ALBERT

Beschreibung: A combined year round assessment of selected oceanographic data and a macrobiotic community assessment was performed from October 2013 to November 2014 in the littoral zone of the polar fjord systems Kongsfjorden on the west coast of Svalbard (Norway). A state of the art remote controlled cabled underwater observatory technology was used for daily vertical profiles of temperature, salinity and turbidity together with a stereo-optical assessment of the macrobiotic community, including fish. The results reveal a distinct seasonal cycle in total species abundances with a significantly higher total abundance and species richness during the polar winter when no light is available under water compared to the summer months when 24-h light is available. During the winter months, a temporally highly segmented community was observed with respect to species occurrence with single species dominating the winter community for restricted times. In contrast, the summer community showed an overall lower total abundance, as well as a significantly lower number of species. The study clearly demonstrates the high potential of cable connected remote controlled digital sampling devices, especially in remote areas, such as the polar fjord systems, with harsh environmental conditions and limited accessibility. A smart combination of such new digital ?sampling? methods with classic sampling procedures can provide a possibility to significantly extend the sampling time and frequency especially in remote and difficult to access areas. This can help to provide a sufficient data density and therefore statistical power for a sound scientific analysis without increasing the invasive sampling pressure in ecologically sensitive environments.

Beschreibung: Increasing climate variability may pose an even greater risk to species than climate warming because temperature fluctuations can amplify adverse impacts of directional warming on fitness-related traits. Here, the influence of directional warming and increasing climate variability on marine stickleback fish (Gasterosteus aculeatus) offspring size variation was investigated by simulating changes to the mean and variance of ocean temperatures predicted under climate change. Reproductive traits of mothers and offspring size reaction norms across four climate scenarios were examined to assess the roles of standing genetic variation, transgenerational and within-generation plasticity in adaptive potential. Mothers acclimated to directional warming produced smaller eggs than mothers in constant, ambient temperatures, whereas mothers in a predictably variable environment (weekly change between temperatures) produced a range of egg sizes, possibly reflecting a diversified bet hedging strategy. Offspring size post-hatch was mostly influenced by genotype by environment interactions and not transgenerational effects. Offspring size reaction norms also differed depending on the type of environmental predictability (predictably variable vs. stochastic), with offspring reaching the largest sizes in the stochastic environment. Release of cryptic genetic variation for offspring size in the stochastic environment suggests hidden evolutionary potential in this wild population to respond to changes in environmental predictability.

Beschreibung: The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is however challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong inter-annual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (〉 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward-advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely, or small in magnitude (〈〈 1 per mil RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow.

Beschreibung: Due to methodological challenges there are only a few studies that focus on macrophyte dynamics in large lakes despite their notable role in a lake's ecosystem functioning. This study investigates composition and productivity changes of the submerged vegetation of Lake Karakul, Pamir Mountains (Tajikistan), using sedimentary ancient DNA metabarcoding and elemental (C/N) and isotopic (d13C, d15N) measurements of Stuckenia cf. pamirica ((Baagøe) Z.Kaplan; Potamogetonaceae) leaf remains. No Stuckenia cf. pamirica leaf remains were found for 28.7 to 26.1 cal ka BP, when both Potamogetonaceae and Chara (L.) DNA sequences were recorded, suggesting sparse submerged vegetation at the coring site. This agrees with the inference of a deep lake reached using geochemical proxies. From 26.1 to 17.5 cal ka BP a few macrophyte remains and high numbers of Potamogetonaceae sequences were recovered: lake level was probably low, as suggested by other studies on the lake. Another phase of increased numbers of Chara sequences and the absence of Stuckenia cf. pamirica leaf remains was found between 17.5 and 12.2 cal ka BP, which coincides with a lake-level transgression at Lake Karakul as indicated by paleo-shoreline investigations. Analyses of macrophyte remains reveal intermediate paleo-productivity from 6.9 cal ka BP and high paleo-productivity from 2.2 cal ka BP onwards. From comparisons with other studies, we suggest that lake-level changes are the main driver for the submerged vegetation composition and productivity at the coring site in Lake Karakul and underline our conclusions by depicting the present-day distribution of Stuckenia cf. pamirica and Chara within the lake.

Beschreibung: In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity. Present-day firn models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a universal constant by providing a statistically solid data set of µm-resolution 3D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges. We demonstrate why indirect measurements yield misleading data and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. Incorporation of our results does significantly influence the dating of trace gas records, changing gas age-ice age differences by up to more than 1000 years. This will help resolve inconsistencies, such as differences between East Antarctic d15N records (as a proxy for firn height) and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. The reduced coupling of proxies and surrounding conditions may allow for more sophisticated reinterpretations of trace gas records in terms of paleoclimatic changes and will foster the development of new proxies, such as the air content as a marker of local insolation.

