Changes in ice-season characteristics of a European Arctic lake from 1964 to 2008

The long-term ice record (from 1964 to 2008) of an Arctic lake in northern Europe (Lake Kilpisj?rvi) reveals the response of lake ice to climate change at local and regional scales. Average freeze-up and ice breakup occurred on 9 November and 19 June, respectively. The freeze-up has been significantly delayed at a rate of 2.3 d per decade from 1964 onward (P?<?0.05). No significant change has taken place in ice breakup. Annual average ice thickness has become smaller since the mid-1980s (P?<?0.05). Air temperature during the early ice season significantly affected the ice thickness. The freeze-up date exhibits the highest correlation with the 2-month average daily minimum air temperature centered at the end of October, while the ice breakup date exhibits the highest correlation with the 2-month average daily maximal air temperature centered in mid May. A 1°C increase in the surface air temperature corresponds to a freeze-up later by 3.4?days and an ice breakup earlier by 3.6?days. Snow cover is a critical factor in lake-ice climatology. For cumulative November to March precipitation of less than 0.13?m, the insulating effect of the snow dominated, while higher rates of precipitation favored thicker ice due to the formation of snow ice. Variations in ice records of Lake Kilpisj?rvi can serve as an indicator of climate variations across the northern Europe. The North Atlantic Oscillation (NAO) does not significantly affect the ice season there, although both the local air temperatures and winter precipitation contain a strong NAO signal.     

2010-2018年北极夏季中国北极科学考察航行期间被动微波遥感海冰密集度与船基目视观测资料的比较

为了更有效地将卫星数据应用于北极航行导航,被动微波（PM）产品的海冰密集度（SIC）与从中国北极科学考察中收集到的船基目视观测（OBS）资料进行了比较。在2010、2012、2014、2016和2018年的北极夏季总共收集了3667组目测数据。PM SIC取自基于SSMIS传感器的NASA-Team（NT）、Bootstrap（BT）以及Climate Data Record（CDR）算法和基于AMSR-E/AMSR-2传感器的BT、enhanced NT（NT2）以及ARTIST Sea Ice（ASI）算法。使用PM SIC的日算术平均值和OBS SIC的日加权平均值进行比较。比较了PM SIC和OBS SIC之间的相关系数,偏差和均方根偏差,包括总体趋势以及在轻度/普通/严重冰况下的情况。使用OBS数据,浮冰尺寸和冰厚对不同PM产品SIC反演的影响可以通过计算浮冰尺寸编码和冰厚的日加权平均值来评估。我们的结果显示相关系数的范围为0.89（AMSR-E/AMSR-2 NT2）到0.95（SSMIS NT）,偏差的范围为-3.96%（SSMIS NT）到12.05%（AMSR-E/AMSR-2）,均方根偏差的范围为10.81%（SSMIS NT）到20.15%（AMSR-E/AMSR-2 NT2）。浮冰尺寸对PM产品的SIC反演有显著的影响,大多数PM产品倾向于在小浮冰尺寸情况下低估SIC,而在大浮冰尺寸情况下高估SIC。超过30 cm的冰厚对于PM产品的SIC反演没有明显影响。总体来看,在北极夏季,SSMIS NT SIC与OBS SIC之间有着最好的一致性,而AMSR-E/AMSR-2 NT2 SIC与OBS SIC的一致性最差。     

Fluid inclusions in microstructures of shocked quartz from the Keurusselkä impact site,Central Finland

Granitoid rock samples from the assumed center of the Keurusselkä impact site were subjected to a systematic study of fluid‐inclusion compositions and densities in various microstructures of the shocked quartz. The results are consistent with the following impact‐induced model of formation. After cessation of all major regional tectonic activity and advanced erosional uplift of the Fennoscandian shield, a meteorite impact (approximately 1.1 Ga) caused the formation of planar fractures (PFs) and planar deformation features (PDFs) and the migration of shock‐liberated metamorphic fluid (CO₂ ± H₂O) to the glass in the PDFs. Postimpact annealing of the PDFs led to the formation of CO₂ (±H₂O) fluid‐inclusion decorated PDFs. The scarce fluid‐inclusion implosion textures (IPs) suggest a shock pressure of 7.6–10 GPa. The postimpact pressure release and associated heating initiated hydrothermal activity that caused re‐opening of some PFs and their partial filling by moderate‐salinity/high temperature (>200 °C) H₂O (+ chlorite + quartz) and moderate‐density CO₂. The youngest postimpact endogenic sub‐ and nonplanar microfractures (MFs) are characterized by low‐density CO₂ and low‐salinity/low‐temperature (<200 °C) H₂O.     

