Increased Carbon Sink in Temperate and Boreal Forests   总被引：6，自引：0，他引：6  

Jari Liski  Alexander V. Korotkov  Christopher F. L. Prins  Timo Karjalainen  David G. Victor  Pekka E. Kauppi 《Climatic change》2003,61(1-2):89-99

An intense search is under way to identify the `missing sink' in the world carbon budget of perhaps 2 Pg year^–1 (petagrams, or billiontonnes) of carbon, but its location and mechanism have proved elusive. Here we use a new forest inventory data set to estimate the carbon sink and the carbon pool of woody biomass in 55 countries that account for nearly all temperate or boreal forests and approximately half the world's total forest area. In each country there was a net accumulation of biomass; together, the carbon sink of woody biomass was 0.88 Pg year^–1 during the 1990swith estimated uncertainty from 0.71 to 1.1 Pg year^–1. Thisestimate, already about half of the missing sink, would probably be even larger if carbon accumulation in soil and detritus were also accounted for, but we are unable to quantify that additional sink. The sink is twice that estimated for the woody biomass of these forests a decade ago due to higher estimates for tree growth throughout the region and decreased timber harvests in Russia. In contrast, the new data indicate a carbon pool that is smaller than earlier estimates because of improved data for Russia and Australia.  相似文献   

Footprints and Fetches for Fluxes over Forest Canopies with Varying Structure and Density   总被引：1，自引：1，他引：1  

Tiina Markkanen  Üllar Rannik  Barbara Marcolla  Alessandro Cescatti  Timo Vesala 《Boundary-Layer Meteorology》2003,106(3):437-459

A stochastic trajectory model was used to estimate scalar fluxfootprints in neutral stabilityfor canopies of varying leaf area distributions andleaf area indices. An analytical second-order closure model wasused to predict mean wind speed, second moments and the dissipationrate of turbulent kinetic energy within a forest canopy.The influence of source vertical profile on the flux footprint wasexamined. The fetch is longer for surface sourcesthan for sources at higher levels in the canopy. In order tomeasure all the flux components, and thus the total flux, with adesired accuracy, sources were located at the forest floor in thefootprint function estimation. The footprint functions werecalculated for five observation levels above the canopy top. Itwas found that at low observation heights both canopy density andcanopy structure affect the fetch. The higher abovethe canopy top the flux is measured, the more pronounced is the effectof the canopy structure. The forest fetch for flux measurements isstrongly dependent on the required accuracy: The 90% flux fetchis greater by a factor of two or more compared to the 75% fetch. Theupwind distance contributing 75% of flux is as large as 45 timesthe difference between canopy height and the observation heightabove the canopy top, being even larger for low observationlevels.  相似文献   

Big location‐based social media messages from China's Sina Weibo network: Collection,storage, visualization,and potential ways of analysis          下载免费PDF全文

Michael Jendryke  Timo Balz  Mingsheng Liao 《Transactions in GIS》2017,21(4):825-834

China's social media platform, Sina Weibo, like Twitter, hosts a considerable amount of big data: messages, comments, pictures. Collecting and analyzing information from this treasury of human behavior data is a challenge, although the message exchange on the network is readable by everyone through the web or app interface. The official Application Programming Interface (API) is the gateway to access and download public content from Sina Weibo and is used to collect messages for all mainland China. The nearby_timeline() request is used to harvest only messages with associated location information. This technical note serves as a reference for researchers who do not speak Mandarin but want to collect data from this rich source of information. Ways of data visualization are presented as a point cloud, density per areal unit, or clustered using Density‐Based Spatial Clustering of Applications with Noise (DBSCAN). The relation of messages to census information is also given.  相似文献   

The Seasonal Characteristics of Equatorial Plasma Bubbles in Conjugate Hemispheres During 2015     

Erdinç Timoçin  Temuçin  Hüseyin  İnyurt  Samed 《Geomagnetism and Aeronomy》2022,62(3):309-323

