Quaternary changes in level of the upper Taylor Glacier, Antarctica: implications for paleoclimate and East Antarctic Ice Sheet dynamics

Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. ³He and ¹⁰Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.     

Relative sea-level history and isostatic rebound in Newfoundland, Canada

The island of Newfoundland, Canada, is situated close to the former margins of the Laurentide ice sheet. The post-glacial sea-level history is complex, dominated by the effects of an ice-marginal crustal forebulge produced by isostatic deformation of the lithosphere. Marine fossils found above present sea-level can be ¹⁴C dated, and examination of the temporal and geographical distribution of these ¹⁴C dates in combination with geomorphological indicators of past sea-levels indicates regional trends of relative sea-level change. For most of the island (apart from the Northern Peninsula) no samples have been recovered that date younger than 8000 BP. suggesting that sea-level lay below the present one in these areas for the last 8000 years. The same areas commonly show geomorphological evidence for stands of sea-level both above and below present sea-level. This evidence is interpreted as showing that over most of Newfoundland, following deglaciation, sea-level fell to below present levels, and subsequently rose to the modern level. Exceptions to this pattern are the north of the Northern Peninsula, which shows a history of continuous emergence, or a more complex pattern of sea-levels falling below present, subsequently rising above present, and currently falling; and the northeast Avalon Peninsula, which may have had sea-levels below present throughout post glacial times. This pattern of relative sea-level change is interpreted as being mostly due to isostatic recovery, with the main factor being northerly migration of the forebulge. Mapping the time at which sea-level fell below the present level allows estimation of the rate of northerly migration and collapse of the forebulge at between 4.5 and 11 km/100 years; this is considerably faster than previous estimates.     

Flashfloods, earthquakes and uplift in the Pakistan Himalayas

Catastrophic flooding of parts of the frontal plains of the Pakistan Himalayas has occured throughout the historical past. The largest recorded flood (1841) originated from an earthquaketriggered landslip from the flanks of Nanga Parbat, which blocked the Indus river for six months. The earthquake probably occurred on the Liachar thrust, which has been responsible for uplifting the amphibolite facies Nanga Parbat gneisses to the Earth's surface in the last 10 million years. These movements raise serious problems for hydroelectric engineering project in this and other active mountain belts.     

MOUNTAIN GEOGRAPHY

ABSTRACT. Although mountains have been studied for centuries, they are the subject of only a slender body of formal literature. Instead, those who study high places in specific regions construct working definitions and continually recraft bibliographies. Studies of mountains often focus on comparatively limited themes: physical processes, ecology, or sacred spaces, for example. As scholars become interested in environmental degradation and the development of mountains, there is all the more need to develop a mountain geography literature that expands the study of mountains to include the political, economic, cultural, and social dimensions of their environments and peoples. Three areas‐cultural geography, political ecology, and conservation theory‐are suggested for additional research.     

Origin of well-rounded gravels in glacial deposits from Brøggerhalvøya, northwest Spitsbergen: potential problems caused by sediment reworking in the glacial environment

Well-rounded gravels are described from moraine-mound complexes, diamicton forefields and modern englacial thrusts at the margins of four glaciers on the northern side of Brøggerhalvøya, northwest Spitsbergen. Their shape charcteristics are compared with modern and fossil glacigenic, modern beach and Early Weichselian beach gravels from this peninsula. The best discriminators of the well-rounded gravels have been found to be the percentage-frequency roundness histograms, the roundness mid-point and roundness range diagrams and the sphericity-roundness plots. It is concluded that the gravels have been derived by englacial thrusting from Early Weichselian or last interglacial beaches in the inner parts of the fjord and in the low level cirques when sea level reached at least 50m a.s.l. and deposited the beach gravels. The discrimination between gravel in basal diamictons, proglacial outwash and modern beaches is difficult as the reworking has resulted in little particle shape change. The potential major problem caused by reworking in the glacial environment is emphasised. especially when clast shape comparisons from modern environments to older sediments are used.     

Vertical profiles of biospheric and fossil fuel-derived CO2 and fossil fuel CO2 : CO ratios from airborne measurements of Δ14C, CO2 and CO above Colorado, USA

Measurements of  Δ¹⁴C  in atmospheric CO₂ are an effective method of separating CO₂ additions from fossil fuel and biospheric sources or sinks of CO₂. We illustrate this technique with vertical profiles of CO₂ and  Δ¹⁴C  analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO₂ uptake in some cases. We estimate local industrial CO₂:CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO₂:1 mole CO, higher than expected from emissions inventories. Uncertainty in CO₂ from different sources was ±1.1 to ±4.1 ppm for addition or uptake of −4.6 to 55.8 ppm, limited by  Δ¹⁴C  measurement precision and uncertainty in background  Δ¹⁴C  and CO₂ levels.     

