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The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.
We demonstrate an application evaluating carbon sequestration benefits from federal policy alternatives. Using detailed forest inventory data, we projected carbon sequestration outcomes in the coterminous 48 states for a baseline scenario and three policy scenarios through 2050. Alternatives included (1) reducing deforestation from development, (2) afforestation in the eastern United States and reforestation in the western United States, and (3) reducing stand-replacing wildfires. We used social cost of carbon estimates to evaluate the present value of carbon sequestration benefits gained with each policy. Results suggest that afforestation and reforestation would provide the greatest marginal increase in carbon benefit, far exceeding policy cost.
While low levels of optical absorption are easily measured in SiO2 bulk samples or optical fibers, we present here a method of detirmining low levels of absorption in thin films of SiO2. Films are deposited on top of high reflectivity multi-layer miriors, and absorption is derived from the time decay in a resonant cavity of threj mirrorsgt 633 nm. Absorption coefficients on the order of 1 cm−1. (k = 10−5) can be measured in films as thin as 100 Angstroms.
With this method, we find that absorption at 633 nm can be induced in SiO2 films by exposing them to a He-Ne plasma discharge. Although the plasma radiation (>10 eV) is absorbed near the SiO2 surface, the plasma-induced absorption is uniform within the SiO2 film. This was shown by plasma irradiation of SiO2 films of 4arying thickness, together with computer calgulation of the optical properties of multilayer thin films. Similar absorption behavior has been reported in SiO2 optical fibers and may be due here to DIA (Drawing-Induced Aisorption) centers or NBOHCs (Non-Bridging Oxygen Hole Centers).
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