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601.
Jürgen Titschack Daniel Baum Ricardo De Pol‐Holz Matthias López Correa Nina Forster Sascha Flögel Dierk Hebbeln André Freiwald 《Sedimentology》2015,62(7):1873-1898
Cold‐water coral ecosystems present common carbonate factories along the Atlantic continental margins, where they can form large reef structures. There is increasing knowledge on their ecology, molecular genetics, environmental controls and threats available. However, information on their carbo‐nate production and accumulation is still very limited, even though this information is essential for their evaluation as carbonate sinks. The aim of this study is to provide high‐resolution reef aggradation and carbonate accumulation rates for Norwegian cold‐water coral reefs from various settings (sunds, inner shelf and shelf margin). Furthermore, it introduces a new approach for the evaluation of the cold‐water coral preservation within cold‐water coral deposits by computed tomography analysis. This approach allows the differentiation of various kinds of cold‐water coral deposits by their macrofossil clast size and orientation signature. The obtained results suggest that preservation of cold‐water coral frameworks in living position is favoured by high reef aggradation rates, while preservation of coral rubble prevails by moderate aggradation rates. A high degree of macrofossil fragmentation indicates condensed intervals or unconformities. The observed aggradation rates with up to 1500 cm kyr?1 exhibit the highest rates from cold‐water coral reefs so far. Reef aggradation within the studied cores was restricted to the Early and Late Holocene. Available datings of Norwegian cold‐water corals support this age pattern for other fjords while, on the shelf, cold‐water coral ages are reported additionally from the early Middle Holocene. The obtained mean carbonate accumulation rates of up to 103 g cm?2 kyr?1 exceed previous estimates of cold‐water coral reefs by a factor of two to three and by almost one order of magnitude to adjacent sedimentary environments (shelf, slope and deep sea). Only fjord basins locally exhibit carbonate accumulation rates in the range of the cold‐water coral reefs. Furthermore, cold‐water coral reef carbonate accumulation rates are in the range of tropical reef carbonate accumulation rates. These results clearly suggest the importance of cold‐water coral reefs as local, maybe regional to global, carbonate sinks. 相似文献
602.
Regional- and district-level drivers of timber harvesting in European Russia after the collapse of the Soviet Union 总被引:1,自引:0,他引:1
Kelly J. Wendland David J. Lewis Jennifer Alix-Garcia Mutlu Ozdogan Matthias Baumann Volker C. Radeloff 《Global Environmental Change》2011,21(4):1290-1300
After the collapse of the Soviet Union, the forestry sector in Russia underwent substantial changes: the state forestry sector was decentralized, the timber industry was privatized, and timber use rights were allocated through short- and long-term leases. To date, there has been no quantitative assessment of the drivers of timber harvesting in European Russia following these changes. In this paper we estimate an econometric model of timber harvesting using remote sensing estimations of forest disturbance from 1990–2000 to 2000–2005 as our dependent variable. We aggregate forest disturbance to administrative districts – equivalent to counties in the United States – and test the impact of several biophysical and economic factors on timber harvesting. Additionally, we examine the impact that regions – equivalent to states in the United States and the main level of decentralized governance in Russia – have on timber harvesting by estimating the influence of regional-level effects on forest disturbance in our econometric model. Russian regions diverged considerably in political and economic conditions after the collapse of the Soviet Union, and the question is if these variations impacted timber harvesting after controlling for district-level biophysical and economic drivers. We find that the most important drivers of timber harvesting at the district level are road density, the percent of evergreen forest, and the total area of forest. The influence of these variables on timber harvesting changed over time and there was more harvesting closer to urban areas in 2000–2005. Even though district-level variables explain more than 70 percent of the variation in forest disturbance in our econometric model, we find that regional-level effects remain statistically significant. While we cannot identify the exact mechanism through which regional-level effects impact timber harvesting, our results suggest that sub-national differences can have a large and statistically significant impact on land-use outcomes and should be considered in policy design and evaluation. 相似文献
603.
An Attempt to Close the Daytime Surface Energy Balance Using Spatially-Averaged Flux Measurements 总被引:1,自引:0,他引:1
Matthias Mauder Raymond L. Desjardins Elizabeth Pattey Devon Worth 《Boundary-Layer Meteorology》2010,136(2):175-191
Single-tower eddy-covariance measurements represent the complete surface flux of a scalar only under idealized conditions.
Therefore, we often find an underestimation of energy fluxes expressed as a lack of energy balance closure at many sites.
In this study, a multi-tower approach to measure atmospheric energy fluxes based on spatial averaging is evaluated and possible
mechanisms causing a lack of energy balance closure are analysed, focussing on daytime data only. It is shown that the multi-tower
technique is also unable to measure the entire flux for our site, likely because the assumption of horizontal homogeneity
is violated. Heterogeneity-induced and buoyancy-driven quasi-stationary circulations are probably the dominant processes causing
the underestimation of energy fluxes. A dependence of the energy balance residual on stability is found, with residuals close
to zero for stable stratification, a maximum under unstable to near-neutral conditions and still relatively large residuals
for stronger instability. Assuming the processes transporting energy and CO2 are similar, the implications on long-term CO2 flux measurements are analysed. Accordingly, the resulting selective systematic error of cumulative net ecosystem exchange
estimates for agricultural regions such as ours can be of the order of more than 100%, since mainly the fluxes during periods
of net CO2 uptake are underestimated while periods of net CO2 release are much less affected by this bias. Further investigations about this issue are highly warranted. 相似文献
604.
Extension of the Averaging Time in Eddy-Covariance Measurements and Its Effect on the Energy Balance Closure 总被引:1,自引:0,他引:1
Doojdao Charuchittipan Wolfgang Babel Matthias Mauder Jens-Peter Leps Thomas Foken 《Boundary-Layer Meteorology》2014,152(3):303-327
The modified ogive analysis and the block ensemble average were employed to investigate the impact of the averaging time extension on the energy balance closure over six land-use types. The modified ogive analysis, which requires a steady-state condition, can extend the averaging time up to a few hours and suggests that an averaging time of 30 min is still overall sufficient for eddy-covariance measurements over low vegetation. The block ensemble average, which does not require a steady-state condition, can extend the averaging time to several days. However, it can improve the energy balance closure for some sites during specific periods, when secondary circulations exist in the vicinity of the sensor. These near-surface secondary circulations mainly transport sensible heat, and when near-ground warm air is transported upward, the sensible heat flux observed by the block ensemble average will increase at longer averaging times. These findings suggest an alternative energy balance correction for a ground-based eddy-covariance measurement, in which the attribution of the residual depends on the ratio of sensible heat flux to the buoyancy flux. The fraction of the residual attributed to the sensible heat flux by this energy balance correction is larger than in the energy balance correction that preserves the Bowen ratio. 相似文献
605.
Matthias Kuhle 《第四纪研究》1992,12(2):166-166
十次考察任务期间,我们获得了西藏及其周围山地冰川最大规模的新资料。在喜马拉雅山和喀喇昆仑山南侧低至890m和980m的海拔高度上发现冰碛物。在青藏高原北坡的祁连山,冰碛物发现于2300m的海拔高度。在喀喇昆仑山、Aghil和昆仑山北坡,冰碛物也低达1900m。对冰漂砾的放射性分析表明,青藏高原南部和中部古冰体厚度至 相似文献