«Changing Polar Regions 25th International Congress on Polar Research March 17-22, 2013, Hamburg, Germany German Society for Polar Research Edited by ...»
A strong increase in sediment input documented by a larger depocentre and much higher sedimentation rates is interpret as evidence for glacial conditions in West Antarctica already during the Early Miocene. Warming as the result of the Mid Miocene Climatic Optimum resulted in a wet ice sheet, and led to a higher sediment supply for the period 21-14.1 Ma. Material was input along a broad front but with a focus via PITE and Abbot Trough (AT). Most of the material was transported into the eastern Amundsen deep sea where it was shaped into levee-drifts by a re-circulating bottom current. Two smaller depocentres seaward of AT and Pine Island Trough West (PITW) and reduced sedimentation rates indicate a cooler and dryer ice sheet resulting from the onset of stronger cooling after 14 Ma. A dynamic ice sheet since 4 Ma showing growth and decline during warm and cold phases is documented by a strong increase in sedimentation rates. Since 4 Ma material input was dominant via AT and PITW, where it interacted with a west-setting bottom current resulting in the continued formation of levee-drifts in the eastern and central Amundsen Sea.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 MODELING YEAR-ROUND MARINE MAMMAL HABITAT
PREFERENCES IN THE SOUTHERN OCEAN BASED ON PASSIVE
An understanding of marine mammal distribution patterns forms the basis of the design and implementation of effective management measures. Habitat modeling offers a valuable approach to combine information on species presence (or absence) with local environmental parameters to explore species-specific habitat affinities.
Most habitat modeling approaches require marine mammal presence-absence data which can only be obtained during dedicated visual surveys. However, in the Southern Ocean, the collection of visual data is complicated by the region’s remoteness, limited seasonal accessibility and the dependency on favorable light and weather conditions to conduct visual observations. Passive acoustic monitoring, by contrast, is highly suitable for long-term monitoring of marine mammals as they use sound in many behavioural contexts and species can be readily identified by their acoustic signatures. Passive acoustic data provide accurate information on temporal patterns in acoustic presence and time spent in the vicinity of the recorders.
Furthermore, knowledge on the behavioral context in which specific sound types are produced can be used to derive information on habitat usage.
Here we describe an approach for combining multi-year, year-round marine mammal presence data from passive acoustic recorders with a selected set of relevant environmental parameters to develop species-specific habitat models. Our project comprises multi-year passive acoustic data collected in Antarctic coastal as well as offshore areas throughout the Weddell Sea. Some of the species recorded are sighted only rarely during visual surveys, but are acoustically abundant in our recordings, such as the Antarctic blue whale (Balaenoptera musculus intermedia), humpback whale (Megaptera novaeangliae), fin whale (B. physalus), leopard seal (Hydrurga leptonyx), crabeater seal (Lobodon carcinophaga) and Ross seal (Ommatophoca rossii). The model will incorporate both static environmental variables, such as depth or slope, and dynamic variables, such as sea surface temperature, sea surface height, sea ice concentration and their derivatives.
