ALBERT

Description: Understanding the Holocene is particularly important for providing the context for recent ice sheet dynamics –i.e. understanding whether current ice sheet dynamics are unusual or part of Holocene natural variability (Bentley et al., 2014). Knowledge on the most recent millennia of Antarctic Ice Sheet history is vital for evaluating the response of the ice sheet to various forcing agents, such as sea-level rise, atmospheric and oceanographic temperature changes, and for constraining grounding-line retreat on Holocene to recent time scales (Bentley et al., 2014). The main objective of this thesis is to add new data to reconstruct the Holocene deglaciation history of King George Island, South Shetland Islands, northwest Antarctic Peninsula, by investigating morpho-sedimentary records of glacigenic and coastal landforms and associated sediments from the on-shore ice-free areas around Maxwell Bay (King George Island), namely Potter Peninsula and Fildes Peninsulas. In order to accomplish the thesis objectives, I used (i) cosmogenic exposure dating and radiocarbon dating for absolute chronological constraints; (ii) stratigraphy and sedimentology for relative chronological constraints and reconstruction of paleoenvironmental conditions; (iii) geomorphological mapping for spatial distribution of landsystems; (iv) and ground-penetrating radar (GPR) investigations for the study of internal sedimentary architecture of coastal landforms. Radiocarbon dating results yield new age constraints for the onset of deglaciation on Potter Peninsula, which occurred around at or before 7.8 ka cal BP instead of an earlier accepted age of 9.5 ka cal BP. I provide additional evidence for a short-lived glacier re-advance between 7.2 and 7.0 ka cal BP. This re-advance is likely linked to a glacier re-advance or still-stand documented on South Shetland Islands for that time period. Nevertheless, climatic conditions associated with this glacial re-advance remain unclear. In contrast, on Fildes Peninsula, exposure and radiocarbon dating indicate that glacial oscillations were minimal during the last 7 ka. I applied radiocarbon dating to remnants of mosses preserved in moraines. The moraines were formed close to the present glacier limit between 0.5 and 0.1 ka cal BP, during the last glacier re-advance in South Shetland Islands. This advance is linked to reductions in summer/annual insolation coupled with a shift to more intense Southern Hemisphere westerly winds in the Southern Ocean. Stronger, and possibly more poleward-shifted southern westerly winds produced more precipitation-laden storm fronts passing over the South Shetland Islands and thus, increased ice accumulation. The data also show that between 1.9 and 1.3 ka cal BP a climatic optimum was reached on Fildes and Potter Peninsula, which lasted until the last glacier readvance. GPR investigations and radiocarbon dating from a gravel spit system on Potter Peninsula document coastal progradation during the late phase of the last glacier re-advance, with a stable relative sea-level. Results also show an interruption of spit progradation that coincides with a proposed onset of accelerated isostatic rebound in reaction to glacier retreat subsequent to the last glacier re-advance. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The findings of this thesis support both, glacio-isostatic adjustment (GIA) models that show limited and those which show more pronounced ice-load changes on the South Shetland Islands during the late Holocene, suggesting that some GIA model parameters for the South Shetland Islands (e.g., vi lithospheric thickness, mantle viscosity) need to be better constrained. Furthermore, my findings have implications for regional paleoclimatic reconstructions and on ice sheet modeling for the Holocene of the northwest Antarctic Peninsula region.