Lithology and trace-metal content in till in the kuhmo granite-greenstone terrain, eastern Finland

Rocks of the Archaean Kuhmo greenstone belt and the fine fraction (− 63 μm) of 236 till samples were analysed for Co, Cr, Cu, Mn, Ni, Pb, Zn and Fe mainly with the AAS method. The influence of bedrock upon the lithology and geochemistry of till is clear, and can be seen immediately at the proximal contact. Expected trace-metal contents for the fine fraction of till were calculated using the average metal contents of the rock types and the proportions of these rock types in the till (2–6 cm pebbles). The expected values were then compared with the measured values in the fine fraction of till at the same locality. This approach seems effective for lithological comparison between various grain-size fractions of till.In general, the measured metal contents are clearly lower than expected. This indicates that the proportion of the greenstone material in the fine fraction of the till is smaller than in the coarse fraction. Correlations between measured and expected values of individual trace metals as well as their correlation with the different rock types are low, in most cases indicating inconsistent variation in the lithology of the coarse and fine fraction of the till. Good positive correlations between the number of pebbles of mafic metavolcanics and contents of Cu, Co, Mn and Fe in the fine fraction of till show that the influence of these rocks on the trace-element geochemistry of the tills in the study area is most significant as might be expected.     

Evaluation of drilling priorities using lead isotopes at the Lady Loretta lead-zinc-silver deposit, Australia

The weathered surface expression of the Lady Loretta lead-zinc-silver deposit outcrops almost continuously over a distance of about 4 km. Lead isotope ratios have been determined for samples, some of which contain > 4000 ppm Pb, from geochemically anomalous areas in order to assign drilling priorities to the anomalies.Twelve of the 43 samples analyzed contain isotopically homogeneous lead with ratios (²⁰⁷Pb/²⁰⁶Pb 0.9532–0.9549) similar to the expected targets for major ore deposits in the Mount Isa-McArthur River metallogenic province (²⁰⁷Pb/²⁰⁶Pb 0.955–0.962). Three main zones of interest can be outlined on the basis of lead isotopic data. The top priority is assigned to a 100-m-long section of the ironstone which coincides with the known outcrop of the ore. Lower priority for drilling is given to the two other zones which outcrop over smaller areas and have more radiogenic lead in their immediate surroundings. Several samples with anomalously high lead contents (> 1000 ppm) contain more radiogenic lead (²⁰⁷Pb/²⁰⁶Pb < 0.950) which was most likely derived from the weathering country rocks by supergene leaching and redeposition. Of the 22 samples containing ≥ 380 ppm Pb, lead isotopic analyses would have reduced the number deserving further attention to 10. Lead isotopic analyses in the early stages of exploration could have assisted in minimizing exploration expenditure at Lady Loretta.     

Sm−Nd and Pb isotopic study of mafic rocks associated with early Proterozoic continental rifting: the Peröpohja schist belt in northern Finland

The Peräpohja schist belt in northern Finland rests unconformably on Archaean granitoids, and marks the early stages of Proterozoic crustal evolution in the Fennoscandian (Baltic) shield. 2440 Ma old layered mafic intrusions predate the supracrustal , and ca. 2200 Ma old sills of the gabbro-wehrlite association intrude the lowest quartzites and volcanics (Runkaus) of the sequence. The Sm-Nd mineral isochron of the Penikat layered intrusion gives an age of 2410±64 Ma. The initial _Nd-values of the Penikat intrusion (_Nd(2440) = –1.6) and the Runkausvaara sill (_Nd(2200) 0) suggest that these mafic magmas were contaminated by older crustal material. The Sm-Nd and Pb isotopic results on the 2.44–2.2 Ga old Runkaus volcanics indicate mobility of Pb, fractionation of Sm/Nd during late greenschist facies metamorphism, and crustal contamination. The Pb-Pb data provide an age of 1972±80 Ma with a high initial ²⁰⁷Pb/²⁰⁴Pb ratio (₁ = 8.49), while scattered Sm-Nd data result in an imprecise age of 2330±180 Ma, with an initial _Nd-value of about zero. Secondary titanite gives an U-Pb age of ca. 2250 Ma. The Jouttiaapa basalts, in contrast, ascended from the mantle without interaction with older crust. These LREE depleted tholeiites mark a break in continental sedimentation, and yield a Sm-Nd age of 2090±70 Ma. Their initial _Nd = + 4.2 ±0.5 implies that the subcontinental early Proterozoic mantle had been depleted in LREE for a long period of time. The first lava flows are strongly depleted in LREE, suggesting that their source was significantly more depleted than the source of mid-ocean ridge basalts today.     