Beschreibung: Abstract: We investigated the bacterial community structure in surface waters along a 2500 km transect in the eastern Indian Ocean. Using high throughput sequencing of the 16S rRNA gene we measured a significant latitudinal increase in bacterial richness from 800 to 1400 OTUs (42% increase; r2=0.65; p〈0.001) from the tropical Timor Sea to the colder temperate waters. Total dissolved inorganic nitrogen, chl a, phytoplankton community structure and primary productivity strongly correlated with bacterial richness (all p〈0.01). Our data suggest that primary productivity drives greater bacterial richness. Because, N2-fixation accounts for up to 50% of new production in this region we tested whether higher N2-fixation rates are linked to a greater nifH diversity. The nifH diversity was dominated by heterotrophic Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. We did not found any mechanistic links between nifH amplicon data, bacterial richness and primary productivity due to the overall low nifH evenness in this region. Scientific statement: Geographic gradients of marine microbial diversity is currently thought to be explained by two mechanisms, 1) diversity increases with increased productivity, and 2) it increases with increasing temperature. However, conclusive evidence for these mechanisms has been lacking from studies that span gradients in both, and it is unclear which organisms are responsible for the changes in diversity along these gradients. Here we present the first analysis of bacterial richness along the West Australian boundary current, the Leeuwin Current. Our analysis of bacterial richness along a latitudinal gradient in the eastern Indian Ocean shows support for the productivity mechanism rather than the temperature mechanism. Further, we show that bacterial richness increases towards the productive temperate waters are driven by productive eukaryotes (NO3- based) and heterotrophic N2-fixers.

Beschreibung: Upper air soundings onboard Polarstern are normally performed once a day to measure vertical profiles of air pressure, temperature, relative humidity and the wind vector. Helium filled balloons (TOTEX 600 g) were used to carry Vaisala RS92-SGP radiosondes. Whenever possible, the launches were carried out shortly before 11 UTC, in order to reach 100 hPa at 12 UTC. Condensed measurements (TEMP Format FM-35, BUFR) were transferred without delay into the Global Telecommunication System GTS, were they contribute to the world wide weather forecast analysis. The profile data were taken every 5 seconds, which results in a vertical resolution of about 25 meter. The profiles start at the helideck 10 m above sea level and terminate at the burst level of the balloons, normally at heights between 25 and 37 km.

Beschreibung: Past sea ice conditions and open water phytoplankton production were reconstructed from a sediment core taken in Disko Bugt, West Greenland, using the sea ice biomarker IP~25~ and other specific phytoplankton biomarker (i.e., brassicasterol, dinosterol, HBI III) records. Our biomarker record indicates that Disko Bugt experienced a gradual expansion of seasonal sea ice during the last 2.2 kyr. Maximum sea ice extent was reached during the Little Ice Age around 0.2 kyr BP. Superimposed on this longer term trend, we find short-term oscillations in open water primary production and terrigenous input, which may be related to the Atlantic Multidecadal Oscillation and solar activity changes as potential climatic trigger mechanisms. A direct sample-to-sample multiproxy comparison of our new biomarker record with microfossil (i.e., benthic foraminifera, dinocysts, and diatoms) and other geochemical records (i.e., alkenone biomarkers) indicates that different proxies are influenced by the complex environmental system with pronounced seasonal changes and strong oceanographic gradients, e.g., freshwater inflow from the Greenland Ice Sheet. Differences in sea ice reconstructions may indicate that the IP~25~ record reflects only the relatively short sea ice season (spring), whereas other microfossil reconstructions may reflect a longer (spring–autumn) interval.

Beschreibung: Using a microprofiler and electrochemical oxygen sensors after Revsbech (1989) in situ oxygen profiles measurements were conducted with a spatial resolution if 100 µm and a temporal resolution of 30 seconds at three stations in Potter Cove in austral summer 2015.

Beschreibung: This is a dataset from an in situ experiment at station S2 from the LTER monitoring site HAUSGARTEN, performed in June-July 2013 during Maria S Merian expedition MSM29. The in situ responses of Arctic deep-sea benthos to input of phytodetritus of a diatom (Thalassiosira sp.) as opposed to a coccolithophorid (Emiliania huxleyi) were investigated in incubation chambers of benthic landers. Using 13C and 15N labelled phytodetritus harvested from cultures of these species, we traced the fate of the respective phytodetritus into different parts of the food web (respiration, assimilation by bacteria and infauna 〉250 µm), in a short (4d) and long (14d) term experiment. The benthic landers were lowered to the sea floor, where they enclosed ~ 20cm of sediment and ~10 cm of overlying water. During respectively 4d and 14d, the temperature and concentrations of O2, DIC, 13C-DIC, NHx, NOx, 15N-NH4, 15N-NOx were measured. Upon recovery of the landers, the sediment was retrieved and subsampled in vertical horizons to measure pigment, TOC and TN, 13C-POC and 15N-PN concentrations, pore water concentrations of DIC, 13C-DIC, NHx, NOx, 15N-NH4 and 15N-NOx and the assimilation of 13C in bacterial fatty acids (iC15:0 and aiC15:0) and in fauna 〉 250 µm