Siga este enlace para ver otros tipos de publicaciones sobre el tema: Bottom-up forcings.
Artículos de revistas sobre el tema "Bottom-up forcings"
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte los 50 mejores artículos de revistas para su investigación sobre el tema "Bottom-up forcings".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Explore artículos de revistas sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.
1
Pielke, Roger A., Jimmy Adegoke, Faisal Hossain y Dev Niyogi. "Environmental and Social Risks to Biodiversity and Ecosystem Health—A Bottom-Up, Resource-Focused Assessment Framework". Earth 2, n.º 3 (12 de julio de 2021): 440–56. http://dx.doi.org/10.3390/earth2030026.
Texto completoResumen
Risks from human intervention in the climate system are raising concerns with respect to individual species and ecosystem health and resiliency. A dominant approach uses global climate models to predict changes in climate in the coming decades and then to downscale this information to assess impacts to plant communities, animal habitats, agricultural and urban ecosystems, and other parts of the Earth’s life system. To achieve robust assessments of the threats to these systems in this top-down, outcome vulnerability approach, however, requires skillful prediction, and representation of changes in regional and local climate processes, which has not yet been satisfactorily achieved. Moreover, threats to biodiversity and ecosystem function, such as from invasive species, are in general, not adequately included in the assessments. We discuss a complementary assessment framework that builds on a bottom-up vulnerability concept that requires the determination of the major human and natural forcings on the environment including extreme events, and the interactions between these forcings. After these forcings and interactions are identified, then the relative risks of each issue can be compared with other risks or forcings in order to adopt optimal mitigation/adaptation strategies. This framework is a more inclusive way of assessing risks, including climate variability and longer-term natural and anthropogenic-driven change, than the outcome vulnerability approach which is mainly based on multi-decadal global and regional climate model predictions. We therefore conclude that the top-down approach alone is outmoded as it is inadequate for robustly assessing risks to biodiversity and ecosystem function. In contrast the bottom-up, integrative approach is feasible and much more in line with the needs of the assessment and conservation community. A key message of our paper is to emphasize the need to consider coupled feedbacks since the Earth is a dynamically interactive system. This should be done not just in the model structure, but also in its application and subsequent analyses. We recognize that the community is moving toward that goal and we urge an accelerated pace.
2
Molero, Francisco, Alfonso Javier Fernández, María Aránzazu Revuelta, Isabel Martínez-Marco, Manuel Pujadas y Begoña Artíñano. "Effect of Vertical Profile of Aerosols on the Local Shortwave Radiative Forcing Estimation". Atmosphere 12, n.º 2 (30 de enero de 2021): 187. http://dx.doi.org/10.3390/atmos12020187.
Texto completoResumen
In this work, the effect of the aerosol vertical distribution on the local shortwave aerosol radiative forcing is studied. We computed the radiative forcing at the top and bottom of the atmosphere between 0.2 and 4 microns using the libRadTran package and compared the results with those provided by AERONET (AErosol RObotic NETwork). Lidar measurements were employed to characterize the aerosol vertical profile, and collocated AERONET measurements provided aerosol optical parameters required to calculate its radiative forcing. A good correlation between the calculated radiative forcings and those provide by AERONET, with differences smaller than 1 W m−2 (15% of estimated radiative forcing), is obtained when a gaussian vertical aerosol profile is assumed. Notwithstanding, when a measured aerosol profile is inserted into the model, differences between radiative forcings can vary up to 6.54 W m−2 (15%), with a mean of differences = −0.74 ± 3.06 W m−2 at BOA and −3.69 W m−2 (13%), with a mean of differences = −0.27 ± 1.32 W m−2 at TOA due to multiple aerosol layers and aerosol types. These results indicate that accurate information about aerosol vertical distribution must be incorporated in the radiative forcing calculation in order to reduce its uncertainties.
3
Pradeep Ram, A. S., S. Chaibi-Slouma, J. Keshri, J. Colombet y T. Sime-Ngando. "Functional Responses of Bacterioplankton Diversity and Metabolism to Experimental Bottom-Up and Top-Down Forcings". Microbial Ecology 72, n.º 2 (14 de mayo de 2016): 347–58. http://dx.doi.org/10.1007/s00248-016-0782-0.
Texto completo
4
Dinápoli, Matías G., Claudia G. Simionato y Diego Moreira. "Model Sensitivity during Extreme Positive and Negative Surges in the Río de la Plata Estuary: Highlighting the Need for an Appropriate Hindcast/Forecast System". Weather and Forecasting 35, n.º 3 (15 de mayo de 2020): 1097–112. http://dx.doi.org/10.1175/waf-d-19-0171.1.
Texto completoResumen
Abstract The large and fast-flowing Río de la Plata (RdP) estuary is affected by extreme storm surges (above ±2 m with respect to tidal datum), which have large impacts on the millions of inhabitants and for navigation. In this work the Coastal and Regional Ocean Community Model (CROCO) numerical model was modified and implemented as a set of regional one-way nested 2D applications for the hindcast/forecast of water level in the RdP. A sensitivity analysis (SA) was carried out to determine the impact on the numerical solutions of the uncertainties in the different modeling parameter forcings and to highlight the need for the construction of a modeling system that provides meaningful information to the potential users. The SA included the friction coefficients, the wind speed and direction, the atmospheric surface pressure, and the continental discharge. Water level is most sensitive to uncertainties in the wind forcing; even small changes in this input can create large errors in the water level forecast/hindcast. Forcing with different analyses’ wind products yielded differences of up to 50% in the peak water levels. Results also showed that the modeling system requires a reasonable adjustment of the bottom friction parameters; that it is important to include the atmospheric surface pressure forcing; and that, from the point of view of water level forecast, it is not necessary to couple a hydrological model in spite of the enormous runoff of this estuary. Given the strong sensitivity to errors in the wind forcing, we believe it is important to provide estimates of uncertainty together with hindcast/forecast water level for these predictions to be of greatest quality and practical applicability.
5
Habib, Md Ahsan y Gary A. Zarillo. "Construction of a Real-Time Forecast Model for Coastal Engineering and Processes Nested in a Basin Scale Model". Journal of Marine Science and Engineering 11, n.º 7 (21 de junio de 2023): 1263. http://dx.doi.org/10.3390/jmse11071263.
Texto completoResumen
A numerical model was developed using Delft3D to simulate the circulation dynamics in Port Everglades, FL, and the adjacent coastal area. The model was nested within the HYCOM (Hybrid Coordinate Ocean Model), while meteorological data were obtained from the NARR (North American Regional Reanalysis) model. To evaluate the model, model outputs were compared with observed data from the NOAA. Calibration experiments were conducted on the model parameters, including the bottom friction, wind forcings, and vertical layer specification. These experiments revealed that implementing a 10-layer model slightly improved the vertical stratification, while the utilization of 2-D wind data resulted in more pronounced surface layer characteristics in temperature and velocity profiles and employing moderate values of the Chezy coefficient produced optimal outcomes for the bottom roughness parameter. The model demonstrated satisfactory performance across major parameters, including water level, salinity, temperature, and currents. A real-time forecast system has been constructed with this nested model, providing up to 3-day forecasts that are updated daily. To facilitate automated forecasting without manual intervention, an automation system has been developed using a combination of bash, MATLAB, and Python scripts. This study provides a comprehensive documentation of the concepts and detailed methods involved in developing a real-time forecast model for estuarine and coastal regions.
6
Anet, J. G., S. Muthers, E. V. Rozanov, C. C. Raible, A. Stenke, A. I. Shapiro, S. Brönnimann et al. "Impact of solar versus volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum". Climate of the Past 10, n.º 3 (9 de mayo de 2014): 921–38. http://dx.doi.org/10.5194/cp-10-921-2014.
