Description: Antarctica and especially its ice sheets play a major role in both the global ocean current system andclimate. The ANDRILL (Antarctic Geological Drilling) MIS deep drilling project (McMurdo Sound, NE Ross Ice Shelf, drilled core AND-1B during austral summer 2006/2007) is located in a flexural moat basin filled with glaciomarine, terrigenous, volcanic, and biogenic sediments (Horgan et al., 2005). This basin contains a well-preserved outstanding record of paleoclimate history. During the drilling phase, some major and minor chemical elements were measured directly using a non-destructive X-Ray Fluorescence Core Scanner (XRF-CS) method. For the first time, sediments beneath an iceshelf were drilled, which provides a unique opportunity to investigate the variability of the Ross Ice Shelf. The sediment core covers a time period much longer than any Antarctic ice core record. The high-resolution data set of non-destructive XRF-core scans makes it possible to estimate climate changes on small time scales. Due to the early stage of the project phase, this report will focus mainly on data preparation and correction and provides a first rough interpretation of the measured data.

Description: The threat, in terms of sea level rise, posed by the potential rapid deglaciation of West Antarctica means there is an urgent need to know more about the speed and style of marine ice sheet retreat. Quaternary deglacial events recorded in marine sediments provide an opportunity to understand the future of the modern day ice sheet. In this context, we examine the glacial history of a particularly poorly understood sector of the West Antarctic continental shelf the Amundsen Sea Embayment using new data from two recent research cruises. This extended abstract describes how marine geological and geophysical data are being used alongside terrestrial dating methods to understand the full extents, dynamics and retreat pattern of the West Antarctic Ice Sheet in the Amundsen Sea region during the last glacial cycle. These data hold significance for understanding and accurately modelling the stability and climate sensitivity of the West Antarctic Ice Sheet.

Description: Marine geoscience data indicate that during the Last Glacial Maximum (LGM) grounded ice extended to the shelf edge along most, if not all, of the 2500 km-long continental margin from the northern Antarctic Peninsula to the Amundsen Sea. Past extent of grounded ice is indicated by swath bathymetry data from the outer parts of cross-shelf troughs, which reveal relict elongated subglacial bedforms. The bedforms show that the troughs were paths of fast-flowing (streaming) ice. Geomorphological evidence regarding the nature of ice flow over intervening outer shelf banks has been erased through pervasive post-glacial ploughing by icebergs. However, seismic profiles across the banks reveal widespread shelf edge progradation and numerous glacial unconformities that indicate grounded ice has extended across them many times during the Pleistocene, and before. Subglacial tills in the outer parts of shelf troughs are overlain by up to 2 m of postglacial sediments, which are no older than the LGM in any core yet dated. A layer of soft, intermediate shear strength (12¬25 kPa) till, interpreted as deformation till, underlies the postglacial sediments in cores in the troughs. These observations are consistent with the interpretation that streaming ice extended along the troughs during the LGM, but the duration of such flow, and whether or not it spanned the entire period when ice extended to the outer shelf remains undetermined.To determine when, and how rapidly, ice retreated from the continental shelf, ages of core samples from near the base of postglacial sediments in several troughs have been determined by AMS radiocarbon dating. Samples to constrain glacial retreat have been taken from either the base of muds deposited in seasonally open-marine conditions similar to today, or underlying sandy muds interpreted as having been deposited close to the grounding line. Modern sea-floor sediments on some parts of the margin contain sufficient calcareous microfossils for dating to constrain the local marine 14C reservoir correction. However, even where they occur, contents of planktonic foraminifera decrease downcore, and most deglaciation ages have been obtained from acid insoluble organic material (AIOM). In some areas these ages are significantly affected by reworked fossil carbon, as shown by apparent ages from AIOM in modern sea-floor sediments that range up to ~6000 years. Thus radiocarbon results from this margin must be treated with caution and there is a clear need for development of alternative dating methods.Notwithstanding these uncertainties, deglaciation ages obtained thus far suggest variable retreat histories along the margin. Results from the Antarctic Peninsula shelf and Amundsen Sea embayment suggest relatively rapid post-LGM ice retreat from the outer and middle shelf, followed by slower Holocene retreat to the present day ice margin. However, initial results from the Bellingshausen Sea (Belgica Trough) suggest a slower, progressive retreat commencing about 25 ka (corrected radiocarbon years). These results show that local factors are important in controlling the rate of ice retreat, and this needs to be taken into account in numerical models that attempt to predict the dynamic behaviour of large ice sheets.

Description: In Antarctica, the largest inland ice masses on Earth are stored. The growth and the retreat of ice sheets play a major role in the global ocean current system and climate. The melting and collapse of large ice shelves may cause a significant sea level rise, because of accelerated inland ice glacier surges into the ocean.The ANDRILL (Antarctic Geological Drilling) MIS deep drilling project (McMurdo Sound, NE Ross Ice Shelf, core AND-1B drilled during austral summer 2006/2007) is located in a flexural moat basin filled with glaciomarine, terrigenous, volcanic, and biogenic sediments. This basin contains a well-preserved, outstanding record of approximately 14 million years of paleoclimate history. For the first time, sediments beneath an ice shelf were drilled, which provides a unique opportunity to investigate the variability of the Ross Ice Shelf. The sediment core covers a time period much longer than any Antarctic ice core record.During the drilling phase, some major and minor chemical elements were measured directly on split cores using a non-destructive X-Ray Fluorescence Core Scanner method (XRF-CS). In addition, colour data were collected using an integrated Line Scan camera in the XRF-CS system and a Minolta 2002 handheld spectrophotometer. Furthermore wet chemical analysis like the investigation of TOC, biogenic opal, major and minor elements with ICP-MS and conventional XRF were done on core samples to contribute to the better understanding of geochemical sediment properties. Colour data will be correlated to the XRF-CS data to received more and higher resolved information about the sediment composition.The interpretation of rapid paleoclimatic changes in the Antarctic realm, especially to understand the behaviour of the Ross Ice Shelf during the past million years, is one target of our study. The high-resolution data set of non-destructive XRF-core and colour scans make it possible to estimate environmental changes on small time scales that will be linked to climate changes. From the Late Pliocene a transition from diamictite to diatomites is described which implies a shifting from a retreating ice sheet to open marine conditions. In the Early Pleistocene, a number of cycles, alternating from glacial ice transported sediments to open water sedimentation, were observed. The diatomites represent time spans with high bioproductivity and reflect warmer conditions at the Antarctic margin than today.

