Baja California 边缘PC14 岩芯海水表层温度及生产力变化的百年尺度记录

加利福尼亚流是北太平洋环流的重要组成部分,它的变化对全球气候及碳循环有重要影响.对位于东北太平洋低纬区BajaCalifornia外海的PC14柱状样进行了有机地球化学分析,重建了过去14ka来这一地区百年尺度的海水表面温度及生产力变化,发现其存在明显的B/A(Bling-Aller)和YD(Younger Drays)事件,但B/A和YD事件温度变化幅度小于中纬度地区.与中纬度加利福尼亚流系早中全新世温度降低不同,PC14全新世温度无明显变化趋势.这些结果表明了东太平洋低纬地区对高纬地区的气候响应以及沿岸上升流和ENSO现象对加利福尼亚流系中纬和低纬地区的影响不同.从冰消期到全新世,PC14生产力呈现阶段上升趋势,指示了由E1 Nino气候向La Nifia气候的转化以及沿岸上升流加强的总体趋势.在全新世中后期(6.5-3.8ka)生产力的降低,则可能是受ENSO加强的影响.在B/A暖期,PC14生产力增加不多,但氧最小层强度增加,这表明生产力变化不是东太平洋边缘海的氧最小层强化的控制因素.     

15,000-yr pollen record of vegetation change in the high altitude tropical Andes at Laguna Verde Alta, Venezuela

Pollen analysis of sediments from a high-altitude (4215 m), Neotropical (9°N) Andean lake was conducted in order to reconstruct local and regional vegetation dynamics since deglaciation. Although deglaciation commenced 15,500 cal yr B.P., the area around the Laguna Verde Alta (LVA) remained a periglacial desert, practically unvegetated, until about 11,000 cal yr B.P. At this time, a lycopod assemblage bearing no modern analog colonized the superpáramo. Although this community persisted until 6000 cal yr B.P., it began to decline somewhat earlier, in synchrony with cooling following the Holocene thermal maximum of the Northern Hemisphere. At this time, the pioneer assemblage was replaced by a low-diversity superpáramo community that became established 9000 cal yr B.P. This replacement coincides with regional declines in temperature and/or available moisture. Modern, more diverse superpáramo assemblages were not established until 4600 cal yr B.P., and were accompanied by a dramatic decline in Alnus, probably the result of factors associated with climate, humans, or both. Pollen influx from upper Andean forests is remarkably higher than expected during the Late Glacial and early to middle Holocene, especially between 14,000 and 12,600 cal yr B.P., when unparalleled high values are recorded. We propose that intensification of upslope orographic winds transported lower elevation forest pollen to the superpáramo, causing the apparent increase in tree pollen at high altitude. The association between increased forest pollen and summer insolation at this time suggests a causal link; however, further work is needed to clarify this relationship.     

The importance of interactions for mass loss from satellite galaxies in cold dark matter haloes

We investigate the importance of interactions between dark matter substructures for the mass loss they suffer whilst orbiting within a sample of high-resolution galaxy cluster mass cold dark matter (CDM) haloes formed in cosmological N -body simulations. We have defined a quantitative measure that gauges the degree to which interactions are responsible for mass loss from substructures. This measure indicates that interactions are more prominent in younger systems when compared to older more relaxed systems. We show that this is due to the increased number of encounters a satellite experiences and a higher mass fraction in satellites. This is in spite of the uniformity in the distributions of relative distances and velocities of encounters between substructures within the different host systems in our sample.
Using a simple model to relate the net force felt by a single satellite to the mass loss it suffers, we show that interactions with other satellites account for ∼30 per cent of the total mass loss experienced over its lifetime. The relation between the age of the host and the importance of interactions increases the scatter about this mean value from ∼25 per cent for the oldest to ∼45 per cent for the youngest system we have studied. We conclude that satellite interactions play a vital role in the evolution of substructure in dark matter haloes and that a significant fraction of the tidally stripped material can be attributed to these interactions.     

Anthropogenic nitrogen deposition induces rapid ecological changes in alpine lakes of the Colorado Front Range (USA)

Recent sediments from two alpine lakes (> 3300 m asl) in the Colorado Front Range (USA) register marked and near-synchronous changes that are believed to represent ecological responses to enhanced atmospheric deposition of fixed nitrogen from anthropogenic sources. Directional shifts in sediment proxies include greater representations of mesotrophic diatoms and increasingly depleted ¹⁵N values. These trends are particularly pronounced since ~ 1950, and appear to chronicle lake responses to excess N derived from agricultural and industrial sources to the east. The rate and magnitude of recent ecological changes far exceed the context of natural variability, as inferred from comparative analyses of a long core capturingthe entire 14,000-year postglacial history of one of the lakes. Nitrogen deposition to these seemingly pristine natural areas has resulted in subtle but detectable limnological changes that likely represent the beginning of a stronger response to nitrogen enrichment.     

Optimized NMR spectroscopic strategy to characterize water dynamics in soil samples

¹H wideline NMR spectra of soil samples offer the possibility to analyze soil material based on their proton mobility. Care has to be taken to remove unwanted signal contributions from the probe background. We demonstrate that unstructured wideline spectra can be analyzed quantitatively by a combination of a Gaussian line for rigid and a Lorentzian line for mobile protons. This is used to study effects of hydrogen-bonded water networks upon heat treatment for a series of different soil samples with varying water content as a contribution to study physical aging of soil organic matter (SOM). Results are combined with ¹H projections from ¹³C 2D WISE (wideline separation) experiments representing solely the broad Gaussian line. Furthermore, for the first time applied to soils, ¹H structural information from soil samples is obtained from 2D PMLG phase modulated Lee-Goldburg measurements under magic angle spinning (MAS). Low water contents improve the resolution of main functional groups significantly.     

Constructing the Coronal Magnetic Field By Correlating Parameterized Magnetic Field Lines With Observed Coronal Plasma Structures

A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (i) the normal component of the photospheric field remains unchanged, (ii) the field is given in the entire corona over an active region, (iii) the field remains divergence-free, and (iv) electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10^–5.5 g cm s^–2 resulting from an electric current density of 0.079 A m^–2. Calculations show that the plasma beta becomes larger than unity at a relatively low height of 0.25 r supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients to maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.