Texto completoResumen
Abstract. The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles versus volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, AD 1780–1840). Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere–ocean chemistry–climate model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decreased global mean temperature by up to 0.5 K for 2–3 years after the eruption. However, while the volcanic effect is clearly discernible in the Southern Hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only an insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top–down processes (stemming from changes at λ < 250 nm) relative to bottom–up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2%) decrease in the ocean heat content (OHC) between 0 and 300 m in depth, whereas the changes in irradiance at λ < 250 nm or in energetic particles have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 years after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift in the intertropical convergence zone.
7
Anet, J. G., S. Muthers, E. V. Rozanov, C. C. Raible, A. Stenke, A. I. Shapiro, S. Brönnimann et al. "Impact of solar vs. volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum". Climate of the Past Discussions 9, n.º 6 (4 de noviembre de 2013): 6179–220. http://dx.doi.org/10.5194/cpd-9-6179-2013.
Texto completoResumen
Abstract. The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles vs. volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, 1780–1840 AD). Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere-ocean chemistry-climate-model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decrease global mean temperature by up to 0.5 K for 2–3 yr after the eruption. However, while the volcanic effect is clearly discernible in the southern hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree-ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top-down processes (stemming from changes at λ < 250 nm) relative to bottom-up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2%) decrease of the ocean heat content (OHC) between the 0 and 300 m of depth, whereas the changes in irradiance at λ < 250 nm or in energetic particle have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 yr after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift of the intertropical convergence zone.
8
Rumín-Caparrós, A., A. Sanchez-Vidal, A. Calafat, M. Canals, J. Martín, P. Puig y R. Pedrosa-Pàmies. "External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea". Biogeosciences Discussions 9, n.º 12 (18 de diciembre de 2012): 18571–600. http://dx.doi.org/10.5194/bgd-9-18571-2012.
Texto completoResumen
Abstract. Atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14 211 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1597 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼ 1 m s−1) down Cap de Creus canyon, as measured by current-meters in mooring lines deployed inside the canyon at 300 m and 1000 m water depth. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation of dense shelf water. Particle fluxes were concurrently measured by using sediment traps at the same mooring stations. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to 1000 m deep within the canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winters points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated to the plankton spring bloom during March and April of both years. Our measurements of particle fluxes (including major components and grain size distribution), together with meteorological and oceanographic parameters such as wind speed, turbulent heat flux, near-bottom water temperature, current speed and suspended sediment concentration, during winters 2009–2010 and 2010–2011 along the Cap de Creus submarine canyon, show the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea.
9
Rumín-Caparrós, A., A. Sanchez-Vidal, A. Calafat, M. Canals, J. Martín, P. Puig y R. Pedrosa-Pàmies. "External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea". Biogeosciences 10, n.º 6 (3 de junio de 2013): 3493–505. http://dx.doi.org/10.5194/bg-10-3493-2013.
Texto completoResumen
Abstract. Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009–2010 and 2010–2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.
10
Cerralbo, Pablo, Manuel Espino, Manel Grifoll y Arnoldo Valle-Levinson. "Subtidal circulation in a microtidal Mediterranean bay". Scientia Marina 82, n.º 4 (16 de enero de 2019): 231. http://dx.doi.org/10.3989/scimar.04801.16a.
Texto completoResumen
We examine the role of different forcings on the subtidal circulation in a microtidal bay with freshwater inputs in the NW Mediterranean Sea: Alfacs Bay. Observations of subtidal flow in summer 2013 and winter 2014 reveal a two-layered, vertically sheared circulation. During the summer, there is a significant positive correlation between surface currents and winds along the main axis of the bay, while a negative correlation is observed between wind and the bottom layers. During the winter, the cross-shore response is correlated with the most energetic winds, showing a two-layered vertical structure inside the bay and a nearly depth-independent water motion caused by high wind speeds at the bay mouth. The vertical structure of the velocities, as determined through empirical orthogonal function analysis, confirms that surface layers are affected by winds and bottom currents correlated negatively with winds as a response of the wind set-up. Seasonal mean circulation reveals gravitational exchange at the bay mouth during the summer. However, mean circulation is unclear in the inner bay and close to the drainage channels. Observed flow patterns are supported by modelling results that confirm the persistence of averaged current in the low-frequency dynamics. Re-circulation areas in the inner bay indicate the rich spatial variability in flow at low-frequency time scales.
11
Brady, Esther C., Bette L. Otto-Bliesner, Jennifer E. Kay y Nan Rosenbloom. "Sensitivity to Glacial Forcing in the CCSM4". Journal of Climate 26, n.º 6 (15 de marzo de 2013): 1901–25. http://dx.doi.org/10.1175/jcli-d-11-00416.1.
Texto completoResumen
Abstract Results are presented from the Community Climate System Model, version 4 (CCSM4), simulation of the Last Glacial Maximum (LGM) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) at the standard 1° resolution, the same resolution as the majority of the CCSM4 CMIP5 long-term simulations for the historical and future projection scenarios. The forcings and boundary conditions for this simulation follow the protocols of the Paleoclimate Modeling Intercomparison Project, version 3 (PMIP3). Two additional CCSM4 CO2 sensitivity simulations, in which the concentrations are abruptly changed at the start of the simulation to the low 185 ppm LGM concentrations (LGMCO2) and to a quadrupling of the preindustrial concentration (4×CO2), are also analyzed. For the full LGM simulation, the estimated equilibrium cooling of the global mean annual surface temperature is 5.5°C with an estimated radiative forcing of −6.2 W m−2. The radiative forcing includes the effects of the reduced LGM greenhouse gases, ice sheets, continental distribution with sea level lowered by approximately 120 m from the present, and orbital parameters, but not changes to atmospheric aerosols or vegetation biogeography. The LGM simulation has an equilibrium climate sensitivity (ECS) of 3.1(±0.3)°C, comparable to the CCSM4 4×CO2 result. The LGMCO2 simulation shows a greater ECS of 4.2°C. Other responses found at the LGM in CCSM4 include a global precipitation rate decrease at a rate of ~2% °C−1, similar to climate change simulations in the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4); a strengthening of the Atlantic meridional overturning circulation (AMOC) with a shoaling of North Atlantic Deep Water and a filling of the deep basin up to sill depth with Antarctic Bottom Water; and an enhanced seasonal cycle accompanied by reduced ENSO variability in the eastern Pacific Ocean’s SSTs.
12
Hansen, J., M. Sato, P. Hearty, R. Ruedy, M. Kelley, V. Masson-Delmotte, G. Russell et al. "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous". Atmospheric Chemistry and Physics Discussions 15, n.º 14 (23 de julio de 2015): 20059–179. http://dx.doi.org/10.5194/acpd-15-20059-2015.
Texto completoResumen
Abstract. There is evidence of ice melt, sea level rise to +5–9 m, and extreme storms in the prior interglacial period that was less than 1 °C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disintegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge. Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic as well as the Southern Ocean, increases tropospheric horizontal temperature gradients, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean's role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate. The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10–40 year range. We conclude that 2 °C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth's energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.
13
Iglesias, Virginia y Cathy Whitlock. "If the trees burn, is the forest lost? Past dynamics in temperate forests help inform management strategies". Philosophical Transactions of the Royal Society B: Biological Sciences 375, n.º 1794 (27 de enero de 2020): 20190115. http://dx.doi.org/10.1098/rstb.2019.0115.
