Global carbon dioxide emissions from inland waters. Nature, 503(7476): 355-359http://dx

[1] Mountains are important sources of freshwater for the adjacent lowlands. In view of increasingly scarce freshwater resources, this contribution should be clarified. While earlier studies focused on selected river systems in different climate zones, we attempt here a first spatially explicit, global typology of the so-called ''water towers'' at the 0.5°Â 0.5°resolution in order to identify critical regions where disproportionality of mountain runoff as compared to lowlands is maximum. Then, an Earth systems perspective is considered with incorporation of lowland climates, distinguishing four different types of water towers. We show that more than 50% of mountain areas have an essential or supportive role for downstream regions. Finally, the potential significance of water resources in mountains is illustrated by including the actual population in the adjacent lowlands and its water needs: 7% of global mountain area provides essential water resources, while another 37% delivers important supportive supply, especially in arid and semiarid regions where vulnerability for seasonal and regional water shortage is high.

[1] This paper assesses global water stress at a finer temporal scale compared to conventional assessments. To calculate time series of global water stress at a monthly time scale, global water availability, as obtained from simulations of monthly river discharge from the companion paper, is confronted with global monthly water demand. Water demand is defined here as the volume of water required by users to satisfy their needs. Water demand is calculated for the benchmark year of 2000 and contrasted against blue water availability, reflecting climatic variability over the period . Despite the use of the single benchmark year with monthly variations in water demand, simulated water stress agrees well with long-term records of observed water shortage in temperate, (sub)tropical, and (semi)arid countries, indicating that on shorter (i.e., decadal) time scales, climatic variability is often the main determinant of water stress. With the monthly resolution the number of people experiencing water scarcity increases by more than 40% compared to conventional annual assessments that do not account for seasonality and interannual variability. The results show that blue water stress is often intense and frequent in densely populated regions (e.g., India, United States, Spain, and northeastern China). By this method, regions vulnerable to infrequent but detrimental water stress could be equally identified (e.g., southeastern United Kingdom and northwestern Russia).

[1] The exchange of CO 2 between the atmosphere and the global coastal ocean was evaluated from a compilation of air-water CO 2 fluxes scaled using a spatially-explicit global typology of inner estuaries (excluding outer estuaries such as large river deltas) and continental shelves. The computed emission of CO 2 to the atmosphere from estuaries (+0.27 ± 0.23 PgC yr −1 ) is ∼26% to ∼55% lower than previous estimates while the sink of atmospheric CO 2 over continental shelf seas (−0.21 ± 0.36 PgC yr −1 ) is at the low end of the range of previous estimates (−0.22 to −1.00 PgC yr −1 ). The air-sea CO 2 flux per surface area over continental shelf seas (−0.7 ± 1.2 molC m −2 yr −1 ) is the double of the value in the open ocean based on the most recent CO 2 climatology. The largest uncertainty of scaling approaches remains in the availability of CO 2 data to describe the spatial variability, and to capture relevant temporal scales of variability. Citation: Laruelle, G. G., H. H. Dürr, C. P. Slomp, and A. V. Borges (2010), Evaluation of sinks and sources of CO 2 in the global coastal ocean using a spatially-explicit typology of estuaries and continental shelves,

[1] Chemical weathering is an integral part of both the rock and carbon cycles and is being affected by changes in land use, particularly as a result of agricultural practices such as tilling, mineral fertilization, or liming to adjust soil pH. These human activities have already altered the terrestrial chemical cycles and land-ocean flux of major elements, although the extent remains difficult to quantify. When deployed on a grand scale, Enhanced Weathering (a form of mineral fertilization), the application of finely ground minerals over the land surface, could be used to remove CO 2 from the atmosphere. The release of cations during the dissolution of such silicate minerals would convert dissolved CO 2 to bicarbonate, increasing the alkalinity and pH of natural waters. Some products of mineral dissolution would precipitate in soils or be taken up by ecosystems, but a significant portion would be transported to the coastal zone and the open ocean, where the increase in alkalinity would partially counteract "ocean acidification" associated with the current marked increase in atmospheric CO 2 . Other elements released during this mineral dissolution, like Si, P, or K, could stimulate biological productivity, further helping to remove CO 2 from the atmosphere. On land, the terrestrial carbon pool would likely increase in response to Enhanced Weathering in areas where ecosystem growth rates are currently limited by one of the nutrients that would be released during mineral dissolution. In the ocean, the biological carbon pumps (which export organic matter and CaCO 3 to the deep ocean) may be altered by the resulting influx of nutrients and alkalinity to the ocean. This review merges current interdisciplinary knowledge about Enhanced Weathering, the processes involved, and the applicability as well as some of the consequences and risks of applying the method.