Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr

All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMAGIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50  kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (¹⁰Be and ¹⁴C). This comparison generally lends support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding  40  kyr, and that  4 · 10²²  Am² appears to represent a critical threshold below which geomagnetic excursions and reversals occur.     

Low velocity shock-cloud encounters II.

We report on a comparative study of nearby shocked clouds with and without star formation, based on IRAS, HI(21cm), CO(1-0) NH₃ (and other molecular line) observations. The dark clouds L1780 (no star formation) and L1251 (high SFE) are discussed here. Their density and velocity structure are compared with the predictions of the HD model of Horváth & Tóth (1995), Paper I.     

On the parameterization of precipitation in warm clouds

The Sundqvist parameterization for warm rain production by autoconversion processes as the function of cloud liquid water mixing ratio m is tested by defining a realistic ‘driving’ profile m(z) for a maritime low, warm stratocumulus cloud, and comparing with various recent observations. The results show that the parameterization is acceptable, especially after tuning its rain collection constant C₁. It is somewhat sensitive to the vertical resolution of the host model, though. Extending the calculations by considering typical cloud and raindrop size spectra, extra variables such as drizzle amounts and droplet effective radii (forced by the bulk Sundqvist rain rates) could be estimated by numerical integration. Also, these seem to agree fairly well with the available observations.     

Uraniferous bitumen nodules in the Talvivaara Ni–Zn–Cu–Co deposit (Finland): influence of metamorphism on uranium mineralization in black shales

In the central part of the Fennoscandian Shield, the Talvivaara Ni–Zn–Cu–Co deposit, hosted by Palaeoproterozoic metamorphosed black schists, contains low uranium concentrations ranging from 10 to 30 ppm. The Talvivaara black schists were deposited 2.0–1.9 Ga ago and underwent subsequent metamorphism during the 1.9–1.79 Ga Svecofennian orogeny. Anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium. U–Pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1,878?±?17 and 1,871?±?43 Ma, during peak metamorphism. Rare earth element patterns and high Th content (average 6.38 wt%) in disseminated uraninite crystals indicate that U was concentrated during high temperature metamorphism (>400 °C). The formation of bitumen rims around uraninite may be explained by two distinct scenarios: (a) a transport of U coincident with the migration of hydrocarbons or (b) post-metamorphic formation of bitumen rims, through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite.     

Impact structures and events - a Nordic perspective

Impact cratering is one of the fundamental processes in the formation of the Earth and our planetary system, as reflected, for example in the surfaces of Mars and the Moon. The Earth has been covered by a comparable number of impact scars, but due to active geological processes, weathering, sea floor spreading etc, the number of preserved and recognized impact craters on the Earth are limited. The study of impact structures is consequently of great importance in our understanding of the formation of the Earth and the planets, and one way we directly, on the Earth, can study planetary geology.
The Nordic-Baltic area have about thirty confirmed impact structures which makes it one of the most densely crater-populated terrains on Earth. The high density of identified craters is due to the level of research activity, coupled with a deterministic view of what we look for. In spite of these results, many Nordic structures are poorly understood due to the lack of 3D-geophysical interpretations, isotopeor other dating efforts and better knowledge of the amount of erosion and subsequent tectonic modifications.
The Nordic and Baltic impact community is closely collaborating in several impact-related projects and the many researchers （about forty） and PhD students （some seventeen） promise that this level will continue for many more years. The main topics of research include geological, geophysical and geochemical studies in combination with modeling and impact experiments. Moreover, the Nordic and Baltic crust contains some hundred suspect structures which call for detailed analysis to define their origin.
New advanced methods of analyzing geophysical information in combination with detailed geochemical analyses and numerical modeling will be the future basic occupation of the impact scientists of the region. The unique Cretaceous/Tertiary boundary （K-T） occurrences in Denmark form an important source of information in explaining one of the major mass extinctions on Earth.     

On the mean zonal and meridional circulations and the flux of moisture in the northern hemisphere during the summer season

Summary The mean zonal and meridional wind components of the northern hemisphere at different pressure levels for the summer season June–August have been determined and the mean meridional mass circulation has been computed as a function of latitude. From the mass circulation the meridional flux of moisture is computed for the latitudinal belt 0°–45° N. Using the horizontal divergence of this flux the average difference between precipitation and evapotranspiration from the earth's surface is evaluated.     

