188 resultados para 382.940
Resumo:
Arctic sea ice has declined and become thinner and younger (more seasonal) during the last decade. One consequence of this is that the surface energy budget of the Arctic Ocean is changing. While the role of surface albedo has been studied intensively, it is still widely unknown how much light penetrates through sea ice into the upper ocean, affecting sea-ice mass balance, ecosystems, and geochemical processes. Here we present the first large-scale under-ice light measurements, operating spectral radiometers on a remotely operated vehicle (ROV) under Arctic sea ice in summer. This data set is used to produce an Arctic-wide map of light distribution under summer sea ice. Our results show that transmittance through first-year ice (FYI, 0.11) was almost three times larger than through multi-year ice (MYI, 0.04), and that this is mostly caused by the larger melt-pond coverage of FYI (42 vs. 23%). Also energy absorption was 50% larger in FYI than in MYI. Thus, a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems.
Resumo:
Hydrogenous manganese nodules form on the ocean floor by slow authigenic precipitation (1-6 mm/Ma) of the oxyhydroxides of manganese and iron that continuously scavenge trace elements from the marine environment. Consequently, these nodules represent independent marine deposits useful for the study of the chemical signatures of the paleomarine environments. The results presented are a continuation of a study of the Zetes-3D nodule from the Pacific Ocean. It is a large (24x17x10 cm) hydrogenous nodule whose slow growth rate of 1.3 mm/Ma was detremined using 10Be techniques. A positive cerium anomaly is observed throughout the nodule and its Ir content indicates a sharp spike at 54-62 Ma in fair agreement with the K-T event.