Palaeoecological evidence of changes in vegetation and climate during the Holocene in the pre‐Polar Urals,northeast European Russia

This study investigated Holocene tree‐line history and climatic change in the pre‐Polar Urals, northeast European Russia. A sediment core from Mezhgornoe Lake situated at the present‐day alpine tree‐line was studied for pollen, plant macrofossils, Cladocera and diatoms. A peat section from Vangyr Mire in the nearby mixed mountain taiga zone was analysed for pollen. The results suggest that the study area experienced a climatic optimum in the early Holocene and that summer temperatures were at least 2°C warmer than today. Tree birch immigrated to the Mezhgornoe Lake area at the onset of the Holocene. Mixed spruce forests followed at ca. 9500–9000 ¹⁴C yr BP. Climate was moist and the water level of Mezhgornoe Lake rose rapidly. The hypsithermal phase lasted until ca. 5500–4500 ¹⁴C yr BP, after which the mixed forest withdrew from the Mezhgornoe catchment as a result of the climate cooling. The gradual altitudinal downward shift of vegetation zones resulted in the present situation, with larch forming the tree‐line. Copyright © 2003 John Wiley & Sons, Ltd.     

Mode of occurrence of Cu and Zn in till over three mineralized areas in Finland

The variation of Cu and Zn contents with grain size was studied in the size fractions: 2000-500 μm, 500-64 μm, 64-2 μm and minus 2 μm. The fixation to different minerals was investigated in the 500-64 μm and minus 64 μm fractions with microscope, microprobe, electron microscope and X-ray diffraction after heavy-liquid separation.The distribution of Cu and Zn between the four size fractions is very similar in all target areas. The contents tend to be highest in the minus 2 μm fraction, and to decrease with increasing grain size except for an increase in the coarsest material. This feature is typical in mineralized areas with till having anomalously high Cu and Zn contents.The anomalous Cu and Zn in the till of Talvivaara are mainly fixed to chalcopyrite and sphalerite, respectively, which indicates that the main part of the material originates from fresh bedrock and that postglacial alterations are slight. In the till of Outokumpu and Maaselkä sulphides are rare. We assume that in Outokumpu the reason for this is the postglacial weathering of sulphides and that in Maaselkä a great deal of till derives from highly weathered, sulphide-poor, preglacial regolith. In both target areas Cu in till seems to fix to limonite and also to clay minerals, particularly in Maaselkä. Zinc seems mainly to be hosted by limonite in Outokumpu.     

水库冰气泡含量和密度对探地雷达测厚的影响分析(英文)

在水库现场试验了RIS K2型探地雷达探测水库冰厚度的能力,试验时所用天线频率为600MHz;同步钻孔测量雷达探测处的冰厚度;以及在一个点上取样测试分析冰晶体、冰内气泡和冰密度。试验时冰面积雪厚度0.03-0.05m,冰层上部有0.24m粒状冰,其下均为柱状冰;冰内气泡含量呈表层高底层低分布;冰密度随气泡含量变化;冰厚度在平面内不均一。通过探测厚度和实测厚度的对比分析以及气泡含量对介电系数影响的理论分析,建立了积雪、粒状冰和柱状冰三层介质模型,获取雷达波在冰内的理论传递时间。结果发现:能够利用等效介电常数或等效传播速度评价雷达波传递时间,结冰期冰层1/3深度处的对应介电常数或传递速度可以作为等效值;另外因冰内大气泡造成的理论传递时间大于雷达探测时间,其差值随理论传递时间或冰厚的增加呈非线性增加。