Particulate Organic Carbon Export Fluxes in The Canada Basin and Bering Sea as Derived from 234Th/238U Disequilibria

Seawater samples were collected in the water column of the Canada Basin and the Bering Sea from aboard the R/V Xue Long during August 1999. Activity concentrations of dissolved and particulate 234Th were measured using beta counting techniques to quantify the scavenging and residence time of 234Th and organic carbon export fluxes. Primary production (PP) and bacterial production were also determined in the study areas through in situ incubation experiments. Significant 234Th scavenging was observed in the upper 100 m of the water column in both study areas, with up to 40% of 234Th deficit found at Bering Sea stations and ~15% of 234Th deficit at the Canada Basin station. Measured PP decreased from ~12.5 µmol C/m³/h in surface water to near zero at ~100 m depth, with an integrated PP of 3.83 mmol C/m²/d in the Canada Basin. Bacterial production, on the other hand, was on the order of 2.0 mmol C/m²/d, which is up to 52% of the integrated PP. Particulate organic carbon (POC) export fluxes derived from 234Th/238U disequilibrium were ~1 mmol C/m²/d in the Canada Basin and ~10 mmol C/m²/d in the Bering Sea, with fluxes in the latter area being 5 to 10 times higher than those found in the Canada Basin. These export fluxes correspond to a ThE ratio (the ratio of 234Th-derived POC export to primary production) of 0.26 for the Canada Basin and 0.7 for the Bering Sea. The higher ThE ratios in the study areas suggest a decoupling of production and particulate export in the high-latitude ocean. Ratios of POC to particulate 234Th (µmol C/dpm) decreased consistently with increasing depth, suggesting that organic carbon is preferentially remineralized relative to 234Th. Interestingly, the profile of particulate 234Th in the Canada Basin showed a unique characteristic: particulate 234Th activities increased with increasing depth, suggesting a continuous scavenging of 234Th and a rapid settling rate of the particles.Au cours du mois d'août 1999, on a prélevé des échantillons d'eau de mer dans la colonne d'eau du bassin Canada et de la mer de Béring depuis le vaisseau RV Xue-Long. L'activité volumique du 234Th dissous et particulaire a été mesurée à l'aide de techniques de comptage au rayonnement bêta afin de quantifier le temps de balayage et le temps de séjour du 234Th et les flux d'exportation du carbone organique. On a aussi établi la production primaire (PP) et la production bactérienne dans les zones d'étude en réalisant des expériences d'incubation in situ. Dans les deux zones d'étude, on a observé un balayage marqué du 234Th dans les 100 m supérieurs de la colonne d'eau, avec jusqu'à 40 p. cent de déficit de 234Th aux postes de la mer de Béring et environ 15 p. cent au poste du bassin Canada. La PP mesurée baissait d'environ 12,5 µmol C/m³/h dans l'eau de surface à près de zéro à environ 100 m de profondeur, avec une PP intégrée de 3,83 mmol C/m²/j dans le bassin Canada. D'autre part, la production bactérienne était de l'ordre de 2,0 mmol C/m²/j, ce qui représente jusqu'à 52 p. cent de la PP intégrée. Les flux d'exportation du carbone organique particulaire (COP) calculés à partir du déséquilibre 234Th /238U étaient d'environ 1 mmol C/m²/j dans le bassin Canada et d'environ 10 mmol C/m²/j dans la mer de Béring, les flux dans cette région étant de 5 à 10 fois plus élevés que ceux trouvés dans le bassin Canada. Ces flux d'exportation correspondent à un rapport ThE (le rapport de l'exportation du COP dérivé du 234Th à la production primaire) de 0,26 pour le bassin Canada et de 0,7 pour la mer de Béring. Les rapports plus élevés de ThE dans les zones d'étude suggèrent un découplage de la production et de l'exportation de particules dans l'océan septentrional. Les rapports de COP au 234Th particulaire (µmol C/dpm) diminuaient de façon uniforme avec l'augmentation de la profondeur, ce qui suggère que le carbone organique est reminéralisé préférentiellement par rapport au 234Th. Il est à noter que le profil du 234Th particulaire dans le bassin Canada affichait une caractéristique unique: l'activité du 234Th particulaire augmentait avec la profondeur, ce qui suggère un balayage continu du 234Th et un taux rapide de sédimentation des particules

