Description: Continental shelves and shelf seas play a central role in the global carbon cycle. However, their importance with respect to trace element and isotope (TEI) inputs to ocean basins is less well understood. Here, we present major findings on shelf TEI biogeochemistry from the GEOTRACES programme as well as a proof of concept for a new method to estimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEI cycling in the Arctic, transformations within a major river estuary (Amazon), shelf sediment micronutrient fluxes and basin-scale estimates of submarine groundwater discharge. The proposed shelf flux tracer is 228-radium (T1/2 = 5.75 yr), which is continuously supplied to the shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf 228Ra fluxes are combined with TEI/ 228Ra ratios to quantify ocean TEI fluxes from the western North Atlantic margin. The results from this new approach agree well with previous estimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmospheric deposition by factors of approximately 3–23. Lastly, recommendations are made for additional GEOTRACES process studies and coastal margin-focused section cruises that will help refine the model and provide better insight on the mechanisms driving shelf-derived TEI fluxes to the ocean.

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: Trace elements are powerful tracers – and in some instances drivers – of ocean interactions with the atmosphere, the hydrological cycle, the geology of the seafloor, and life on Earth. The concentration and the isotopic composition of trace elements are, therefore, diagnostic tools for the state of the ocean and its role as part of Earth’s dynamic system. Dissolved and particulate transport mechanisms determine how fast the ocean responds to change. The new wealth of data from the international GEOTRACES programme reveals new sources and sinks at all ocean boundaries, highlighting a much more dynamic equilibrium between the seafloor and the ocean than previously thought.

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 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.