(Tables 2) The bPSi:POC ratio of the total diatom community, and abundance of full, empty, and broken diatom cells compared to heavily silicified diatoms during the EIFEX experiment

During the European Iron Fertilisation Experiment (EIFEX), performed in the Southern Ocean, we investigated the reactions of different phytoplankton size classes to iron fertilization, applying measurements of size fractionated pigments, particulate organic matter, microscopy, and flow cytometry. Chlorophyll a (Chl a) concentrations at 20-m depth increased more than fivefold following fertilization through day 26, while concentrations of particulate organic carbon (POC), nitrogen (PON), and phosphorus (POP) roughly doubled through day 29. Concentrations of Chl a and particulate organic matter decreased toward the end of the experiment, indicating the demise of the iron-induced phytoplankton bloom. Despite a decrease in total diatom biomass at the end of the experiment, biogenic particulate silicate (bPSi) concentrations increased steadily due to a relative increase of heavily silicified diatoms. Although diatoms >10 µm were the main beneficiaries of iron fertilization, the growth of small diatoms (2-8 mm) was also enhanced, leading to a shift from a haptophyte- to a diatom-dominated community in this size fraction. The total biomass had lower than Redfield C : N, N : P, and C : P ratios but did not show significant trends after iron fertilization. This concealed various alterations in the elemental composition of the different size fractions. The microplankton (>20 µm) showed decreasing C : N and increasing N : P and C : P ratios, possibly caused by increased N uptake and the consumption of cellular P pools. The nanoplankton (2-20 µm) showed almost constant C : N and decreasing N : P and C : P ratios. Our results suggest that the latter is caused by a shift in composition of taxonomic groups.

Susceptibility, magnetization and S-ratio of ODP Sites 201-1225 and 201-1227

Samples were collected at Sites 1225 and 1227 to investigate the occurrence of fine-grained, biogenic magnetic particles (magnetosomes). Several magnetic methods, including anhysteretic remanent magnetization and isothermal remanent magnetization, were used to characterize the main magnetic carriers in the samples. Extracts were made to isolate the fine-grained fraction, which was then examined under a transmission electron microscope. Grains with the unique characteristics of magnetosomes were found in samples from regions in the core with both high and low concentrations of magnetic minerals. This suggests they have the potential to be a persistent proxy of paleoredox conditions.

Compression and expansion index and void ratio of samples from Lomonosov Ridge and Yermak Plateau

With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (~ 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.

Sediment composition and stable isotopic ratio of Neogloboquadrina pachyderma from DSDP Site 94-609_Site, North Altlantic

Digitized records of optical desnity in many North Atlantic cores exihibt rapid changes from lighter to darker extrems, typically within less than 200 years, at the 5d/5e, 5b/5c and 4/5 boundaries. In cores from DSDP site 609 the changes from lighter to darker color coincide with increasing in relative abundance of Neogloboquadrina pachyderma (l.c.), with increases in abundances of lithic grains and with decreasing in carbonate content. The rapid changes to dark color, therefore, are climate-driven and correspond to a lowering of seas surface temperatures and to increases in amounts of ice rafted debris relative to biogenic carbonate. At the 5d&4c boundary, delta18O in N. pachyderma (l.c.) increases abruptly with the change to darker sediments as expected for cooler sea surface temperatures. At the 4/5 boundary, however, delta18O decreases with the change to darker sediment and cooler sea surface temperatures, suggesting that a layer of fresh surface water was present in the North Atlantic at that time.