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2.
We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North
Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic
Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal
variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand
the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation.
Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world
ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models,
owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential
temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the
high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed
estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador
Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are
converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the
diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water)
leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive
to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar
convection is found in other models, we discuss broader implications. 相似文献
3.
The popular picture of the greenhouse effect emphasises the radiation transfer but fails to explain the observed climate change. An old conceptual model for the greenhouse effect is revisited and presented as a useful resource in climate change communication. It is validated against state-of-the-art data, and nontraditional diagnostics show a physically consistent picture. The earth’s climate is constrained by well-known and elementary physical principles, such as energy balance, flow, and conservation. Greenhouse gases affect the atmospheric optical depth for infrared radiation, and increased opacity implies higher altitude from which earth’s equivalent bulk heat loss takes place. Such an increase is seen in the reanalyses, and the outgoing long-wave radiation has become more diffuse over time, consistent with an increased influence of greenhouse gases on the vertical energy flow from the surface to the top of the atmosphere. The reanalyses further imply increases in the overturning in the troposphere, consistent with a constant and continuous vertical energy flow. The increased overturning can explain a slowdown in the global warming, and the association between these aspects can be interpreted as an entanglement between the greenhouse effect and the hydrological cycle, where reduced energy transfer associated with increased opacity is compensated by tropospheric overturning activity. 相似文献
4.
Raúl Prellezo Paolo AccadiaJesper L. Andersen Bo S. AndersenErik Buisman Alyson LittleJ. Rasmus Nielsen Jan Jaap PoosJeff Powell Christine Röckmann 《Marine Policy》2012,36(2):423-431
The lessons learned from a review of thirteen existing European bio-economic models used in the evaluation of EU policies are presented. How these models compare and differ in terms of their biological and economic components, the integration between the components, which indicators are selected and how they are used, are described and analysed. The article concludes that the multitude of construction differences reflects the necessity of adapting the modelling approach to answer different questions. Since real life questions in fisheries are so diverse, answering them requires a diversity of models. 相似文献
5.
Bo Elberling Rasmus Fensholt L. Larsen A-I. S. Petersen Inge Sandholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):47-56
Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO2 to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO2 effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO2 production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO2 effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO2 m?2 s?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO2 production was simulated to be in the range of 31–38 mol C m?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter. 相似文献
6.
Sirpa Tani Kalle Juuti Seija Kairavuori 《Norsk geografisk tidsskrift. Norwegian journal of geography》2013,67(3):172-178
The article investigates the potential and challenges of integrating geography with other school subjects. The analysis is based on the outcomes of a course that introduced the principles of discipline-based integration. The course was included in multicultural-class teacher education programme at the University of Helsinki. For a project within the course, the students worked in small groups and made short films that integrated three subjects – geography, physics, and visual arts – in order to evoke questions of space in children's minds. The students were asked to write essays in which they analysed their understanding of space from the three subjects’ viewpoints, describe the aims and contents of their short films, and lastly reflect on their experiences of the potential and possible problems in discipline integration. In this article, the authors analyse the students’ experience of the integration between the geography, physics, and visual arts. In general, the students experienced discipline-based integration as an interesting way of working. Moreover, the project seemed to deepen their understanding of different grounds for integrative pedagogy. Although the students reported some difficulties regarding the subject knowledge required for fruitful integration, the process enabled them to construct a better understanding of the identity of each discipline. 相似文献
7.