The project aims at furthering our current understanding of marine mammal habitat affinities in the Southern Ocean by constructing species-specific habitat models at yet unprecedented spatial and temporal time scales.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 RECONSTRUCTION OF THE ANAEROBIC CARBON CYCLING IN
DEEP ARCTIC ENVIRONMENTS
Microbiological studies over the last two decades have shown the existence of diverse and active microbial ecosystems in the deep subsurface. It has been estimated that out of the total pool of prokaryotes inhabiting the Earth, between 75% and 94% occur in deeply buried marine and terrestrial sediments. Another surprising fact is that the biomass of the deep subsurface ecosystems is greater in numbers than the one in surface near habitats. This indicates the fundamental role of biomass from the deep biosphere for the global biogeochemical cycles over short and long time scales. However, the deep subsurface of the Earth, especially in arctic environments, remains relatively unexplored in the field of microbiology. Deep sediments of the Arctic play a key role for the Earths’ climate because of the huge amounts of belowground carbon that are preserved in the frozen ground and the fact that global warming is most pronounced in polar regions. Especially the thawing of terrestrial permafrost is suggested to be associated with a massive release of greenhouse gases, in particular methane. To understand how the system will respond to climate changes it is not only important to investigate the current status of microbial carbon turnover but also to reconstruct the systems’ response to climate changes in the past. Therefore, a comprehensive study was conducted, comprising 400 ka old archives of past microbial activity and recently active microorganisms in terrestrial permafrost deposits recovered from central Lena Delta and lake sediments in Chukotka, NE-Russia. Using a broad set of analytical methods (including ribosomal RNA gene based approach and lipid biomarker analyses) in Middle- to Late Pleistocene deposits we show a strong correlation between organic matter concentration and microorganism abundance. Lipid biomarkers that are stable in geological time scales were used to reconstruct the past microbial communities and their response to climate changes. In particular, archaeol demonstrated changes in the abundance of methanogenic archaea throughout the last 42 ka. This suggests, past warming trends caused an increase of methanogenic communities, while cooling trends cause a decline. Furthermore, analyses of phospholipid esters (PLFAs) and ethers (PLELs), characteristic markers for living bacteria and archaea, suggest the presence of living microbial cells in up to 400 ka old deposits. This was supported with incubation experiments, where significant methane production rates were observed. Our results show a quantitative and qualitative temperature response "Changing Polar Regions" - 25th International Congress on Polar Research 2013 of the microbial communities in deep arctic deposits to past climate changes.
Microorganisms do not only survive in the frozen ground, but they can be also metabolic active under energy limited conditions contributing to the carbon transformation in arctic environments.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 ICEBERG ALLEY – ANTARCTIC GATEWAY TO LOWER LATITUDES
To understand the natural sea-level rise during the last deglaciation is a key to understand current and future climate change. Here, the role of the Antarctic Ice Sheet is poorly understood, yet crucial because ice-sheet collapse in a warming world could cause rapid sea-level rise. We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet (EAIS) that, combined with ages from other Antarctic ice-sheets, indicates that the advance to (at 29 –28 ka) and retreat from their maximum extent (at 19 ka, and again, at 16 ka) was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J.
X., Hostetler, S. W., and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity
during the Last Glacial Maximum. – Science, 334, 1265-1269, doi:
Using an atmospheric general circulation model we conclude that surface climate forcing of Antarctic ice mass balance would likely cause an opposite response, whereby a warming climate would increase accumulation but not surface melting.
Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling.
Also, changes in North Atlantic Deepwater formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.
Recent data from two well-dated deep-sea sites from the Scotia Sea (Weber, M.E., Kuhn, G., Sprenk, D., Rolf, C., Ohlwein, C., and Ricken, W. (2012): Dust transport from Patagonia to Antarctica – a new stratigraphic approach from the Scotia Sea and its implications for the last glacial cycle. – Quaternary Science Reviews, 36, 177-188, "Changing Polar Regions" - 25th International Congress on Polar Research 2013 doi: 10.1016/j.quascirev.2012.01.016) provide the first integrative and representative record of Antarctic Ice Sheet instability. These sites, located in the central transport route of virtually all Antarctic icebergs, the so-called Iceberg Alley, demonstrate a highly dynamic Antarctic Ice Sheet during the last deglaciation with eight distinct phases of enhanced iceberg routing, dubbed Antarctic Ice Sheet Events (AIE), in contrast to existing models of a late and monotonous ice-sheet retreat with little contribution to the last, natural, sea-level rise 19,000 to 9,000 years ago. We found the first direct evidence for an Antarctic contribution to Meltwater Pulse 1A in the flux rates of ice-rafted debris.