Walking-by-Logic: Signal Temporal Logic-Guided Model Predictive Control for Bipedal Locomotion Resilient to External Perturbations

This study proposes a novel planning framework based on a model predictive control formulation that incorporates signal temporal logic (STL) specifications for task completion guarantees and robustness quantification. This marks the first-ever study to apply STL-guided trajectory optimization for bipedal locomotion push recovery, where the robot experiences unexpected disturbances. Existing recovery strategies often struggle with complex task logic reasoning and locomotion robustness evaluation, making them susceptible to failures caused by inappropriate recovery strategies or insufficient robustness. To address this issue, the STL-guided framework generates optimal and safe recovery trajectories that simultaneously satisfy the task specification and maximize the locomotion robustness. Our framework outperforms a state-of-the-art locomotion controller in a high-fidelity dynamic simulation, especially in scenarios involving crossed-leg maneuvers. Furthermore, it demonstrates versatility in tasks such as locomotion on stepping stones, where the robot must select from a set of disjointed footholds to maneuver successfully

Zonal Patterns of Delta C-13, Delta N-15 and Po-210 In the Tropical and Subtropical North Pacific

Nitrogen fixation process may supply a significant fraction of bioavailable nitrogen to surface waters, increase the oceanic sequestration of atmospheric CO2, and alter the distribution of geochemical parameters. We report a zonal pattern of delta N-15 and delta C-13 in particulate organic matter (POM), and ratios of particulate Po-210 to dissolved Po-210 along a transect through the subtropical and tropical North Pacific. Both N-15 and Po-210 signals indicated an enhanced N-2 fixation in the northwestern subtropical North Pacific. The eastward decrease of N-2 fixation along this transect testified the role of aeolian Fe and P in controlling marine N-2 fixation. Associated with the zonal variations of N-15 and Po-210, the delta C-13 of suspended POM increased eastward, reflecting the decrease of anthropogenic CO2 concentration in surface seawater from west to east in the study area. Our results highlight the need to examine more closely the mechanisms of possible longitudinal variation in N-2 fixation in the ocean and the role of aeolian Fe and P in controlling marine N-2 fixation and anthropogenic CO2

The mean residence time of river water in the Canada Basin

Seawater was collected from the western Arctic Ocean for measurements of (18)O, (226)Ra and (228)Ra. The fractions of river runoff and sea ice melt-water in water samples were estimated by using delta (18)O-S-PO* tracer system. The mean residence time of river water in the Canada Basin was calculated based on the relationship between (228)Ra/(226)Ra)(A.R.) and the fractions of river runoff in the shelf and deep ocean. Our results showed that the river runoff fractions in the Canada Basin were significantly higher than those in the shelf regions, suggesting that the Canada Basin is a major storage region for Arctic river water. (228)Ra activity concentrations in the Chukchi shelf and the Beaufort shelf ranged from 0.16 to 1.22 Bq/m(3), lower than those reported for shelves in the low and middle latitudes, indicating the effect of sea ice melt-water. A good positive linear relationship was observed between (228)Ra/(226)Ra)(A.R.) and the fraction of river runoff for shelf waters, while the (228)Ra/(226)Ra)(A.R.) in the Canada Basin was located below this regressive line. The low (228)Ra/(226)Ra)(A.R.) in the Canada Basin was ascribed to (228)Ra decay during shelf waters transporting to the deep ocean. The residence time of 5.0-11.0 a was estimated for the river water in the Canada Basin, which determined the time response of surface freshening in the North Atlantic to the river runoff into the Arctic Ocean

Assessing the value of commercial building low-carbon retrofit in Edinburgh City in Scotland