Description: Climate variability of the late Quaternary, especially the Last Glacial (LG) to the Holocene, has become the most heated topic for the recent decades, which helps to better understand the shape of current and future climate on our planet. The long term glacial/interglacial changes have been associated to insolation changes controlled by earth’s orbit, whereas the millennial scale variations are mostly accepted to be modulated by the “bipolar seesaw” mechanism which redistributes heat between the northern and southern hemispheres through the Atlantic Meridional Overturning Circulation (AMOC). The validation of such hypothesis is hampered by the very limited high resolution records from the high latitudes Southern Ocean. Situated at the southern end of the AMOC, Southern Ocean Atlantic sector represents one of the key regions for understanding the global climate change. The warm and cold water routes (WWR, south of Africa and CWR, Drake Passage/Scotia Sea) connect the South Atlantic to South Indian and Pacific Oceans, respectively; and the Weddell Gyre connects the open ocean South Atlantic to the Western Antarctic Shelf Ice (WASI), where nowadays the cold surface water and Antarctic Bottom Water (AABW) are generated beneath. These water masses represent the most important constituents of the AMOC in the Southern Hemisphere. This PhD project generated a series of new diatom based high resolution marine records covering wide area of the high latitudes South Atlantic, including from the Bouvet Island area and the Scotia Sea, aimed to provide new insights of the response and drive in Southern Ocean in the context of late Quaternary global climate change. With focusing on the LG to Holocene time period, by integration of our new generated and other existing records from the Southern Ocean Atlantic and Western Indian sectors, a detailed regional age model for the past 30 kyrs is established by AMS 14C dating and regional core correlation, which can be a template for further paleoenvironment reconstructions in this area. Our reconstructions suggest 2-3_C cooling in the LG south of the modern Polar Front compared to modern conditions. Winter sea ice in the Bouvet Island area expanded by 5_ latitude, the more expanded sea ice field resulted in the stronger tropical Atlantic cooling than other tropical oceans by the reduction of warm water to the South Atlantic via the WWR, and intensive export of carbon to the deep Southern Ocean. The two steps of deglacial warming are mainly concurrent with the Heinrich stadial 1 and Younger Dryas cooling in the northern hemisphere which support the bipolar seesaw from the marine archives. The North Atlantic Deep Water (NADW) provided the second source of warming from below to the high latitudes South Atlantic which extended the first step warming till 14 cal. ka (kyr BP). The temporal cooling at ca. 14-12 cal. ka is possibly caused by the melt water input from the Antarctica. Our records support the Southern Ocean control of the deglacial atmospheric CO2 rise. The early Holocene optimum marks the warmest period and the strongest cold water reduction and confined at ca. 11-10 cal. ka in the southern cores in the study area. Sea ice probably retreated south of modern conditions and maximum opal deposition southward expanded to at least 55_S. The mid-late Holocene cooling in the study area may be related to the cold water expansion from the Weddell Gyre with the developing cavity under the WASI. The Holocene climate development may have also interplayed with the NADW which represents a rapid resumption at the early Holocene and slight decline during the mid-late Holocene. The high resolution Holocene record from the central Scotia Sea suggests a stable climate at the core site. The early Holocene high productivity is maintained by the enhanced upwelling at that time. The Holocene reservoir change at the core site is evidenced, which is in agreement with the Southern II Abstract Ocean ventilation history. The pre-Holocene release of CO2 from the Southern Ocean strongly lowered the d14Catm which caused the low surface ocean reservoir at the early Holocene at the core site. The centennial scale climate variability may be mainly linked to solar activity and also influenced by the sea ice induced freshwater variability. Stratigraphis of long term records from the Scotia Sea covering the past 300 kyrs were established by a combination of radiocarbon chronology, correlation of magnetic susceptibility (MS) to Antarctic ice core dust/climate records, diatom biofluctuation stratigraphy, and geomagnetic chronology. Good consistency of the age models by these proxies improves the reliability of our stratigraphies and indicates the applicability of these approaches. However, detailed investigation show that, the radiocarbon chronology can be affected by the changes in carbon reservoir and fossil carbon contamination in the study area; the abundance pattern of diatom species Eucampia antarctica can be used to identify the past 6 marine isotope stages (MIS) while the fluctuation weakens during MIS 7 and 8; the reliability of geomagnetic chronology weakens at low sedimentation rates conditions. The MS-Antarctic ice core correlations represent high efficiency and the best reliability due to the high sensitivity to the changes of surrounding source regions and current systems, which is closely related to the climate changes in the Southern Ocean. In addition, a possible correlation between the ash layers found in our Scotia Sea cores and the Antarctic ice cores is established, which can be used as additional age markers for further studies in this area.

