Set of Matlab function to study geometrical parameters or channels

This set of functions allows one to compute the radius of curvature of a river in planform for the purpose of making correlations with other geometric parameters of a channel. The code may also be used to compute the width of a channel.

Paleomagnetic of igneous rocks of ODP Leg 114

A paleomagnetic study was made of 12 samples of trachytic basalt from the base of ODP Hole 698A on the Northeast Georgia Rise (southwest Atlantic) and four samples of andesitic basalt and nine samples of volcanic breccia from the base of ODP Hole 703A on the Meteor Rise (southeast Atlantic). The magnetic intensities of the Hole 703A samples are anomalously low, possibly reflecting alteration effects. The mean magnetic intensity of the Hole 698A samples is high, and compatible with the model of Bleil and Petersen (1983) for the variation of magnetic intensity with age in oceanic basalts, involving progressive low-temperature oxidation of titanomagnetite to titanomaghemite for some 20 m.y. followed by inversion to intergrowths of magnetite and other Fe-Ti oxides during the subsequent 100 m.y. These results support the interpretation of the Hole 698A basalts as true oceanic basement of Late Cretaceous age rather than a younger intrusion. Well-defined stable components of magnetization were identified from AF and thermal demagnetization of the Hole 698A basalts, and less well-defined components were identified for the Hole 703A samples. Studies of the magnetic homogeneity of the Hole 698A basalts, involving harmonic analysis of the spinner magnetometer output, indicate the presence of an unevenly distributed low-coercivity component superimposed on the more homogeneous high-coercivity characteristic magnetization. The former component is believed to reside in irregularly distributed multidomain magnetite grains formed along cracks within the basalt, whilst the latter resides in more uniformly distributed finer magnetic grains. The inclination values for the high-coercivity magnetization of five Hole 698A basalt samples form an internally consistent set with a mean value of 59° ± 5°. The corresponding Late Cretaceous paleolatitude of 40° ± 5° is shallower than expected for this site but is broadly compatible with models for the opening of the South Atlantic involving pivoting of South America away from Africa since the Early Cretaceous. The polarity of the stable characteristic magnetization of the Site 698 basalts is normal. This is consistent with their emplacement during the long Campanian to Maestrichtian normal polarity Chron C33N.

Geochemistry of dark-light rhythm sediments of the Japan Sea

Ocean Drilling Program Legs 127 and 128 in the Japan Sea have revealed the existence of numerous dark-light rhythms of remarkable consistency in sediments of late Miocene, latest Pliocene, and especially Pleistocene age. Light-colored units within these rhythms are massive or bioturbated, consist of diatomaceous clays, silty clays, or nannofossil-rich clays, and are generally poor in organic matter. Dark-colored units are homogeneous, laminated, or thinly bedded and include substantial amounts of biogenic material such as well-preserved diatoms, planktonic foraminifers, calcareous nannofossils, and organic matter (maximum 7.4 wt%). The dark-light rhythms show a similar geometrical pattern on three different scales: First-order rhythms consist of a cluster dominated by dark-colored units followed by a cluster dominated by light-colored units (3-5 m). Spectral analysis of a gray-value time series suggests that the frequencies of the first-order rhythms in sediments of latest Pliocene and Pleistocene age correlate to the obliquity and the eccentricity cycles. The second-order dark-light rhythms include a light and a dark-colored unit (10-160 cm). They were formed in time spans of several hundred to several ten thousand years, with variance centering around 10,500 yr. This frequency may correspond to half the precessional cycle. Third-order rhythms appear as laminated or thinly bedded dark-light couplets (2-15 mm) within the dark-colored units of the second-order rhythms and may represent annual frequencies. In interpreting the rhythms, we have to take into account that (1) the occurrence of the first- and second-order rhythms is not necessarily restricted to glacial or interglacial periods as is shown by preliminary stable-isotope analysis and comparison with the published d18O record; (2) they appear to be Milankovitch-controlled; and (3) a significant number of the rhythms are sharply bounded. The origin of the dark-light rhythms is probably related to variations in monsoonal activity in the Japan Sea, which show annual frequencies, but also operates in phase with the orbital cycles.

