Report series in Geophysics

 

Recent Submissions

  • Järvinen, Onni (Helsingin yliopisto, 2013)
    Antarctica is a major component in the climate system of the earth, acting as a large heat sink in the energy balance. The climatic conditions of Antarctica maintain the snow and ice cover that blankets almost completely the surface area of the continent. Physical properties of snow readily respond to changing environmental conditions and remote sensing signals are sensitive to these properties. The annual changes in the physical properties of the snow cover, especially in the coastal area, must be taken into account when snow cover and climate models are produced. In situ observations are needed for calibration and validation of these models. The aim of the present study was to examine the annual cycle of the active 10-m surface layer in western Dronning Maud Land, Antarctica. The data were collected along a 300-km-long transect from the coast to the edge of the high plateau during the field campaigns in austral summers 2004-2005, 2009-2010 and 2010-2011 as a part of the Finnish Antarctic Research Programme (FINNARP). The studies were focused on the uppermost part of the ice sheet covering the most recent annual accumulation in the coastal area. The results showed that the present study lakes froze completely during winter and showed similar evolution but the exact timing depended on the location. In January, the general structure of lake Suvivesi was following: two layers, each about 1 m thick, an upper layer with a thin ice layer on top and main body of liquid water, and a lower layer containing slush and hard ice sub-layers. The formation and the depth scale of the present study lakes are determined by the light extinction distance and thermal diffusion coefficient, limiting the growth to less than ~1.5 m in one summer. In Antarctica, the mean spectral diffuse extinction coefficient varied between 0.04 and 0.31 cm-1 (10-20-cm snow layer) and varied only slightly between locations when the grain type was the same. The theoretically calculated average depth where broadband irradiance (400-700-nm band) was 1 % of the downwelling irradiance at the surface, was 50 cm. On the continental ice sheet, the compaction rate of the snowpack was 0.0201 ± 0.02 y-1 and the power spectra revealed a daily cycle, synoptic scale variability (~10 days), and variability in a low-frequency band of 60-120 days at a depth of 54 cm. The investigations of snow patches in Basen nunatak revealed that much more snow was lost in summer 2010-2011 (6.3 mm d-1 water equivalent (w.e.)) than in 2004-2005 (4 mm d-1 w.e.).
  • Kitaigorodskii, Sergey (2013)
    The several conclusions of similarity theory for wind driven waves are discussed together with experimental data being revisited by the author (Kitaigorodskii, 1983, 1998). First of them is so-called wind speed scaling, often being used in literature on wind waves as Kitaigorodskii scaling. It is stressed that existing data cannot be served for rejection of concept of fully developed (mature) wind waves. Second of them is the derivation of so-called law omega–4 (Kitaigorodskii, 1962, 1983) for replacement of Phillips law (Phillips, 1958). The main question related to this problem is about existence of the transition from direct cascade regime to wind wave breaking dissipation scales. It is established "a bridge" between description of wave spectra used in Kitaigorodskii (1962) and weakly nonlinear theory of waves. This was the third question discussed here.
  • Uusikivi, Jari (Helsingin yliopisto, 2013)
    Sea ice has been recognized as one of the key elements of polar and sub-polar seas, including Baltic Sea. The existence of sea ice cover and its properties have influence to many aspects of marine biology, climate and seafaring. This thesis is concentrated on describing physical and optical properties of landfast ice, and also pack ice, in the Baltic Sea. The aim of the thesis is to use measurements to study the interactions between optical and physical properties of sea ice and how these can affect the biology in sea ice. Decade long observations of ice properties were used to construct a statistical model of properties of landfast ice. Temperature was found to be the most important factor determining ice thickness and contribution of snow ice to the ice thickness was determined by the amount of winter time precipitation. Stratigraphy of ice and growth history had influence to the vertical distribution of organisms in the ice cover as snow ice layers and columnar ice layers were found to favor different types of organisms. Thickness of meteoric ice layer, including snow ice and superimposed ice, controlled the albedo of ice cover when no snow cover was on the ice. Based on the observations of fast ice conditions and albedo, the effects of snow thickness and meteoric ice thickness to the albedo of sea ice were formulated as albedo parameterization equations. The optical properties of sea ice with spectral resolution were studied on the landfast sea ice. Emphasis in these studies was given to optical properties in the ultraviolet and visible wavelengths. Organic matter, dissolved and particulate, was the most important factor determining the ultraviolet properties of sea ice cover. The optical properties in the ultraviolet were also actively modified by the living organisms in the ice cover by producing mycosporine like amino acids (MAAs) in relatively high amounts. MAAs are a family of photoprotective compounds that absorb UV radiation efficiently. At the visible part of spectrum the ice by itself and the thickness of meteoric ice layer were the most important determinants. Salinity and the initial salt entrapment during ice growth in the Baltic Sea were measured to be less than in the oceans with equal ice growth rates. The turbulent fluxes of heat and salinity under the landfast sea ice were measured to be small.
