On the Elimination of Bias Averaging-Errors in Proxy Records   总被引：2，自引：2，他引：0  

Veerle Beelaerts  Fjo De Ridder  Nele Schmitz  Maite Bauwens  Frank Dehairs  Johan Schoukens  Rik Pintelon 《Mathematical Geosciences》2009,41(2):129-144

Knowledge of and insight into past environmental conditions can be obtained by processing and analyzing proxies. The proxies need to be processed as precisely and accurately as possible, otherwise the conclusion of the analysis will be biased. A calibration method which reduces bias errors in the proxy measurements due to averaging is presented. Sampling with nonzero sample sizes causes an averaging of the true proxy signal over the volume of the sample. The method is applied on a linear synthetic record which results in an optimal correction for frequency components ranging from the dc-frequency (DC) to one half of the sample frequency (f _s /2). Next, the method is tested on non-linear synthetic data where the signal is reconstructed reasonably well. Finally, the method is applied to a real vessel density record of R. mucronata from Makongeni, Kenya, and to a real delta deuterium record of ice core EDC from dome C, Antarctica. The method discussed in this paper is a valuable tool for the calibration of proxy measurements; it can be applied as a correction for low resolution measurements and expanded to other types of samples and proxies. Working with small sample sizes (high resolution) amounts to working near the detection limit, where the signal-to-noise-ratio is low. This correction method provides an alternative in which low resolution measurements can be upgraded to minimize the loss of information due to larger sample sizes.  相似文献   

Personal experiences with the governance of the policy-relevant IPCC and Millennium Ecosystem Assessments     

Rik Leemans   《Global Environmental Change》2008,18(1):12-17

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A spatially explicit scenario-driven model of adaptive capacity to global change in Europe   总被引：1，自引：0，他引：1  

Lilibeth Acosta  Richard J.T. Klein  Pytrik Reidsma  Marc J. Metzger  Mark D.A. Rounsevell  Rik Leemans  Dagmar Schröter 《Global Environmental Change》2013,23(5):1211-1224

Traditional impact models combine exposure in the form of scenarios and sensitivity in the form of parameters, providing potential impacts of global change as model outputs. However, adaptive capacity is rarely addressed in these models. This paper presents the first spatially explicit scenario-driven model of adaptive capacity, which can be combined with impact models to support quantitative vulnerability assessment. The adaptive capacity model is based on twelve socio-economic indicators, each of which is projected into the future using four global environmental change scenarios, and then aggregated into an adaptive capacity index in a stepwise approach using fuzzy set theory. The adaptive capacity model provides insight into broad patterns of adaptive capacity across Europe, the relative importance of the various determinants of adaptive capacity, and how adaptive capacity changes over time under different social and economic assumptions. As such it provides a context for the implementation of specific adaptation measures. This could improve integrated assessment models and could be extended to other regions. However, there is a clear need for a better theoretical understanding of the adaptive capacity concept, and its relationship to the actual implementation of adaptation measures. This requires more empirical research and coordinated meta-analyses across regions and economic sectors, and the development of bottom-up modelling techniques that can incorporate human decision making.  相似文献   

Global models meet global policy: How can global and regional modellers connect with environmental policy makers? What has hindered them? What has helped?     

Joseph Alcamo  Eric Kreileman  Rik Leemans 《Global Environmental Change》1996,6(4):255-259

Global modelling has developed over the last two decades largely because of the needs of policymaking, yet it has not yet realized its full potential in assisting policymaking. While the first wave of global models in the 1970s had a clear influence on policy discourse, these models were eventually undermined by attacks on their scientific underpinning. The second wave of global models in the 1990s had a stronger scientific footing than the first wave because they were built on a much larger base of knowledge about the global system. Although the improved scientific credibility of global models has increased their use in policymaking, a more subtle yet important factor has been the direct contact of global model developers with policymakers. Taking an example from the field of climate policy, a global modelling team has conducted formal workshops with a group of international climate policymakers with the aim to increase the relevance of modeling activities to policy issues. This interaction has inspired policyrelevant uses of a global model (IMAGE 2) and spawned the development of a new policy concept ‘Safe Emission Corridors’, which has been discussed in the frame of international climate negotiations. A preliminary conclusion is that both improved scientific credibility and improved interaction between modelers and policymakers are critical ingredients for enhancing the policy-relevance of global models.  相似文献   