Using an ensemble of transient deglacial model simulations we could show that increased export of warmer Circumpolar Deep Water towards Antarctica contributed to Antarctic Ice Sheet melt by ocean thermal forcing (Weber, M. E., Clark, P. U., Kuhn, G., Timmermann, A., Sprenk, D., Gladstone, R., Zhang, X., Lohmann, G., Menviel, L., Chikamoto, M., Friedrich, T., submitted: Millennial-scale variability of the Antarctic Ice Sheet throughout the last deglaciation. – Science, under review). These new findings hold the potential to substantially revise and improve our understanding of the transient response of the ice sheet to external and internal forcings, and the contributions to the postglacial isostatic adjustment as well as to the last, natural, sea-level rise. Our results will also help improving projections of future sea-level rise by implementing enhanced ocean thermal forcing.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 SEISMOSTRATIGRAPHY OF THE SIBERIAN ARCTIC OCEAN AND
ADJACENT LAPTEV SEA SHELF
The contribution presents a new seismostratigraphic model for the East Siberian part of the Arctic developed on the base of multichannel seismic reflection lines collected along a transect at 81°N. Age control for the sedimentary units was acquired via links to seismic lines and drill site data of the Canada Basin, the Lomonosov Ridge, and the adjacent Laptev Shelf. The data provide an insight into the sedimentary cover and crustal surface in which in turn tectonic and glacial processes are documented.
Two distinguished seismic interfaces were mapped throughout the area, which form a crucial link between the stratigraphy of the Laptev Sea and models on the evolution of the Lomonosov Ridge. The lower one, a pronounced sequence of high-amplitude reflectors is the most striking feature in the Siberian Arctic Ocean. It indicates a strong and widespread change in deposition conditions. Probably it developed during Oligocene times when a reorientation of Arctic Plates took place, accompanied by a widespread regression of sea level. The top of the reflector band is suggested to mark the end of Oligocene, and consequently the sedimentary sequences above are younger than 23 Ma. The upper interface parallels the seafloor in a depth of about 200ms. It is marked by a change from a partly transparent sequence with weak amplitude reflections below to a set of continuous high-amplitude reflectors above.
The high amplitudes indicate a strong alternation in deposition conditions. Likely this interface marks the transition to large-scale glaciation of the northern hemisphere, and consequently is dated to top of Miocene (5.3 Ma).
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 SOUTHERN OCEAN ICEBERG DRIFT
Icebergs are fragments of glacier ice, which break-off from the ice shelves and glacier tongues all around Antarctica. After calving, icebergs drift through the ocean, driven by a number of forces. The main forces are the ocean currents and the wind, but also the Coriolis force, sea surface tilt, sea ice concentration and strength, as well as the wave radiation do influence the drift of icebergs. The relative contributions of the individual forces depend on the environmental conditions (e. g. sea ice or open water) and the iceberg size and thickness.
A drift algorithm is used to simulate the drift of icebergs through the Southern ocean.
The iceberg drift algorithm is implemented in the Finite Elemente Sea-ice Ocean Model (FESOM), which has a spatial resolution of 10 km close to the ice shelf edge and 30 km offshore.
A test was carried out to study the effect of iceberg size and thickness as well as model set ups on the drift pattern. “Test icebergs” of a simplified shape were released into the model domain from 77 locations around Antarctica to simulate and analyse their path. The model results were compared with available observations.
Additionally to the drift, the model also calculates the melting of icebergs and therefore the freshwater input into the ocean.
"Changing Polar Regions" - 25th International Congress on Polar Research 2013 LIMITATIONS OF NORTHWARD TREELINE EXPANSION IN SIBERIA:
COMPARING FIELD SURVEY RESULTS WITH INDIVIDUAL-BASED
The Siberian treeline, which is exclusively formed by different Larix species, follows approximately today’s 10-12° C July isotherm. A northward expansion of boreal forests into tundra regions due to climate change is assumed and might result in e.g.