Experimental investigation and application of the equilibrium rutile + orthopyroxene = quartz + ilmenite

Equilibria in the Sirf (Silica-Ilmenite-Rutile-Ferrosilite) system: $${\text{SiO}}_{\text{2}} + ({\text{Mg,Fe}}){\text{TiO}}_{\text{3}} {\text{ + (Mg,Fe)SiO}}_{\text{3}} $$ have been calibrated in the range 800–1100° C and 12–26 kbar using a piston-cylinder apparatus to assess the potential of the equilibria for geobarometry in granulite facies assemblages that lack garnet. Thermodynamic calculations indicate that the two end-member equilibria involving quartz + geikielite = rutile + enstatite, and quartz + ilmenite = rutile + ferrosilite, are metastable. We therefore reversed equilibria over the compositional range Fs_40–70, using Ag₈₀Pd₂₀ capsules with \(f_{{\text{O}}_{\text{2}} } \) buffered at or near iron-wüstite. Ilmenite compositions coexisting with orthopyroxene are \(X_{{\text{MgTiO}}_{\text{3}} }^{{\text{Ilm}}} \) of 0.06 to 0.15 and \(X_{{\text{Fe}}_{\text{2}} {\text{O}}_{\text{3}} }^{{\text{Ilm}}} \) of 0.00 to 0.01, corresponding toK _D values of 13.3, 10.2, 9.0 and 8.0 (±0.5) at 800, 900, 1000 and 1100° C, respectively, whereK _D =(XMg/XFe)^Opx/(XMg/XFe)^Ilm. Pressures have been calculated using equilibria in the Sirf system for granulites from the Grenville Province of Ontario and for granulite facies xenoliths from central Mexico. Pressures are consistent with other well-calibrated geobarometers for orthopyroxeneilmenite pairs from two Mexican samples in which oxide textures appear to represent equilibrium. Geologically unreasonable pressures are obtained, however, where oxide textures are complex. Application of data from this study on the equilibrium distribution of iron and magnesium between ilmenite and orthopyroxene suggests that some ilmenite in deep crustal xenoliths is not equilibrated with coexisting pyroxene, while assemblages from exposed granulite terranes have reequilibrated during retrogression. The Sirf equilibria are sensitive to small changes in composition and may be used for determination of activity/composition (a/X) relations of orthopyroxene if an ilmenite model is specified. A symmetric regular solution model has been used for orthopyroxene in conjunction with activity models for ilmenite available from the literature to calculatea/X relations in orthopyroxene of intermediate composition. Data from this study indicate that FeSiO₃?MgSiO₃ orthopyroxene exhibits small, positive deviations from ideality over the range 800–1100°C.     

Middle Campanian–lowermost Maastrichtian nannofossil and foraminiferal biostratigraphy of the northwestern Australian margin

The middle–late Campanian was marked by an increase in the bioprovinciality of calcareous microfossil assemblages into distinct Tethyan, Transitional, and Austral Provinces that persisted to the end of the Maastrichtian. The northwestern Australian margin belonged to the Transitional Province and the absence of key Tethyan marker species such as Radotruncana calcarata and Gansserina gansseri has led petroleum companies operating in the area to use the locally developed KCCM integrated calcareous microfossil zonation scheme. The KCCM zonation is a composite scheme comprising calcareous nannofossil (KCN), planktonic foraminiferal (KPF) and benthonic foraminiferal (KBF) zones. This paper presents the definitions and revisions of Zones KCCM8–19, from the highest occurrence (HO) of Aspidolithus parcus constrictus to the lowest occurrence (LO) of Ceratolithoides aculeus, and builds on our previous early–late Maastrichtian study. The presence of a middle–upper Campanian disconformity is confirmed by microfossil evidence from the Vulcan Sub-basin, Exmouth and Wombat plateaus, and the Southern Carnarvon Platform. In the Vulcan Sub-basin and on the Exmouth Plateau (ODP Hole 762C) the hiatus extends from slightly above the LO of common Rugoglobigerina rugosa to above the LO of Quadrum gothicum. On the Wombat Plateau (ODP Hole 761B) it spans from above the LO of Heterohelix semicostata to above the LO of Quadrum gothicum; and in the Southern Carnarvon Platform the disconformity has its longest duration from above the HO of Heterohelix semicostata to above the LO of Quadrum sissinghii. A significant revision of the events which define Zones KCCM18 and 19 was necessary owing to the observation that the LO of Ceratolithoides aculeus occurs below the HOs of Archaeoglobigerina cretacea and Stensioeina granulata incondita and the LO of common Rugoglobigerina rugosa. In the original zonation these events were considered to be coincident.     

Climatic change and great lakes levels the impact on shipping

This paper represents an attempt to combine the output of several models that deal with future climatic, hydrologic and economic conditions in the Great Lakes and makes some predictions about the possible impact of one scenario of 2 × CO₂ climate on Great Lakes shipping. It is realized that there is a great deal of uncertainty in all the models and that improvements are continually being made. Data from a General Circulation Model of future temperature and precipitation in the Great Lakes basin, a Great Lakes levels and flows model from the Canada Centre for Inland Waters and an International Joint Commision's Great Lakes economic model modified by the University of Wisconsin were used. The 1900–1976 period of lake levels and flows was used. The hydrologic model indicated that future mean lake levels may be reduced by one-half meter, and that the extreme low levels of the mid 1960's could occur 77% of the time in the future. No ice cover is predicted for any lake except Erie, permitting an eleven month shipping season. Five scenarios of future impact on shipping were evaluated. It was found that mean annual shipping costs may increase by 30% and the frequency of years when costs exceed those of the period of low lake levels (1963–65) could rise to 97%. Possible policy options in a future with climatically induced lower lake levels could include regulation to keep levels artificially high by diversions into the system, or increased dredging of the connecting channels.     

