ALBERT

Description: The Antarctic Peninsula experiences a fast retreat of glaciers, which correlates with an increased release of particles and related increased sedimentation and thus, a decrease in the available light for benthic primary production. We investigated how changes in the general sedimentation and shading patterns affect the primary production by benthic microalgae, the microphytobenthos. In order to determine potential net primary production and respiration of the microphytobenthic community, sediment cores from locations exposed to different sedimentation rates and shading were exposed to photosynthetic active radiation (PAR, 400–700 nm) of 0–70 µmol photons m-2 s-1. Total oxygen fluxes and microphytobenthic diatom community structure, density, and biomass were determined. Our study revealed that the net primary production of the microphytobenthos decreased with increasing sedimentation and shading, while the microphytobenthic diatom density and composition remained similar. By comparing our experimental results with in situ measured PAR intensities, we furthermore assessed the microphytobenthic primary production as an important carbon source within Potter Cove's benthic ecosystem. We propose that the microphytobenthic contribution to the total primary production may drop drastically due to Antarctic glacial retreat and correlated sedimentation and shading, with yet unknown consequences for the benthic heterotrophic community, its structure, and diversity.

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.