Geomagnetism and Aeronomy - In this paper, using the Total Electron Content (TEC) data obtained from GUAM (13.58° N, 144.86° E) and PNGM (2.04° S, 147.36° E) Global Positioning...  相似文献   

Decreasing nutrient concentrations in soils and trees with increasing elevation across a treeline ecotone in Rolwaling Himal,Nepal   总被引：1，自引：0，他引：1  

Simon Drollinger  Michael Müller  Timo Kobl  Niels Schwab  Jürgen Böhner  Udo Schickhoff  Thomas Scholten 《山地科学学报》2017,14(5):843-858

At a global scale, tree growth in alpine treeline ecotones is limited by low temperatures. At a local scale, however, tree growth at its upper limit depends on multiple interactions of influencing factors and mechanisms. The aim of our research was to understand local scale effects of soil properties and nutrient cycling on tree growth limitation, and their interactions with other abiotic and biotic factors in a near-natural Himalayan treeline ecotone. Soil samples of different soil horizons, litter, decomposition layers, and foliage samples of standing biomass were collected in four altitudinal zones along three slopes, and were analysed for exchangeable cations and nutrient concentrations, respectively. Additionally, soil and air temperature, soil moisture, precipitation, and tree physiognomy patterns were evaluated. Both soil nutrients and foliar macronutrient concentrations of nitrogen (N), magnesium (Mg), potassium (K), and foliar phosphorus (P) decrease significantly with elevation. Foliar manganese (Mn) concentrations, by contrast, are extraordinarily high at high elevation sites. Potential constraining factors on tree growth were identified using multivariate statistical approaches. We propose that tree growth, treeline position and vegetation composition are affected by nutrient limitation, which in turn, is governed by low soil temperatures and influenced by soil moisture conditions.  相似文献   

Moho depth of the European Plate from teleseismic receiver functions     

Marek Grad  Timo Tiira 《Journal of Seismology》2012,16(2):95-105

Crustal structure and the Moho depth are exceptionally well known beneath Europe. The first digital, high-resolution map of the Moho depth for the whole European Plate was compiled in 2007 and recently published in Geophysical Journal International. In the past few years, considerable developments have taken place in the receiver function techniques. Different receiver function techniques provide new, independent information, in particular on the S-wave velocity distribution in the crust and on the Moho depth. This gives an opportunity to compare the Moho depth from the Moho depth map of the European Plate (H _MM) and the Moho depth from receiver function studies (H _RF). Herein, we also compile and analyze the uncertainty of the crustal thickness determinations data obtained with receiver function analysis. The uncertainty is found to be ±2 km for 20-km-thick crust and about ±4 km for 60-km-thick crust. Comparison of the Moho depths shows an approximately linear trend between H _RF and H _MM. For the Moho depth of 30–40 km, the values are approximately equal, while for thin crust, H _RF is about 5 km shallower than H _MM, and for thick crust, it is about 5 km deeper than H _MM. Possible reasons for this, the observed discrepancy between the Moho depths H_MM and H_RF, are discussed.  相似文献   

Epiphytic Diatoms along Environmental Gradients in Western European Shallow Lakes          下载免费PDF全文

Saúl Blanco  Cristina Cejudo‐Figueiras  Irene Álvarez‐Blanco  Ellen van Donk  Elisabeth M. Gross  Lars‐Anders Hansson  Erik Jeppesen  Timo Kairesalo  Brian Moss  Tiina Nõges  Eloy Bécares 《洁净——土壤、空气、水》2014,42(3):229-235

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Extreme Cold Events from East Asia to North America in Winter 2020/21: Comparisons,Causes, and Future Implications     

Xiangdong ZHANG  Yunfei FU  Zhe HAN  James E.OVERLAND  Annette RINKE  Han TANG  Timo VIHMA  Muyin WANG 《大气科学进展》2022,39(4):553-565

