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Spatially extensive evidence for nitrogen-induced stimulation of forest growth has been lacking. Analysis of forest inventory data from the northeastern and north-central US collected during the 1980s and 1990s indicates that nitrogen deposition enhanced above-ground carbon storage by 61 kg per kg of nitrogen deposited.
Most climate models consider only short-term processes such as cloud and sea-ice formation when assessing Earth's sensitivity to greenhouse-gas forcing. Mounting evidence indicates that the response could be stronger if boundary conditions change drastically.
Water movement in upland humid watersheds from the soil surface to the stream is often described using the concept of translatory flow, which assumes that water at any soil depth is well mixed. A study of water isotopes in an Oregon watershed instead suggests that trees and streams tap into separate water reservoirs.
Earth-system climate sensitivity includes the effects of long-term feedbacks such as changes in continental ice-sheet extent and terrestrial ecosystems. A reconstruction of atmospheric carbon dioxide levels 4.5 million years ago suggests that Earth-system climate sensitivity is significantly higher than that estimated from global climate models, which includes only fast feedback mechanisms such as changes in clouds and sea ice.
Delta morphology is thought to be controlled by factors such as river discharge, tides and waves. Numerical modelling shows that sediment cohesion also strongly influences the development of a delta’s characteristics.
The concentration of chemicals that absorb low-frequency sound in the ocean has declined as a result of anthropogenic increases in ocean acidity. Model simulations predict large reductions in sound absorption in the high latitudes and areas of deep-water formation over the twenty-first century.
Antarctic Intermediate Water is an oxygen-rich water mass that spreads throughout the Southern Hemisphere oceans. Marine sediment chemistry indicates that the water mass was produced at higher rates and had higher oxygen concentrations during the Last Glacial Maximum.
Bangladesh relies heavily on groundwater for the irrigation of dry-season rice. Analysis of soil porewater and floodwater in rice paddy fields during the monsoon season in Bangladesh suggests that flooding removes a significant amount of arsenic from the soils.
The collision history of asteroids in the early Solar System is difficult to reconstruct. A study of plagioclase breakdown using X-ray diffraction measurements under increasing pressures and temperatures suggests that peak pressures in collisions that formed shocked meteorites have been overestimated.
The equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is difficult to quantify. Simulations and proxy data of the mid-Pliocene warm climate suggest that the response is 30 to 50% higher than traditionally calculated when slowly adjusting components of the Earth system, such as ice sheets and vegetation, are included in the estimate.
The movement of tectonic plates before the Cretaceous period is poorly understood. A global mantle tomography model suggests that the longitude of oceanic subduction zones up to 300 million years ago was offset by up to 18∘ compared with tectonic reconstructions for the same period.