Texto completoResumen
Forest dynamics are driven by top-down changes in climate and bottom-up positive (destabilizing) and negative (stabilizing) biophysical feedbacks involving disturbance and biotic interactions. When positive feedbacks prevail, the resulting self-propagating changes can potentially shift the system into a new state, even in the absence of climate change. Conversely, negative feedbacks help maintain a dynamic equilibrium that allows communities to recover their pre-disturbance characteristics. We examine palaeoenvironmental records from temperate forests to assess the nature of long-term stability and regime shifts under a broader range of environmental forcings than can be observed at present. Forest histories from northwestern USA, Patagonia, Tasmania and New Zealand show long-term trajectories that were governed by (i) the biophysical template, (ii) characteristics of climate and disturbance, (iii) historical legacies that condition the ecological capacity to respond to subsequent disturbances, and (iv) thresholds that act as irreversible barriers. Attention only to current forest conditions overlooks the significance of history in creating path dependency, the importance of individual extreme events, and the inherent feedbacks that force an ecosystem into reorganization. A long-time perspective on ecological resilience helps guide conservation strategies that focus on environmental preservation as well as identify vulnerable species and ecosystems to future climate change. This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.
14
de Rooij, G. H. "Is the groundwater reservoir linear? A mathematical analysis of two limiting cases". Hydrology and Earth System Sciences Discussions 11, n.º 1 (6 de enero de 2014): 83–108. http://dx.doi.org/10.5194/hessd-11-83-2014.
Texto completoResumen
Abstract. Storage–discharge relationships of the groundwater reservoirs of several catchments in a temperate-humid climate were reported in the literature to be seemingly non-linear. Once recharge was adequately accounted for during model calibration they turned out to be linear. The question was posed if this linearity was a fundamental property of groundwater reservoirs in general. A mathematical analysis based on analytical solutions for several cases involving parallel flow in horizontal aquifers shows that this is not the case when the surface water level is close to the aquifer bottom. When the aquifer is of constant thickness, linear-reservoir behaviour arises when the forcings remain constant for a sufficiently long time. This can range from a few weeks for aquifers with a dense drainage network of streams or ditches to years or centuries for large aquifers drained by rivers many kilometers apart. The characteristic time of the groundwater reservoir depends on whether or not the aquifer is leaky and recharge is non-zero. It is concluded that groundwater reservoirs can only be linear if their thickness can be assumed independent of the hydraulic head, and if they have a dense drainage network. Even then, they behave non-linearly up to several weeks after a change in recharge. Models that conceptualize the catchment as a configuration of coupled reservoirs will normally assign the groundwater discharge surplus generated because of the initially non-linear behaviour of the groundwater to their fast-responding reservoirs, thereby exaggerating the importance of fast-responding flow routes in a catchment.
15
Saba, Vincent S., James R. Spotila, Francisco P. Chavez y John A. Musick. "BOTTOM-UP AND CLIMATIC FORCING ON THE WORLDWIDE POPULATION OF LEATHERBACK TURTLES". Ecology 89, n.º 5 (mayo de 2008): 1414–27. http://dx.doi.org/10.1890/07-0364.1.
Texto completo
16
Pierce, Becky M., Vernon C. Bleich, Kevin L. Monteith y R. Terry Bowyer. "Top-down versus bottom-up forcing: evidence from mountain lions and mule deer". Journal of Mammalogy 93, n.º 4 (14 de septiembre de 2012): 977–88. http://dx.doi.org/10.1644/12-mamm-a-014.1.
Texto completo
17
Stock, Charles A., Thomas M. Powell y Simon A. Levin. "Bottom–up and top–down forcing in a simple size-structured plankton dynamics model". Journal of Marine Systems 74, n.º 1-2 (noviembre de 2008): 134–52. http://dx.doi.org/10.1016/j.jmarsys.2007.12.004.
Texto completo
18
Di Lorenzo, Emanuele, David Mountain, Harold Batchelder, Nicholas Bond y Eileen Hofmann. "Advances in Marine Ecosystem Dynamics from US GLOBEC: The Horizontal-Advection Bottom-up Forcing Paradigm". Oceanography 26, n.º 4 (1 de diciembre de 2013): 22–33. http://dx.doi.org/10.5670/oceanog.2013.73.
Texto completo
19
Mcowen, Chris J., William W. L. Cheung, Ryan R. Rykaczewski, Reg A. Watson y Louisa J. Wood. "Is fisheries production within Large Marine Ecosystems determined by bottom-up or top-down forcing?" Fish and Fisheries 16, n.º 4 (19 de mayo de 2014): 623–32. http://dx.doi.org/10.1111/faf.12082.
Texto completo
20
Mengis, Nadine, David P. Keller y Andreas Oschlies. "Systematic Correlation Matrix Evaluation (SCoMaE) – a bottom–up, science-led approach to identifying indicators". Earth System Dynamics 9, n.º 1 (15 de enero de 2018): 15–31. http://dx.doi.org/10.5194/esd-9-15-2018.
Texto completoResumen
Abstract. This study introduces the Systematic Correlation Matrix Evaluation (SCoMaE) method, a bottom–up approach which combines expert judgment and statistical information to systematically select transparent, nonredundant indicators for a comprehensive assessment of the state of the Earth system. The methods consists of two basic steps: (1) the calculation of a correlation matrix among variables relevant for a given research question and (2) the systematic evaluation of the matrix, to identify clusters of variables with similar behavior and respective mutually independent indicators. Optional further analysis steps include (3) the interpretation of the identified clusters, enabling a learning effect from the selection of indicators, (4) testing the robustness of identified clusters with respect to changes in forcing or boundary conditions, (5) enabling a comparative assessment of varying scenarios by constructing and evaluating a common correlation matrix, and (6) the inclusion of expert judgment, for example, to prescribe indicators, to allow for considerations other than statistical consistency. The example application of the SCoMaE method to Earth system model output forced by different CO2 emission scenarios reveals the necessity of reevaluating indicators identified in a historical scenario simulation for an accurate assessment of an intermediate–high, as well as a business-as-usual, climate change scenario simulation. This necessity arises from changes in prevailing correlations in the Earth system under varying climate forcing. For a comparative assessment of the three climate change scenarios, we construct and evaluate a common correlation matrix, in which we identify robust correlations between variables across the three considered scenarios.
21
Ayón, Patricia, Gordon Swartzman, Arnaud Bertrand, Mariano Gutiérrez y Sophie Bertrand. "Zooplankton and forage fish species off Peru: Large-scale bottom-up forcing and local-scale depletion". Progress in Oceanography 79, n.º 2-4 (octubre de 2008): 208–14. http://dx.doi.org/10.1016/j.pocean.2008.10.023.
Texto completo
22
Scrosati, Ricardo A. y Julius A. Ellrich. "Benthic-pelagic coupling and bottom-up forcing in rocky intertidal communities along the Atlantic Canadian coast". Ecosphere 9, n.º 5 (mayo de 2018): e02229. http://dx.doi.org/10.1002/ecs2.2229.
Texto completo
23
Haverd, Vanessa, Benjamin Smith, Lars Nieradzik, Peter R. Briggs, William Woodgate, Cathy M. Trudinger, Josep G. Canadell y Matthias Cuntz. "A new version of the CABLE land surface model (Subversion revision r4601) incorporating land use and land cover change, woody vegetation demography, and a novel optimisation-based approach to plant coordination of photosynthesis". Geoscientific Model Development 11, n.º 7 (27 de julio de 2018): 2995–3026. http://dx.doi.org/10.5194/gmd-11-2995-2018.