Variability of C02 distributions and sea-air fluxes in the central and eastern equatorial Pacific during the 199–1994 El Nin˜o     

Richard A. Feely  Rik Wanninkhof  Catherine Goyet  David E. Archer  Taro Takahashi 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

As part of the U.S. JGOFS Program and the NOAA Ocean-Atmosphere Carbon Exchange Study (DACES), measurements of C02 partial pressure were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992, the spring of 1993, and the spring and autumn of 1994. Surface-water pC0₂ data indicate significant diurnal, seasonal, and interannual variations. The largest variations were associated with the 1991–1994 ENSO event, which reached maximum intensity in the spring of 1992. The lower values of surface-water ΔpC0₂ observed during the 1991–1994 ENSO period were the result of the combined effects of both remotely and locally forced physical processes. The warm pool, which reached a maximum eastward extent in January-February of 1992, began in September of 1991 as a series of westerly wind events lasting about 30 days. Each wind event initiated an eastward propagating Kelvin wave which caused a deepening of the thermocline. By the end of January 1992 the thermocline was at its maximum depth, so that the upwelled water was warm and C0₂-depleted. In April of the same year, the local winds were weaker than normal, and the upwelling was from shallow depths. These changes resulted in a lower-than-normal C02 flux to the atmosphere. The results show that for the one-year period from the fall of 1991 until the fall of 1992, approximately 0.3 GtC were released to the atmosphere; 0.6 GtC were released in 1993, and 0.7 GtC in 1994, in good agreement with the model results of Ciais et al. [Science,269,1098–1102;J. Geophys. Res.,100, 5051–5070]. The net reduction of the ocean-atmosphere C02 flux during the 1991–1994 El Nifio was on the order of 0.8 – 1.2 GtC. Thus, the total amount of C02 sequestered in the equatorial oceans during the prolonged 1991–1994 El Nin˜o period was about 25% higher than the severe El Nin˜o of 1982–1983.  相似文献   

Characterisation of ground motion recording stations in the Groningen gas field     

Rik Noorlandt  Pauline P. Kruiver  Marco P. E. de Kleine  Marios Karaoulis  Ger de Lange  Antonio Di Matteo  Julius von Ketelhodt  Elmer Ruigrok  Benjamin Edwards  Adrian Rodriguez-Marek  Julian J. Bommer  Jan van Elk  Dirk Doornhof 《Journal of Seismology》2018,22(3):605-623

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity (V_S). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ V_S values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed V_S profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent V_S information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative V_S profiles at the accelerograph station sites. The measured V_S profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the V_S profile and the observed amplification from vertical array stations is also excellent.  相似文献   

Sensitivity of terrestrial carbon storage to CO2-induced climate change: Comparison of four scenarios based on general circulation models   总被引：3，自引：0，他引：3  

Thomas M. Smith  Rik Leemans  Herman H. Shugart 《Climatic change》1992,21(4):367-384

The potential impacts of CO₂-induced climate change on terrestrial carbon storage was estimated using the Holdridge Life-Zone Classification and four climate change scenarios derived from general circulation models. Carbon values were assigned to life-zones and their associated soils from published studies. All four scenarios suggest an increase in area occupied by forests although details of predicted patterns vary among the scenarios. There is a poleward shift of the forested zones, with an increase in the areal extent of tropical forests and a shift of the boreal forest zone into the region currently occupied by tundra. Terrestrial carbon storage increased from 0.4% (8.5 Gt) to 9.5% (180.5 Gt) above estimates for present conditions. These changes represent a potential reduction of 4 to 85 ppm on elevated atmospheric CO₂ levels.  相似文献   

