«Changing Polar Regions 25th International Congress on Polar Research March 17-22, 2013, Hamburg, Germany German Society for Polar Research Edited by ...»
Phytoplankton Chl a and primary production (PP) were investigated during two summer-autumn seasons in ten lakes of the Bunger Hills, East Antarctica. The Chl a varied over all water bodies within 0.05-9.6 and 0.11-5.0 mg Chl a m-3 during the first and second season, respectively. The variations of daily PP in first and second season, respectively, were within 0.18-110 and 0.60-172 mgC m-3 d-1. General trend of increasing PP with growing water salinity was observed. In most lakes the differences of average Chl a and PP between two seasons were 2-4 times due to variable environmental conditions (presence/absence of ice cover, light, mixing conditions). In one of the largest antarctic lake, Lake Algae, Chl a and PP increased several times and remained at higher levels for at least 6 weeks after a major storm thoroughly mixed the lake and probably inoculated particles of algal mats into water column. In the marine Rybiy Khvost Gulf the average Chl a and PP varied c. twofold between the two seasons and the values were close to typical antarctic near-coast marine ecosystems. The chlorophyll-specific assimilation rates (AR) varied commonly within 0.1-2.0 mg C(mg Chl a)-1 h-1 in freshwater lakes and 0.7-5.9 mg C(mg Chl a)-1 h-1 in saline lakes. Much lower and higher AR were observed by decreased light and increased water temperature, respectively.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 LANGZEITPROJEKTE MIT SCHÜLERGRUPPEN UND
Mit drei aufeinanderfolgenden Schülergruppen von 2004 bis 2012 wurden am Marien-Gymnasium in Werl (ab 2004) und Heinrich-Heine-Gymnasium Dortmund (ab
2007) experimentelle Langzeitprojekte durchgeführt, die jeweils eine Dauer von etwa drei Jahren hatten. Den Start in die gemeinsame Arbeit stellte jedes Mal das TonnenProjekt dar, ein ökologisches Langzeitprojekt mit künstlichen Mesokosmen in Regentonnen. Projektpartner hierzu war das HIGHSEA-Schulprojekt am AWI in Bremerhaven. Höhepunkte der Projektarbeit waren zwei „Forschungsreisen“ mit Schülergruppen nach Tromsø in Nord-Norwegen in den Jahren 2008 und 2011.
Zentrales Ziel aller Teilprojekte war das Heranführen von interessierten Jugendlichen an wissenschaftliches Arbeiten. Dabei sollte das eigene Tun – Vorbereitung, Untersuchung, Auswertung, Dokumentation, Präsentation – im Vordergrund stehen.
Im Rückblick auf die abgeschlossenen Projekte ergab sich, dass neben diesen Zielen ein weiterer wichtiger Aspekt resultierte, nämlich die Bedeutung für die Persönlichkeits-Bildung der beteiligten Jugendlichen. Dieser Aspekt soll nach einem Überblick zu den Projekten den Schwerpunkt des Vortrages bilden.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 NEW MARINE GEOLOGICAL AND GEOPHYSICAL EVIDENCE FOR
THE EXTENT, FLOW, AND RETREAT OF A WEST ANTARCTIC
PALAEO-ICE STREAM OFFSHORE FROM THE HOBBS COAST
Palaeo-ice stream beds that are exposed today on polar continental shelves provide unique archives of conditions at the base of ice sheets that are difficult to assess beneath their modern counterparts. During the last decade, several of these palaeoice stream beds have been studied in detail to reconstruct the extent of the West Antarctic Ice Sheet (WAIS) at the Last Glacial Maximum (LGM), the patterns of ice drainage, and the timing of grounding-line retreat during the last deglaciation.
However, despite significant advances, such information still remains poorly constrained in numerous drainage sectors of the WAIS. In particular, the maximum extent of ice at the LGM remains ambiguous for key drainage basins of the ice sheet.
Whether the WAIS extended to the shelf break in the entire Pacific sector, or it advanced, at least locally, only to a middle or outer shelf position, is a crucial piece of information required for reconstructing and modeling patterns of ice-sheet change from past to present.