The purpose of current work is to assess the economics in the retrofit of non-domestic buildings in the UK, and recommend policy mechanisms to bridge the gap. This paper gives an overview of evaluation methodologies, incl. the technology assessment mechanism, financial cash flow valuation method, and the novel real option approach for assessing the value of new buildings designed in a low carbon retrofit readiness status. Detailed analysis of potential benefits from retrofitting existing commercial buildings in Edinburgh City is carried out. Resultshows substantial financial value in retrofitting a buildingover a lifetime through assessing the option value.The economic viability of retrofitting a commercialbuilding to low carbon design in Edinburgh is proven to be very high. Thus, new buildings are proposed to design in a ‘Low Carbon Building Retrofit Readiness’ status (‘LCB Readiness’) and it would be beneficial to develop a standard orbest practice for low carbon design for commercialbuildings.link_to_OA_fulltex

The Evolution of Ecological Space in an Urban Agglomeration Based on a Suitability Evaluation and Cellular Automata Simulation

Changing and reconstructing the ecological space of urban agglomerations is inevitable for ecological conservation and a scientific problem that needs urgent attention from geography, ecology, and urban and rural planning. Using ArcGIS and other software for data processing, this study established a spatial attribute database, constructed a land use conversion matrix of the Changsha-Zhuzhou-Xiangtan (CZX) urban agglomeration’s ecological space, and quantitatively analyzed the main changes in ecological land. Using a trained cellular automata model with predicted land use in 2035 as the threshold value, the simulation research was presented by creating two simulation scenarios for the spatial distribution of land use by 2035 in the “Green Heart” area of the CZX urban agglomeration. The simulation results were compared, and the constraining role of land use suitability evaluation on ecological space evolution was analyzed. This study found that the total area of ecological space in the Green Heart area saw a rapid reduction, and it predicted that, by 2035, the total area of the CZX Green Heart area will have decreased. Comparing the two simulation scenarios proved the hypothesis that zoning ecological space reconstruction based on a land suitability evaluation can effectively protect ecological space and ensure ecological network functions are harnessed

The Evolution of Ecological Space in an Urban Agglomeration Based on a Suitability Evaluation and Cellular Automata Simulation

Changing and reconstructing the ecological space of urban agglomerations is inevitable for ecological conservation and a scientific problem that needs urgent attention from geography, ecology, and urban and rural planning. Using ArcGIS and other software for data processing, this study established a spatial attribute database, constructed a land use conversion matrix of the Changsha-Zhuzhou-Xiangtan (CZX) urban agglomeration’s ecological space, and quantitatively analyzed the main changes in ecological land. Using a trained cellular automata model with predicted land use in 2035 as the threshold value, the simulation research was presented by creating two simulation scenarios for the spatial distribution of land use by 2035 in the “Green Heart” area of the CZX urban agglomeration. The simulation results were compared, and the constraining role of land use suitability evaluation on ecological space evolution was analyzed. This study found that the total area of ecological space in the Green Heart area saw a rapid reduction, and it predicted that, by 2035, the total area of the CZX Green Heart area will have decreased. Comparing the two simulation scenarios proved the hypothesis that zoning ecological space reconstruction based on a land suitability evaluation can effectively protect ecological space and ensure ecological network functions are harnessed

Bacterial productivity in the Prydz Bay and its adjacent waters, Antarctic

Bacterial productivity was measured using (3)H-thymidine methods in the Prydz Bay and its adjacent waters in the Southern Ocean during the 16th National Antarctic Research Expedition of China (CHINARE). The results showed that bacterial productivity in our study areas ranged from 4.5 to 191 ngC * dm(-3) * h(-1), with an average of 50.4 ngC * dm(-3) * h(-1). These values were comparable to those reported for the Ross Sea. The mean ratio of bacterial productivity to primary productivity in our study areas was 41%. The general characteristics in the vertical profiles showed a sub-surface maximum at most of the stations, which was also consistent with those observed in the other sea areas in the Southern Ocean. The spatial distribution of bacterial productivity and dissolved organic carbon in the surface waters showed that their variations were inversely correlative. The relationship among bacterial productivity, primary productivity and dissolved organic carbon suggested that bacterial productivity in the Prydz Bay and its adjacent water was influenced mostly by phytoplankton activities and the hydrologic conditions