Description: Radionuclide concentrations were studied in sediment cores taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial Western Pacific. High resolution deposition records of anthropogenic radionuclides were collected at this site. Excess 210Pb together with excess 228Th and anthropogenic radionuclides provided information about accumulation rates. Concentrations of Am and Pu isotopes were detected by gamma spectrometry, alpha spectrometry and ICP-MS. The Pu ratios indicate a high portion (minimum of 60%) of Pu from the Pacific Proving Grounds (PPG). This implies that the transport of PPG derived plutonium with the Mindanao Current southward is similarly effective as the previously known transport towards the north with the Kuroshio Current. The record is compared to other studies from northwest Pacific marginal seas and Lombok basin in the Indonesian Archipelago. The sediment core top at site GeoB17409 was found to contain a 6 cm thick layer dominated by terrestrial organic matter, which was interpreted as a result of the 2012 Typhoon Pablo-related fast deposition.

Description: Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator mass spectrometry data together with radiometric dating of the core provide a high-resolution record of ongoing deposition of anthropogenic radionuclides. A plutonium signature characteristic of the Pacific Proving Grounds (PPG) dominates in the first two decades after the start of the high yield atmospheric tests in 1950's. Approximately 40?70% of plutonium at this site in the post 1970 period originates from the PPG. This sediment record of transuranic isotopes deposition over the last 55 years provides evidence for the continuous long-distance transport of particle-reactive radionuclides from the Pacific Ocean towards the Indian Ocean.

Description: Radionuclide concentrations were studied in a sediment core GeoB17409-1 taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial Western Pacific. High resolution deposition records of anthropogenic radionuclides were collected at this site. Excess 210Pb together with excess 228Th and anthropogenic radionuclides provided information about accumulation rates. Concentrations of Am and Pu isotopes were detected by gamma spectrometry, alpha spectrometry and ICP-MS. The Pu ratios indicate a high portion (minimum of 60%) of Pu from the Pacific Proving Grounds (PPG). This implies that the transport of PPG derived plutonium with the Mindanao Current southward is similarly effective as the previously known transport towards the north with the Kuroshio Current. The record is compared to other studies from northwest Pacific marginal seas and Lombok basin in the Indonesian Archipelago. The sediment core top was found to contain a 6 cm thick layer dominated by terrestrial organic matter, which was interpreted as a result of the 2012 Typhoon Pablo-related fast deposition.

Description: Particulate organic matter (POM) discharged by rivers and deposited offshore their mouths is generally assumed to record an integrated signal from the watershed and therefore provides an archive of past environmental changes. Yet, in large river systems the riverine POM might be trapped in flood plains and the lower reaches resulting in an inefficient transport of POM particularly from the distal parts of the watershed. Further, the POM likely undergoes degradation during transport from source to sink. The Lena River is one of these large river systems stretching from 53°N to 71°N in central Siberia. The watershed can be broadly divided into two different biomes, taiga in the south and tundra in the northernmost part. The relative contribution of these biomes to the POM load of the river and its discharge to the ocean as well as the changes it is undergoing during transport are not well understood. Here we present the lignin phenol composition of different grain size fractions (bulk, 2mm-63µm, 〈63µm) of soil samples taken along a latitudinal transect (63°N to 72°N) as well as in marine surface sediments and two short sediment cores covering the last 120 years offshore the main Lena discharge channels. The lignin phenol composition of the soil samples (bulk, 2mm-63µm, 〈63µm) reflects the change in vegetation from south to north with increasing contribution of tundra vegetation. The degree of degradation between the soil sample locations as well as grain size fractions was very heterogeneous and did not show a clear trend. However, the POM seems to be slightly more degraded in the tundra, which is unexpected as the summer period when degradation in the upper thawed part of the soil can take place is shorter in the tundra compared to the southern taiga region. The marine surface sediments were dominated by gymnosperm-derived POM, particularly close to the river mouth and in the 〈63µm fraction. Because of the large heterogeneity of organic matter degradation in the soil samples and their grain size fractions, it is not quite clear to which degree the POM gets mineralized within the soils and during transport in the river compared to degradation occurring during cross shelf transport.

Description: Release of carbon from thawing permafrost in high northern latitudes is a potential positive feedback in a warming climate, particularly since large quantities of carbon-rich organic matter have been stored in the permafrost soils for many millennia. Thawing of permafrost is expected to make this ancient organic matter bioavailable resulting in increased emissions of greenhouse gases. Thawing of permafrost may also result in increased transport of particulate organic matter through river systems to the ocean, where parts of this organic matter may escape remineralization and will be buried in marine sediments. This process might have accelerated over the past century in a warming Arctic with more frequent thaw slumping and increased river discharge leading to increased mobilization of ancient terrestrial organic matter previously freeze-locked in permafrost. We therefore studied short sediment cores that were recovered off two of the main branches of the Lena River Delta, receiving the suspended matter transported from the mainly permafrost covered catchment of this great Russian Arctic river. The cores were recovered in 2013 from water depths of approximately 15 m and dated using 210Pbxs and 137Cs. The sediment records cover the past 70 to 120 years. By direct combustion of isolated analytes using an elemental analyser (EA) directly coupled to the accelerator mass spectrometer (MICADAS, Ionplus) via a Gas Interface System, we obtained compound-specific radiocarbon ages for a suite of n-alkanoic acids. We studied C16 to C28 even carbon number n-alkanoic acids, a homologous series containing both aquatic (C16 and C18 n-alkanoic acids) and terrigenous (C26 and C28 n-alkanoic acids) biomarkers. Besides, we analysed biomarker concentrations and the geochemical composition of the sediment. Our results reveal that throughout the records’ length, the age at deposition of the terrigenous biomarkers remained constant, while that of the aquatic biomarker decreased in the most recent decades. We will discuss these findings in context of the increases in Lena River discharge observed since the late 1980ies. The results allow estimation of the rapidly cycling biospheric contribution to each biomarker.