the solid phases. Upward advection and diffusion of cool, U?depleted basement fluids occurs at many coring sites. At the 0.36 Ma site the oxic basal?fluids strip the plume derived sediment of the excess U, effectively migrating the U upwards through the sediment into the overlying water column. At the ridge flank sites the pore fluid advection rates are highest at bathymetric/basement highs and advection velocities of up to 7.5 mm yr?1 are inferred from the pore fluid profiles. These estimates are consistent with previous calculations based on fluoride pore fluid distributions. The basal?fluid U depletions are in the range 10–70% relative to seawater depending on temperature and redox state. Low?temperature uptake of U during basalt alteration is a significant sink from seawater in the global seawater U budget (6.7–29 Mmol yr?1). Pore fluid U content is a sensitive tracer of extremely low?temperature ( advection through ridge flank systems and the basal sediment U/Fe ratio is potentially a useful proxy for basement alteration history where low ratios indicate extensive oxic alteration of basal?sediments during fluid flow.

Flying along the supply chain: accounting for emissions from student air travel in the higher education sector

ABSTRACT Higher education institutions (HEIs) can play a key role in facilitating the transition to a low carbon economy, where reporting greenhouse gas emissions is an important step in this process. While most UK HEIs are required to report estate emissions, engagement with supply chain emissions has been inconsistent. This research examined emissions arising from the air travel of international and study-abroad students and their visiting friends and relatives (VFR). Survey results demonstrated that flight frequencies were substantially higher than those assumed in sector guidance. An analysis of 25 UK HEIs found student and VFR flight emissions were significant, each being greater than other Scope 3 travel and comparable to Scope 2 emissions. Scenario analysis suggests that by 2020/2021, increases in flight emissions are likely to exceed reductions in estate emissions unless HEIs reinvigorate efforts to achieve reduction targets, and/or there is close to zero growth in inbound and outbound student numbers. It is thus imperative that HEIs develop an accurate picture of these emissions in order to inform their carbon management and internationalization strategies. In doing so, the risk of a rebound-type effect must also be considered, where if action is taken to reduce student flights, VFR flights may increase.

Engineering Development of the Free Ocean CO 2 Enrichment (FOCE) Experiment

Globally, the burning of fossil fuels for energy production produces over 25 gigatons of CO2 per year and this material is released directly into the atmosphere. While approximately half of the CO2 has remained in the atmosphere long-term, most of the rest has been absorbed by the surface ocean. This has resulted in a lowering of the surface ocean pH by about 0.1 units since the beginning of the industrial revolution and if society is able to stabilize atmospheric CO2 levels at twice their pre-industrial concentrations will result in a lowering of surface ocean pH by 0.25 units. While many are asking the question of whether we should pursue direct ocean CO2 sequestration, the FOCE experiment is asking what will be the impact of the pH change on the ocean. In order to address this question, MBARI science and engineering have designed a small-scale in situ CO2 enrichment experiment to assess the chemical and biological impacts in a manner analogous to the land-based Free Air CO2 Enrichment (FACE) experiments. This prototype design is testing the ability to control pH within a fixed but freely exchanging volume of sea water. The technology concept for the experiment is based on a small ring structure using a central valve to direct the flow of pH altering fluid. The initial phase of the project uses concentrated HCl mixed with sea water and includes directional and volume control to achieve a desired pH offset. Control feedback is obtained by using pH sensors in the center of the control volume. Other aspects of the design that address the inherent time delays and noise of the associated pH signal are also discussed. Test results will show the capability of the system to maintain close loop control of pH in a given volume. Sea trials then demonstrate the ability of this initial system at a selected site to control pH to specified average level over a given amount of time. Further discussion includes systems in-situ results analysis, corrective actions, upgrades, and the anticipated next phase for FOCE including the use of CO2 addition to change the local chemistry

Participation and retention in a green tourism certification scheme

ABSTRACT Tourism certification schemes offer a transitional procedure to a more transparent and sustainable tourism product. Engaging current and previous Green Tourism Business Scheme (GTBS) members in Scotland, this research addresses issues of retention affecting progression of sustainable tourism supply. Quantitative analysis tracking GTBS members over three time points reveals 2% growth but conceals significant flux in membership. Retention was calculated at 66%, where business type analysis discloses distinct issues among accommodation providers with 42% departing the scheme. Decline is greatest among B&Bs and guesthouses (−61%), where poor and falling recruitment coincides with very poor retention (33%). Our analysis demonstrates that slow growth in membership is primarily a result of enterprises choosing to leave the scheme, rather than poor recruitment. Questionnaires from past and present GTBS members (n = 109) confirm the importance of personal pro-environmental philosophies and perceived business benefits in attracting members, yet anticipated benefits do not always materialise. The main reasons for leaving the GTBS relate to membership cost and unrealised benefits. Lack of scheme awareness, management, criteria, bureaucracy and time commitment were further departure factors. The paper offers some suggestions to address issues and enhance retention leading to sustainable growth among tourism certification schemes.