Description: Enhanced glacier and polar ice sheet melting during the last decades is one of the major focuses of geosciences. The understanding of the effects of future global warming is important due to raising sea level. Antarctic ice masses play a key role in global climate. Melting of Antarctic ice would result in a sea level rise of about ~3-6 m due to the West Antarctic Ice Sheet and 60 m due to the East Antarctic Ice Sheet. Because of its marine-based nature, especially the West Antarctic Ice Sheet is sensitive to rising temperatures. Additionally, the Ross Sea, as a part of the west Antarctic system, and its shelf are a key region stabilizing the west Antarctic ice masses. It is thus essential to understand the processes and changes in this area in order to interpret the past and predict the future climate developments. Sedimentary archives are a unique opportunity to get insights into past climate variability and the ice response due to increased temperature (~3°C), as the earth had experienced in the last 14 Ma since the mid Miocene cooling. The multi-national drilling program ANDRILL (ANtarctic geological DRILLing, McMurdo Ice Shelf project, MIS) focuses on the changes of climatic influences on the West Antarctic Ice Sheet during the past ~14 Ma. During austral summer 2006/07, an approximately 1300 m long sedimentary succession beneath the northwestern Ross Ice Shelf was cored. In this study geochemical investigations were carried out and interpreted using a multiproxy approach. The results of major element measurements from X-ray fluorescence on discrete samples and high-resolution non-destructive XRF analyses on split-cores, using an XRF core scanner, total organic carbon, total inorganic carbon, opal, and mineral data, as well as optical microscope and visual colour reflectance investigations were used to reveal different processes controlling the depositional environment in the southern Ross Sea. Provenance analyses reveal three main sources for fine-grained terrigenous sediments at the MIS site. First, close-by McMurdo Group volcanoes (MVG) are a source for sedimentary deposits of AND-1B (mainly diamictites) during times of extended glaciations. Second, in interglacial periods, sediment composition (mainly mudstones) is controlled by southern Transantarctic Mountains (S TAM) and finally a geochemical mixture of both sources is visible in the record, which also can be indicative for a western Transantarctic Mountain source (W TAM). According to sediment architecture (McKay, 2008) and source, different transport mechanisms are existing. MVG sediments are mainly transported by subglacial erosion, whereas S TAM and W TAM sediments represent ice proximal to distal conditions with transport processes such as fluvial meltwater and gravity flows. The entire AND-1B core can be divided into 5 major sections of provenance. These geochemical facies (GCF) represent colder phases during Late Miocene and Late Pleistocene (GCF1, dominated by MVG); warm intervals during early Pliocene and late Pliocene are dominated by input from southern provenances (GCF 2), and oscillations between material from MVG and W TAM dominate the mid Pliocene (GCF 3). In sedimentary successions indicating glacial terminations and extended sea ice conditions dolomite, Fe-dolomite siderite and other traces of carbonate minerals were found. Micritic crystal size and distribution within the sediment matrix reveal an authigenic, early diagenetic precipitation. These precipitates form in concert with freezing processes that result in a hyper-saline brine formation, saturating pore waters with respect to dolomite phases. Within the layers of hyper-saline brines, dolomite or unstable carbonate phases occur that are later on recrystallized to dolomite. An additional factor for dolomite formation is sulphate reduction, indicated by pyrite and biomarkers of sulphate reducing bacteria. The features of the AND-1B dolomite are likely to be transferable to global cap-carbonates of Precambrian times and can be likely an explanation for dolomite formation due to rapid deglaciations at glacial terminations. During open water conditions in the southern Ross Sea, when no West Antarctic Ice Sheet had existed (Naish et al., 2009), mass accumulation and paleoproductivity estimations from the AND-1B record reveal the Ross Sea as a high production area during Pliocene and Pleistocene. Opal accumulation is in the same ranges as for modern analogues in front of the present Ross Ice Shelf edge and even higher during specific times in the Pliocene. In contrast, paleoproduction and organic carbon accumulation rates are low and reveal a decoupling between organic carbon and opal preservation, where opal evidences good preservation efficiency while organic carbon shows low preservation rates. These results suggest that the Ross Shelf was an oxic environment with strong organic carbon degradation during the Pliocene. Nevertheless, accumulation of organic carbon was high enough to make the Ross Shelf a major sink for organic carbon. In a global comparison, the Ross Sea area removed more carbon from the atmospheric CO2 cycle as some highly productive up-welling systems do.