Texto completoResumen
Abstract. The Community Atmosphere–Biosphere Land Exchange model (CABLE) is a land surface model (LSM) that can be applied stand-alone and provides the land surface–atmosphere exchange within the Australian Community Climate and Earth System Simulator (ACCESS). We describe new developments that extend the applicability of CABLE for regional and global carbon–climate simulations, accounting for vegetation responses to biophysical and anthropogenic forcings. A land use and land cover change module driven by gross land use transitions and wood harvest area was implemented, tailored to the needs of the Coupled Model Intercomparison Project 6 (CMIP6). Novel aspects include the treatment of secondary woody vegetation, which benefits from a tight coupling between the land use module and the Population Orders Physiology (POP) module for woody demography and disturbance-mediated landscape heterogeneity. Land use transitions and harvest associated with secondary forest tiles modify the annually resolved patch age distribution within secondary vegetated tiles, in turn affecting biomass accumulation and turnover rates and hence the magnitude of the secondary forest sink. Additionally, we implemented a novel approach to constrain modelled GPP consistent with the coordination hypothesis and predicted by evolutionary theory, which suggests that electron-transport- and Rubisco-limited rates adjust seasonally and across biomes to be co-limiting. We show that the default prior assumption – common to CABLE and other LSMs – of a fixed ratio of electron transport to carboxylation capacity at standard temperature (Jmax, 0∕Vcmax, 0) is at odds with this hypothesis; we implement an alternative algorithm for dynamic optimisation of this ratio such that coordination is achieved as an outcome of fitness maximisation. The results have significant implications for the magnitude of the simulated CO2 fertilisation effect on photosynthesis in comparison to alternative estimates and observational proxies. These new developments enhance CABLE's capability for use within an Earth system model and in stand-alone applications to attribute trends and variability in the terrestrial carbon cycle to regions, processes and drivers. Model evaluation shows that the new model version satisfies several key observational constraints: (i) trend and interannual variations in the global land carbon sink, including sensitivities of interannual variations to global precipitation and temperature anomalies; (ii) centennial trends in global GPP; (iii) coordination of Rubisco-limited and electron-transport-limited photosynthesis; (iv) spatial distributions of global ET, GPP, biomass and soil carbon; and (v) age-dependent rates of biomass accumulation in boreal, temperate and tropical secondary forests. CABLE simulations agree with recent independent assessments of the global land–atmosphere flux partition that use a combination of atmospheric inversions and bottom-up constraints. In particular, there is agreement that the strong CO2-driven sink in the tropics is largely cancelled by net deforestation and forest degradation emissions, leaving the Northern Hemisphere (NH) extratropics as the dominant contributor to the net land sink.
24
Barbraud, Christophe y Cedric Cotte. "Short Note: Paradigms need hypothesis testing: no evidence for top-down forcing on Adélie and emperor penguin populations". Antarctic Science 20, n.º 4 (16 de mayo de 2008): 391–92. http://dx.doi.org/10.1017/s0954102008001260.
Texto completoResumen
In their recent review article “Paradigm lost, or is top-down forcing no longer significant in the Antarctic marine ecosystem?” Ainley et al. (2007) questioned why Southern Ocean marine ecologists apparently have shifted to a central paradigm where bottom-up forcing by physics and climate change has become the single most important driver of food web dynamics in the Southern Ocean. Ainley et al. (2007) suggest that top-down forcing (forcing by biotic processes) is no longer considered in the interpretation of ecological research results aimed at understanding ecosystem processes of the Southern Ocean. Based on two examples from the literature they suggest that population trends could better be explained by including species interactions in the modelling rather than by changes in climate related physical processes alone. Nicol et al. (2007) questioned the paradigm shift proposed by Ainley et al. (2007) and made a broad review of the ecological research conducted in the Southern Ocean ecosystems. They concluded that there has been considerable research effort into ecosystem interactions over the last 25 years in the Southern Ocean, and that there seems little evidence that there has been an almost complete shift in paradigms; rather both bottom-up and top-down processes are recognized to govern ecosystems functioning.
25
Obradovich, Shannon G., Erin H. Carruthers y George A. Rose. "Bottom-up limits to Newfoundland capelin (Mallotus villosus) rebuilding: the euphausiid hypothesis". ICES Journal of Marine Science 71, n.º 4 (21 de noviembre de 2013): 775–83. http://dx.doi.org/10.1093/icesjms/fst184.
Texto completoResumen
Abstract Capelin (Mallotus villosus) is the key forage fish species in the Newfoundland and Labrador Shelf ecosystem. Capelin stocks collapsed in the early 1990s, concurrent with declines in “northern” Atlantic cod, Gadus morhua. Neither has fully recovered yet. Changes in growth, condition, and behaviour accompanied capelin declines on the northern Grand Banks (NGB), and remain two decades later. Feeding, growth, and condition of NGB capelin were all lower when compared with capelin from the eastern Scotian Shelf (ESS), where abundance increased following predator declines. For age 2–5 capelin of both sexes, all but one of five comparable age–sex groups were significantly larger on the ESS (e.g. age 3 females average 169 mm on the ESS and 151 mm on the NGB). Neither temperature nor density-dependence explain these differences. However, dietary differences were prominent. ESS capelin had higher total fullness indices (TFIs) than NGB fish at all sizes [mean TFIESS = 1.43 (± 1.14), mean TFINGB = 0.48 (± 0.70)]. Euphausiids (especially Thysanoessa spp.) were a main dietary component on the ESS but not on the NGB. Stable isotope analyses (δ15N and δ13C) for NGB capelin also indicated few dietary euphausiids. Trophic fractionation of δ 15N was 4.740/00, suggesting NGB capelin were food limited. Capelin recovery on the Newfoundland and Labrador Shelf appears limited by bottom-up forcing, in particular lack of euphausiid prey.
26
Petzold, Willy y Ricardo A. Scrosati. "Differential recolonization of Atlantic intertidal habitats after disturbance reveals potential bottom-up community regulation". F1000Research 3 (20 de octubre de 2014): 247. http://dx.doi.org/10.12688/f1000research.5545.1.
Texto completoResumen
In the spring of 2014, abundant sea ice that drifted out of the Gulf of St. Lawrence caused extensive disturbance in rocky intertidal habitats on the northern Atlantic coast of mainland Nova Scotia, Canada. To monitor recovery of intertidal communities, we surveyed two wave-exposed locations in the early summer of 2014. Barnacle recruitment and the abundance of predatory dogwhelks were low at one location (Tor Bay Provincial Park) but more than 20 times higher at the other location (Whitehead). Satellite data indicated that the abundance of coastal phytoplankton (the main food source for barnacle larvae) was consistently higher at Whitehead just before the barnacle recruitment season, when barnacle larvae were in the water column. These observations suggest bottom-up forcing of intertidal communities. The underlying mechanisms and their intensity along the NW Atlantic coast could be investigated through studies done at local and regional scales.
27
Zhang, Jian, Hong Qian, Marco Girardello, Vincent Pellissier, Scott E. Nielsen y Jens-Christian Svenning. "Trophic interactions among vertebrate guilds and plants shape global patterns in species diversity". Proceedings of the Royal Society B: Biological Sciences 285, n.º 1883 (25 de julio de 2018): 20180949. http://dx.doi.org/10.1098/rspb.2018.0949.
