The Gröbminger Mitterberg (Austria): A time machine to the pre-LGM?

<p>The Last Glacial Maximum (LGM) is well understood in many parts of the European Alps, but open questions remain concerning glacial phases prior to the LGM as the record is fragmentary. The Gröbminger Mitterberg (GM), located among the Enns Valley in Styria (Austria) is one such location where pre-LGM glacial and paraglacial processes can be studied. The GM emerges roughly 200 m from the Enns Valley floor and is situated between unmetamorphosed Mesozoic carbonates in the north and crystalline basement units in the south. Strata occur below a cover of up to more than 10 m thick basal till attributed to the LGM. The sedimentary record rests on the phyllites and greenschists that crop out at the steep southern flank of the GM. The sediment consists of an assortment of pebble-sand deposits with individual sand lenses, sand bodies with climbing ripples and undulose bedding, and fine-sand/silt laminated strata. In grain-supported intervals, cracked pebbles occur, which are interpreted to record subglacial loading. Cross-bedding orientations, together with the limited amount of unmetamorphosed carbonate pebbles in the sequence, imply that sediment was sourced from the GM and deposited at its margins, rather than from surrounding mountains towards the centre of the Enns Valley. Three depositional regimes have been recognised: deltaic sediment (both distal sands with ripples and proximal, cross-bedded gravel), lake bottom sediment (laminated fine-sand and silt) and fluvial deposits (channels with basal lag deposits and local cross bedding). The delta facies testify to the presence of lacustrine conditions. By analogy to the Unterangerberg in the Inn Valley (Tyrol, Austria; Starnberger et al. 2013), the following sequence of events is proposed. Before the LGM, sediment derived from the wider catchment area accumulated in the Enns Valley in lakes and rivers. Aggradation within the whole Enns valley resulted in deposition on the present day GM. During the LGM, the large Enns Glacier eroded much of the sediment record, especially around the GM. Deposits on top of the GM were then concealed by > 10 m thick diamicts and thereby preserved. Future age dating of the sediments will provide a better-constrained chronology to the sequence of events proposed above.</p>

Post-Pollution: Characterizing Ecological Recovery in a Historically Nutrient Enriched Lake.

An iconic story of recovery from nutrient pollution is the restoration of the heavily enriched Lake Washington in Seattle, Washington State. Originally an integral part of the municipal septic system, a diversion of wastewater in 1968 has allowed Lake Washington to return to what has been recently described as a natural and healthy state. Yet is it accurate to characterize a lake as “recovered” based purely on chemical measurements? Does a legacy of pollution linger on in the ecology of a lake system long after the lake has been given a clean bill of health?Using paleolimological reconstructive techniques it is possible to compare pre-pollution and post-pollution communities of algae by looking at microfossils stored chronologically in the lake-bottom sediment. Use of this technique has afforded a test of the assumption that once pollution stress in a lake is alleviated, the algal communities quickly return to the pre-pollution state. Work on Lake Washington indicates that this does not always hold true. Instead, it suggests that a legacy of pollution persists in the algae and ecological community of the lake long after the nutrient levels have returned to normal.

Biogeochemical processes and the diversity of Nhecolândia lakes, Brazil

The Pantanal of Nhecolândia, the world's largest and most diversified field of tropical lakes, comprises approximately 10,000 lakes, which cover an area of 24,000 km² and vary greatly in salinity, pH, alkalinity, colour, physiography and biological activity. The hyposaline lakes have variable pHs, low alkalinity, macrophytes and low phytoplankton densities. The saline lakes have pHs above 9 or 10, high alkalinity, a high density of phytoplankton and sand beaches. The cause of the diversity of these lakes has been an open question, which we have addressed in our research. Here we propose a hybrid process, both geochemical and biological, as the main cause, including (1) a climate with an important water deficit and poverty in Ca2+ in both superficial and phreatic waters; and (2) an elevation of pH during cyanobacteria blooms. These two aspects destabilise the general tendency of Earth's surface waters towards a neutral pH. This imbalance results in an increase in the pH and dissolution of previously precipitated amorphous silica and quartzose sand. During extreme droughts, amorphous silica precipitates in the inter-granular spaces of the lake bottom sediment, increasing the isolation of the lake from the phreatic level. This paper discusses this biogeochemical problem in the light of physicochemical, chemical, altimetric and phytoplankton data.

Preliminary paleomagnetic studies of lake sediments in Eastern Canada

Nine lake bottom sediment cores from small lakes in Eastern Canada, three of which were oriented to an azimuth, have been analyzed magnetically in an attempt to delineate the paleomagnetic character of the late-Pleistocene and Holocene sediments as an aid to stratigraphy and chronology. Secular variations are discernable in mineral sediments and in overlying organic sediments when intensities are strong enough to produce reliable results. Where organic content was high and intensities low, erratic results were obtained. Short segments of some cores, involving at most several centimetres, showed negative values for inclination, but whether or not these can be related to magnetic reversals or excursions or are spurious results, cannot be determined at this time.