Water chemistry, sediment radiocarbon age and diatom zonation at Peterson Inlet and Browning Bay, Antarctica

The late Quaternary palaeoenvironmental history of the southern Windmill Islands, East Antarctica, has been reconstructed using diatom assemblages from two long, well-dated sediment cores taken in two marine bays. The diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late Pleistocene. During the following glacial, the Windmill Islands were covered by grounded ice preventing any in situ bioproductivity. Following deglaciation, a sapropel with a well-preserved diatom assemblage was deposited from ~10500 cal yr BP. Between ~10500 and ~4000 cal yr BP, total organic carbon (Corg) and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures. Hydrological conditions in coastal bays were characterised by combined winter sea-ice and open water conditions. This extensive period of glacial retreat was followed by the Holocene optimum (~4000 to ~1000 cal yr BP), which occurred later in the southern Windmill Islands than in most other Antarctic coastal regions. Diatom assemblages in this period suggest ice-free conditions and meltwater-stratified waters in the marine bays during summer, which is also reflected in high proportions of freshwater diatoms in the sediments. The diatom assemblage in the upper sediments of both cores indicates Neoglacial cooling from ~1000 cal yr BP, which again led to seasonally persistent sea-ice on the bays. The Holocene optimum and cooling trends in the Windmill Islands did not occur contemporaneously with other Antarctic coastal regions, showing that the here presented record reflects partly local environmental conditions rather than global climatic trends.

Radiocarbon age of bottom sediments from the Atlantic and Pacific Oceans

Procedures for radiocarbon dating of ocean sediments on board the ship using the benzene variant of the method are described. The main features of the benzene synthesis scheme, together with its differences from the method usually used onshore laboratories, are discussed briefly. Parameters of radiometric installation, in which activity of synthesized benzenes is determined are cited. The method was used successfully during Cruise 14 of R/V Dmitry Mendeleev (45 datings) and Cruise 24 of R/V Akademik Kurchatov (81 datings).

Radiocarbon age, and sedimentation and accumulation rate of core JM05-G001 obtained during Jan Mayen cruise JM050704 to the Barents Sea

Instrumental monitoring of the climate at high northern latitudes has documented the ongoing warming of the last few decades. Climate modelling has also demonstrated that the global warming signal will be amplified in the polar region. Such temperature increases would have important implications on the ecosystem and biota of the Barents Sea. This study therefore aims to reconstruct the climatic changes of the Barents Sea based on benthic foraminifera over approximately the last 1400 years at the decadal to sub-decadal scale. Oxygen and carbon isotope analysis and benthic foraminiferal species counts indicate an overall warming trend of approximately 2.6°C through the 1400-year record. In addition, the well-documented cooling period equating to the 'Little Ice Age' is evident between c. 1650 and 1850. Most notably, a series of highly fluctuating temperatures are observed over the last century. An increase of 1.5°C is shown across this period. Thus for the first time we are able to demonstrate that the recent Arctic warming is also reflected in the oceanic micro-fauna.

Radiocarbon age and sedimentation rates of bottom sediments in the Obskaya Gube (Ob River estuary

Complex geological-geochemical studies of water column and bottom sediments were carried out during Cruise 49 of R/V "Dmitry Mendeleev" in the Kara Sea shelf zone along the Obskaya Guba (Ob River estuary) from the Pur River and Taz River mouths to 76°N. Carbon-14 concentrations in organic matter from bottom sediments were determined at 5 stations. Constant initial 14C concentration model was used to determine sedimentation rates that were taken as a basis for calculating ages of sediment cores and their separate parts and for inferring location of a depocenter, i.e. a region of maximal discharge of fine-dispersed fraction of suspended matter of river run-off. Sedimentation rate in the depocenter is 170 cm/ka. Southward moves of the depocenter were recorded for periods of sea-level rises 2 and 5 thousand years ago. Bottom sediments in the depocenter contain 45% of organic matter primary produced in the Obskaya Guba. This organic matter is an energetic basis for bottom fauna life. About 55% of organic matter comes with river run-off.

Radiocarbon-age differences among coexisting planktic foraminifera shells

For slowly accumulating sediments, a major contrast exists in the radiocarbon-age differences among coexisting shells of planktic foraminifera between those experiencing little dissolution and those experiencing significant dissolution. In the former, the ages generally agree to within a couple of hundred years. In the latter, age differences as large as 1000 years are common. The most likely explanation appears to be the Barker Effect, which involves the preferential fragmentation of dissolution-prone G. sacculifer and G. ruber. The whole shells of these species picked for radiocarbon dating have shorter residence times in the bioturbation zone than those for dissolution-resistant species (including benthics). As low accumulation rate sediment cores often fail to yield reliable radiocarbon-based ocean ventilation ages, where possible, such studies should be conducted on high accumulation rate cores.

Radiocarbon age determination of 16 sites

The thermal diffusion enrichment apparatus in use in Amsterdam before 1967, has been rebuilt in the Groningen Radiocarbon Dating Laboratory. It has been shown to operate reliably and reproducibly. A reasonable agreement exists between the theoretical calculations and the experimental results. The 14C enrichment of a CO sample is deduced from the simultaneous mass 30 enrichment, which is measured with a mass spectrometer. The relation between both enrichments follows from a series of calibration measurements. The over-all accuracy in the enrichment is a few percent, equivalent to a few hundred years in age. The main problem in dating very old samples is their possible contamination with recent carbon. Generally, careful sample selection and rigorous pretreatment reduce sample contamination to an acceptable value. Also, it has been established that laboratory contamination, due to a memory effect in the combustion system and to impurities in the oxygen and nitrogen gas used for combustion, can be eliminated. A detailed analysis shows that the counter background in our set-up is almost exclusively caused by cosmic ray muons. The measurement of 28 early glacial samples, mostly from North-west Europe, has yielded a consistent set of ages. These indicate the existence of three early glacial interstadials; using the Weichselian definitions: Amersfoort starting at 68 200 ± 1100, Brørup at 64 400 ± 800 and Odderade at 60 500 ± 600 years BP. This 14C chronology shows good agreement with the Camp Century chronology and the dated palaeo sea levels. The discrepancy in the age of the early part of the Last Glacial on the 14C time scale and on that adopted for the deep-sea d18 record, must probably be attributed to the use of a generalized d18 curve and a wrong interpretation of this curve in terms of three Barbados terraces.