Direct solar and earth-albedo radiation pressure effects on the orbit of Pageos 1

The orbit of the Pageos 1 balloon satellite has been investigated in detail over the early part of the balloon's lifetime. The analysis herein focuses on how Pageos's orbit was affected by direct solar and albedo radiation pressure. Near the end of the second year of the satellite's lifetime, anomalous behavior was found in the orbital acceleration. This behavior may be the result of a change in the shape of the satellite: Pageos's original spherical shape had become slightly oblate, spinning about a minor axis and precessing about the direction to the sun. In fact, we have been able to represent this effect quite well by accounting for a small component of force in the plane perpendicular to the sun and allowing this component to rotate about the solar direction. By analyzing the balloon-inflation process, attained with sublimating compounds, and the consequent variation of the satellite's mass due to leakage through the holes caused by micrometeoroid bombardment, we have evaluated the near-earth micrometeoroid-particle flux, which turns out to be 5×10^–8 cm^–2 sec^–1. With the assumptions we made for the satellite's area-to-mass ratio and reflection coefficient, we would need a solar constant of 1.95 cal cm^–2 min^–1 to give a best-fit to our data.     

Magnetotactic bacteria from the human gut microbiome associated with orientation and navigation regions of the brain

Journal of Oceanology and Limnology - Magnetotactic bacteria (MTB), ubiquitous in soil and fresh and saltwater sources have been identified in the microbiome of humans and many animals. MTB...     

Particulate organic carbon (POC) in surface sediments of the Baltic Sea

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm^–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm^–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm^–3) and moderate POC concentrations (4–7 mg cm^–3). Furthermore, sediment mass accumulation rates (MAR), based on ²¹⁰Pb and ¹³⁷Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m^–2 year^–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.     

Holocene aquatic ecosystem change in the boreal vegetation zone of northern Finland

We studied multiple variables in a sediment core from Lake Kipojärvi, northern Finland, to investigate Holocene ecosystem changes in relation to catchment characteristics and known climate variations. We focused on a forested catchment because previous paleolimnological studies conducted in Fennoscandia focused mainly on subarctic lakes within a range of shifting treeline(s). Data on aquatic macrophytes, diatoms, Cladocera, C:N ratio, organic matter (LOI) and regional vegetation (pollen), revealed a three-phase limnological development. The early Holocene, species-rich, mesotrophic lake was transformed into an oligotrophic, species-poor aquatic ecosystem by the early middle Holocene, ca. 7,500 cal years BP, earlier than has generally been reported. The transition involved considerable changes in aquatic macrophytes. Changes in the Cladocera and diatom communities appear to have been linked to aquatic macrophyte development, which in turn, was probably regulated by catchment development and hydrology, and a consequent decrease in nutrient input from the catchment. During the more humid late Holocene, surface flow from the catchment probably increased, but the lake??s nutrient status remained oligotrophic. Possible reasons for low nutrient concentration in the late Holocene include: 1) slower biogeochemical cycling due to cooler climate, 2) a new hydrologic outlet and associated shorter water-retention times, and 3) accelerated peatland development in the catchment that affected water flow patterns and nutrient cycling.     

Assessment of the possible contribution of space ties on-board GNSS satellites to the terrestrial reference frame

The realization of the international terrestrial reference frame (ITRF) is currently based on the data provided by four space geodetic techniques. The accuracy of the different technique-dependent materializations of the frame physical parameters (origin and scale) varies according to the nature of the relevant observables and to the impact of technique-specific errors. A reliable computation of the ITRF requires combining the different inputs, so that the strengths of each technique can compensate for the weaknesses of the others. This combination, however, can only be performed providing some additional information which allows tying together the independent technique networks. At present, the links used for that purpose are topometric surveys (local/terrestrial ties) available at ITRF sites hosting instruments of different techniques. In principle, a possible alternative could be offered by spacecrafts accommodating the positioning payloads of multiple geodetic techniques realizing their co-location in orbit (space ties). In this paper, the GNSS–SLR space ties on-board GPS and GLONASS satellites are thoroughly examined in the framework of global reference frame computations. The investigation focuses on the quality of the realized physical frame parameters. According to the achieved results, the space ties on-board GNSS satellites cannot, at present, substitute terrestrial ties in the computation of the ITRF. The study is completed by a series of synthetic simulations investigating the impact that substantial improvements in the volume and quality of SLR observations to GNSS satellites would have on the precision of the GNSS frame parameters.     

利用1996年丽江地震序列反演震区应力状态

本文以1996年丽江M_S7.0地震为例,以地震目录和强震震源模型为输入参数,将力学计算与统计分析相结合,反演计算了1986～1996年间丽江震区2.5°×3.0°空间范围内的地壳应力状态.结果表明,丽江地区应力场最大主应力为近南北向,方位角为355°,最小主应力方位角为241°,二者倾角为近水平,应力形因子为0.398,最大主应力大小约为53 MPa,远小于完整岩石的强度.该方法可获得地壳深部绝对应力大小、有效摩擦系数,反演获得的震区地壳深部应力状态的方向性特征与震源机制解结果基本一致;该研究表明地震活动的空间分布可以为我们提供有关强震孕震的地壳深部应力状态信息.这些结果对了解震区应力场具有理论上和实践上的意义.     

Estimates of live-tree carbon stores in the Pacific Northwest are sensitive to model selection

Background  

Estimates of live-tree carbon stores are influenced by numerous uncertainties. One of them is model-selection uncertainty: one has to choose among multiple empirical equations and conversion factors that can be plausibly justified as locally applicable to calculate the carbon store from inventory measurements such as tree height and diameter at breast height (DBH). Here we quantify the model-selection uncertainty for the five most numerous tree species in six counties of northwest Oregon, USA.     

Biogeographic variability in the physiological response of the cold‐water coral Lophelia pertusa to ocean acidification

While ocean acidification is a global issue, the severity of ecosystem effects is likely to vary considerably at regional scales. The lack of understanding of how biogeographically separated populations will respond to acidification hampers our ability to predict the future of vital ecosystems. Cold‐water corals are important drivers of biodiversity in ocean basins across the world and are considered one of the most vulnerable ecosystems to ocean acidification. We tested the short‐term physiological response of the cold‐water coral Lophelia pertusa to three pH treatments (pH = 7.9, 7.75 and 7.6) for Gulf of Mexico (USA) and Tisler Reef (Norway) populations, and found that reductions in seawater pH elicited contrasting responses. Gulf of Mexico corals exhibited reductions in net calcification, respiration and prey capture rates with decreasing pH. In contrast, Tisler Reef corals showed only slight reductions in net calcification rates under decreased pH conditions while significantly elevating respiration and capture rates. These differences are likely the result of environmental differences (depth, pH, food supply) between the two regions, invoking the potential for local adaptation or acclimatization to alter their response to global change. However, it is also possible that variations in the methodology used in the experiments contributed to the observed differences. Regardless, these results provide insights into the resilience of L. pertusa to ocean acidification as well as the potential influence of regional differences on the viability of species in future oceans.