Integrating lysimeter drainage and eddy covariance flux measurements in a groundwater recharge model
Vicente Vásquez Anton Thomsen Bo V. Iversen Rasmus Jensen Rasmus Ringgaard 《水文科学杂志》2013,58(9):1520-1537
AbstractField-scale water balance is difficult to characterize because controls exerted by soils and vegetation are mostly inferred from local-scale measurements with relatively small support volumes. Eddy covariance flux and lysimeters have been used to infer and evaluate field-scale water balances because they have larger footprint areas than local soil moisture measurements. This study quantifies heterogeneity of soil deep drainage (D) in four 12.5-m2 repacked lysimeters, compares evapotranspiration from eddy covariance (ETEC) and mass balance residuals of lysimeters (ETwbLys), and models D to estimate groundwater recharge. Variation in measured D was attributed to redirection of snowmelt infiltration and differences in lysimeter hydraulic properties caused by surface soil treatment. During the growing seasons of 2010, 2011 and 2012, ETwbLys (278, 289 and 269 mm, respectively) was in good agreement with ETEC (298, 301 and 335 mm). Annual recharge estimated from modelled D was 486, 624 and 613 mm for three calendar years 2010, 2011 and 2012, respectively. In summary, lysimeter D and ETEC can be integrated to estimate and model groundwater recharge.
Editor D. Koutsoyiannis 相似文献
8.
In current scientific efforts to harness complementarity between resilience and vulnerability theory, one response is an ‘epistemological shift’ towards an evolutionary, learning based conception of the ‘systems-actor’ relation in social-ecological systems. In this paper, we contribute to this movement regarding the conception of stakeholder agency within social-ecological systems. We examine primary evidence from the governance of post-disaster recovery and disaster risk reduction efforts in Thailand's coastal tourism-dependent communities following the 2004 Indian Ocean Tsunami. Through an emerging storyline from stakeholders, we construct a new framework for conceptualising stakeholder agency in social-ecological systems, which positions the notion of resilience within a conception of governance as a negotiated normative process. We conclude that if resilience theory is proposed as the preferred approach by which disaster risk reduction is framed and implemented, it needs to acknowledge much more explicitly the role of stakeholder agency and the processes through which legitimate visions of resilience are generated. 相似文献
9.
Søren Jessen Flemming Larsen Dieke Postma Pham Hung Viet Nguyen Thi Ha Pham Quy Nhan Dang Duc Nhan Mai Thanh Duc Nguyen Thi Minh Hue Trieu Duc Huy Tran Thi Luu Dang Hoang Ha Rasmus Jakobsen 《Applied Geochemistry》2008
To study the geological control on groundwater As concentrations in Red River delta, depth-specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta, and the literature on the Red River delta’s Quaternary geological development was reviewed. The water samples (n = 30) were analyzed for As, major ions, Fe2+, H2S, NH4, CH4, δ18O and δD, and the geophysical log suite included natural gamma-ray, formation and fluid electrical conductivity. The SW part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15–20 km wide and 50–60 m deep Holocene incised valley. The NE part of the transect consists of 60–120 m of Pleistocene yellowish alluvial deposits underneath 10–30 m of estuarine clay overlain by a 10–20 m veneer of Holocene sediments. The distribution of δ18O-values (range −12.2‰ to −6.3‰) and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper Holocene aquifer and a lower Pleistocene aquifer. The groundwater samples were all anoxic, and contained Fe2+ (0.03–2.0 mM), Mn (0.7–320 μM), SO4 (<2.1 μM–0.75 mM), H2S (<0.1–7.0 μM), NH4 (0.03–4.4 mM), and CH4 (0.08–14.5 mM). Generally, higher concentrations of NH4 and CH4 and low concentrations of SO4 were found in the SW part of the transect, dominated by Holocene deposits, while the opposite was the case for the NE part of the transect. The distribution of the groundwater As concentration (<0.013–11.7 μM; median 0.12 μM (9 μg/L)) is related to the distribution of NH4, CH4 and SO4. Low concentrations of As (?0.32 μM) were found in the Pleistocene aquifer, while the highest As concentrations were found in the Holocene aquifer. PHREEQC-2 speciation calculations indicated that Fe2+ and H2S concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite. An elevated groundwater salinity (Cl range 0.19–65.1 mM) was observed in both aquifers, and dominated in the deep aquifer. A negative correlation between aqueous As and an estimate of reduced SO4 was observed, indicating that Fe sulphide precipitation poses a secondary control on the groundwater As concentration. 相似文献
10.