Here we present new marine geological and geophysical data that we collected on R/V “Polarstern” expedition ANT-XXVI/3 in early 2010 to investigate the extent, flow, and retreat of the WAIS from an especially poorly studied part of the West Antarctic shelf, offshore from the Hobbs Coast in the western Amundsen Sea. Here, a landward deepening palaeo-ice stream trough is incised into the shelf. The seafloor within the western-central part of the trough is characterized by a large grounding zone wedge (GZW), ~70 m thick and ~17 km long, which overlies a high of seaward dipping sedimentary strata. Directly seaward of the GZW a ~20 km wide 80±10 m deep relatively flat basin is mapped. The back-slope of the GZW is characterized by highly elongate streamlined bedforms suggesting fast palaeo-ice flow towards NW. In contrast, the outer shelf seafloor offshore from the GZW is predominantly smooth, at numerous locations scoured by icebergs and characterized by a distinct and ~2 mdeep subbottom reflector. As in other Antarctic shelf sectors, this subbottom reflector is likely to mark the top of a subglacial stiff till that is probably of LGM age, because a calcareous microfossil from the thin layer above the subbottom reflector provided a radiocarbon age of ~9.0 corr. ka BP at 98 cmbsf (centimeter below seafloor). A radiocarbon date from the inner shelf shows that the grounded ice here had retreated landward from the GZW remarkably early (before ~13.0 cal 14C yrs). This early deglaciation is in agreement with other minimum deglaciation ages from the "Changing Polar Regions" - 25th International Congress on Polar Research 2013 Amundsen Sea embayment (e.g. Pine Island Bay and Dotson-Getz Trough). For the GZW we propose two possible formation scenarios: either (1) that it formed during a prolonged stillstand when the WAIS retreated from the outer shelf following the LGM, or (2) it marks the maximum grounding-line extent at the LGM. Although we rather propose, that grounded ice extended all the way or close to the shelf edge during the LGM, we cannot yet exclude the possibility that the GZW marks the LGM limit of grounded ice. Here we specifically point to the size and volume of the GZW, which are more comparable to grounding-line features marking LGM-positions around Antarctica (e.g. in Prydz Bay), and less similar to GZWs deposited during episodic ice-stream retreat (e.g. in Pine Island Trough and Marguerite Trough). In order to test these two formation scenarios for the GZW and constrain the timing and duration of its formation, we will try to obtain additional ages from seasonal-open marine units in cores seaward of the GZW. This will help to decide whether LGM-or older ice was grounded in the basin directly seaward of the GZW.
We will present preliminary interpretations of these data, which will aim to resolve the extent of the WAIS in this sector, provide new information on GZW formation in this trough and, at the same time, contribute an update on the dynamics of West Antarctic palaeo-ice streams, which drained the former ice sheet.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 PAN-AFRICAN GRANITOID MAGMATISM IN CENTRAL DRONNING
MAUD LAND DERIVED FROM A MANTLE SOURCE, NOT A LOWER
CRUSTAL SOURCE: EVIDENCE FROM GEOCHEMICAL AND SR-ND
Dronning Maud Land represents the southern end of the East African-Antarctic orogen (EAAO) that was constructed during the Neoproterozoic collision of parts of East- and West-Gondwana. The orogen spans more than 8000 km from the northern part in present Egypt-Arabia down to present Mozambique and Antarctica. The EAAO shows a strong along strike variation in orogenic styles separated by the E-Wtrending Lurio belt in Mozambique with accretion in its northern part and continentcontinent collision in the southern part. South of the Lurio belt numerous Pan-African granitoids are observed. Two different models are debated to explain the occurrence of these late-tectonic Pan-African melts (530-485 Ma): (i) SE-directed thrusting of nappes from the combined Damara-Zambesi mobile belt towards Dronning Maud Land  explaining the granitoid magmatism via crustal melting through crustal thickening; (ii) extensional tectonics with delamination of the orogenic root  explaining the granitoid magmatism by upwelling of hot asthenosphere under a thinned continental crust. We present major and trace element data and Sr-Nd WR signatures of granitoids that constitute an E-W profile along the 72°S-latitude starting from the Mühlig-Hofmann mountains (MH) (4°-7°E) via central Dronning Maud Land (cDML) (8°-14°E) and finally samples from Sør Rondane (SR) (23°-25°E). Most granitoid from MH and cDML show subalkaline ferroan signatures. This coincides with their interpretation as extension-related granitoids in the scheme of