Mechanisms of microbial carbon sequestration in the ocean – future research directions

This paper reviews progress on understanding biological carbon sequestration in the ocean with special reference to the microbial formation and transformation of recalcitrant dissolved organic carbon (RDOC), the microbial carbon pump (MCP). We propose that RDOC is a concept with a wide continuum of recalcitrance. Most RDOC compounds maintain their levels of recalcitrance only in a specific environmental context (RDOCt). The ocean RDOC pool also contains compounds that may be inaccessible to microbes due to their extremely low concentration (RDOCc). This differentiation allows us to appreciate the linkage between microbial source and RDOC composition on a range of temporal and spatial scales. Analyses of biomarkers and isotopic records show intensive MCP processes in the Proterozoic oceans when the MCP could have played a significant role in regulating climate. Understanding the dynamics of the MCP in conjunction with the better constrained biological pump (BP) over geological timescales could help to predict future climate trends. Integration of the MCP and the BP will require new research approaches and opportunities. Major goals include understanding the interactions between particulate organic carbon (POC) and RDOC that contribute to sequestration efficiency, and the concurrent determination of the chemical composition of organic carbon, microbial community composition and enzymatic activity. Molecular biomarkers and isotopic tracers should be employed to link water column processes to sediment records, as well as to link present-day observations to paleo-evolution. Ecosystem models need to be developed based on empirical relationships derived from bioassay experiments and field investigations in order to predict the dynamics of carbon cycling along the stability continuum of POC and RDOC under potential global change scenarios. We propose that inorganic nutrient input to coastal waters may reduce the capacity for carbon sequestration as RDOC. The nutrient regime enabling maximum carbon storage from combined POC flux and RDOC formation should therefore be sought

Real Time Analysis of Thermal Activation via Sphaleron Transitions

We study the process of thermal activation mediated by sphaleron transitions by analyzing the real-time dynamics of the decay out of equilibrium in a $1+1$ dimensional field theory with a metastable state. The situation considered is that of a rapid supercooling in which the system is trapped in a metastable state at a temperature larger than the mass of the quanta, but smaller than the energy to create a critical droplet. The initial density matrix is evolved in time and the nucleation rate (probability current at the saddle point) is computed. The nucleation rate is {\it time dependent}, vanishing at early times, reaching a maximum at a time $t \approx 1/m$ with $m$ the mass of quanta in the metastable state, and decreasing at long times as a consequence of unitarity. An estimate for the average number of particles of ``true vacuum'' produced as a function of time during the nucleation process is obtained.Comment: 26 pages 6 figures (available upon request), PITT-93-06, LATE

Temperature and UV light affect the activity of marine cell-free enzymes

Abstract. Microbial extracellular enzymatic activity (EEA) is the rate-limiting step in the degradation of organic matter in the oceans. These extracellular enzymes exist in two forms: cell-bound, which are attached to the microbial cell wall, and cell-free, which are completely free of the cell. Contrary to previous understanding, cell-free extracellular enzymes make up a substantial proportion of the total marine EEA. Little is known about these abundant cell-free enzymes, including what factors control their activity once they are away from their sites (cells). Experiments were run to assess how cell-free enzymes (excluding microbes) respond to ultraviolet radiation (UVR) and temperature manipulations, previously suggested as potential control factors for these enzymes. The experiments were done with New Zealand coastal waters and the enzymes studied were alkaline phosphatase (APase), β-glucosidase, (BGase), and leucine aminopeptidase (LAPase). Environmentally relevant UVR (i.e. in situ UVR levels measured at our site) reduced cell-free enzyme activities by up to 87 % when compared to controls, likely a consequence of photodegradation. This effect of UVR on cell-free enzymes differed depending on the UVR fraction. Ambient levels of UV radiation were shown to reduce the activity of cell-free enzymes for the first time. Elevated temperatures (15 °C) increased the activity of cell-free enzymes by up to 53 % when compared to controls (10 °C), likely by enhancing the catalytic activity of the enzymes. Our results suggest the importance of both UVR and temperature as control mechanisms for cell-free enzymes. Given the projected warming ocean environment and the variable UVR light regime, it is possible that there could be major changes in the cell-free EEA and in the enzymes contribution to organic matter remineralization in the future. </jats:p

Reconciliation of the carbon budget in the ocean’s twilight zone

Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean1, 2. The rate at which the sinking carbon is converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage3. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude4, 5, 6, 7, 8. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink

Exploring the role of Facebook in re-shaping backpacker’s social interactions

The recent Facebook launch of Timeline, Social Graph Search, and the increased use of the mobile Facebook apps has resulted in some important implications for the use of Facebook by backpackers. The purpose of this paper is to (re) explore how Facebook has impacted social relationships between backpackers and their personal, professional, and ‘fellow traveller’ networks, particularly in-light of these recent changes to Facebook and the increased reduction of anonymity while travelling. An exploratory survey was administered to 216 backpackers through social media. Descriptive analysis was conducted to explore the perceived social risks and benefits of Facebook in the context of the backpacking experience

Allostatic load and subsequent all-cause mortality: which biological markers drive the relationship? Findings from a UK birth cohort