Experiment: Influence of CO2 and nitrogen limitation on the coccolith volume of Emiliania huxleyi (Haptophyta)

Coccolithophores, a key phytoplankton group, are one of the most studied organisms regarding their physiological response to ocean acidification/carbonation. The biogenic production of calcareous coccoliths has made coccolithophores a promising group for paleoceanographic research aiming to reconstruct past environmental conditions. Recently, geochemical and morphological analyses of fossil coccoliths have gained increased interest in regard to changes in seawater carbonate chemistry. The cosmopolitan coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler was cultured over a range of pCO2 levels in controlled laboratory experiments under nutrient replete and nitrogen limited conditions. Measurements of photosynthesis and calcification revealed, as previously published, an increase in particulate organic carbon production and a moderate decrease in calcification from ambient to elevated pCO2. The enhancement in particulate organic carbon production was accompanied by an increase in cell diameter. Changes in coccolith volume were best correlated with the coccosphere/cell diameter and no significant correlation was found between the coccolith volume and the particulate inorganic carbon production. The conducted experiments revealed that the coccolith volume of E. huxleyi is variable with aquatic CO2 concentration but its sensitivity is rather small in comparison with its sensitivity to nitrogen limitation. Comparing coccolith morphological and geometrical parameters like volume, mass and size to physiological parameters under controlled laboratory conditions is an important step to understand variations in fossil coccolith geometry.

The CoastColour Round Robin datasets: a database to evaluate the performance of algorithms for the retrieval of water quality parameters in coastal waters

The CoastColour project Round Robin (CCRR) project (http://www.coastcolour.org) funded by the European Space Agency (ESA) was designed to bring together a variety of reference datasets and to use these to test algorithms and assess their accuracy for retrieving water quality parameters. This information was then developed to help end-users of remote sensing products to select the most accurate algorithms for their coastal region. To facilitate this, an inter-comparison of the performance of algorithms for the retrieval of in-water properties over coastal waters was carried out. The comparison used three types of datasets on which ocean colour algorithms were tested. The description and comparison of the three datasets are the focus of this paper, and include the Medium Resolution Imaging Spectrometer (MERIS) Level 2 match-ups, in situ reflectance measurements and data generated by a radiative transfer model (HydroLight). The datasets mainly consisted of 6,484 marine reflectance associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: Total Suspended Matter (TSM) and Chlorophyll-a (CHL) concentrations, and the absorption of Coloured Dissolved Organic Matter (CDOM). Inherent optical properties were also provided in the simulated datasets (5,000 simulations) and from 3,054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three datasets are compared. Match-up and in situ sites where deviations occur are identified. The distribution of the three reflectance datasets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.

Using ground-penetrating radar, topography and classification of vegetation to model the sediment and active layer thickness in a periglacial lake catchment, Western Greenland, link to shapefiles

The geometries of a catchment constitute the basis for distributed physically based numerical modeling of different geoscientific disciplines. In this paper results from ground-penetrating radar (GPR) measurements, in terms of a 3D model of total sediment thickness and active layer thickness in a periglacial catchment in western Greenland, is presented. Using the topography, thickness and distribution of sediments is calculated. Vegetation classification and GPR measurements are used to scale active layer thickness from local measurements to catchment scale models. Annual maximum active layer thickness varies from 0.3 m in wetlands to 2.0 m in barren areas and areas of exposed bedrock. Maximum sediment thickness is estimated to be 12.3 m in the major valleys of the catchment. A method to correlate surface vegetation with active layer thickness is also presented. By using relatively simple methods, such as probing and vegetation classification, it is possible to upscale local point measurements to catchment scale models, in areas where the upper subsurface is relatively homogenous. The resulting spatial model of active layer thickness can be used in combination with the sediment model as a geometrical input to further studies of subsurface mass-transport and hydrological flow paths in the periglacial catchment through numerical modelling.