  • Koistinen, Esa (2007)
  • Rasmus, Kai; Granberg, Harry; Kanto, Kimmo; Kärkäs, Eija; Lavoie, C.; Leppäranta, Matti (2003)
    The project ’Seasonal Snow in Antarctica’ was set up to measure the physical properties of Antarctic snow cover in 1999-2001. The present document is the project data report. An introduction is given of the project, descriptions of the experiments are made, and the data obtained by the scientists in the different working groups during the two expeditions to Antarctica are described
  • Leppäranta, Matti (1998)
  • Leppäranta, Matti (1998)
  • Järvinen, Onni; Leppäranta, Matti; Vehviläinen, Juho (University of Helsinki, Division of Geophysics and Astronomy, 2012)
    Field programme on the surface layer of the ice sheet in the Dronning Maud Land, Antarctica has been performed in 2009-2011. The objectives were to examine the annual accumulation and sublimation history, snow melting, chemistry of snow impurities, and life history of supraglacial and epiglacial lakes in blue ice regions. Fieldwork was done during FINNARP 2009 and 2010 expeditions. The sites were at the Finnish research station Aboa (73 02.5'S, 013 24.4'W), a snow line from Rampen at the edge of the ice shelf pass Aboa to the station Svea, and blue ice at Basen and neighboring nunataks. Snow measurements were made using classical snow pit method, ice and snow sampling, and with automatic observation stations (surface radiation balance, penetration of sunlight into snow and ice, and temperature within the surface layer of snow and ice). Life history, physics, and ecological state of lakes were mapped. This document is the data report including a brief project introduction, descriptions of the experiments, and the data obtained.
  • Raiskila, Selen (Helsingin yliopisto, 2013)
    Meteorite impact cratering has played a key role in Earth's geological past and has left a dramatic effect on biological and geological records forming large volumes of igneous rocks and important mineral deposits. By studying terrestrial impact craters we can have valuable information of impact generated changes in rocks and minerals. Integrated geophysical study in this dissertation combines different methods to distinguish the meteorite impact related features from features caused by endogenic processes. Optical microscopy provides diagnostic evidence of shock produced deformations in minerals.Shocked and un-shocked rocks have contrasts in petrophysical properties, which cause anomalies to regional magnetic and gravity fields over meteorite impact structures.Magnetic minerals may re-magnetize during impact and thus provide information of the past geomagnetic field and the ancient paleoposition of impact site. This dissertation focuses to the Finnish impact structure, Keurusselkä, which was discovered in 2003. The structure is situated in central Finland (62°08 N, 24°37 E) within the Central Finland Granitoid Complex, which formed 1890 1860 million years ago during the Svecofennian orogeny. Keurusselkä is deeply eroded remain of a complex crater, named after the Lake Keurusselkä, which is the dominant present day feature of the crater area. For this study rock and drill core samples were collected from Keurusselkä region. The samples were chosen according to a sampling strategy, where samples were taken in and outside the impact region to investigate the impact related features and their radial distance from the centre of the impact. The main focus was to prove or disprove the impact origin of Keurusselkä. First indication of impact was shatter cones, which are conical features in rocks formed by an impact shock and pressure. Shatter cones were found in a circular area interpreted as the central uplift of the original crater. In this dissertation petrographic analysis of thin sections was done to find evidence of deformational features in minerals. Diagnostic evidence for Keurusselkä was achieved when planar deformation features(PDFs) were found from quartz grains in shatter cones indicating impact pressures up to 20 GPa. Samples from 3 shallow drillings in southwest part of the Keurusselkä structure were also studied. Impact like monomictic breccia was found from one of the drill cores. Petrographic analysis revealed clay minerals (illite, smectite-group), which most likely have altered from impact glass. Magnetic minerals were obtained for paleomagnetic purposes, i.e. to examine the ancient position and drift of Baltica. Paleomagnetic directions obtained from shatter cones indicate re-magnetization. The virtual geomagnetic pole implies that the impact event took place ~1120 million years ago during the formation of Rodinia supercontinent. Petrophysical properties (density, susceptibility) of rocks were measured for differences between shocked and un-shocked rocks. The exposed bedrock in Keurusselkä was noticed to be fractured and damaged, which causes anomalies to the regional magnetic and gravity field. The geophysical signals were modelled along two profiles using measured physical properties of Keurusselkä rocks. The highly magnetized centre of the structure forms an eroded circular central uplift with diameter of 6 km. Based on the gravity minimum around the structure an area of ~16 km in diameter and depth of ~1200 meters was modelled to explain the observed anomalies. The original size of the crater is estimated to be 24-27 km in diameter.