Texto completoResumen
Trophic interactions play critical roles in structuring biotic communities. Understanding variation in trophic interactions among systems provides important insights into biodiversity maintenance and conservation. However, the relative importance of bottom-up versus top-down trophic processes for broad-scale patterns in biodiversity is poorly understood. Here, we used global datasets on species richness of vascular plants, mammals and breeding birds to evaluate the role of trophic interactions in shaping large-scale diversity patterns. Specifically, we used non-recursive structural equation models to test for top-down and bottom-up forcing of global species diversity patterns among plants and trophic guilds of mammals and birds (carnivores, invertivores and herbivores), while accounting for extrinsic environmental drivers. The results show that trophic linkages emerged as being more important to explaining species richness than extrinsic environmental drivers. In particular, there were strong, positive top-down interactions between mammal herbivores and plants, and moderate to strong bottom-up and/or top-down interactions between herbivores/invertivores and carnivores. Estimated trophic interactions for separate biogeographical regions were consistent with global patterns. Our findings demonstrate that, after accounting for environmental drivers, large-scale species richness patterns in plant and vertebrate taxa consistently support trophic interactions playing a major role in shaping global patterns in biodiversity. Furthermore, these results suggest that top-down forces often play strong complementary roles relative to bottom-up drivers in structuring biodiversity patterns across trophic levels. These findings underscore the importance of integrating trophic forcing mechanisms into studies of biodiversity patterns.
28
SMITH, WALKER O. y CHRISTIANE LANCELOT. "Bottom-up versus top-down control in phytoplankton of the Southern Ocean". Antarctic Science 16, n.º 4 (30 de noviembre de 2004): 531–39. http://dx.doi.org/10.1017/s0954102004002305.
Texto completoResumen
Oceanic phytoplankton communities are a mixture of various algal functional groups, all of which are of different sizes, have variable physiologies, and interact differently with disparate herbivores. We suggest that polar plankton communities, and specifically the larger phytoplankton of Southern Ocean HNLC (high nutrient, low chlorophyll) systems, are controlled primarily by bottom-up processes, but that smaller (pico- and nanoplankton) reach an equilibrium that is set simultaneously by light, iron and grazing by microzooplankton. Thus Southern Ocean phytoplankton conforms to the “ecumenical iron hypothesis”, albeit with the further addition of light as an environmental control. Examples of bottom-up controls include iron availability, irradiance regulation (either by the incident surface irradiance as controlled by season and sea ice cover, or by the effects of vertical turbulence and mixed layer depths), and macronutrient availability (silicic acid and nitrate). While the contribution of various phytoplankton taxa varies spatially and temporally within the Antarctic, we suggest that this is largely due to the specific responses of the important functional groups to the patterns of physical forcing and micronutrient inputs, rather than to changes in controls by small and large grazers. Examples of abiotic and biotic controls are examined from representative regions of the Antarctic, including continental shelf regions and open ocean HNLC systems. Results from models further support our contention that bottom-up control of large forms is paramount in the Southern Ocean, but top-down controls play an important part in regulating the equilibrium standing stocks of smaller taxa. If bottom-up control is indeed universal in the Antarctic, then it has profound implications for the understanding of interannual variability, food web structure, and population dynamics of higher trophic levels in both the present and past Southern Ocean.
29
Pershing, Andrew J., Katherine E. Mills, Nicholas R. Record, Karen Stamieszkin, Katharine V. Wurtzell, Carrie J. Byron, Dominic Fitzpatrick, Walter J. Golet y Elise Koob. "Evaluating trophic cascades as drivers of regime shifts in different ocean ecosystems". Philosophical Transactions of the Royal Society B: Biological Sciences 370, n.º 1659 (5 de enero de 2015): 20130265. http://dx.doi.org/10.1098/rstb.2013.0265.
Texto completoResumen
In ecosystems that are strongly structured by predation, reducing top predator abundance can alter several lower trophic levels—a process known as a trophic cascade. A persistent trophic cascade also fits the definition of a regime shift. Such ‘trophic cascade regime shifts' have been reported in a few pelagic marine systems—notably the Black Sea, Baltic Sea and eastern Scotian Shelf—raising the question of how common this phenomenon is in the marine environment. We provide a general methodology for distinguishing top-down and bottom-up effects and apply this methodology to time series from these three ecosystems. We found evidence for top-down forcing in the Black Sea due primarily to gelatinous zooplankton. Changes in the Baltic Sea are primarily bottom-up, strongly structured by salinity, but top-down forcing related to changes in cod abundance also shapes the ecosystem. Changes in the eastern Scotian Shelf that were originally attributed to declines in groundfish are better explained by changes in stratification. Our review suggests that trophic cascade regime shifts are rare in open ocean ecosystems and that their likelihood increases as the residence time of water in the system increases. Our work challenges the assumption that negative correlation between consecutive trophic levels implies top-down forcing.
30
Daleo, Pedro, Juan Alberti, Carlos Martín Bruschetti, Jesús Pascual, Oscar Iribarne y Brian R. Silliman. "Physical stress modifies top-down and bottom-up forcing on plant growth and reproduction in a coastal ecosystem". Ecology 96, n.º 8 (agosto de 2015): 2147–56. http://dx.doi.org/10.1890/14-1776.1.
Texto completo
31
Terborgh, John W. "Toward a trophic theory of species diversity". Proceedings of the National Academy of Sciences 112, n.º 37 (15 de septiembre de 2015): 11415–22. http://dx.doi.org/10.1073/pnas.1501070112.
Texto completoResumen
Efforts to understand the ecological regulation of species diversity via bottom-up approaches have failed to yield a consensus theory. Theories based on the alternative of top-down regulation have fared better. Paine’s discovery of keystone predation demonstrated that the regulation of diversity via top-down forcing could be simple, strong, and direct, yet ecologists have persistently failed to perceive generality in Paine’s result. Removing top predators destabilizes many systems and drives transitions to radically distinct alternative states. These transitions typically involve community reorganization and loss of diversity, implying that top-down forcing is crucial to diversity maintenance. Contrary to the expectations of bottom-up theories, many terrestrial herbivores and mesopredators are capable of sustained order-of-magnitude population increases following release from predation, negating the assumption that populations of primary consumers are resource limited and at or near carrying capacity. Predationsensu lato(to include Janzen–Connell mortality agents) has been shown to promote diversity in a wide range of ecosystems, including rocky intertidal shelves, coral reefs, the nearshore ocean, streams, lakes, temperate and tropical forests, and arctic tundra. The compelling variety of these ecosystems suggests that top-down forcing plays a universal role in regulating diversity. This conclusion is further supported by studies showing that the reduction or absence of predation leads to diversity loss and, in the more dramatic cases, to catastrophic regime change. Here, I expand on the thesis that diversity is maintained by the interaction between predation and competition, such that strong top-down forcing reduces competition, allowing coexistence.
32
Quaas, Johannes, Hailing Jia, Chris Smith, Anna Lea Albright, Wenche Aas, Nicolas Bellouin, Olivier Boucher et al. "Robust evidence for reversal of the trend in aerosol effective climate forcing". Atmospheric Chemistry and Physics 22, n.º 18 (21 de septiembre de 2022): 12221–39. http://dx.doi.org/10.5194/acp-22-12221-2022.
Texto completoResumen
Abstract. Anthropogenic aerosols exert a cooling influence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime of only several days, the aerosol forcing responds quickly to emissions. Here, we present and discuss the evolution of the aerosol forcing since 2000. There are multiple lines of evidence that allow us to robustly conclude that the anthropogenic aerosol effective radiative forcing (ERF) – both aerosol–radiation interactions (ERFari) and aerosol–cloud interactions (ERFaci) – has become less negative globally, i.e. the trend in aerosol effective radiative forcing changed sign from negative to positive. Bottom-up inventories show that anthropogenic primary aerosol and aerosol precursor emissions declined in most regions of the world; observations related to aerosol burden show declining trends, in particular of the fine-mode particles that make up most of the anthropogenic aerosols; satellite retrievals of cloud droplet numbers show trends in regions with aerosol declines that are consistent with these in sign, as do observations of top-of-atmosphere radiation. Climate model results, including a revised set that is constrained by observations of the ocean heat content evolution show a consistent sign and magnitude for a positive forcing relative to the year 2000 due to reduced aerosol effects. This reduction leads to an acceleration of the forcing of climate change, i.e. an increase in forcing by 0.1 to 0.3 W m−2, up to 12 % of the total climate forcing in 2019 compared to 1750 according to the Intergovernmental Panel on Climate Change (IPCC).
