Description: Ice cores provide several environmental archives that give us insights into the history of the climate of the earth. Stable water isotopes can be used for long term temperature trends during Holocene and young Pleistocene while trace elements indicate seasonal patterns on short term and glacials on long term scales. Nevertheless, syn- and postdepositional processes influence the originally deposited signal of those proxies. As there is lack of continuous data-based annual accumulation distribution in Antarctica, it is still not clear, how single species are deposited in snow and how the signal can be interpreted. Especially the temporal variability of deposition dependent on seasonal accumulation is a fact that needs to be unterstood. Therefore, in this master thesis we try to explain, how the deposition of proxies is coupled with accumulation and show implications for an interpretation of distinct proxy signals. For this purpose, snow profiles with a length of 50 cm were taken at four different locations, which are along a path of 40 m. The main site was sampled 41 times within a period of 53 days, while the other three locations were used as reference for spatial variance. With that setup, especially the temporal resolution was in the focus of interest. The liner were cut into distinct samples of 1 cm (0-30 cm depth) and 2 cm (30-50 cm depth) and analyzed on several trace elements (Na+, Cl-, NO3 -, SO42-, Ca2+, Mg2+ and MSA) using a Dionex IC 2100 ion chromatograph. δ18O and δ2H measurements were conducted using cavity ring-down spectroscopy (CRDS) and an Picarro analyzer. Study area is the EPICA drill site Kohnen (75°0‘ S; 0°4‘ E) in Dronning Maud Land, Antarctica with an accumulation rate of 64 mm w.e. per year and upward tendency towards higher values. We performed a time-depth-correlation taking recent ablation stake measurements into account and plotted the isotopic and aerosol record on the basis of an estimated accumulation distribution. We used a value of 0.5 cm a-1 snow per winter month which is, based on density data from the snow liner, about 1.83 mm w.e. The validity of the temporal correlation was done by conservative aerosol records of sea salt components Na+ and Cl-. In general, the case study reveals poor correlation between isotopic record and surface temperature on the small temporal and special scale. We observed a lack of summer signal and high dependence on short term climate fluctuations like high precipitation events during extended winter season. Nevertheless, those small scale variations cannot be seen in the isotopic record as smoothing exceeds the temporal resolution. 2H-excess in uppermost snow layers and the trend of δ18O versus δ2H confirms high influence of evaporation and sublimation effects on the snow surface that alter the real deposition signal. The allocation of summer and winter to ice core data therefore seems to be based on a high noise influence. Furthermore we showed that local and short time intervals can drastically influence the deposited tracer signals. Wind erosion by strong wind events or squalls may highly disturb the continuous stratigraphy of snow and firn. Finally, we state the urgent need of continuous accumulation distribution in Antarctica to verify patterns shown in this thesis and carry out further observations in higher resolution.

Description: Forests worldwide are threatened by various environmental and anthropogenic hazards, especially tropical forests. Knowledge on the impacts of these hazards on forest structure and dynamics has been compiled in empirical studies. However, the results of these studies are often not sufficient for long-term projections and extrapolations to large spatial scales especially for unprecedented environmental conditions, which require both the identification and understanding of key underlying processes. Forest models bridge this gap by incorporating multiple ecological processes in a dynamic framework (i.e. including a realistic model structure) and addressing the complexity of forest ecosystems. Here, we describe the evolution of the individual-based and process-based forest gap model FORMIND and its application to tropical forests. At its core, the model includes physiological processes on tree level (photosynthesis, respiration, tree growth, mortality, regeneration, competition). During the past two decades, FORMIND has been used to address various scientific questions arising from different forest types by continuously extending the model structure. The model applications thus provided understanding in three main aspects: (1) the grouping of single tree species into plant functional types is a successful approach to reduce complexity in vegetation models, (2) structural realism was necessary to analyze impacts of natural and anthropogenic disturbances such as logging, fragmentation, or drought, and (3) complex ecological processes such as carbon fluxes in tropical forests – starting from the individual tree level up to the entire forest ecosystem – can be explored as a function of forest structure, species composition and disturbance regime. Overall, this review shows how the evolution of long-term modelling projects not only provides scientific understanding of forest ecosystems, but also provides benefits for ecological theory and empirical study design.

Description: Reliable statements about variability and change in marine ecosystems and their underlying causes are needed to report on their status and to guide management. Here we use the Framework on Ocean Observing (FOO) to begin developing ecosystem Essential Ocean Variables (eEOVs) for the Southern Ocean Observing System (SOOS). An eEOV is a defined biological or ecological quantity, which is derived from field observations, and which contributes significantly to assessments of Southern Ocean ecosystems. Here, assessments are concerned with estimating status and trends in ecosystem properties, attribution of trends to causes, and predicting future trajectories. eEOVs should be feasible to collect at appropriate spatial and temporal scales and are useful to the extent that they contribute to direct estimation of trends and/or attribution, and/or development of ecological (statistical or simulation) models to support assessments. In this paper we outline the rationale, including establishing a set of criteria, for selecting eEOVs for the SOOS and develop a list of candidate eEOVs for further evaluation. Other than habitat variables, nine types of eEOVs for Southern Ocean taxa are identified within three classes: state (magnitude, genetic/species, size spectrum), predator–prey (diet, foraging range), and autecology (phenology, reproductive rate, individual growth rate, detritus). Most candidates for the suite of Southern Ocean taxa relate to state or diet. Candidate autecological eEOVs have not been developed other than for marine mammals and birds.Wec onsider some of the spatial and temporal issues that will influence the adoption and use of eEOVs in an observing system in the Southern Ocean, noting that existing operations and platforms potentially provide coverage of the four main sectors of the region—the East and West Pacific, Atlantic and Indian. Lastly, we discuss the importance of simulation modelling in helping with the design of the observing system in the long term. Regional boundary: south of 30°S.

Description: We compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal. In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean, and as a result, the biota tends to be similar within a given broad latitudinal band. South of the Southern Boundary of the ACC, there is a large-scale divergence that brings nutrient-rich water to the surface. This divergence, along with more localized upwelling regions and deep vertical convection in winter, generates elevated nutrient levels throughout the Antarctic at the end of austral winter. However, such elevated nutrient levels do not support elevated phytoplankton productivity through the entire Southern Ocean, as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters. However, coastal regions, with the upward mixing of iron, maintain greatly enhanced rates of production, especially in coastal polynyas. In these coastal areas, elevated primary production supports large biomasses of zooplankton, fish, seabirds, and mammals. As climate warming affects these advective processes and their heat content, there will likely be major changes in the distribution and abundance of polar biota, in particular the biota dependent on sea ice.