Absence of seasonal patterns in MBT-CBT indices in mid-latitude soils

The degree of methylation and cyclization of bacteria-derived branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in soils depends on temperature and soil pH. Expressed in the methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT), these relationships are used to reconstruct past annual mean air temperature (MAT) based on the distribution of branched GDGTs in ancient sediments; the MBT-CBT proxy. Although it was shown that the best correlation of this proxy is with annual MAT, it remains unknown whether a seasonal bias in temperature reconstructions could occur, such as towards a seasonal period of ‘optimal growth’ of the, as yet, unidentified soil bacteria which produce branched GDGTs. To investigate this possibility, soils were sampled from eight different plots in the USA (Minnesota and Ohio), The Netherlands (Texel) and the UK (Devon) in time series over 1 year and analyzed for their branched GDGT content. Further analyses of the branched GDGTs present as core lipids (CLs; the presumed fossil pool) and intact polar lipids (IPLs; the presumed extant pool) were undertaken for two of the investigated soil plots. The amount of IPL-derived branched GDGTs is low relative to the branched GDGT CLs, i.e. only 6-9% of the total branched GDGT pool. In all soils, no clear change was apparent in the distribution of branched GDGT lipids (either core or IPL-derived) with seasonal temperature change; the MBT-CBT temperature proxy gave similar temperature estimates year-round, which generally matched the mean annual soil temperature. In addition to a lack of coherent changes in relative distributions, concentrations of the branched GDGTs did not show clear changes over the seasons. For IPL-derived GDGTs these results suggest that their turnover time in soils is in the order of 1 year or more. Thus, our study does not provide evidence for seasonal effects on the distribution of branched GDGTs in soils, at least at mid-latitudes, and therefore, no direct evidence for a bias of MBT-CBT reconstructed temperatures towards a certain season of optimal growth of the source bacteria. If, however, there is a slight seasonal preference of branched GDGT production, which can easily be obscured by natural variability due to the heterogeneity of soils, then a seasonal bias may potentially still develop over time due to the long turnover time of branched GDGTs.     

Long-period fluctuations in ionospheric absorption and their relation with planetary activity in the stratosphere

Summary By investigating the quasi-regular variations in ionospheric absorption along three distant radio paths with approximately one and the same equivalent frequency during the winters 1983/84 and 1984/85, an attempt is made to study the stratospheric-mesospheric relations at typical geographic mid latitudes. It is shown that the quasi-regular oscillations of ionospheric absorption, investigated in this paper, reach maximum development in each time series at one and the same time. This means, that if they are provoked by an external source when it starts acting, a spectrum of frequencies is generated rather than a definite fixed frequency. By studying the variation of the instantaneous amplitudes of the quasi-regular oscillations in ionospheric absorption with time, their connection with the amplification of the quasi-stationary planetary waves in the stratosphere with a zonal wave number 2 during the winter periods under investigation is shown.

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Резюме Иссле?rt;овaнuем квaзuре улярных вaрuaцuŭ в uоносферном nо лощенuu в mрех nросmрaнсmвенно оm?rt;aленных рa?rt;uо-mрaссaх с nрuблuзumельно о?rt;ноŭ u mоŭ же эквuвaленmноŭ чaсmовоŭ зuмоŭ 1983/84 u 1984/85 . ?rt;елaеmся nоnыmкa uзучumь сmрamосферно-мезос ферные связu в munuчных сре?rt;ных щuроmaх. Покaзaно, чmо рaссмоmренные в рaбоmе квaзuре улярные колебaнuя в uоносферном nо лощенuu ?rt;осmu aюm мaксuмaльно о рaзвumuя в кaж?rt;ом временном ря?rt;у в о?rt;но u mо же время. Эmо ознaчaеm, чmо, еслu онu возбуж?rt;ены внещнuм uсmочнuком, mо nрu е о включенuu енерuруюmся не о?rt;нa чaсmоma, a целыŭ сnекmр чaсmоm. Изученuем временных uзмененuŭ м новенных aмnлumу?rt; квaзuре улярных колебaнuŭ в uоносфермон nо лощенuu зa uссле?rt;овaнные зuмнuе nерuо?rt;ы nокaзaнa uх связь с квaзu-сmaцuонaрнымu nлaнеmaрнымu колебaнuямu в сmрamосфере с зонaльным волновымu чuслом 2.

