The ManTIS Field Spectro-Goniometer Movie - Presentation of the Instrument and Measurement Scheme

This article presents and technically describes a new field spectro-goniometer system for the ground-based characterization of the surface reflectance anisotropy under natural illumination conditions developed at the Alfred Wegener Institute (AWI). The spectro-goniometer consists of a Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS), and a hyperspectral sensor system. The presented measurement strategy shows that the AWI ManTIS field spectro-goniometer can deliver high quality hemispherical conical reflectance factor (HCRF) measurements with a pointing accuracy of ±6 cm within the constant observation center. The sampling of a ManTIS hemisphere (up to 30° viewing zenith, 360° viewing azimuth) needs approx. 18 min. The developed data processing chain in combination with the software used for the semi-automatic control provides a reliable method to reduce temporal effects during the measurements. The presented visualization and analysis approaches of the HCRF data of an Arctic low growing vegetation showcase prove the high quality of spectro-goniometer measurements. The patented low-cost and lightweight ManTIS instrument platform can be customized for various research needs and is available for purchase.

hyDRaCAT Spectral Reflectance Library: Hyperspectral Field Spectroscopy and Field Spectro-Goniometry of Siberian and Alaskan Tundra

hyDRaCAT Spectral Reflectance Library for tundra provides the surface reflectance data and the bidirectional reflectance distribution function (BRDF) of important Arctic tundra vegetation communities at representative Siberian and Alaskan tundra sites. The aim of this dataset is the hyperspectral and spectro-directional reflectance characterization as basis for the extraction of vegetation parameters, and the normalization of BRDF effects in off-nadir and multi-temporal remote sensing data. The spectroscopic and field spectro-goniometric measurements were undertaken on the YAMAL2011 expedition of representative Siberian vegetation fields and on the North American Arctic Transect NAAT2012 expedition of Alaskan vegetation fields both belonging to the Greening-of-the-Arctic (GOA) program. For the field spectroscopy each 100 m2 vegetation study grid was divided into quadrats of 1 × 1 m. The averaged reflectance of all quadrats represents the spectral reflectance at the scale of the whole grid at the 10 × 10 m scale. For the surface radiometric measurements two GER1500 portable field spectroradiometers (Spectra Vista Corporation, Poughkeepsie, NY, USA) were used. The GER1500 measures radiance across the wavelength range of 350-1,050 nm, with sampling intervals of 1.5 nm and a radiance accuracy of 1.2 × 10**-1 W/cm**2/nm/sr. In order to increase the signal-to-noise ratio, 32 individual measurements were averaged per one target scan. To minimize variations in the target reflectance due to sun zenith angle changes, all measurements at one study location have been performed under similar sun zenith angles and during clear-sky conditions. The field spectrometer measurements were carried out with a GER1500 UV-VIS spectrometer The spectrogoniometer measurements were carried out with a self-designed spectro-goniometer: the Manual Transportable Instrument platform for ground-based Spectro-directional observations (ManTIS, patent publication number: DE 10 2011 117 713.A1). The ManTIS was equipped with the GER1500 spectrometer allowing spectro-directional measurements with up to 30° viewing zenith angle by full 360° viewing azimuth angles. Measurements in central Yamal (Siberia) at the research site 'Vaskiny Dachi' were carried out in the late summer phenological state from August 12 2011 to August 28 2011. All measurements in Alaska along the North South transect on the North Slope were taken between 29 June and 11 July 2012, ensuring that the vegetation was in the same phenological state near peak growing season.

Geochemistry of bulk sediment from the Cape Basin

A technique for onsite application of X-ray fluorescence (XRF) spectrometry to samples from sediment cores aboard a research vessel was developed and tested. The method is sufficiently simple, precise, and fast to be used routinely for high-resolution analyses of depth profiles as well as surface samples. Analyses were performed with the compact high-performance energy-dispersive polarisation X-ray fluorescence (EDPXRF) analyser Spectro Xepos. Contents of the elements Si, Ti, Al, Fe, Mn, Mg, Ca, K, Sr, Ba, Rb, Cu, Ni, Zn, P, S, Cl and Br were simultaneously determined on 200-225 samples of each core within 24 h of recovery. This study presents a description of the employed shipboard preparation and analysis technique, along with some example data. We show land-based datasets that support our decisions to use powder samples and to reduce the original measuring time for onboard analyses. We demonstrate how well the results from shipboard measurements for the various elements compare with the land-based findings. The onboard geochemical data enabled us to establish an element stratigraphy already during the cruise. Correlation of iron, calcium and silicon enrichment trends with an older reference core provided an age model for the newly retrieved cores. The Spectro Xepos instrument performed without any analytical and technical difficulties which could have been caused by rougher weather conditions or continuous movement and vibration of the research vessel. By now, this XRF technique has been applied during three RV Meteor cruises to approximately 5,000 Late Quaternary sediment samples from altogether 23 gravity cores, 25 multicorer cores and two box cores from the eastern South Atlantic off South Africa/Namibia and the eastern Atlantic off NW Africa.

Geochemistry of sediment core GeoB7920-2

The X-ray fluorescence (XRF) core scanner provides bulk-sediment chemistry data measured nondestructively at the split core sediment surface. Although this method is widely accepted, there is little known about the effects of physical properties such as density and water content on XRF core scanner data. Comparison of XRF scanner measurements from the sediment surface and dry powder samples of sediment core GeoB7920 indicates strongly reduced element intensities for the lighter elements Al and Si. We relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the XRF core scanner. The heavier elements K, Ca, Ti, and Fe remain relatively unaffected by the variation of any physical property within sediment core GeoB7920. Additionally, we successfully use the elemental intensity of Cl as a proxy for the seawater content in the sample volume analyzed by the XRF core scanner. This enables the establishment of a correction function for the elements Al and Si that corrects for the radiation absorption of the water content in sediment core GeoB7920 off Cape Blanc, NW Africa.

Seawater carbonate chemistry and biological processes during experiments with Limacina helicina, 2009

Thecosome pteropods (pelagic mollusks) can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO2 levels of 280, 380, 550, 760 and 1020 µatm and at control (0°C) and elevated (4°C) temperatures. The respiration rate was unaffected by pCO2 at control temperature, but significantly increased as a function of the pCO2 level at elevated temperature. pCO2 had no effect on the gut clearance rate at either temperature. Precipitation of CaCO3, measured as the incorporation of 45Ca, significantly declined as a function of pCO2 at both temperatures. The decrease in calcium carbonate precipitation was highly correlated to the aragonite saturation state. Even though this study demonstrates that pteropods are able to precipitate calcium carbonate at low aragonite saturation state, the results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH. A decline of pteropod populations would likely cause dramatic changes to various pelagic ecosystems.