Description: Im südlichen Polarsommer 2006/07 wurde im Rahmen des internationalen Bohrprojektes ANDRLL ( Antarctic geological drilling) mit Hilfe des AVAATECH XRF (X-ray fluorescence) Core Scanners ein geochemischer Datensatz erzeugt. Gemessen wurden ca. 30 Elemente im Bereich von Al. (Atomnr. 13) bis Ba (Atomnr. 56). Der Hauptteil, des aus einer finalen Tiefe v0on 1284,87 mbsf stammenden Kaerns wurde mit einer Messfläche von 1x1 cm und einem Messabstand von 10 cm analysiert. In Fällen besonderer Lithologien wurde die Auflösung bis zu 0,5cm über kurze Abschnitte erhöht.Die aus den aufgezeichneten Spektren gewonnen Daten wurden hinsichtlich einiger Fehlerquellen und Heterogenitäten korrigiert, z.B. in der Matrix enthaltene Steine, Instabilitäten der Röntgenröhre und Feuchtigkeit des Kerns. Für die Korrektur der Matrix gegenüber enthaltenen Steinen wurde diskrete Proben genommen, gefriergetrocknet und analysenfein gemahlen und wiederrum mit dem XRF Scanner gemessen. Anhand dieser Messungen wurde ebenfalls der Einfluss des Porenwassers, dass einem Wasserfilm zwischen kernoberfläche und Messfolie erzeugt abgeschätzt. Für einige Elemente kam es zu Mehrfunden in den trockenen Proben und wiederum für andere Elemente zu Minderbefunden.Innerhalb der Messphase kam es zu einem Energieverlust der Rh-Röntgenröhre, die bei einigen Elementen eine deutliche Absenkung der durchschnittlich detektierten Counts verursachte. Um diese Minderbefunde zu einem späteren Zeitpunkt angleichen zu können, sind aus den betroffenen Kernsektionen einige Meter erneut gemessen worden. Die Anhebung der Daten erfolgte mittels linearer Regression oder arithmetischer Mittelwertsbildung und Faktorbildung zwischen erster und zweiter Messung.Die Elementverteilungen einiger Indikatorelemente zeigen deutliche Übereinstimmungen mit der Kernbeschreibung der Sedimentologen.Bei den Core Scanner Daten handelt es sich umrelative Daten, die in weiteren Laboranalysen zunächst quantifiziert werden müssen, damit eine gesicherte Dateninterpretation in geochemischer Sicht möglich ist.

Description: In austral summer 2006/07 a more than 1200 m long sediment core was drilled beneath McMurdo Ice Shelf near Ross Island (Antarctica) with the purpose of contributing to a better understanding of the Late Cenozoic history of the Antarctic Ice Sheet (ANDRILL-MIS Project). Dating back to about 13 Ma this core offers the great potential to study the long-term global cooling trend at an ice-proximal location. High-resolution multi-sensor core logger measurements of whole-core physical properties serve as a numerical expression of lithologic changes in the core and therefore, represent a quantitative tool for approaching past ice dynamics. This is especially applicable for the repeating sequences of diatomites and diamtictites in the upper half of the core with a prominent cyclicity between 140-300 mbsf. Rather abrupt high-amplitude variations in wet-bulk density (WBD) and magnetic susceptibility (MS) reflect rapid changes between two main end-member facies generated by the alternation between a grounded ice sheet and open marine conditions. For the whole core, the WBD signal, ranging from 1.4 kg/cu.m in the diatomites to 2.3 kg/cu.m in diamitctites from the lower part of the core, represents the influence of three variables: (i) the degree of compaction seen as reduced porosities with depth from about 55 % in the top part to about 25 % at the bottom, (ii) the clast content with clasts being almost absent in diatomite deposits and (iii) the individual grain density (GD). GD itself ranges from about 2.15 kg/cu.m in diatomites to 2.9 kg/cu.m for volcanic sandstones and thereby reflects the variety of lithologies as well as the influence of cement (mainly pyrite and carbonate) on the matrix grain density. The calculation of residual porosities demonstrates the strong imprint of glacial loading for especially diamictites from the upper 150 m. This over-consolidation signature preserved in the sediments can be used to characterize the Pleistocene ice sheet in terms of ice thickness derived from past stresses. MS on the other hand mainly documents a marine vs. terrestrial source of sediments where the latter can be divided into younger local material from the McMurdo Volcanic Province and basement clasts from the Transantarctic Mountains. Values range over several orders of magnitude from 〈10 (10-5 SI) in the diatomites to 8000 (10-5 SI) in single clasts (mainly dolerite). Synchronous minima and maxima in both WBD and MS support dramatic changes in the depositional environment, driven by oscillations in ice extent in response to climate fluctuations. According to the age model, cyclicity occurs on Milankovich timescales with changes in obliquity being the dominant forcing until the Early Pleistocene. Additionally, small-amplitude variations within diatomite units propose sub-Milankovich forcing as superimposed control on system dynamics.