Palaeoecology and taxonomy of Pentoxylales from the Albian of Antarctica

Reproductive pentoxylalean material from the Albian Triton Point Formation, Fossil Bluff Group of Alexander Island, Antarctica is the youngest record of this group globally. Leaves are referred to Taeniopteris daintreei McCoy, ovulate reproductive organs to Carnoconites cranwelli Harris, and stem material to Pentoxylon sp. Occurring in leaf litter layers on palaeosol surfaces the sedimentology suggests that pentoxylalean plants grew upon areas of the floodplain distal to the river channel, where they covered the forest floor in a similar habit to modern brambles. The forest floor was shared with Equisetales and liverworts, an abundance of ferns [Cladophlebis Brongniart, Gleichenites Goeppert, Phyllopteroides Medwell, Sphenopteris (Brongniart) Sternberg], as well as angiosperms. Bennettitales, Ginkgoites Seward and Nilssonia Brongniart were rare within these communities, as were coniferous trees.     

Variations in solar sub-surface rotation from GONG data 1995–1998

We have completed an analysis of the first 35 GONG Months (1 GM = 36 days) covering the last solar minimum and the rising phase of cycle 23. The mode parameters have been estimated from 33 time series, each of 3-GM duration, with centers spaced by 1 GM. We report on the temporal evolution of the rotational splitting coefficients up to 15th order. The coefficients do not correlate well with any surface magnetic flux measure yet considered, but we find small but significant trends in their temporal evolution. Inverting the coefficients for two-dimensional rotation information and looking at deviations from the mean produces a picture of a systematic zonal flow migrating towards lower latitudes during the rising phase of the cycle. This flow is probably associated with the torsional oscillation. Similar trends are seen in the 1986–1990 BBSO data.     

Public perceptions of rainfall change in India

People’s perceptions of changes in local weather patterns are an important precursor to proactive adaptation to climate change. In this paper, we consider public perceptions of changes in average rainfall in India, analyzing the relationship between perceptions and the instrumental record. Using data from a national sample survey, we find that local instrumental records of precipitation are a strong predictor of perceived declines in rainfall. Perceptions of decreasing rainfall were also associated with perceptions of changes in extreme weather events, such as decreasing frequency of floods and severe storms, increasing frequency of droughts, and decreasing predictability of the monsoon. Higher social vulnerability—including low perceived adaptive capacity and greater food and livelihood dependence on local weather—was also associated with perceptions of decreasing rainfall. While both urban and rural respondents were likely to perceive local changes in precipitation, we show that rural respondents in general were more sensitive to actual changes in precipitation. Individual perceptions of changes in local climate may play an important role in shaping vulnerability to global climate change, adaptive behavior, and support for adaptation and mitigation policies. Awareness of local climate change is therefore particularly important in regions where much of the population is highly exposed and sensitive to the impacts of climate change.     

Ice caps existed throughout the Lateglacial Interstadial in northern Scotland

We constrain, in detail, fluctuations of two former ice caps in NW Scotland with multibeam seabed surveys, geomorphological mapping and cosmogenic ¹⁰Be isotope analyses. We map a continuous sequence of 40 recessional moraines stretching from ～10 km offshore to the Wester Ross mountains. Surface‐exposure ages from boulders on moraine ridges in Assynt and the Summer Isles region show that substantial, dynamic, ice caps existed in NW Scotland between 13 and 14 ka BP. We interpret this as strong evidence that large active glaciers probably survived throughout the Lateglacial Interstadial, and that during the Older Dryas period (ca. 14 ka BP) ice caps in NW Scotland were thicker and considerably more extensive than in the subsequent Younger Dryas Stadial. By inference, we suggest that Lateglacial ice‐cap oscillations in Scotland reflect the complex interplay between changing temperature and precipitation regimes during this climatically unstable period (ca. 15–11 ka BP). © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons, Ltd.     

Solar-Cycle Variation of Subsurface-Flow Divergence: A Proxy of Magnetic Activity?

We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have analyzed Global Oscillation Network Group (GONG) Dopplergrams with a ring-diagram analysis covering about 15 years and Helioseismic and Magnetic Imager (HMI) Dopplergrams covering more than 6 years. After subtracting the average rotation rate and meridional flow, we have calculated the divergence of the horizontal residual flows from the maximum of Solar Cycle 23 through the declining phase of Cycle 24. The subsurface flows are mainly divergent at quiet regions and convergent at locations of high magnetic activity. The relationship is essentially linear between divergence and magnetic activity at all activity levels at depths shallower than about 10 Mm. At greater depths, the relationship changes sign at locations of high activity; the flows are increasingly divergent at locations with a magnetic activity index (MAI) greater than about 24 G. The flows are more convergent by about a factor of two during the rising phase of Cycle 24 than during the declining phase of Cycle 23 at locations of medium and high activity (about 10 to 40 G MAI) from the surface to at least 10 Mm. The subsurface divergence pattern of Solar Cycle 24 first appears during the declining phase of Cycle 23 and is present during the extended minimum. It appears several years before the magnetic pattern of the new cycle is noticeable in synoptic maps. Using linear regression, we estimate the amount of magnetic activity that would be required to generate the precursor pattern and find that it should be almost twice the amount of activity that is observed.