The evidence of an early stellar encounter in Edgeworth-Kuiper belt

We investigate the influence of a stellar fly-by encounter on the Edgeworth-Kuiper belt objects through numerical orbital calculations, in order to explain both mass depletion and high orbital inclinations of the classical Edgeworth-Kuiper belt (CEKB) objects, which have semimajor axis of 42-48 AU and perihelia beyond 35 AU. The observationally inferred total mass of the CEKB is ∼1/10 Earth masses, which is only ∼0.02 of that extrapolated from the minimum-mass solar nebula model. The CEKB consists of bimodal population: “hot population” with inclinations i?0.2-0.6 radians and “cold population” with i?0.1. The observationally suggested difference in size and color of objects between the two populations may imply different origins of the two populations. We find that both the depletion of solid materials in the CEKB and the formation of the hot population are accounted for by a single close stellar encounter with pericenter distance of 80-100 AU and inclination relative to the initial protoplanetary disk ?50°-70°. Such a stellar encounter highly pumps up eccentricities of most objects in the CEKB and then their perihelia migrate within 35 AU. These objects would be removed by Neptune's perturbations after Neptune is formed at or migrates to the current position (30 AU). Less than 10% of the original objects remain in stable orbits with small eccentricities and perihelion distances larger than 35 AU, in the CEKB, which is consistent with the observation. We find that i of the remaining objects are as large as that of the observed hot population. The only problem is how to stop Neptune's migration at ∼30 AU, which is addressed in a separate paper. The depletion by the stellar encounter extends deeply into ∼30-35 AU, which provides the basis of the formation model for the cold population through Neptune's outward migration by Levison and Morbidelli (2003, Nature, 426, 419-421). The combination of our model with Levison and Morbidelli's model could consistently explain the mass depletion, truncation at 50 AU, bimodal distribution in i, and differences in size and color between the hot and the cold populations in the CEKB.     

Variability in temperature and geometry of the Norwegian Current over the past 600 yr; stable isotope and grain size evidence from the Norwegian margin

Core P1‐003MC was retrieved from 851 m water depth on the southern Norwegian continental margin, close to the boundary between the Norwegian Current (NC) and the underlying cold Norwegian Sea Deep Water. The core chronology was established by using ²¹⁰Pb measurements and ¹⁴C dates, suggesting a sampling resolution of between 2 and 9 yr. Sea‐surface temperature (SST) variations in the NC are reconstructed from stable oxygen isotope measurements in two planktonic Foraminifera species, Neogloboquadrina pachyderma (d.) and Globigerina bulloides. The high temporal resolution of the SST proxy records allows direct comparison with instrumental ocean temperature measurements from Ocean Weather Ship (OWS) Mike in the Norwegian Sea and an air temperature record from the coastal island Ona, western Norway. The comparison of the instrumental and the proxy SST data suggests that N. pachyderma (d.) calcify during summer, whereas G. bulloides calcify during spring. The δ¹⁸O records of both species suggest that the past 70 yr have been the warmest throughout the past 600 yr. The spring and summer proxy temperature data suggest differences in the duration of the cold period of the Little Ice Age. The spring temperature was 1–3°C colder throughout most of the period between ca. AD 1400 and 1700, and the summer temperature was 1–2°C colder throughout most of the period between ca. AD 1400 and 1920. Fluctuations in the depth of the lower boundary of the NC have been investigated by examining grain size data and benthic foraminiferal assemblages. The data show that the transition depth of the lower boundary of the NC was deeper between ca. AD 1400 and 1650 than after ca. AD 1750 until present. Copyright © 2003 John Wiley & Sons, Ltd.     

Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example

Characterizing, understanding and better estimating uncertainties are key concerns for drawing robust conclusions when analyzing changing socio-hydrological systems. Here we suggest developing a perceptual model of uncertainty that is complementary to the perceptual model of the socio-hydrological system and we provide an example application to flood risk change analysis. Such a perceptual model aims to make all relevant uncertainty sources – and different perceptions thereof – explicit in a structured way. It is a first step to assessing uncertainty in system outcomes that can help to prioritize research efforts and to structure dialogue and communication about uncertainty in interdisciplinary work.     

