The Importance of Posidonia oceanica and Cymodocea nodosa as Contributors of Free Amino Acids in Water and Sediment of Seagrass Beds

Abstract. Dissolved free amino acids (DFAA) were measured in sediment porewater and overlying sea water in seagrass beds of Posidonia oceanica and Cymodocea nodosa at a water depth of 8–10 m in Corsica, France. In the sea water, DFAA concentrations from 0.5 to 1.9μM were found. Lowest concentrations occurred in the afternoon in surface water samples, while higher concentrations were measured in morning surface samples and in all bottom samples. The most abundant amino acids were serine, glycine, and alanine. In the sediment, the upper 4cm contained the highest concentrations of DFAA (177nmol cm^-3 or 367 μM), while lower concentrations (<50nmol cm^-3 or 104 μM) prevailed deeper in the sediment. Glycine, glutamic acid, alanine, and β-alanine were the major components of the DFAA. The photosynthetic activity of the seagrasses influenced sediment porewater pools of DFAA. When a Posidonia bed was covered with a black polyethylene shield, the interstitial amino acids were reduced at a rate of 16nmol cm^-2 h^-1 (0-10cm depth). Conversely, extended daylight (floodlight) increased the DFAA pool in sediment depths below 4 cm. Free amino acids were released to the overlying sea water from both seagrass sediment and individual shoots, the rates being highest in the dark. The present investigation indicates that a substantial portion of the N-cycling of the seagrass sediment includes free amino acids.     

An Afterthought: Ecosystem Metrics and Pressure Indicators

Editing the symposium contributions has been an interestingand instructive experience, because they provide a broad overviewof the well-nigh unlimited creativity of marine scientists totry and find building blocks for an ecosystem approach to fisherymanagement. A wealth of ideas appears to be emerging on howdifferent aspects of the state of exploited marine ecosystemscan be measured. Although the metrics produced are commonlyreferred to as "ecosystem indicators", however, it is generallyless clear what they actually indicate. The concept that management must take the wider ranging     

Using modular 3D digital earth applications based on point clouds for the study of complex sites

This article discusses the use of 3D technologies in digital earth applications (DEAs) to study complex sites. These are large areas containing objects with heterogeneous shapes and semantic information. The study proposes that DEAs should be modular, have multi-tier architectures, and be developed as Free and Open Source Software if possible. In DEAs requiring high reliability in the 3D measurements, point clouds are proposed as basis for the 3D Digital digital earth representation. For the development of DEAs, we propose to follow a workflow with four components: data acquisition and processing, data management, data analysis and data visualization. For every component, technological challenges of using 3D technologies are identified and solutions applied for a case study are presented. The case study is a modular 3D DEA developed for the archaeological project Mapping the Via Appia. The 3D DEA allows archaeologists to virtually analyze a complex study area.     

Twentieth century changes in winter climatic regions

The configuration of the northern hemispheric general atmospheric circulation system shifted from a zonal to a meridional pattern in the early 1950s. Winter climatic regions in the conterminous United States are developed for a ten year period dominated by zonal flow and a second decade of meridional flow using a combination of principal components factor analysis and a Euclidean distance clustering algorithm. The results demonstrate that regional patterns in the surface climatic data substantially changed as the circulation system shifted its basic configuration. The regional structures of the eastern United States and the Great Plains appeared to be particularly sensitive to the change in the upperlevel flow pattern.     

A palaeomagnetic experiment on crustal uplift in West Greenland

In the Nordre Strømfjord shear zone of central West Greenland it is believed that the gneisses exposed at the coast reached a maximum depth of burial about 10 km deeper than those now adjacent to the inland ice. This theory was tested palaeomagnetically. Further sampling up the mountain K?llingeh?tten was carried out to ascertain changes of direction of magnetization with height.The magnetic susceptibility ellipsoids were determined for each specimen and were used to correct their directions of magnetization for the effects of anisotropy. Complicated but compact polar wander paths were derived for both the fjord and mountain traverses. The path for the fjord is consistent with the geological model but does not support it. This inconclusive result may be the consequence of a low rate of polar wander. The mean palaeomagnetic poles are 27.7°N, 276.6° E (dp = 13.8°,dm = 17.3°) for Nordre Strømfjord and 25.3°N, 300.4°E (dp = 11.5°,dm = 14.1°) for K?llingeh?tten.     

Strontium-isotope studies of “brown water” (organic-rich groundwater) from Denmark

 Groundwater from some Quaternary and upper Tertiary aquifers in western Jutland, Denmark, is heavily influenced by "brown water", i.e., groundwater with a high content of naturally occurring dissolved organic matter. Stable-isotope analyses (¹⁸O/¹⁶O and D/H) indicate that both Quaternary and upper Tertiary aquifers are dominated by meteoric water. However, strontium-isotope analyses make it possible to distinguish between water samples from Quaternary and Miocene aquifers. Relatively low ⁸⁷Sr/⁸⁶Sr ratios, i.e., ∼0.7083, in Sr-rich water samples indicate that the majority of dissolved Sr in groundwater from Miocene as well as Quaternary strata is probably derived from Miocene marine skeletal carbonate matter in the subsurface. This situation is probably the result of Quaternary glacial reworking of upper Tertiary material and/or hydraulic contact between Quaternary and Miocene aquifers. A positive correlation between Sr contents and non-volatile organic carbon indicates that the remarkably high contents of organic matter recorded in these aquifers almost certainly are derived from Miocene sources as well. Received, February 1999 / Revised, July 1999 / Accepted, July 1999