Geometric test field calibration of digital photogrammetric sensors

Test field system calibration will be a fundamental part of the future photogrammetric production line. Accurate calibration and performance evaluations are necessary for fully assessing the stability and accuracy of digital sensing techniques. In this paper, a method of comprehensive geometric calibration in a test field has been developed and empirically tested using eight image blocks collected with three UltraCamD digital large format photogrammetric cameras. Permanent photogrammetric test fields form the basis of the method. Important components of the method are determination of system parameters, evaluation of systematic errors, and assessment of geometric accuracy. The results showed that UltraCamD images contained systematic deformations that could not be modeled with single lens additional parameter models. Good point determination accuracy was obtained despite the systematic errors; the typical accuracy was 2–3 μm in image space in the horizontal coordinates and 0.05–0.09‰ of the object distance in height. One of the cameras had significantly poorer performance. In the worst cases, the horizontal accuracy was 5 μm in image space and the height accuracy was 0.18‰ of the object distance. The analog cameras gave better results than the UltraCamD, but the development of appropriate mathematical models for UltraCamD as well as improvements in digital sensors may change the situation in the near future.     

Spatial and temporal variation in particle size and particulate organic matter content in suspended particulate matter from peatland‐dominated catchments in Finland

Properties of suspended particulate matter play a vital role in transport processes, but information from boreal lowland river systems with high organic loads is limited. This study analysed data from 2 years of sampling at 30 locations in Finland (204 samples in total) using suspended particulate matter samplers to determine effective and absolute particle size and organic fractions. Mean d₅₀ value was 22 and 49 µm for absolute and effective particle size, respectively. The organic fraction content ranged from 2.1% to 36% (mean 9.6%), highlighting the importance of particle organic matter for suspended particulate matter flux in the region. The results indicated that the suspended particulate matter particle size distribution and load in the study region is dominated by composite particles. There were considerable spatial and temporal variations in transport of organic fractions, effective particle size and degree of aggregation (range 1.5–93%). Headwaters and, in particular, late summer and spring flood conditions with flow peaks produced the largest composite particles, whereas agriculture‐dominated sites produced smaller but more tightly compacted particles. Organic plant fibres appeared to play a vital role in floc formation in peat‐covered catchments, whereas in agriculture‐dominated catchments, land use‐derived aggregates dominated the composition. This study provides empirical evidence of the importance of effective particle size measurement in understanding the dynamics of suspended particulate matters in boreal lowland river systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Adaptive management to climate change for Norway spruce forests along a regional gradient in Finland

We hypothesized that the responses of boreal Norway spruce (Picea abies) forests to climate change would be region-specific due to regional differences in temperature and water availability. In this context, we analyzed the adaptive effects of varied thinning intensities on the gross primary production (GPP), total stem wood growth, and timber yield over a 100-year period using a process-based ecosystem model. Our simulations represented Norway spruce forests for five different bioclimatic zones spanning southern to northern Finland (61–67^oN). Ten thinning regimes with thinning intensities ranging from 5 to 50 %, as well as an unthinned regime, were included in the calculations. The results showed that at the southern sites without thinning, the cumulative GPP and total stem wood growth were lower under the changing climate than in the current climate over the simulation period due to greater water depletion via evapotranspiration and reduced soil water availability. At the central and the northern sites, the climate changes increasingly enhanced the GPP and total stem wood growth due to the mitigation of low-temperature limitation and the improved soil water availability. Thinning generally mitigated the soil water deficit by reducing water evaporation and led to a reduction of the natural mortality. At the southern sites, light and moderate thinning intensities increased the GPP and total stem wood growth relative to sites with a changing climate that experienced no thinning. Moreover, moderate thinning resulted in the greatest timber yield. Heavy thinning, in which a large proportion of standing trees were removed, reduced the GPP and total stem wood growth despite allowing increased soil water availability. At the northern sites, all levels of thinning, including light thinning, decreased the GPP and stem wood growth, indicating that soil water availability was not a limiting factor for growth prior to thinning.