H2O Abundance in Depleted to Moderately Enriched Mid-ocean Ridge Magmas; Part I: Incompatible Behaviour, Implications for Mantle Storage, and Origin of Regional Variations

The H₂O contents and trace-element abundances are presentedfor two well-studied suites of mid-ocean ridge basalt (MORB)glasses from the Northern East Pacific Rise (EPR, 9–11°N)and the South East Indian Ridge (SEIR, 127–129°E).Exactly the same region of the glass samples has been analysedfor these components using microbeam techniques. Our data allowexamination of the fine details of H₂O geochemical behaviourduring MORB genesis. We demonstrate that relative H₂O contents[i.e. H₂O/(another incompatible element)] vary systematicallywith increasing (La/Sm)_N in MORB glasses from both the EPR andSEIR. This indicates that H₂O behaves like other incompatible(in peridotite mineralogies) elements during MORB petrogenesis,and is primarily controlled by solid–melt partitioning.However, the relative H₂O contents of MORB glasses from theSEIR are higher than in glasses from the EPR at a given (La/Sm)_N,demonstrating global variations in the H₂O contents of MORB.Despite regional differences in relative H₂O contents, the incompatiblebehaviour of H₂O is similar in both studied regions. The relativeincompatibility of H₂O varies systematically with increasing(La/Sm)_N: in depleted MORB, H₂O is similar to La whereas inEMORB, H₂O is similar to Ce. Similar patterns of varying relativeincompatibility (to REE) are displayed by Zr, Hf, and P. Ourdata are best explained if H₂O is stored in the mantle in thesame phase with LREE (clinopyroxene?) at sub-solidus. Regionalvariations in relative H₂O contents in EMORB that have moreradiogenic Sr, Nd and Pb isotopes might be explained by differencesin the nature of enriched components recycled via subductionprocesses. However, when EMORB have the same radiogenic isotopecompositions as NMORB within a segment, relative H₂O contentsin EMORB probably reflect local processes that lead to enrichmentin incompatible elements. Regional differences in relative H₂Ocontents of NMORB may reflect either initial variations in theEarth’s mantle or inhomogeneities left after formationof the continental crust. KEY WORDS: glass; geochemistry; H₂O; MORB; petrology     

The Little Ice Age glacier maximum in Iceland and the North Atlantic Oscillation: evidence from Lambatungnajökull, southeast Iceland

This article examines the link between late Holocene fluctuations of Lambatungnajökull, an outlet glacier of the Vatnajökull ice cap in Iceland, and variations in climate. Geomorphological evidence is used to reconstruct the pattern of glacier fluctuations, while lichenometry and tephrostratigraphy are used to date glacial landforms deposited over the past ˜400 years. Moraines dated using two different lichenometric techniques indicate that the most extensive period of glacier expansion occurred shortly before c . AD 1795, probably during the 1780s. Recession over the last 200 years was punctuated by re-advances in the 1810s, 1850s, 1870s, 1890s and c . 1920, 1930 and 1965. Lambatungnajökull receded more rapidly in the 1930s and 1940s than at any other time during the last 200 years. The rate and style of glacier retreat since 1930 compare well with other similar-sized, non-surging, glaciers in southeast Iceland, suggesting that the terminus fluctuations are climatically driven. Furthermore, the pattern of glacier fluctuations over the 20th century broadly reflects the temperature oscillations recorded at nearby meteorological stations. Much of the climatic variation experienced in southern Iceland, and the glacier fluctuations that result, can be explained by secular changes in the North Atlantic Oscillation (NAO) Advances of Lambatungnajökull generally occur during prolonged periods of negative NAO index. The main implication of this work relates to the exact timing of the Little Ice Age in the Northeast Atlantic. Mounting evidence now suggests that the period between AD 1750 and 1800, rather than the late 19th century, represented the culmination of the Little Ice Age in Iceland.     

THE CONTRASTING EFFECTS OF WILDFIRE AND CLEARFELLING ON THE HYDROLOGY OF A SMALL CATCHMENT

A wildfire in an afforested research catchment presented the rare opportunity to compare the hydrological effects of wildfire with the effects of clearfelling in the same catchment in the Jonkershoek Valley, in the south-western Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km² catchment, had been clearfelled and re-planted to Pinus radiata roughly five years before the fire. The effects of the two treatments on total flow, storm-flow and quick-flow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the significance of treatments. Both clearfelling and wildfire caused significant increases in all the stream-flow variables analysed. But the clearfelling effect was dominated by large increases in total flow (96% over three years), of which storm-flow and quick-flow volumes formed only minor parts. After the wildfire, by contrast, increases in total flow were small (12%) but the storm flow increases were three- to four-fold in the first year and roughly double in the second year. The wildfire caused fire-induced water repellency in the soils which led to overland flow on mid-slope sites, where soil infiltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-flow generation processes were changed by the wildfire in that overland flow made a direct contribution to storm flows, but that clearfelling had no such effect. © 1997 by John Wiley & Sons, Ltd.