33
Jochum, Malte, Florian D. Schneider, Tasman P. Crowe, Ulrich Brose y Eoin J. O'Gorman. "Climate-induced changes in bottom-up and top-down processes independently alter a marine ecosystem". Philosophical Transactions of the Royal Society B: Biological Sciences 367, n.º 1605 (5 de noviembre de 2012): 2962–70. http://dx.doi.org/10.1098/rstb.2012.0237.
Texto completoResumen
Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of top-down and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas ) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.
34
Petersen, Marcell Elo, Marie Maar, Janus Larsen, Eva Friis Møller y Per Juel Hansen. "Trophic cascades of bottom-up and top-down forcing on nutrients and plankton in the Kattegat, evaluated by modelling". Journal of Marine Systems 169 (mayo de 2017): 25–39. http://dx.doi.org/10.1016/j.jmarsys.2017.01.006.
Texto completo
35
TRITES, ANDREW W., ARTHUR J. MILLER, HERBERT D. G. MASCHNER, MICHAEL A. ALEXANDER, STEVEN J. BOGRAD, JOHN A. CALDER, ANTONIETTA CAPOTONDI et al. "Bottom-up forcing and the decline of Steller sea lions (Eumetopias jubatus) in Alaska: assessing the ocean climate hypothesis". Fisheries Oceanography 16, n.º 1 (enero de 2007): 46–67. http://dx.doi.org/10.1111/j.1365-2419.2006.00408.x.
Texto completo
36
Shurin, Jonathan B., Jessica L. Clasen, Hamish S. Greig, Pavel Kratina y Patrick L. Thompson. "Warming shifts top-down and bottom-up control of pond food web structure and function". Philosophical Transactions of the Royal Society B: Biological Sciences 367, n.º 1605 (5 de noviembre de 2012): 3008–17. http://dx.doi.org/10.1098/rstb.2012.0243.
Texto completoResumen
The effects of global and local environmental changes are transmitted through networks of interacting organisms to shape the structure of communities and the dynamics of ecosystems. We tested the impact of elevated temperature on the top-down and bottom-up forces structuring experimental freshwater pond food webs in western Canada over 16 months. Experimental warming was crossed with treatments manipulating the presence of planktivorous fish and eutrophication through enhanced nutrient supply. We found that higher temperatures produced top-heavy food webs with lower biomass of benthic and pelagic producers, equivalent biomass of zooplankton, zoobenthos and pelagic bacteria, and more pelagic viruses. Eutrophication increased the biomass of all organisms studied, while fish had cascading positive effects on periphyton, phytoplankton and bacteria, and reduced biomass of invertebrates. Surprisingly, virus biomass was reduced in the presence of fish, suggesting the possibility for complex mechanisms of top-down control of the lytic cycle. Warming reduced the effects of eutrophication on periphyton, and magnified the already strong effects of fish on phytoplankton and bacteria. Warming, fish and nutrients all increased whole-system rates of net production despite their distinct impacts on the distribution of biomass between producers and consumers, plankton and benthos, and microbes and macrobes. Our results indicate that warming exerts a host of indirect effects on aquatic food webs mediated through shifts in the magnitudes of top-down and bottom-up forcing.
37
Giuliano, Elise. "Secessionism from the Bottom Up: Democratization, Nationalism, and Local Accountability in the Russian Transition". World Politics 58, n.º 2 (enero de 2006): 276–310. http://dx.doi.org/10.1353/wp.2006.0025.
Texto completoResumen
Do ethnic federations undergoing democratization promote or discourage regional secessionism? This article argues, based on evidence from the Russian Federation, that when democratization produces a transfer of political accountability from center to region, the incentives of regional leaders shift, forcing them to react to local constituencies in order to retain office. If these constituencies desire autonomy, regional leaders must respond, making separatism not merely an opportunistic strategy but a necessary one for their own political survival. Democratization, then, can transform administrative regions into electoral arenas.However, the case of Russia also demonstrates that regional demands for autonomy are not inevitable and may dissipate after they have begun. Popular support for nationalism and separatism varied significantly among Russia's sixteen ethnic republics in the late Soviet and early post-Soviet period. This variation is explained by showing that mass nationalism, contrary to conventional wisdom, is neither a latent attribute of federal regions, nor a simple function of natural resource endowments, nor something summoned into existence by the manipulations of regional leaders. Rather, it is argued that increasing competition for jobs in the Soviet Union's failing economy allowed particular issues articulated by nationalist leaders to resonate with ethnic populations. Through the framing of issues of ethnic economic inequality, nationalist leaders were able to politicize ethnicity by persuading people to view their personal life chances as dependent on the political fate of their ethnic community. Thus, secession in democratizing ethnic federations can be best understood by directing attention toward the origins of popular support for nationalism and the role that support plays in the elite contest for power within subfederal regions.
38
Castelao, Renato, Robert Chant, Scott Glenn y Oscar Schofield. "The Effects of Tides and Oscillatory Winds on the Subtidal Inner-Shelf Cross-Shelf Circulation". Journal of Physical Oceanography 40, n.º 4 (1 de abril de 2010): 775–88. http://dx.doi.org/10.1175/2009jpo4273.1.
Texto completoResumen
Abstract A two-dimensional numerical model is used to investigate the effects of tidal forcing and oscillatory winds on the subtidal cross-shelf circulation on the inner shelf. Bottom topography and initial stratification are representative of the South and Middle Atlantic Bights along the U.S. east coast. Results from simulations forced by upwelling winds and no tides are consistent with previous studies of inner-shelf circulation. The inclusion of tidal forcing leads to increased mixing, larger eddy viscosity coefficients, and reduced stratification over the shallow regions, effectively reducing the wind efficiency to drive cross-shelf currents on the inner shelf. Tidally averaged cross-shelf currents are weaker compared to when no tides are considered. There is an increase in the width of the region of surface wind-driven transport divergence, which changes the cross-shelf location where upwelling occurs. Lagrangian analyses indicate that tidal forcing substantially reduces the transport of offshore waters toward the coast and increases the residence time over the inner shelf by up to 70%. Fluctuating winds with zero mean lead to a rectification of the cross-shelf flow on the inner shelf, resulting in net upwelling. The rectification occurs because the cross-shelf transport is nonzero during upwelling wind forcing (since dense water is brought to the inner shelf maintaining the stratification), but is approximately zero during downwelling winds (since surface water is forced under near-bottom water, destroying the stratification). The rectification is more clearly observed when stratification is strong, when tidal forcing is weak or absent, and when the wind fluctuates at low frequency.
39
Thiéblemont, Rémi y Katja Matthes. "Solar influence on Earth's climate". Proceedings of the International Astronomical Union 11, A29A (agosto de 2015): 372–76. http://dx.doi.org/10.1017/s1743921316003306.
Texto completoResumen
AbstractUnderstanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions and observations, as well as mechanisms determining the response of the Earth's climate system. A summary of our current understanding from observational and modeling studies is presented with special focus on the “top-down” stratospheric UV and the “bottom-up” air-sea coupling mechanisms linking solar forcing and natural climate variability.
