Strontium isotope geochemistry of ODP Leg 113 sites

The concentration of dissolved Sr and the distribution of 87Sr/86Sr isotope ratios in Leg 113 interstitial waters may be interpreted in terms of mixing of Sr from four different reservoirs: indigenous seawater, marine carbonate minerals, and basaltic and siliceous detrital material. The input to the pore water from these reservoirs is determined by the reactivity of the reservoir rather than its size. The presence of strontium derived from siliceous detrital material is unequivocally demonstrated in the pore waters of the hemipelagic deposits, and is also significant in the calcareous Maud Rise sediments due to the unusually low degree of carbonate recrystallization. Also, alteration of basic volcanic material is important at several sites.

Holocene DBD and Ti/LOI timeseries from Lake Hajeren on Svalbard, indicators of past glacier activity

The Arctic is warming faster than anywhere else on Earth. Holocene proxy time-series are increasingly used to put this amplified response in perspective by understanding Arctic climate processes beyond the instrumental period. However, available datasets are scarce, unevenly distributed and often of coarse resolution. Glaciers are sensitive recorders of climate shifts and variations in rock-flour production transfer this signal to the lacustrine sediment archives of downstream lakes. Here, we present the first full Holocene record of continuous glacier variability on Svalbard from glacier-fed Lake Hajeren. This reconstruction is based on an undisturbed lake sediment core that covers the entire Holocene and resolves variability on centennial scales owing to 26 dating points. A toolbox of physical, geochemical (XRF) and magnetic proxies in combination with multivariate statistics has allowed us to fingerprint glacier activity in addition to other processes affecting the sediment record. Evidence from variations in sediment density, validated by changes in Ti concentrations, reveal glaciers remained present in the catchment following deglaciation prior to 11,300 cal BP, culminating in a Holocene maximum between 9.6 and 9.5 ka cal BP. Correspondence with freshwater pulses from Hudson Strait suggests that Early Holocene glacier advances were driven by the melting Laurentide Ice Sheet (LIS). We find that glaciers disappeared from the catchment between 7.4 and 6.7 ka cal BP, following a late Hypsithermal. Glacier reformation around 4250 cal BP marks the onset of the Neoglacial, supporting previous findings. Between 3380 and 3230 cal BP, we find evidence for a previously unreported centennial-scale glacier advance. Both events are concurrent with well-documented episodes of North Atlantic cooling. We argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling. These findings highlight the climate-sensitivity of the small glaciers studied, which rapidly responded to climate shifts. The start of prolonged Neoglacial glacier activity commenced during the Little Ice Age (LIA) around 700 cal BP, in agreement with reported advances from other glaciers on Svalbard. In conclusion, this study proposes a three-stage Holocene climate history of Svalbard, successively driven by LIS meltwater pulses, episodic Atlantic cooling and declining summer insolation.

In situ experiment on Calanus finmarchicus egg production and grazing rates using fecal pellet production as proxy. North Atlantic spring 2013

The pre-bloom grazing and egg production rates of Calanus finmarchicus were studied at in situ temperature and chlorophyll concentration during spring on North Atlantic cruise. The sampled transects covered the Iceland, Irminger and Labrador basins.

Rock magnetic properties of ODP Hole 109-670A

The magnetic properties of 11 samples from Site 670 of Leg 109, 3 harzburgites and 8 highly serpentinized peridotites, have been studied. Reflected light microscopy and Curie temperatures confirm that magnetite is the dominant magnetic mineral in all samples. However, both rock types show different magnetic behavior. Susceptibility, saturation magnetization, and NRM are higher for the serpentinites, because of the higher magnetite content. The hysteresis parameters indicate magnetite particles with pseudosingle domain structure for both rock types. For the remarkable anisotropy of the magnetic susceptibility no definite explanation could be found, because of the complex texture of the samples. In both rock types the presence of maghemite, a product of low temperature oxidation of magnetite, has been indicated by reflected light microscopy and by thermomagnetic analysis. As the maghemite converts to hematite at temperatures above 350°C, the temperature during the serpentinization was below this value assuming that the maghemitization took place at the same time.

Paleomagnetism of basalts from ODP Hole 109-648A

Paleomagnetic parameters of 55 basalt samples from Hole 648B on the Mid-Atlantic Ridge were studied. Negative NRM inclinations were found for 10 samples between 10 and 25 m sub-bottom depth. Several hypotheses related to this phenomenon are discussed. NRM intensities, susceptibilities, median destructive fields, and Koenigsberger ratios are slightly different for pillow and massive basalts. One can suggest from measured parameters that magnetic carriers for massive and pillow basalts are PSD titanomagnetite grains more or less close to PSD-MD threshold size with a low degree of alteration.

Age determination and stable isotope ratios of three sediment cores from the Great Belt

The marine transgression Into the Baltic Sea through the Great Belt took place around 9,370 calibrated C-14-years B.P. The sedimentary sequence from the early brackish phase and the change to marine conditions has been investigated in detail through C-14-datings, and oxygen and carbon isotope measurements, and is interpreted by comparison with modern analogs. The oldest brackish sediments are the strongly laminated clays and silts rich in organic carbon followed by non-laminated heavily bioturbated silts. The bedding and textural characteristics and stable isotope analyses on Ammonia beccarii (dextral) and A. beccarii (sinistral) show that the deposltlonal conditions respond to a change at about 9,100 cal. a B.P. from an unstratified brackish water environment in the initial stage of the Littorina Transgression to a thermohaline layered milieu in the upper unit. The oxygen isotope results indicate that the bottom waters of this latter period had salinities and temperatures comparable to the present day Kiel Bay waters. The isotopic composition of the total organic carbon and the d13C-values of A. beccarii reveal a gradual change from an initially lacustrine/terrestrial provenance toward a brackish/marine dominated depositional environment. A stagnation of the sea level at around 9,100 to 9,400 B.P. is indicated.

Paleomagnetism of serpentinized peridotites from ODP Hole 109-970A

Paleomagnetic studies on the serpentinized peridotites recovered from ODP Hole 670A were conducted in three laboratories. High NRM intensities and magnetic susceptibilities were observed in the serpentinized peridotites, which suggest that the remanent and the induced magnetizations of the peridotites cannot be neglected as a source of the magnetic anomalies observed at sea surface. The in situ low inclination of the magnetization indicated from the laboratory studies suggests that the peridotite body has been subjected to a large-scale deformation after the acquisition of the magnetization.

Multibeam bathymetry of Timmiarmiut and Skjoldungen-Fjord, Southeast-Greenland

During an expedition with the topsail-schooner ACTIV in July 2014, parts of the Timmiarmiut-Fjord and nearly the entire Skjoldungen-Fjord in Southeast-Greenland have been mapped using a temporarily installed Seabeam-1050 multibeam echosounder. In addition, at 11 positions in the fjords, depth profiles of temperature, conductivity, salinity and sound velocity have been measured with a CTD.