Description: The Weddell Sea Embayment (WSE) in Antarctica is one of the least explored environments on Earth. Ice streams and glaciers draining into it discharge more than 22 % of Antartic continental ice to the Southern Ocean. Due to extensive sea ice cover and harsh weather conditions throughout the year, this region is largely inaccessible, leaving it with only sparse knowledge about the deglacial history since the Last Glacial Maximum (LGM). Understanding the post–LGM evolution of the Antarctic Ice Sheet (AIS) in this sector is crucial in order to test and calibrate numerical ice sheet models that aim at predicting future AIS stability and dynamics. Especially the grounded ice sheet extent and retreat history within the cross–shelf Filchner Trough, a paleo–ice stream trough incising the southern continental shelf of the WSE, is controversial. For this thesis I investigated giant gravity cores (GGC) recovered from the deepest parts of the inner Filchner Trough, just seawards the ice shelf edge position during the Austral summer 1987/1988. Apart from describing the sedimentary lithologies and structures, a multi–proxy approach, including the determination of grain–size distributions, TC/TOC contents, magnetic susceptibilities, water contents and shear strengths has been applied in order to define sedimentary facies. Furthermore, ten new and reliable 14C radiocarbon ages, derived from calcareous foraminifera, are provided in order to reach a better understanding about the deglacial history of the WSE. Detailed analyses of the sediments reveal a retreat stratigraphy on the southern Wed-dell Sea continental shelf, containing distal glaciomarine sediments overlying sediments that have been deposited rather proximal to the ice sheets grounding line (GL). The distinction between these two sedimentary facies is largely based on grain–size analysis, determination of water contents, wet bulk densities (WBD) and shear strengths. These results in combination with the constrained 14C radiocarbon ages indicate that since the last ~5.8 cal. 14C ka BP the depositional environment in the Southern Weddell Sea must have been comparable to those observed today and hence, that the ice sheet must have started its landward retreat prior to that. Unusually high TOC contents in only one of the two investigated cores not only show that the GGC’s must have been fed from different catchments, but also that TOC contents in this region have to be treated with caution, since fossil carbon from the hinterland may contaminate samples significantly and would have a˙ected potential AIO ages, thereby leading to erroneous interpretations of postglacial retreat. This fact shows that 14C radiocarbon dating of calcareous microfossils is the most reliable dating method for sediments from Antarctic continental shelves, thus for reliably characterising long–term glacial changes in Antarctica.

Description: Lambert, cosmological letters, fixed stars, nebulae, island universe, teleology, teleological, enlightenment, enlightened, romanticism, romantic, hypothesis, physical-teleological, speculation, imagination, stability, solar system, cosmology, astronomy, comet, magic, alchemy, pietism, science, arts, philosophy, Newtonian. - Johann Heinrich Lamberts Cosmological Letters was published 1761 in Augsburg. Lambert tried to expose a theory of the structure of the universe as a whole, that is, a theory that was able to involucrate all sorts of observed celestial bodies, like 'fixed stars' und nebulae. Lambert tackles his task mixing two disciplines, which in principle seem to be incompatible: Newtonian physics and teleology. Lambert's speculative and imaginative way to formulate his hypotheses shows resemblances to the way of making science developed during the romantic period, disagreeing with the methods of enlightenment, movement to which Lambert is usually associated. A central aspect of this thesis is to study Lambert's figure in relation to this two traditions, with the finality to deal with the compression of his ideas in depth, in light of the transition between the enlightened vision of the world and the romantic one.

Description: thesis

Description: The different benthic foraminiferal species (epibenthic as well as endobenthic) colonize wide areas of the ocean floor and are widely used for paleoceanographic reconstructions. To improve these reconstructions, it is an important part in research to continuously develop and refine proxies by e.g. improving measuring techniques as well as introducing other species in paleoceanograhpy. The main focus of the presented thesis is a regional examination of the trace element ratios of the rarely used benthic foraminifer Oridorsalis umbonatus and the investigation of their suitability for paleoceanographic applications. Since O. umbonatus is not very abundant in the sediments, it was necessary . as a prerequisite for such studies . to investigate, whether laser ablation ICP-MS can be used for trace element measurements on benthic foraminifera. Therefore, as a first step, trace elements were measured using laser ablation ICP-MS on a set of modern core top samples collected along a depth transect on the continental slope off Namibia at 25.5.S (320 . 2300m water depth; 2.9. to 10.4.C). The Mg/Ca ratios where than calibrated against bottom water temperatures (BWT). The study demonstrates clearly that benthic foraminiferal trace elements can be reliably measured with the laser ablation technique and that the Mg/Ca ratio of O. umbonatus has the potential to be used as a proxy for BWTs...