The concept of allostatic load (AL) refers to the idea of a global physiological ‘wear and tear’ resulting from the adaptation to the environment through the stress response systems over the life span. The link between socioeconomic position (SEP) and mortality has now been established, and there is evidence that AL may capture the link between SEP and mortality. In order to quantitatively assess the role of AL on mortality, we use data from the 1958 British birth cohort including eleven year mortality in 8,113 adults. Specifically, we interrogate the hypothesis of a cumulative biological risk (allostatic load) reflecting 4 physiological systems potentially predicting future risk of death (N = 132). AL was defined using 14 biomarkers assayed in blood from a biosample collected at 44 years of age. Cox proportional hazard regression analysis revealed that higher allostatic load at 44 years old was a significant predictor of mortality 11 years later [HR = 3.56 (2.3 to 5.53)]. We found that this relationship was not solely related to early-life SEP, adverse childhood experiences and young adulthood health status, behaviours and SEP [HR = 2.57 (1.59 to 4.15)] . Regarding the ability of each physiological system and biomarkers to predict future death, our results suggest that the cumulative measure was advantageous compared to evaluating each physiological system sub-score and biomarker separately. Our findings add some evidence of a biological embodiment in response to stress which ultimately affects mortality

Submesoscale physicochemical dynamics directly shape bacterioplankton community structure in space and time

Submesoscale eddies and fronts are important components of oceanic mixing and energy fluxes. These phenomena occur in the surface ocean for a period of several days, on scales between a few hundred meters and few tens of kilometers. Remote sensing and modeling suggest that eddies and fronts may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0–400 m) revealed enhanced mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical characteristics. Compared to the surrounding waters, the filament was characterized by a distinct phytoplankton bloom, associated with depleted inorganic nutrients, elevated chlorophyll a concentrations, as well as twofold higher phyto- and bacterioplankton cell abundances. High-throughput 16S rRNA gene sequencing of bacterioplankton communities revealed enrichment of typical phytoplankton bloom-associated taxonomic groups (e.g., Flavobacteriales) inside the filament. Furthermore, linked to the strong water subduction, the vertical export of organic matter to 400 m depth inside the filament was twofold higher compared to the surrounding waters. Altogether, our results show that physical submesoscale mixing can shape distinct biogeochemical conditions and microbial communities within a few kilometers of the ocean. Hence, the role of submesoscale features in polar waters for surface ocean biodiversity and biogeochemical processes need further investigation, especially with regard to the fate of sea ice in the warming Arctic Ocean

Desarrollo de una plataforma de diseño e ingeniería naval

Due to the increase in complexity in production operations, and the low delivery times required by the current market in the naval sector, it is necessary to handle CAD / CAE applications that acquire the role of integrators between the design, planning and manufacturing processes In a newly built vessel the amount of information that is handled is very high, being managed entirely in two dimensions until reaching the last phase of the project, prior to manufacturing, where the development of steel in three dimensions is already beginning to be common. Therefore, during the evolution of the project, a 3D representation of the complete ship is not available at any time, forcing numerous modifications to be made once the ship is already built, thus raising the cost of its manufacture and delaying delivery times. Such modifications could be avoided with a 3D model that allows simultaneous visualization of all its components, just as it is when it is already built.Debido al incremento de complejidad en las operaciones de producción, y a los bajos tiempos de entrega que exige el mercado actual del sector naval, es necesario el manejo de aplicaciones CAD/CAE que adquieran el papel de integradoras entre las fases de diseño, la planificación y los procesos de fabricación. En un buque de nueva construcción la cantidad de información que se maneja es muy elevada, gestionándose íntegramente en dos dimensiones hasta alcanzar la última fase de proyecto, previa a la fabricación, donde ya empieza a ser común realizar el desarrollo del acero en tres dimensiones. Por lo tanto, durante la evolución del proyecto no se dispone en ningún momento de una representación 3D del buque completo, lo que obliga en numerosas ocasiones a realizar modificaciones una vez que el buque está ya construido, elevando de esta manera el coste de su fabricación y retrasando los tiempos de entrega. Dichas modificaciones se podrían evitar con un modelo 3D que permita la visualización simultánea de todos sus componentes, tal y como sucede cuando ya está construid

Desarrollo de una plataforma de diseño e ingeniería naval

Due to the increase of the complexity in the production operations, and to the low times of delivery that demands the present market of the naval sector, it is necessary to use of CAD/CAE programs that acquire the paper of integrators of the phases of design, planning and the processes of manufacture. In a new ship, a high amount of information is handled, and totally managed in two dimensions until the finish stage of the project, previous to the manufacture. Then, begins the development of the steel in three dimensions. Therefore, during the project evolution there is not a complete 3D representation of the ship, which forces in numerous occasions to make modifications when the ship is already constructed. This increases the manufacture’s cost and delays the delivery time. These modifications could be avoided with a 3D model that allows the synchronized visualization of all its components, as happen when they are constructed.MSC: 68Nxx, 68U07Debido al incremento de complejidad en las operaciones de producción, y a los bajos tiempos de entrega que exige el mercado actual del sector naval, es necesario el manejo de aplicaciones CAD/CAE que adquieran el papel de integradoras entre las fases de diseño, la planificación y los procesos de fabricación. En un buque de nueva construcción la cantidad de información que se maneja es muy elevada, gestionándose íntegramente en dos dimensiones hasta alcanzar la última fase de proyecto, previa a la fabricación, donde ya empieza a ser común realizar el desarrollo del acero en tres dimensiones. Por lo tanto, durante la evolución del proyecto no se dispone en ningún momento de una representación 3D del buque completo, lo que obliga en numerosas ocasiones a realizar modificaciones una vez que el buque está ya construido, elevando de esta manera el coste de su fabricación y retrasando los tiempos de entrega. Dichas modificaciones se podrían evitar con un modelo 3D que permita la visualización simultánea de todos sus componentes, tal y como sucede cuando ya está construidoMSC: 68Nxx, 68U0