40
Pillet, G., E. V. Ermanyuk, L. R. M. Maas, I. N. Sibgatullin y T. Dauxois. "Internal wave attractors in three-dimensional geometries: trapping by oblique reflection". Journal of Fluid Mechanics 845 (20 de abril de 2018): 203–25. http://dx.doi.org/10.1017/jfm.2018.236.
Texto completoResumen
We study experimentally the propagation of internal waves in two different three-dimensional (3D) geometries, with a special emphasis on the refractive focusing due to the 3D reflection of obliquely incident internal waves on a slope. Both studies are initiated by ray tracing calculations to determine the appropriate experimental parameters. First, we consider a 3D geometry, the classical set-up to get simple, two-dimensional (2D) parallelogram-shaped attractors in which waves are forced in a direction perpendicular to a sloping bottom. Here, however, the forcing is of reduced extent in the along-slope, transverse direction. We show how the refractive focusing mechanism explains the formation of attractors over the whole width of the tank, even away from the forcing region. Direct numerical simulations confirm the dynamics, emphasize the role of boundary conditions and reveal the phase shifting in the transverse direction. Second, we consider a long and narrow tank having an inclined bottom, to simply reproduce a canal. In this case, the energy is injected in a direction parallel to the slope. Interestingly, the wave energy ends up forming 2D internal wave attractors in planes that are transverse to the initial propagation direction. This focusing mechanism prevents indefinite transmission of most of the internal wave energy along the canal.
41
Ji, Rubao, Christoph Stegert y Cabell S. Davis. "Sensitivity of copepod populations to bottom-up and top-down forcing: a modeling study in the Gulf of Maine region". Journal of Plankton Research 35, n.º 1 (25 de septiembre de 2012): 66–79. http://dx.doi.org/10.1093/plankt/fbs070.
Texto completo
42
Song, Hyo-Jong y Jong-Yeon Park. "Bottom-Up Drivers for Global Fish Catch Assessed with Reconstructed Ocean Biogeochemistry from an Earth System Model". Climate 9, n.º 5 (14 de mayo de 2021): 83. http://dx.doi.org/10.3390/cli9050083.
Texto completoResumen
Identifying bottom-up (e.g., physical and biogeochemical) drivers for fish catch is essential for sustainable fishing and successful adaptation to climate change through reliable prediction of future fisheries. Previous studies have suggested the potential linkage of fish catch to bottom-up drivers such as ocean temperature or satellite-retrieved chlorophyll concentration across different global ecosystems. Robust estimation of bottom-up effects on global fisheries is, however, still challenging due to the lack of long-term observations of fisheries-relevant biotic variables on a global scale. Here, by using novel long-term biological and biogeochemical data reconstructed from a recently developed data assimilative Earth system model, we newly identified dominant drivers for fish catch in globally distributed coastal ecosystems. A machine learning analysis with the inclusion of reconstructed zooplankton production and dissolved oxygen concentration into the fish catch predictors provides an extended view of the links between environmental forcing and fish catch. Furthermore, the relative importance of each driver and their thresholds for high and low fish catch are analyzed, providing further insight into mechanistic principles of fish catch in individual coastal ecosystems. The results presented herein suggest the potential predictive use of their relationships and the need for continuous observational effort for global ocean biogeochemistry.
43
Schaeffer, Amandine, Moninya Roughan y Bradley D. Morris. "Cross-Shelf Dynamics in a Western Boundary Current Regime: Implications for Upwelling". Journal of Physical Oceanography 43, n.º 5 (1 de mayo de 2013): 1042–59. http://dx.doi.org/10.1175/jpo-d-12-0177.1.
Texto completoResumen
Abstract The cross-shelf dynamics up- and downstream of the separation of the South Pacific Ocean’s Western Boundary Current (WBC) are studied using two years of high-resolution velocity and temperature measurements from mooring arrays. The shelf circulation is dominated by the East Australian Current (EAC) and its eddy field, with mean poleward depth-integrated magnitudes on the shelf break of 0.35 and 0.15 m s−1 up- and downstream of the separation point, respectively. The high cross-shelf variability is analyzed though a momentum budget, showing a dominant geostrophic balance at both locations. Among the secondary midshelf terms, the bottom stress influence is higher upstream of the separation point while the wind stress is dominant downstream. This study investigates the response of the velocity and temperature cross-shelf structure to both wind and EAC intrusions. Despite the deep water (up to 140 m), the response to a dominant along-shelf wind stress forcing is a classic two-layer Ekman structure. During weak winds, the shelf encroachment of the southward current drives an onshore Ekman flow in the bottom boundary layer. Both the bottom velocity and the resultant bottom cross-shelf temperature gradient are proportional to the magnitude of the encroaching current, with similar linear regressions up- and downstream of the WBC separation. The upwelled water is then subducted below the EAC upstream of the separation point. Such current-driven upwelling is shown to be the dominant driver of cold water uplift in the EAC-dominated region, with significant impacts expected on nutrient enrichment and thus on biological productivity.
44
Stragauskaitė, Vaiva, Martynas Bučas y Georg Martin. "Distribution of Charophyte Oospores in the Curonian Lagoon and their Relationship to Environmental Forcing". Water 13, n.º 2 (6 de enero de 2021): 117. http://dx.doi.org/10.3390/w13020117.
Texto completoResumen
Lack of knowledge about distribution of charophyte fructifications and importance of environmental conditions in the Baltic Sea coastal waters fostered us to assess the spatial-temporal patterns of oospore bank in relationship with environmental factors in the Curonian Lagoon (Lithuanian part). We mapped the distribution of oospores in 2017–2019. The importance of environmental factors was determined by the cluster analysis and boosted regression trees. Four oospores species were recorded up to 4 m depth. The highest mean densities (58,000 ind·m−2) of viable fructifications were found along the eastern shore, where the densest charophyte stands were recorded. Viable fructifications showed a clear pattern of filling the oospore bank after the vegetation season and a depletion during the summer as they germinated. The distance from charophyte stands, salinity, bottom slope aspect, and wave exposure were the most important environmental variables. Full fructifications mostly occurred within <0.5 km distance from the charophyte stands restricted to flat and sheltered areas exposed to the northern and eastern slopes. Empty fructifications were mostly found within <2 km distance from the charophyte stands but their high density was limited to <1 km distance from the charophyte stands and on the northeastern bottom slopes and >1.5 salinity.
45
Stukel, M. R., V. J. Coles, M. T. Brooks y R. R. Hood. "Top-down, bottom-up and physical controls on diatom-diazotroph assemblage growth in the Amazon River plume". Biogeosciences 11, n.º 12 (19 de junio de 2014): 3259–78. http://dx.doi.org/10.5194/bg-11-3259-2014.
Texto completoResumen
Abstract. The nutrient-rich waters of the Amazon River plume (ARP) support dense blooms of diatom-diazotroph assemblages (DDAs) that introduce large quantities of new nitrogen to the planktonic ecosystem and, unlike other nitrogen-fixers, are likely to directly fuel vertical carbon flux. To investigate the factors controlling DDA blooms, we develop a five phytoplankton (cyanobacteria, diatoms, unicellular microbial diazotrophs, DDAs, and Trichodesmium), two zooplankton model and embed it within a 1/6° resolution physical model of the tropical and subtropical Atlantic. The model generates realistic DDA blooms in the ARP and also exhibits basin-wide primary production, nitrogen fixation, and grazing rates consistent with observed values. By following ARP water parcels with synthetic Lagrangian drifters released at the river mouth we are able to assess the relative impacts of grazing, nutrient supply, and physical forcing on DDA bloom formation. DDA bloom formation is stimulated in the nitrogen-poor and silica-rich water of the ARP by decreases in grazing pressure when mesozooplankton (which co-occur in high densities with coastal diatom blooms) concentrations decrease. Bloom termination is driven primarily by silica limitation of the DDAs. In agreement with in situ data, this net growth niche for DDAs exists in a salinity range from ∼20–34 PSU, although this co-occurrence is coincidental rather than causative. Because net growth rates are relatively modest, bloom formation in ARP water parcels depends critically on the time spent in this ideal habitat, with high DDA biomass only occurring when water parcels spent >23 days in the optimal habitat niche.
