Burying response of an intertidal gastropod to freshwater and copper contamination

The effects of sublethal concentrations of freshwater and copper on the burying responses of the intertidal marine gastropod, Polinices incei, are presented. Such responses are inhibited by both pollutants and the two also act additively. Behavioural responses obtained in a 30 min assay were found to be good predictors of the results of 96 h lethal assays. The results are discussed in light of previous work.     

On inertial currents over a sloping continental shelf

Using simple mathematical models, it is shown that an equatorward flowing coastally confined eastern boundary current (or poleward flowing western boundary current) may have two conjugate forms which transport the same flux of each water type. In a slowly varying environment, these two conjugate forms coalesce at some critical latitude which depends on the flow. For lower latitudes there is no defined form. As the coalescence latitude is approached from higher latitudes, one of the two conjugate forms narrows, while the other widens. Furthermore, in the neighborhood of the critical latitude the wider form is subcritical and the narrower form is supercritical to possible long small amplitude shelf waves. It is also shown that a poleward flowing coastally confined eastern boundary current (or an equatorward flowing western boundary current) may be traced poleward to some critical latitude beyond which the possibility of a current in juxtaposition with the coast terminates. For latitudes higher than this terminating latitude the current separates from the coast.     

The last interglacial ocean

The final effort of the CLIMAP project was a study of the last interglaciation, a time of minimum ice volume some 122,000 yr ago coincident with the Substage 5e oxygen isotopic minimum. Based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean, last interglacial sea-surface temperatures (SST) were compared with those today. There are small SST departures in the mid-latitude North Atlantic (warmer) and the Gulf of Mexico (cooler). The eastern boundary currents of the South Atlantic and Pacific oceans are marked by large SST anomalies in individual cores, but their interpretations are precluded by no-analog problems and by discordancies among estimates from different biotic groups. In general, the last interglacial ocean was not significantly different from the modern ocean. The relative sequencing of ice decay versus oceanic warming on the Stage 6/5 oxygen isotopic transition and of ice growth versus oceanic cooling on the Stage 5e/5d transition was also studied. In most of the Southern Hemisphere, the oceanic response marked by the biotic census counts preceded (led) the global ice-volume response marked by the oxygen-isotope signal by several thousand years. The reverse pattern is evident in the North Atlantic Ocean and the Gulf of Mexico, where the oceanic response lagged that of global ice volume by several thousand years. As a result, the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years. These regional lead-lag relationships agree with those observed on other transitions and in long-term phase relationships; they cannot be explained simply as artifacts of bioturbational translations of the original signals.     

Source induced vertical components in geomagnetic pulsation signals

We show how large vertical components may be induced in geomagnetic pulsation signals because of the localised nature of the source. The effect is greatest when the signal varies on a horizontal scale length which is shorter than the skin depth of the signal in the Earth. However, the horizontal scale length is also constrained to be equal or larger than the height of the ionospheric E-region (～ 120 km) as signals varying on a shorter scale are severely attenuated. Such conditions are best met by high latitude pulsations and some recent high latitude observations are explained by our results. We find that the vertical component is best correlated with the horizontal component in the direction in which the signal varies most rapidly.     

Frequency-Dependent Climate Signal in Upper and Lower Forest Border Tree Rings in the Mountains of the Great Basin

We examine the relationships, over the past millennium, between tree-ring chronologies from long-lived pines at their upper and lower limits in four mountain ranges in and near to the semi-arid Great Basin. We confirm LaMarche's (1974a) finding, based on a single mountain range in this same region, and a much shorter period of comparison, that climate responses are frequency dependent. In particular, upper and lower forest border chronologies in each mountain range are strongly coherent at decadal periods and less, with particular strength in the 3–7 year band. Thisvariability is significantly correlated with precipitation. Conversely, we find no significant correlation between the low frequency fluctuations (60 years and longer) of upper and lower forest border chronologies. There are, however, significant correlations between the low-frequency components of the upper forest border chronologies in the different ranges, consistent with their containing a growing season temperature signal on decadal time scales. The four upper forest border chronologies all show an anomalous increase in growth since the late 19th century, and an apparent change in climate control of ring growth.     

Quaoar and the Edgeworth–Kuiper belt

Is it a planet? Is it a comet? David W Hughes takes a look at the wilder reaches of the solar system, beyond Neptune, and finds that we know just a little about an awful lot.     

The European Gravity Field and Steady-State Ocean Circulation Explorer Satellite Mission Its Impact on Geophysics

Current knowledge of the Earth's gravity field and its geoid, as derived from various observing techniques and sources, is incomplete. Within a reasonable time, substantial improvement will come by exploiting new approaches based on spaceborne gravity observation. Among these, the European Space Agency (ESA) Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission concept has been conceived and designed taking into account multi-disciplinary research objectives in solid Earth physics, oceanography and geodesy. Based on the unique capability of a gravity gradiometer combined with satellite-to-satellite high-low tracking techniques, an accurate and detailed global model of the Earth's gravity field and its corresponding geoid will be recovered. The importance of this is demonstrated by a series of realistic simulation experiments. In particular, the quantitative impact of the new and accurate gravity field and geoid is examined in studies of tectonic composition and motion, Glaciological Isostatic Adjustment, ocean mesoscale variability, water mass transport, and unification of height systems. Improved knowledge in each of these fields will also ensure the accumulation of new understanding of past and present sea-level changes.     

Deadly oasis:Recurrent annihilation of Cretaceous desert bryophyte colonies;the role of solar,climate and lithospheric forcing

Many oases(wet interdunes)are sedimentary systems characterized by high-frequency water-level oscillations,marked changes in salinity and intense biological activity at their margins.They are considered to be one of the most challenging environments on Earth for ecosystem development.These dynamic,depositional settings are usually unfavourable for fossilization and subsequent preservation of vegetal remains.This paper describes bryophyte(liverwort)assemblages occurring in three successive horizons interpreted to represent(i)recurrent early successional phases of biological soil crust colonization of wet interdune margins or(ii)exceptional preservation of floating or riparian liverworts in oasis pond waters associated with a progressive fall of the interdune water level.The record of in situ colonization surfaces characterized by delicate(e.g.lignin-free)three-dimensional structures represents an exceptional type of preservation herein associated with a rapid variation in phreatic interdune water level and the subsequent establishment of anoxic and reducing conditions.The occurrence of exceptionally preserved liverwort colonies coincides with the sedimentary record of,at least,three seismite levels in the oasis.Data gathered from the site suggests that the water table of the oasis was controlled by a combination of(i)a positive creation of accommodation space due to subsidence associated with movement on syn-sedimentary extensional faults,and(ii)the rise and fall of the oasis water table controlled by the oscillations of the groundwater system due to orbital changes which appear to drive the variability of the climate system.Rising groundwater levels flooded the oasis soil crusts and lead to the exceptional recurrent preservation of liverwort colonies at the oasis margins.Alternatively,considering the hypothesis of floating or riparian liverworts in the oasis pond waters,the fall in the level of the oasis water table placed the floating liverworts in contact with the oasis bottom sediments.This fall in the level of the oasis water table could indicate a cessation of accommodation space by syn-sedimentary extensional faults and/or a regional lowering of the groundwater system level associated with drought periods.Preliminary results indicate that oasis lamination between liverwort colonies records decadal and sub-decadal cyclicity,related with 11-year Schwabe sunspot and sub-decadal NAO cyclicities,conferring for every sedimentary cycle between liverwort colonies a duration of approximately 200 years,that otherwise matches the expected recurrence period for the De Vries cycle of solar activity.