Advances in Deep-Ocean CO2 Sequestration Experiments

Publisher Summary This chapter reports on advances made in carrying out small-scale experiments on the direct injection of CO 2 in the deep ocean using ROV technology. A carbon-fiber composite accumulator of 56L internal capacity for safe CO 2 containment and delivery has been developed, and has been used for a series of experiments at 3600m ocean depth, thus enabling delivery of sufficient CO 2 for biological response studies. A time-lapse camera for recording events associated with the CO 2 pool has also been developed. A newly developed laser Raman spectrometer has been used to obtain spectroscopic information in situ, thus enabling detection of the state of the CO 2 , and the fate of impurities. CO 2 dissolution rate of 1.7μmol/cm 2 /sec was measured by direct insertion of a pH probe into the liquid surface, thereby forming a pocket of water. This technique provides confirmation of the very rapid re-building of the hydrate skin in which surface cracks are quickly annealed. The presence of a hydrate skin exerts a strong effect on CO 2 chemical and physical properties, and it has been observed quasi-chaotic instabilities associated with this phenomenon in which a transformation from thin film to massive hydrate formation has occurred within a few hours.

CAN HYDRATE DISSOLUTION EXPERIMENTS PREDICT THE FATE OF A NATURAL HYDRATE SYSTEM

Here, we present a dissolution study of exposed hydrate from outcrops at Barkley Canyon. Previously, a field experiment on synthetic methane hydrate samples showed that mass transfer controlled dissolution in undersaturated seawater. However, seafloor hydrate outcrops have been shown to have significant longevity compared to expected dissolution rates based upon convective boundary layer diffusion calculations. To help resolve this apparent disconnect between the dissolution rates of synthetic and natural hydrate, an in situ dissolution experiment was performed on two distinct natural hydrate fabrics.

Lessons Learned while Optimizing Instrument Sensitivity for Deep Ocean Raman Spectroscopy

Over the last several years, scientists and engineers at the Monterey Bay Aquarium Research Institute (MBARI) have successfully developed and deployed two generations of deep ocean laser Raman spectrometers. There are many advantages to this type of Spectroscopy: it is rapid, non-destructive, and can be used to analyze solids, liquids, and gases. Unfortunately, one of the disadvantages of using Raman Spectroscopy is that the return signal measured is very weak. Thus, it is difficult to detect dilute chemical compounds in solution, such as bicarbonate and carbonate ions at natural concentrations. This paper discusses the efforts we have made to increase the sensitivity of our second generation Deep Ocean Raman In Situ Spectrometer (DORISS2). In developing this second generation instrument, we incorporated new components which improved system performance. These components include a new ruggedized U-shaped spectrometer and a back-illuminated CCD camera which is much more sensitive than our original front-illuminated CCD camera. The element which has had the most impact on system sensitivity is a set of new custom-made fiber optic cables. We had built several sets of custom fiber optic cables, but despite our efforts, their performance degraded substantially over time. Recently, we developed a new oil-filled pressure-compensated fiber optic cable which performs far better in pressure testing and is much more robust. At 6000 psig, this cable shows losses of only 2-3 dB versus our previous cables where losses of 25-30 dB were common. This new fiber optic cable was field tested in May and showed markedly improved performance

A Novel Impact Assessment Methodology for Evaluating Distributional Impacts in Scottish Climate Change Adaptation Policy

While it is widely recognised that the impacts of both climate change and the policy response will be distributed, there is an absence of complete information regarding the socio-economic and geographic patterning of such impacts in the intra-national context. This paper seeks to address this gap, presenting a climate justice toolkit (indicator set and guidance) that enables the consistent assessment of distributional impacts of climate policy, and thus allows cumulative impacts to be assessed across the broad suites of policies that comprise national adaptation programmes. The objective in so doing is to inform the selection of appropriate policy options and to identify situations where supplementary policy may be required to redress negative or inequitable impacts.