Deglaciation and catchment ontogeny in coastal south‐west Greenland: implications for terrestrial and aquatic carbon cycling     

Melanie J. Leng  Bernd Wagner  N. John Anderson  Ole Bennike  Ewan Woodley  Simon J. Kemp 《第四纪科学杂志》2012,27(6):575-584

Here we present Holocene organic carbon, nitrogen, sulphur, carbon isotope ratio and macrofossil data from a small freshwater lake near Sisimiut in south‐west Greenland. The lake was formed c. 11 cal ka BP following retreat of the ice sheet margin and is located above the marine limit in this area. The elemental and isotope data suggest a complex deglaciation history of interactions between the lake and its catchment, reflecting glacial retreat and post‐glacial hydrological flushing probably due to periodic melting of local remnant glacial ice and firn areas between 11 and 8.5 cal ka BP. After 8.5 cal ka BP, soil development and associated vegetation processes began to exert a greater control on terrestrial–aquatic carbon cycling. By 5.5 cal ka BP, in the early Neoglacial cooling, the sediment record indicates a change in catchment–lake interactions with consistent δ¹³C while C/N exhibits greater variability. The period after 5.5 cal ka BP is also characterized by higher organic C accumulation in the lake. These changes (total organic carbon, C/N, δ¹³C) are most likely the result of increasing contribution (and burial) of terrestrial organic matter as a result of enhanced soil instability, as indicated by an increase in Cenococcum remains, but also Sphagnum and Empetrum. The impact of glacial retreat and relatively subdued mid‐ to late Holocene climate variation at the coast is in marked contrast to the greater environmental variability seen in inland lakes closer to the present‐day ice sheet margin. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Patterns of Cenozoic sediment flux from western Scandinavia     

Bartosz Gołędowski  Søren B. Nielsen  Ole R. Clausen 《Basin Research》2012,24(4):377-400

The significance of variations in the sediment flux from western Scandinavia during the Cenozoic has been a matter of debate for decades. Here we compile the sediment flux using seismic data, boreholes and results from other publications and discuss the relative importance of causal agents such as tectonism, climate and climate change. Western Scandinavia, the northern British Isles and the Faeroe‐Shetland Platform were significant sediment sources during the Paleocene, which is well founded in tectonic causes related to the opening of the North Atlantic. From the Eocene and onward, variations in the sediment flux from western Scandinavia correlate better with climate and climate change. During the Eocene, sediment production was low. From the late Eocene onward, increased seasonality may have contributed to stimulating the sediment flux. Significant climatic cooling episodes correlate with Oligocene deposits in the North Sea, the post‐mid‐Miocene Molo and Kai Formations of the Norwegian Shelf, the southern North Sea delta system and large volumes of the Late Pliocene‐Holocene Naust Formation. The sediment flux from Scandinavia during the Cenozoic is in general agreement with the detrital flux to the world's oceans. Furthermore, the large variations in the size of sediment catchment areas as well as the possibility of submarine and glacial erosion must be incorporated to understand regional variations in climate driven sediment flux.  相似文献   

IAG Newsletter     

Ole Baltazar Andersen 《Journal of Geodesy》2001,75(9-10):553-555

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Refraction studies in the North American Levelling Datum NAVD 88     

Ole Remmer 《Journal of Geodesy》1994,69(1):21-25

Despite the noisy character of the data in the new North American levelling net (Zilkoski et al. 1989) it is quite easy to see the refraction corrections mirrored in the polygon closing errors if one takes only those polygons with sufficiently high refraction corrections. The following table illustrates this point. In the table the first column denotes the limit of the accumulated refraction corrections (found from temperature measurements) along a polygon, that is only polygons where the refraction correction exceeds this limit participate in the analysis. The second column is the estimate of the correlation coefficient between refraction corrections and the closing errors of the polygons while the third column is the significance level in the conventional student-test of whetherr is different from zero.  相似文献   

Radiative heat transfer in lithospheric geodynamics: implications for asthenospheric partial melting and basin modelling concepts     

Ole Valdemar Vejbk 《Tectonophysics》1994,240(1-4):115-131

In geodynamic models describing basin formation by stretching, the base of the lithosphere is commonly defined by a fixed temperature. An alternative definition is proposed where the base of the lithosphere is determined by the solidus of mantle rocks. Some consequences of this definition are illustrated in a one-dimensional model. The model applies the finite-difference method and approximates the temperature regime in the upper 400 km of the Earth. The model uses temperature-dependent thermal conductivity and includes effects from heat storage by partial melting in the mantle low-velocity layer (MLV). Radiative heat transfer contributes significantly at elevated temperatures giving rise to a steepening of the thermal gradient below the lithosphere. This change in gradient allows the perturbed geotherm to exceed the mantle solidus in a limited depth interval, which accounts for the MLV, and thus defines the base of the lithosphere.

In the model, variations in thickness of, and degree of partial melting in the MLV, results from thinning of the overlying lithospheric plate. Thus, the thickness of the MLV is roughly inversely proportional to the thickness of the lithosphere, whereas the base of the MLV is almost flat.