Comparison of ecosystem services provided by grasslands with different utilization patterns in China’s Inner Mongolia Autonomous Region   总被引：1，自引：0，他引：1  

Bingzhen Du  Lin Zhen  Yunfeng Hu  Huimin Yan  Rudolf De Groot  Rik Leemans 《地理学报(英文版)》2018,28(10):1399-1414

Although several previous studies in Inner Mongolia examined the effects of ecological conservation on the delivery of ecosystem services, they were often limited in scope (few ecosystem services were assessed) and often suffered from confounding by spatial variation. In this study, we examined the impact of conservation measures (changes in grassland utilization patterns) on the provision of selected ecosystem services in three types of grasslands (meadow steppe in Hulun Buir, typical steppe in Xilin Gol, and semi-desert steppe in Ordos) in Inner Mongolia. We examined five utilization patterns: no use (natural grasslands), light use, moderate use, intensive use, and recovery sites (degraded sites protected from further use). Through household surveys and vegetation and soil surveys, we measured the differences in ecosystem services among the different grassland utilization patterns. We also identified spatial factors that confounded the quantification of ecosystem services in different types of grasslands. We found that light use generally provided high levels of ecosystem services in meadow steppe and typical steppe, with the main differences in the supporting ecosystem services. Surprisingly, we found no consistently positive impacts of strict conservation activities across the sites, since the results varied spatially and with respect to differences in the land-use patterns. Our study suggests that appropriate grassland utilization patterns can enhance the supply of ecosystem services and reduce negative effects on both household livelihoods and the environment.  相似文献   

软性海洋沉积物中水含量对XRF测试的影响     

Rik Tjallingii  Ursula R 《海洋地质前沿》2008,24(3):24-26

Avaatech型X荧光扫描仪是由计算机控制的柱状样扫描装置，可以从剖开样品表面直接获得沉积物的化学组成，无需破坏样品的整体性。能够实现几乎连续的测试，快速地得到从Al到u的所有元素的相对含量。XRF扫描仪已经成功地应用于高分辨率、不同时间序列和时间尺度的地层对比以及沉积相和古气候重建。  相似文献   

Increase in anthropogenic CO2 in the Atlantic Ocean in the last two decades     

Tsung-Hung Peng  Rik Wanninkhof 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(6):755-770

Data from the first systematic survey of inorganic carbon parameters on a global scale, the GEOSECS program, are compared with those collected during WOCE/JGOFS to study the changes in carbon and other geochemical properties, and anthropogenic CO₂ increase in the Atlantic Ocean from the 1970s to the early 1990s. This first data-based estimate of CO₂ increase over this period was accomplished by adjusting the GEOSECS data set to be consistent with recent high-quality carbon data. Multiple Linear Regression (MLR) and extended Multiple Linear Regression (eMLR) analyses to these carbon data are applied by regressing DIC with potential temperature, salinity, AOU, silica, and PO₄ in three latitudinal regions for the western and eastern basins in the Atlantic Ocean. The results from MLR (and eMLR provided in parentheses) indicate that the mean anthropogenic CO₂ uptake rate in the western basin is 0.70 (0.53) mol m^?2 yr^?1 for the region north of 15°N; 0.53 (0.36) mol m^?2 yr^?1 for the equatorial region between 15°N and 15°S; and 0.83 (0.35) mol m^?2 yr^?1 in the South Atlantic south of 15°S. For the eastern basin an estimate of 0.57 (0.45) mol m^?2 yr^?1 is obtained for the equatorial region, and 0.28 (0.34) mol m^?2 yr^?1 for the South Atlantic south of 15°S. The results of using eMLR are systematically lower than those from MLR method in the western basin. The anthropogenic CO₂ increase is also estimated in the upper thermocline from salinity normalized DIC after correction for AOU along the isopycnal surfaces. For these depths the results are consistent with the CO₂ uptake rates derived from both MLR and eMLR methods.  相似文献