Description: thesis

Description: In the early 1990`s the first IPCC report stated the effect of anthropogenic CO2 emissions on global warming and John Martin`s Iron Hypothesis (Martin and J.H 1990), relating atmospheric dust deposition, a major source of iron to the surface ocean, to the CO2 concentration in the atmosphere and the last ice age, culminating in the well known sentence Give me (half) a tanker of iron and I’ll give you a new ice age!. Since then, several large-scale in situ Fe fertilisation experiments revealed that in large areas of the ocean, the so called high nutrient low chlorophyll (HNLC) areas, phytoplankton growth is partly limited by depleted Fe conditions (Geider et al. 1994; De Baar and Boyed 2000; Boyd et al. 2007). The ocean receives Fe from upwelling, riverine input, melting icebergs, atmospheric dust input, input from anoxic sediments, hydrothermal vents and direct recycling by organisms(Tovar-Sanchez et al. 2007). However, in HNLC regions the Fe input to surface waters is very low resulting in Fe limitation of phytoplankton growth. Fe is an important nutrient for marine phytoplankton (Geider et al. 1994; Falkowski et al. 1998; Morel and Price 2003), being essential in metabolic reactions like the photosynthetic electron transport and the assimilation of nitrogen. It is also required for the synthesis of chlorophyll (Martin et al. 1988; Maldonado et al. 1999) as well as for the functioning of the enzyme superoxide dismutase which inhibits the breakdown of chlorophyll by superoxide radicals (Coale 1991)...

Description: thesis

Description: Mg/Ca ratios in benthic foraminiferal shells are frequently used in paleoceanographic studies to estimate past bottom water temperatures. Apart from temperature, other factors may exert additional influences on foraminiferal Mg/Ca. These include the Mg/Ca ratio of seawater, partial dissolution of shell calcite, salinity, physiological effects, and, probably of capital importance, the carbonate chemistry of seawater. In this context, the seperate effects of temperature and seawater carbonate chemistry on the magnesium incorporation into benthic foraminideral calcite are unraveled and quantified in this thesis...

Description: thesis

Description: Organic-walled dinoflagellate cysts, oxidation, degradation, organic matter. - Species-selective aerobic decomposition affects fossil organic-walled dinoflagellate cyst (dinocyst) records and hence dinocyst-based interpretations of primary productivity and oceanographic conditions. However, since the recognition of dinocyst species sensitive and resistant to oxic degradation (S- and R-cysts, respectively) it has become apparent that R-cysts may still serve as reliable productivity and oceanographic conditions proxies. On the other hand S-cysts provide a way to quantify aerobic degradation of organic matter (OM) and past bottom-water O2 concentrations. OM degradation plays a key role in global carbon cycling and is important for global climate change. Therefore dinocysts are a valuable tool for estimating the rate of diagenetic process. Questions concerning species-selective aerobic degradation still remain and will be adressed here. To obtain information on the rate of S-cyst decomposition, the relationship between S-cyst degradation and O2 concentrations, and the aerobic degradation of extinct dinocyst species, a natural exposure experiment has been conducted and studies of both Quaternary and pre-Quaternary material from sediment cores were executed. The exposure experiment was conducted in the natural setting of the Eastern Mediterranean. During a 15 month exposure period to oxic water masses, concentrations of S-cysts (Brigantedinium spp. and Echinidinium granulatum) decreased by 24 to 57%. However, taxa such as Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum and Impagidinium aculeatum demonstrated a slight increase in concentration, indicating resistance to aerobic degradation. These results show that even short-term exposure to oxygen may cause considerable changes in the dinocyst assemblage ...

Description: thesis

Description: Marine snow, underwater cameras, particle flux, aggregation, suspended particulate matter, particle transport. - This study focusses on the vertical distribution and transportation pathways of marine particles off NW-Africa with aid of optical methodologies. A profiling camera system and a remotely operated vehicle (ROV) was used for in-situ observations on the distribution, transport processes and sinking behaviour of marine particulate matter. Between the regional areas of investigation Cape Blanc, Dakhla and Cape Bojador significant differences could be observed with respect to distribution and transportation patterns. These differences are primarily related to the different primary production conditions between the investigation areas. Primary production is the most important factor for the abundance of particulate matter, where highest particle concentrations in the entire water column were seen off Cape Blanc. Next to primary production, water depth, currents and density gradients are factors influencing the particle distribution patterns. With respect to the prevailing transport processes, the Cape Blanc region is characterised by vertically orientated transport patterns. In addition to the continuous supply of large, relatively fast sinking particle aggregates a sinking event could be documented for the first time in-situ in the water column. These events deliver huge amounts of particulate matter from the ocean surface ...

Description: thesis