Vertical Hydraulic Gradient Estimation in Clay Till,Using MiHPT Advanced Direct-Push Technology

The vertical transport of contaminants from source areas is employed in many risk assessment models and screening tools in order to estimate the contaminant mass discharge (CMD) into underlying aquifers. The key parameters for estimating CMD are the contaminant source area and concentration, and the vertical water flux, the latter of which depends on the vertical hydraulic conductivity and the vertical hydraulic gradient in the subsurface. This study focuses on advancing the use of the combined membrane interface probe hydraulic profiling tool (MiHPT) to investigate the vertical hydraulic gradient across a clay till overlying a sandy aquifer at a contaminated site in Denmark. Only the HPT is necessary for the estimate of vertical hydraulic gradient. The hydraulic head, clay till thickness, and resulting vertical hydraulic gradients found using the MiHPT compared well with observations from nearby nested wells. The parameter with the largest discrepancy was the thickness of the clay till. The advantage of the MiHPT is its relatively quick depth discrete access to information regarding subsurface permeability, vertical hydraulic gradients and contaminant distribution across a site. In this case study, performance of additional dissipationtests during the HPT log to acquire determination of the vertical hydraulic gradient increased the cost by 3% compared to standard HPT logs.     

Burial stress and elastic strain of carbonate rocks

Burial stress on a sediment or sedimentary rock is relevant for predicting compaction or failure caused by changes in, e.g., pore pressure in the subsurface. For this purpose, the stress is conventionally expressed in terms of its effect: “the effective stress” defined as the consequent elastic strain multiplied by the rock frame modulus. We cannot measure the strain directly in the subsurface, but from the data on bulk density and P‐wave velocity, we can estimate the rock frame modulus and Biot's coefficient and then calculate the “effective vertical stress” as the total vertical stress minus the product of pore pressure and Biot's coefficient. We can now calculate the elastic strain by dividing “effective stress” with the rock frame modulus. By this procedure, the degree of elastic deformation at a given time and depth can be directly expressed. This facilitates the discussion of the deformation mechanisms. The principle is illustrated by comparing carbonate sediments and sedimentary rocks from the North Sea Basin and three oceanic settings: a relatively shallow water setting dominated by coarse carbonate packstones and grainstones and two deep water settings dominated by fine‐grained carbonate mudstones and wackestones.     

Comparison of the Climate during Marine Isotope Stage 9 and 11 Inferred from a Speleothem Isotope Record from Northern Norway

A stalagmite from northern Norway is dated with 12 thermal ionization mass spectrometry U-Th dates, and at least four separate growth periods are identified that correspond with marine isotope stages 9, 11, 13, and probably 15. The calcite is tested for isotopic equilibrium with the Hendy test. Oxygen isotope measurements on 231 subsamples on a vertical transect are used as a paleotemperature proxy. The detailed isotopic record from MIS 9 show apparent similarities to a Holocene record from the same cave, both in the climatic evolution and the overall temperatures: both show temperature oscillations changing from high-frequency, low-amplitude cycles in the beginning of the interglacial period to lower frequency, higher amplitude cycles in the later part of the interglacial period. The isotope record from MIS 11 shows a distinct isotopic event toward heavier values. The isotopic record together with the porous, humus-rich calcite are interpreted as indicating a warmer than present interglacial period with several episodes of heavy rainfall.     

Clustering of galaxies around radio quasars at 0.5≤z≤0.8

We have observed the galaxy environments around a sample of 21 radio-loud, steep-spectrum quasars at 0.5≤ z ≤0.82, spanning several orders of magnitude in radio luminosity. The observations also include background control fields used to obtain the excess number of galaxies in each quasar field. The galaxy excess was quantified using the spatial galaxy–quasar correlation amplitude, B _gq, and an Abell-type measurement, N _0.5. A few quasars are found in relatively rich clusters, but on average, they seem to prefer galaxy groups or clusters of approximately Abell class 0. We have combined our sample with literature samples extending down to z ≈0.2 and covering the same range in radio luminosity. By using the Spearman statistic to disentangle redshift and luminosity dependences, we detect a weak, but significant, positive correlation between the richness of the quasar environment and the radio luminosity of the quasar. However, we do not find any epoch dependence in B _gq, as has previously been reported for radio quasars and galaxies. We discuss the radio luminosity–cluster richness link and possible explanations for the weak correlation that is seen.