Maniar & Piccoli . WR Nd isotope signatures show Paleo- to Mesoproterozoic model ages that, as the oldest zircons found in that area to date are Grenville-aged, are taken as indication for the participation of the subcontinental lithospheric mantle (SCLM) during petrogenesis of these granitoids thus favouring the delamination model. Since the WR Nd signatures further are unrelated to the corresponding SiO2-content it can even be proposed that the SCLM represents the source region for the granitoid melts. The situation for the SR granitoids is different as they show calcalkaline magnesian signatures that typically are interpreted in terms of active continental margin derivation. The corresponding TDM (Nd) are Grenville-aged at ~1.1 Ga. We therefore conclude that SR granitoids evolved in a different geodynamic setting and "Changing Polar Regions" - 25th International Congress on Polar Research 2013 possibly represent the eastern suture of the EAAO whereas the MH and cDML granitoids are located in an extensional setting probably related to the orogenic collapse of the EEAO. Sr isotope signatures for both regions are similar and show a homogenisaion during time of emplacement during Pan-African times. Finally, comparison with samples from the Lurio belt allows to place constraints on paleogeographical position as Mozambiquan late-tectonic granitoids show large similarities with results from MH and cDML, but are different to SR granitoids.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 ASSESSMENT OF A MODERN POLLEN-CLIMATE CALIBRATION
SET FOR ARCTIC TUNDRA AND NORTHERN TAIGA BIOMES FROM
The Arctic is expected to respond stronger and earlier to future global warming than other regions world-wide. This region is of particular importance because, on the one hand, even humble climate oscillations can be amplified through complex terrestrial ecosystem reactions. On the other hand, Arctic changes may feedback globally via atmospheric and oceanic circulations or variation of greenhouse gas concentrations.
Past variations need to be documented with high confidence to gain important insights in constraints and magnitude of predicted Arctic changes. Long-term information can be obtained by analyses of sedimentary archives such as pollen records of lacustrine cores. Reliable climate reconstruction from the warmingsensitive Arctic region are hitherto lacking because a) modern pollen spectra were rarely collected from sedimentary origin, and b) because the obtained reconstructions were not rigorously evaluated.
This investigation aims to establish, evaluate, and apply a modern pollen-climate data set from the transition zone between arctic tundra and light taiga in Arctic Siberia. Our study area is located in the Northern Siberian Lowlands of Yakutia.
Lacustrine samples (n=96) were collected along four north-to-south transects, which cover the major vegetation types and span a broad summer temperature and precipitation gradient (TJuly: 7.5–18.8°C; Pann: 114-315mm). Performance of transfer functions for temperature and precipitation were validated and applied to the one lake pollen record, which covers the last 12,000 years and was retrieved in the Siberian Arctic. The application of the models to fossil pollen spectra yielded cold conditions for the Late Glacial period (1-2°C below present TJuly). Warm and moist conditions were reconstructed for the Early to Mid Holocene (2°C higher TJuly than present). Modern conditions were reconstructed for the last 3,500 years.
In conclusion, our regional modern data set fills the gap of existing calibration sets with regard to under-representation of samples from the modern tundra-taiga transition zone and of lake sedimentary origin. Our Holocene climate reconstruction indicates that the Holocene temperature deviation from modern values was only moderate despite the assumed Arctic sensitivity to present climate change.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 LONG-TERM TRACE GAS RELEASE FROM THAWING
The currently observed Arctic warming will increase permafrost degradation followed by mineralization of formerly frozen organic matter to carbon dioxide (CO2) and methane (CH4). Despite increasing awareness of permafrost carbon vulnerability the potential long-term formation of trace gases from thawing permafrost remains unclear. Therefore, the release of trace gases from permafrost organic matter was quantified in Holocene and Pleistocene permafrost deposits in the Lena River Delta, Northeast Siberia. CO2 and CH4 production was measured for 1200 days in aerobic and anaerobic incubations at 4°C. The derived fluxes were used to estimate parameters of a two pool carbon degradation model. Total CO2 production was similar in Holocene permafrost (1.3 ± 0.8 mg CO2-C gdw-1 aerobically, 0.25 ±