  • Bućko, Michał (Helsingin yliopisto, 2012)
    Road traffic is at present one of the major sources of environmental pollution in urban areas. Magnetic particles, heavy metals and others compounds generated by traffic can greatly affect ambient air quality and have direct implications for human health. The general aim of this research was to identify and characterize magnetic vehicle-derived particulates using magnetic, geochemical and micro-morphological methods. A combination of three different methods was used to discriminate sources of particular anthropogenic particles. Special emphasis was placed on the application of various collectors (roadside soil, snow, lichens and moss bags) to monitor spatial and temporal distribution of traffic pollution on roadsides. The spatial distribution of magnetic parameters of road dust accumulated in roadside soil, snow, lichens and moss bags indicates that the highest concentration of magnetic particles is in the sampling points situated closest to the road edge. The concentration of magnetic particles decreases with increasing distance from the road indicating vehicle traffic as a major source of emission. Significant differences in horizontal distribution of magnetic susceptibility were observed between soil and snow. Magnetic particles derived from road traffic deposit on soil within a few meters from the road, but on snow up to 60 m from the road. The values of magnetic susceptibility of road dust deposited near busy urban motorway are significantly higher than in the case of low traffic road. These differences are attributed to traffic volume, which is 30 times higher on motorway than on local road. Moss bags placed at the edge of urban parks situated near major roads show higher values of magnetic susceptibility than moss bags from parks located near minor routes. Enhanced concentrations of heavy metals (e.g. Fe, Mn, Zn, Cu, Cr, Ni and Co) were observed in the studied samples. This may be associated with specific sources of vehicle emissions (e.g. exhaust and non-exhaust emissions) and/or grain size of the accumulated particles (large active surface of ultrafine particles). Significant correlations were found between magnetic susceptibility and the concentration of selected heavy metals in the case of moss bags exposed to road traffic. Low-coercivity magnetite was identified as a major magnetic phase in all studied roadside collectors (soil, snow, moss bags and lichens). However, magnetic minerals such as titanomagnetite, ilmenite, pyrite and pyrrhotite were also observed in the studied samples. The identified magnetite particles are mostly pseudo-single-domain (PSD) with a predominant MD fraction (>10 μm). The ultrafine iron oxides (>10 nm) were found in road dust extracted from roadside snow. Large magnetic particles mostly originate from non-exhaust emissions, while ultrafine particles originate from exhaust emissions. The examined road dust contains two types of anthropogenic particles: (1) angular/aggregate particles composed of various elements (diameter ~1-300 µm); (2) spherules (~1-100 µm) mostly composed of iron. The first type of particles originates from non-exhaust emissions such as the abrasion of vehicle components, road surface and winter road maintenance. The spherule-shaped particles are products of combustion processes e.g. combustion of coal in nearby power plants and/or fuel in vehicle engines. This thesis demonstrates that snow is an efficient collector of anthropogenic particles, since it can accumulate and preserve the pollutants for several months (until the late stages of melting). Furthermore, it provides more information about spatial and temporal distribution of traffic-generated magnetic particles than soil. Since the interpretation of data obtained from magnetic measurements of soil is problematic (due to its complexity), this suggests the application of alternative collectors of anthropogenic magnetic particulates (e.g. snow and moss bags). Moss bags and lichens are well suited for magnetic biomonitoring studies, since they effectively accumulate atmospheric pollution and can thus be applied to monitor the spatio-temporal distribution of pollution effects.
  • Airo, Meri-Liisa; Kiuru, Risto (University of Helsinki, Division of Geophysics and Astronomy, 2012)