ALBERT

Description: In the present study, we report the results of comprehensive amino acid (AA) analyses of four Indian lakes from different climate regimes. We focus on the investigation of sediment cores retrieved from the lakes but data of modern sediment as well as vascular plant, soil, and suspended particulate matter samples from individual lakes are also presented. Commonly used degradation and organic matter source indices are tested for their applicability to the lake sediments, and we discuss potential reasons for possible limitations. A principal component analysis including the monomeric AA composition of organic matter of all analysed samples indicates that differences in organic matter sources and the environmental properties of the individual lakes are responsible for the major variability in monomeric AA distribution of the different samples. However, the PCA also gives a factor that most probably separates the samples according to their state of organic matter degradation. Using the factor loadings of the individual AA monomers, we calculate a lake sediment degradation index (LI) that might be applicable to other palaeo-lake investigations.

Description: Species distribution models (SDM) predict species occurrence based on statistical relationships with environmental conditions. The R-package biomod2 which includes 10 different SDM techniques and 10 different evaluation methods was used in this study. Macroalgae are the main biomass producers in Potter Cove, King George Island (Isla 25 de Mayo), Antarctica, and they are sensitive to climate change factors such as suspended particulate matter (SPM). Macroalgae presence and absence data were used to test SDMs suitability and, simultaneously, to assess the environmental response of macroalgae as well as to model four scenarios of distribution shifts by varying SPM conditions due to climate change. According to the averaged evaluation scores of Relative Operating Characteristics (ROC) and True scale statistics (TSS) by models, those methods based on a multitude of decision trees such as Random Forest and Classification Tree Analysis, reached the highest predictive power followed by generalized boosted models (GBM) and maximum-entropy approaches (Maxent). The final ensemble model used 135 of 200 calculated models (TSS 〉 0.7) and identified hard substrate and SPM as the most influencing parameters followed by distance to glacier, total organic carbon (TOC), bathymetry and slope. The climate change scenarios show an invasive reaction of the macroalgae in case of less SPM and a retreat of the macroalgae in case of higher assumed SPM values.

Description: The Indian Monsoon and the westerlies strongly influence the sedimentation in the northeastern Arabian Sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean. To disentangle the terrestrial and oceanic processes, we analysed mineralogical and bulk geochemical components of a Holocene sediment core offshore Pakistan. Endmember modelling of grain sizes and principal component analyses (PCA) of major and trace elements identify the origin of sediments and their dominant mode of transport. Sedimentation processes during the early Holocene (10.8–8.2 ka BP) were influenced by the post-glacial sea level rise and orbitally forced strengthening of the Indian summer monsoon (ISM) and westerlies. This led to a shift from rather terrestrial-dominated towards a marine-dominated sedimentation, whereas the fluvial source shifted from the Makran rivers to the Hab River near Karachi. During the mid-Holocene (8.2–4.2 ka BP) a combination of weakening ISM and southward displacement of the ITCZ enhanced the influence of the westerlies, together decreasing river discharges and enhancing aeolian input (probably from the Sistan Basin region). This trend continued during the last ca. 4 ka when the increasing aridification of the Hab River catchment further increased the aeolian inputs. Solar and lunar driven short-term variations as well as Bond events known from the North Atlantic Ocean superpose these trends. They lead to a pronounced increase of fluvial inputs between 8.6–8.4 ka BP and at ca. 3 ka BP as well as to dry events around 4.2 ka and 1.2–1 ka BP. Our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern Arabian Sea towards the late Holocene.

Description: To understand the fate of the increasing amount of macroalgal detritus in Antarctic shallow subtidal sediments, a mesocosm experiment was conducted to track 13C and 15N labelled macroalgal detritus into the benthic bacterial, meio- and macrofaunal biomass and respiration of sediments from Potter Cove (King George Island). We compared the degradation pathways of two macroalgae species: one considered palatable for herbivores (the red algae Palmaria decipiens), and one considered non-palatable for herbivores (the brown algae Desmarestia anceps). 15 sediment cores were taken from station Faro at 20m water depth. 13C and 15N labelled macroalgae were added to 10 cores: 5 cores received Desmarestia anceps, 5 cores received Palmaria decipiens. 5 cores did not receive any macroalgae and acted as a control. At different points in time, the cores were closed airtight for a dark incubation of 12h, during which oxygen was measured to calculate Total Oxygen Uptake (TOU), next to 13C-DIC, total nutrients and 15N-labelled nutrients (NH4, NOx and N2). The next day, the cores were sacrificed to determine the assimilation of macroalgae detritus in bacteria, microphytobenthos, meiofauna, macrofauna. Also the remaining large (〉1mm) macroalgae fragments were recovered and the bulk POC and PN of the sediment was measured. The sampling points are 1d after addition, and 7, 14 and 21 and 26 days after addition of macroalgae detritus.

Description: This is a an inventory of 86, mainly published, temperature records of northeastern North America and the northwestern Atlantic, covering the Holocene. Most records were published before and some of these have been updated applying new modern training sets for reconstruction and/or updated chronologies. Reconstructions were obtained from marine and terrestrial sites and a range of proxies, including pollen, dinocysts, chironomids, alkenones, varve characteristics and isotopes. Reconstruction and age uncertainties are provided when available.

Description: Between 07.10.2007 and 28.10.2007, bathymetric data was acquired in the Makran region during the R/V METEOR cruise M74/2. The subduction of the Eurasian plate beneath the Arab plate in the Makran region is associated with continuous sediment input, active mud volcanism and fluid venting. The expedition was dedicated to the investigation of known seeps and the location of new venting sites. Furthermore, the scientists focused on the influence of extreme sediment thickness on the nature of vents and the relationship between local tectonics and spatial distribution of seeps. The multibeam echosounders (MBES) KONGSBERG SIMRAD EM120 and EM710 were utilized for large-scale mapping of vent-related structures on the seafloor. In order to visualize vent-related structures in the shallow subsurface, a deep-tow sidescan sonar, sediment echosounder, and high-resolution multichannel equipment were utilized. These acoustic methods were supplemented by video observations and gravity corer and multicorer samples, which yielded detailed information at many locations. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the M74/2 cruise, the hull-mounted multibeam ecosounder (MBES) KONGSBERG SIMRAD EM710 was utilized to perform bathymetric mapping. The system is optimised to survey with high resolution in water depths of maximum 1,000 m depth and uses a frequency range from 70 to 100 kHz. 256 beams with an acoustical 1°(TX)/1°(RX) footprint are formed for each ping. Combining phase and amplitude bottom detection algorithms allows achieving best possible accuracy. For further information, consult: https://epic.awi.de/id/eprint/26726/1/Kon2007b.pdf. The position and depth of the water column is estimated for each beam by using the detected two-way-travel time and the beam angle known for each beam and taking ray bending due to refraction in the water column by sound speed into account. As most of the working area during M74/2 was deeper than 1,000m water depths, the EM 710 was used sporadically as an addition to the EM120. Systematically biased outer beams produced problems in areas with large overlap of parallel profiles. The applied sound velocity profile and a roll bias were tested as possible error sources, but no significant error was found. As the effect seems to be strongest on steep slopes, it might be a problem in yaw, which was not corrected for so far. Responsible person during this cruise / PI: Markus Brüning Chief Scientist: Volkhard Spiess (vspiess@uni-bremen.de) CR: https://www.tib.eu/en/search/id/awi%3Adoi~10.2312%252Fcr_m74/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2007/20080085.htm