Three striking and impactful extreme cold weather events successively occurred across East Asia and North America during the mid-winter of 2020/21.These events open a new window to detect possible underlying physical processes.The analysis here indicates that the occurrences of the three events resulted from integrated effects of a concurrence of anomalous thermal conditions in three oceans and interactive Arctic-lower latitude atmospheric circulation processes,which were linked and influenced by one major sudden stratospheric warming(SSW).The North Atlantic warm blob initiated an increased poleward transient eddy heat flux,reducing the Barents-Kara seas sea ice over a warmed ocean and disrupting the stratospheric polar vortex(SPV)to induce the major SSW.The Rossby wave trains excited by the North Atlantic warm blob and the tropical Pacific La Nina interacted with the Arctic tropospheric circulation anomalies or the tropospheric polar vortex to provide dynamic settings,steering cold polar air outbreaks.The long memory of the retreated sea ice with the underlying warm ocean and the amplified tropospheric blocking highs from the midlatitudes to the Arctic intermittently fueled the increased transient eddy heat flux to sustain the SSW over a long time period.The displaced or split SPV centers associated with the SSW played crucial roles in substantially intensifying the tropospheric circulation anomalies and moving the jet stream to the far south to cause cold air outbreaks to a rarely observed extreme state.The results have significant implications for increasing prediction skill and improving policy decision making to enhance resilience in“One Health,One Future”.  相似文献   

Post-Impulsive-Phase Acceleration in a Wide Range of Solar Longitudes     

Kocharov  Leon  Torsti  Jarmo  Laitinen  Timo  Teittinen  Matti 《Solar physics》1999,190(1-2):295-307

We have analyzed five solar energetic particle (SEP) events observed aboard the SOHO spacecraft during 1996–1997. All events were associated with impulsive soft X-ray flares, Type II radio bursts and coronal mass ejections (CMEs). Most attention is concentrated on the SEP acceleration during the first 100 minutes after the flare impulsive phase, post-impulsive-phase acceleration, being observed in eruptions centered at different solar longitudes. As a representative pattern of a (nearly) well-connected event, we consider the west flare and CME of 9 July 1996 (S10 W30). Similarities and dissimilarities of the post-impulsive-phase acceleration at large heliocentric-angle distance from the eruption center are illustrated with the 24 September 1997 event (S31 E19). We conclude that the proton acceleration at intermediate scales, between flare acceleration and interplanetary CME-driven shock acceleration, significantly contributes to the production of ≳10 MeV protons. This post-impulsive-phase acceleration seems to be caused by the CME lift-off.  相似文献   

Submarine groundwater springs are characterized by distinct fish communities     

Timo Pisternick  Julian Lilkendey  Anishta Audit-Manna  Danishta Dumur Neelayya  Yashvin Neehaul  Nils Moosdorf 《Marine Ecology》2020,41(5):e12610

The inflow of terrestrial groundwater into the ocean is increasingly recognized as an important local source of nutrients and pollutants to coastal ecosystems. Although there is evidence of a link between fresh submarine groundwater discharge (SGD)-derived nutrients and primary producer and primary consumer abundances, the effects of fresh SGD on the productivity of higher trophic levels such as ichthyofaunal communities remain unclear. To further investigate this relationship, we sampled three sites inside a coral reef lagoon in Mauritius: One site entailing six distinct groundwater springs, a site highly influenced by freshwater influx through the springs, and a strictly marine control site. Using remote underwater video surveys, we found that fish abundances were significantly higher at the groundwater springs than at the other two sampling sites.Principal component analyses showed that the springs and the spring-influenced part of the lagoon were best described by elevated water nutrient loadings, whereas the control site was characterized by higher water salinity and pH. Macroalgae cover was highest at the control site and the springs. Herbivores and invertivores dominated the fish community at the springs, in contrast to generalists at the control site. At the spring-influenced site, we mainly encountered high coral/turf algae cover and high abundances of associated fish feeding groups (territorial farmers, corallivores). Our results provide evidence of a fresh SGD-driven relationship between altered hydrography and distinct fish communities with elevated abundances at groundwater springs in a coral reef lagoon. These findings suggest that the management and assessment of secondary consumer productivity in tropical lagoons should take into account the effects of groundwater springs.  相似文献