Temperature-dependent variations in the carrying capacity of the MLV, where the main isostatic compensation occurs, is proposed as an epeirogenetic agent. This effect may be significant, and is expressed as an enhancement of the initial subsidence if no preexisting MLV is available. A secondary effect occurs as solidification of the MLV ceases a long time (˜ 300 Ma) after stretching, and causes slow uplift.  相似文献   

Statistical estimation of the relative efficiency of natural attenuation mechanisms in contaminated aquifers     

Ole F.?ChristensenEmail author  G.?Cassiani  P. J.?Diggle  P. Ribeiro?Jr  G.?Andreotti 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(5):339-350

Using monitored natural attenuation is an increasingly popular strategy for dealing with contaminated aquifers. This paper provides a statistical methodology for the estimation of the relative efficiency of natural attenuation mechanisms. The methodology provides estimates, with associated measures of uncertainty, of the relative efficiency of four types of bio-degradation (oxidation using oxygen as the electron-acceptor, denitrification, iron reduction and sulfate reduction). A data set from Trecate, Italy, is analysed using the methodology. The analysis shows that sulfate is the main cause of hydrocarbon removal on this site. It is also seen that oxidation using oxygen seems to be more preferential than the other reactions, in the sense that this reaction is relatively more efficient than other reactions at locations where the hydrocarbon concentration is low.  相似文献   

Determining extreme parameter correlation in ground water models   总被引：4，自引：0，他引：4  

Hill MC  Osterby O 《Ground water》2003,41(4):420-430

In ground water flow system models with hydraulic-head observations but without significant imposed or observed flows, extreme parameter correlation generally exists. As a result, hydraulic conductivity and recharge parameters cannot be uniquely estimated. In complicated problems, such correlation can go undetected even by experienced modelers. Extreme parameter correlation can be detected using parameter correlation coefficients, but their utility depends on the presence of sufficient, but not excessive, numerical imprecision of the sensitivities, such as round-off error. This work investigates the information that can be obtained from parameter correlation coefficients in the presence of different levels of numerical imprecision, and compares it to the information provided by an alternative method called the singular value decomposition (SVD). Results suggest that (1) calculated correlation coefficients with absolute values that round to 1.00 were good indicators of extreme parameter correlation, but smaller values were not necessarily good indicators of lack of correlation and resulting unique parameter estimates; (2) the SVD may be more difficult to interpret than parameter correlation coefficients, but it required sensitivities that were one to two significant digits less accurate than those that required using parameter correlation coefficients; and (3) both the SVD and parameter correlation coefficients identified extremely correlated parameters better when the parameters were more equally sensitive. When the statistical measures fail, parameter correlation can be identified only by the tedious process of executing regression using different sets of starting values, or, in some circumstances, through graphs of the objective function.  相似文献   

Late Glacial and Holocene Palaeoenvironmental Changes in the Rostov-Yaroslavl’ Area, West Central Russia     

Barbara Wohlfarth  Pavel Tarasov  Ole Bennike  Terri Lacourse  Dmitry Subetto  Peter Torssander  Fedor Romanenko 《Journal of Paleolimnology》2006,35(3):543-569

Three lake sediment sequences (lakes Nero, Chashnitsy, Zaozer’e) from the Rostov-Jaroslavl’ region north of Moscow were studied to provide information on palaeoclimatic and palaeoenvironmental changes during the past 15,000 cal yr. The multi-proxy study (i.e., pollen, macrofossils, mineral magnetic measurements, total carbon, nitrogen and sulphur) is chronologically constrained by AMS ¹⁴C measurements. Lake Nero provided the longest sedimentary record back to ca. 15,000 cal yr BP, while sediment accumulation began around ca. 11,000 cal yr BP in the two other lakes, possibly due to melting of permafrost. Limnic plant macrofossil remains suggest increased lake productivity and higher mean summer temperatures after 14,500 cal yr BP. While the late glacial vegetation was dominated by Betula and Salix shrubs and various herbs, it appears that Betula sect. Albae became established as early as 14,000 cal yr BP. Major hydrological changes in the region led to distinctly lower lake levels, starting 13,000 cal yr BP in Lake Nero and ca. 9000 cal yr BP in lakes Chashnitsy and Zaozer’e, which are situated at higher elevations. These changes resulted in sedimentary hiatuses in all three lakes that lasted 3500–4500 cal yr. Mixed broad-leaved – coniferous forests were widespread in the area between 8200 and 6100 cal yr BP and developed into dense, species-rich forests between 6100 and 2500 cal yr BP, during what was likely the warmest interval of the studied sequences. Agricultural activity is documented since 500 cal yr BP, but probably began earlier, since Rostov was a major capital by 862 A.D. This apparent gap may be caused by additional sedimentary hiatuses around 2500 and 500 cal yr BP.  相似文献   

IAG Newsletter     

Ole Baltazar Andersen 《Journal of Geodesy》1998,72(3):179-187

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IAG Newsletter     

Ole Baltazar Andersen 《Journal of Geodesy》1997,71(10):660-671

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