46
Stukel, M. R., V. J. Coles, M. T. Brooks y R. R. Hood. "Top-down, bottom-up and physical controls on diatom-diazotroph assemblage growth in the Amazon River Plume". Biogeosciences Discussions 10, n.º 8 (23 de agosto de 2013): 13931–76. http://dx.doi.org/10.5194/bgd-10-13931-2013.
Texto completoResumen
Abstract. The nutrient-rich waters of the Amazon River Plume (ARP) support dense blooms of diatom-diazotroph assemblages (DDA) that introduce large quantities of new nitrogen to the planktonic ecosystem and, unlike other nitrogen-fixers, are likely to directly fuel vertical carbon flux. To investigate the factors controlling DDA blooms, we develop a five phytoplankton (cyanobacteria, diatoms, unicellular microbial diazotrophs, DDA, and Trichodesmium), two zooplankton model and embed it within a 1/6° resolution physical model of the tropical and subtropical Atlantic. The model generates realistic DDA blooms in the ARP and also exhibits basin-wide primary production, nitrogen fixation, and grazing rates consistent with observed values. By following ARP water parcels with synthetic Lagrangian drifters released at the river mouth we are able to assess the relative impacts of grazing, nutrient supply, and physical forcing on DDA bloom formation. DDA bloom formation is stimulated in the silica-rich water of the ARP by decreases in grazing pressure when mesozooplankton (which co-occur in high densities with coastal diatom blooms) concentrations decrease. Bloom termination is driven primarily by silica limitation of the DDA. In agreement with in situ data, this net growth niche for DDA exists in a salinity range from ~ 20–34 PSU, although this co-occurrence is coincidental rather than causative. Because net growth rates are relatively modest, bloom formation in ARP water parcels depends critically on the time spent in this ideal habitat, with high DDA biomass only occurring when water parcels spent > 23 days in the optimal habitat niche.
47
Zhang, Chang Ik, Anne Babcock Hollowed, Jae-Bong Lee y Do-Hoon Kim. "An IFRAME approach for assessing impacts of climate change on fisheries". ICES Journal of Marine Science 68, n.º 6 (1 de enero de 2011): 1318–28. http://dx.doi.org/10.1093/icesjms/fsr073.
Texto completoResumen
Abstract Zhang, C. I., Hollowed, A. B., Lee, J-B., and Kim, D-H. 2011. An IFRAME approach for assessing impacts of climate change on fisheries. – ICES Journal of Marine Science, 68: 1318–1328. A new assessment framework is proposed for evaluating the performance of management strategies relative to the goals of an ecosystem approach to management (EAM) under different climate change scenarios. Earlier studies have demonstrated how global climate model simulations from the Intergovernmental Panel on Climate Change can be used to force regional ocean circulation models and forecast regional changes in bottom-up forcing. We extend this approach to assess the ecosystem impacts of resource use and climate change in marine ecosystems, by developing an Integrated Fisheries Risk Analysis Method for Ecosystems (IFRAME) framework. The IFRAME approach tracks climate change impacts on the flow of energy through the planktonic foodweb using NEMURO and projects the implications of these shifts in bottom-up forcing on the fisheries foodweb using Ecopath with Ecosim. Resource management scenarios are developed and incorporated into the projection framework by characterizing the action for changes in fishing mortality or availability of resources. An integrated suite of ecosystem status indicators are proposed to assess the performance of management scenarios relative to the goals of an EAM. These ecosystem status indicators track four key management objectives of the ecosystem: sustainability, biodiversity, habitat quantity, and quality and socio-economic status.
48
Springer, A. M. y G. B. van Vliet. "Climate change, pink salmon, and the nexus between bottom-up and top-down forcing in the subarctic Pacific Ocean and Bering Sea". Proceedings of the National Academy of Sciences 111, n.º 18 (31 de marzo de 2014): E1880—E1888. http://dx.doi.org/10.1073/pnas.1319089111.
Texto completo
49
Otto, S., T. Trautmann y M. Wendisch. "On realistic size equivalence and shape of spheroidal Saharan mineral dust particles applied in solar and thermal radiative transfer calculations". Atmospheric Chemistry and Physics Discussions 10, n.º 11 (30 de noviembre de 2010): 29191–247. http://dx.doi.org/10.5194/acpd-10-29191-2010.
Texto completoResumen
Abstract. Realistic size equivalence and shape of Saharan mineral dust particles are derived from on in-situ particle, lidar and sun photometer measurements during SAMUM-1 in Morocco (19 May 2006), dealing with measured size- and altitude-resolved axis ratio distributions of assumed spheroidal model particles. The data were applied in optical property, radiative effect, forcing and heating effect simulations to quantify the realistic impact of particle non-sphericity. It turned out that volume-to-surface equivalent spheroids with prolate shape are most realistic: particle non-sphericity only slightly affects single scattering albedo and asymmetry parameter but may enhance extinction coefficient by up to 10%. At the bottom of the atmosphere (BOA) the Saharan mineral dust always leads to a loss of solar radiation, while the sign of the forcing at the top of the atmosphere (TOA) depends on surface albedo: solar cooling/warming over a mean ocean/land surface. In the thermal spectral range the dust inhibits the emission of radiation to space and warms the BOA. The most realistic case of particle non-sphericity causes changes of total (solar plus thermal) forcing by 55/5% at the TOA over ocean/land and 15% at the BOA over both land and ocean and enhances total radiative heating within the dust plume by up to 20%. Large dust particles significantly contribute to all the radiative effects reported.
50
Otto, S., T. Trautmann y M. Wendisch. "On realistic size equivalence and shape of spheroidal Saharan mineral dust particles applied in solar and thermal radiative transfer calculations". Atmospheric Chemistry and Physics 11, n.º 9 (12 de mayo de 2011): 4469–90. http://dx.doi.org/10.5194/acp-11-4469-2011.
Texto completoResumen
Abstract. Realistic size equivalence and shape of Saharan mineral dust particles are derived from in-situ particle, lidar and sun photometer measurements during SAMUM-1 in Morocco (19 May 2006), dealing with measured size- and altitude-resolved axis ratio distributions of assumed spheroidal model particles. The data were applied in optical property, radiative effect, forcing and heating effect simulations to quantify the realistic impact of particle non-sphericity. It turned out that volume-to-surface equivalent spheroids with prolate shape are most realistic: particle non-sphericity only slightly affects single scattering albedo and asymmetry parameter but may enhance extinction coefficient by up to 10 %. At the bottom of the atmosphere (BOA) the Saharan mineral dust always leads to a loss of solar radiation, while the sign of the forcing at the top of the atmosphere (TOA) depends on surface albedo: solar cooling/warming over a mean ocean/land surface. In the thermal spectral range the dust inhibits the emission of radiation to space and warms the BOA. The most realistic case of particle non-sphericity causes changes of total (solar plus thermal) forcing by 55/5 % at the TOA over ocean/land and 15 % at the BOA over both land and ocean and enhances total radiative heating within the dust plume by up to 20 %. Large dust particles significantly contribute to all the radiative effects reported. They strongly enhance the absorbing properties and forward scattering in the solar and increase predominantly, e.g., the total TOA forcing of the dust over land.