Description: In search for critical elements, polymetallic nodules at the deep abyssal seafloor are targeted for mining operations. Nodules efficiently scavenge and retain several naturally occurring uranium-series radioisotopes, which predominantly emit alpha radiation during decay. Here, we present new data on the activity concentrations of thorium-230, radium-226, and protactinium-231, as well as on the release of radon-222 in and from nodules from the NE Pacific Ocean. In line with abundantly published data from historic studies, we demonstrate that the activity concentrations for several alpha emitters are often higher than 5 Bq g −1 at the surface of the nodules. These observed values can exceed current exemption levels by up to a factor of 1000, and even entire nodules commonly exceed these limits. Exemption levels are in place for naturally occurring radioactive materials (NORM) such as ores and slags, to protect the public and to ensure occupational health and radiation safety. In this context, we discuss three ways of radiation exposure from nodules, including the inhalation or ingestion of nodule fines, the inhalation of radon gas in enclosed spaces and the potential concentration of some radioisotopes during nodule processing. Seen in this light, inappropriate handling of polymetallic nodules poses serious health risks.

Description: Rock-derived or petrogenic organic carbon has traditionally been regarded as being non-bioavailable and bypassing the active carbon cycle when eroded. However, it has become apparent that this organic carbon might not be so inert, especially in fjord systems where petrogenic organic carbon influxes can be high, making its degradation another potential source of greenhouse gas emissions. The extent to which subsurface micro-organisms use this organic carbon is not well constrained, despite its potential impacts on global carbon cycling. Here, we performed compound-specific radiocarbon analyses on intact polar lipid–fatty acids of live micro-organisms from marine sediments in Hornsund Fjord, Svalbard. By this means, we estimate that local bacterial communities utilize between 5 ± 2% and 55 ± 6% (average of 25 ± 16%) of petrogenic organic carbon for their biosynthesis, providing evidence for the important role of petrogenic organic carbon as a substrate after sediment redeposition. We hypothesize that the lack of sufficient recently synthesized organic carbon from primary production forces micro-organisms into utilization of petrogenic organic carbon as an alternative energy source. The input of petrogenic organic carbon to marine sediments and subsequent utilization by subsurface micro-organisms represents a natural source of fossil greenhouse gas emissions over geological timescales.

Description: Decades ago, the analysis of ancient air – trapped deep inside of Antarctic glaciers – revealed an astonishing pattern of atmospheric CO2. Ever since we’ve first laid our eyes on these intriguing signals– alternating between glacial lows and interglacial highs – an overall question emerged: Where was the CO2 stored during the glacials and how was it released back to the atmosphere during deglacial transitions? In general, several carbon reservoirs like the terrestrial biosphere or permafrost soils might interact with, and drive the atmosphere on these glacial-interglacial timescales. By far the largest influence however, might come from the deep ocean. Today, this reservoir stores up to 60-times the carbon, of which is stored in the entire atmosphere. Hence, tiny changes in the oceanic C-cycle might have severe ramifications for atmospheric CO2-levels. Parallel to global CO2 atm, Antarctic temperatures rose, while the expanded ice shelves suffered from a massive deglacial collapse. The timing and succession of events pointed to the climatic role of the Southern Hemisphere in general and the Southern Ocean in particular and raised a second question: What was the physical process, which connected these deglacial events? Until today, the international community compiled numerous studies from terrestrial and marine (distal and proximal) archives to shed light onto this dynamic system. These studies revealed a closely connected system between Antarctic sea ice and ice shelves, deep-water and atmospheric circulation, oceanic stratification, the biological pump and also bipolar teleconnections. Here, we want to discuss the current scientific knowledge and present new isotopic data – measured on planktic and benthic foraminifers as well as bulk sediments – that show how Southern Ocean overturning circulation changed on glacial-interglacial timescales and influenced the residence times of circumpolar deep-waters as well as their transport onto the continental shelf regions. In combination with other parameters, the deglacial increase in Southern Ocean overturning represents a plausible link that might explain the parallel evolution of several deglacial climate parameters.

Description: The precise determination of radium-226 (226Ra) in environmental samples is challenging due to its low con- centration. Seawater typically contains between 0.03 and 0.1 fg g−1 226Ra. Thus, this work addresses the need for an easy and precise methodology for 226Ra determination in seawater that may be applied routinely to a large number of samples. For this reason, a new analytical approach has been developed for the quantification of 226Ra in seawater via inductively coupled plasma mass spectrometry (ICP-MS). Analysis by single collector sector-field ICP-MS was shown to be convenient and reliable for this purpose once potential molecular interfer- ences were excluded by a combination of chemical separation and intermediate mass resolution analysis. The proposed method allows purification of Ra from the sample matrix based on preconcentration by MnO2 precipi- tation, followed by two-column separation using a cation exchange resin and an extraction chromatographic resin. The method can be applied to acidified and unacidified seawater samples. The recovery efficiency for Ra ranged between 90% and 99.8%, with precision of 5%, accuracy of 95.7% to 99.9%, and a detection limit of 0.033 fg g−1 (referring to the original concentration of seawater). The method has been applied to measure 226Ra concentrations from the North Sea and validated by analyzing samples from the central Arctic (GEOTRACES GN04). Samples from a crossover station (from GEOTRACES GN04 and GEOTRACES GN01 research cruises) were analyzed using alternative methods, and our results are in good agreement with published values.