     

Subsidence of Surtsey volcano, 1967–1991

The Surtsey marine volcano was built on the southern insular shelf of Iceland, along the seaward extension of the east volcanic zone, during episodic explosive and effusive activity from 1963 to 1967. A 1600-m-long, east-west line of 42 bench marks was established across the island shortly after volcanic activity stopped. From 1967 to 1991 a series of leveling surveys measured the relative elevation of the original bench marks, as well as additional bench marks installed in 1979, 1982 and 1985. Concurrent measurements were made of water levels in a pit dug on the north coast, in a drill hole, and along the coastline exposed to the open ocean. These surveys indicate that the dominant vertical movement of Surtsey is a general subsidence of about 1.1±0.3 m during the 24-year period of observations. The rate of subsidence decreased from 15–20 cm/year for 1967–1968 to 1–2 cm/year in 1991. Greatest subsidence is centered about the eastern vent area. Through 1970, subsidence was locally greatest where the lava plain is thinnest, adjacent to the flanks of the eastern tephra cone. From 1982 onward, the region closest to the hydrothermal zone, which is best developed in the vicinity of the eastern vent, began showing less subsidence relative to the rest of the surveyed bench marks. The general subsidence of the island probably results from compaction of the volcanic material comprising Surtsey, compaction of the sea-floor sediments underlying the island, and possibly downwarping of the lithosphere due to the laod of Surtsey. The more localized early downwarping near the eastern tephra cone is apparently due to greater compaction of tephra relative to lava. The later diminished local subsidence near the hydrothermal zone is probably due to a minor volume increase caused by hydrous alteration of glassy tephra. However, this volume increase is concentrated at depth beneath the bottom of the 176-m-deep cased drillhole.     

Non-hydrostatic model of airflow over irregular topography — Theoretical bases

Summary This article deals with some problems connected with the formulation of a non-hydrostatic mesoscale model of airflow in the atmosphere. Due to an irregular surface a terrain-following coordinate system is used and the equations of the model are transformed into this system. Sound waves are eliminated by the use of the anelastic approximation. The influence of boundaries is minimized by the use of open boundary conditions at the lateral boundaries of the computational domain and of the absorbing layer beneath the upper boundary.     

Geochemical heterogeneity and isotope geochemistry of natural attenuation processes in a gasoline-contaminated aquifer at the Hnevice site,Czech Republic

The geochemical processes, water–rock interactions and stable isotopes distribution (δ¹³C of DIC and δ¹⁸O and δ³⁴S of \({\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} \)) were investigated in the gasoline-contaminated aquifer at the Hnevice site, 50  km northwest of Prague, Czech Republic. Diesel, gasoline and oil leaks originate from a large fuel storage area causing heavy contamination of the saturated and unsaturated zones in an area of about 0.7  km². Groundwater investigations were conducted using five multilevel sampler wells with emphasis on redox parameters and degradation by-products and a solid-phase study focused on iron speciation and determination of principal and secondary minerals. Based on the study of groundwater and solid-phase geochemistry, four different geochemical zones were described. Zone I is thought to be background consisting of an aerobic aquifer and the absence of reduced species in significant concentrations. Zone II is situated in the plume core with methanogenic, sulphate and iron-reducing conditions accompanied by ankerite and kutnahorite precipitates and significant depletion of the oxidation capacity of the aquifer. Zone III is a mixing (corona) zone, situated at the fringe of the plume with high biodegradation rates and Fe(III)-precipitants. In zone IV, reoxidation of Fe(II) minerals (with e.g. the occurrence of psilomelane and cornelite) is typical.     

The baroclinic circulation in Hudson strait

Abstract

The baroclinic circulation in the mouth of Hudson Strait is modelled using general results for nearly geostrophic flow along an indented coastline. A simple T‐junction model is first discussed, followed by a somewhat more faithful idealization that includes the sharp northern tip of Labrador, the southwest tip of Baffin Island and part of Ungava Bay. The results show that the mouth of Hudson Strait does not present a significant obstacle to baroclinic flow in and out of it. We thus conclude that the observed recirculation must be due to other effects.     

Transient compression fault slip detected within andesitic rocks of the Casma Group,Lima, Peru

Studia Geophysica et Geodaetica - A fault slip within the Ñaña tunnel Lima, Peru has been monitored since 2012. The data are recorded using an optical-mechanical 3D extensometer, capable...