First year of routine measurements at the AWI MICADAS 14C dating facility.

In November 2016, the first Mini-Carbon-Dating-System (MICADAS) manufactured by Ionplus AG was delivered and installed at the Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research (AWI), Germany. After one year of establishing the instrument and preparation methods, we started routine operation for scientific purposes in January 2018. The new facility includes a graphitization unit (AGE3) connected to an elemental analyser (EA) or a carbonate handling system (CHS), and a gas inlet system (GIS). The facility at AWI focuses on analysing carbonaceous materials from samples of marine sediments, sea-ice, and water to investigate various aspects of the global carbon cycle. A particular emphasis will be on sediments from high-latitude oceans, in which radiocarbon-based age models are often difficult to obtain due to the scarcity of carbonate microfossils (e.g., foraminifera). One advantage of the MICADAS is the potential to analyse samples as CO2 gas, which allows radiocarbon measurements on samples containing as little as 10 µgC. For example, it is possible to determine 14C ages of foraminifera from carbonate-lean sediments allowing paleoclimate reconstructions in key locations for the Earth’s climate system, such as the Southern Ocean. Likewise, compound-specific 14C analyses receive growing attention in carbon cycle studies and require handling of small samples of typically <100 µgC. The wide range of applications including gas analyses (e.g., foraminifera and isolated compounds), and graphite targets require establishing routine protocols for various methods including sample preparation and precise blank assessment. We report on our standard procedures for dating organic matter from sediments or water including carbonate removal, combustion and graphitization using the AGE3 coupled to the EA, as well as on the methodology applied for carbonate samples using the CHS system and the GIS. We have investigated different sample preparation protocols and present the results using international standard reference materials (e.g., IAEA-C2 F14C = 0.4132 + 0.0052 (n= 14); Ref = 0.4114 + 0.0003). Additionally, we present the first results of process blanks for sediments (Eocene Messel shale F14C= 0.0007; equivalent to an conventional 14C age of > 52000yr (n=29)), as well as Eemian foraminifera (F14C = 0.005; equivalent to an conventional 14C age of >42700yr (n=98)). We are also presenting results of samples processed and analysed as graphite and directly as gas showing a good reproducibility irrespective of the method used

Establishment of routine sample preparation protocols at the newly installed MICADAS 14C dating facility at AWI

In November 2016, the first Mini-Carbon-Dating-System (MICADAS) manufactured by Ionplus AG was delivered and installed at the Alfred-Wegener-Institute (AWI), Germany. The new facility includes a graphitization unit (AGE3) connected with an elementar analyser (EA), a carbonate handling system (CHS), and a gas inlet system (GIS). The main goal for the facility at AWI will be the precise and independent dating of carbonaceous materials in marine sediments, sea-ice, and water to address various processes of the global carbon cycling. A particular focus will be on sediments from the high latitude oceans, in which radiocarbon-based age models are often difficult to obtain due to the scarcity of carbonate microfossils. One advantage of the MICADAS is the potential to analyse samples, which contain only a small amount of carbon as CO2 gas. For example, it will be possible to determine 14C ages of samples of foraminifera from carbonate-lean sediments, allowing for paleoclimate reconstructions in key locations for Earth’s climate system such as the Southern ocean. Likewise, compound-specific 14C analyses receive growing attention in carbon cycle studies and require handling of small samples of typically <100µg carbon. The wide range of applications encompassing gas analyses of foraminifera and compound-specific analysis as well as analyses of graphite targets requires establishing routine protocols of various methods of sample preparation, as well as thorough assessment of the respective carbon blanks. We report on our standard procedures for samples of organic matter from sediments or water including carbonate removal, combustion and graphitization using the AGE3 coupled to the EA, as well as on the methodology applied for carbonate samples using the CHS system and the GIS. We have investigated different sample preparation protocols and present the initial results using materials of known age. Additionally, we present the first results of our assessment of process blanks

Tracing the source of ancient reworked organic matter delivered to the North Atlantic Ocean during Heinrich Events

A major effort of the geochemical and paleoclimate community has been to identify the specific sources of the ice-rafted debris (IRD) in Heinrich Layers (HLs). Although the general consensus is that the majority of the IRD originated from the Hudson area of northern Canada, the specific sources are not well constrained. Here we compare the diagnostic organic geochemical signature of HLs to that of a number of Paleozoic outcrops across the former margin of the Laurentide ice sheet. We show that the biomarker signature of Upper Ordovician strata from Southampton and Baffin Island is compatible with that found in HLs in the Labrador Sea and North Atlantic, while the biomarker signature of other Paleozoic formations from the former margin of the Laurentide ice sheet is not. In addition to the biomarker signature, key-inorganic characteristics (δ18O, εNd, and 87Sr/86Sr ratios) of these formations from Southampton and Baffin Island are consistent with those reported from HLs. The location of these formations in and around the Hudson Strait is compatible with palaeo-ice flow regimes through the Hudson Strait, allowing for easy entrainment and rapid transport to the ocean. Based on these results we propose that these specific Upper Ordovician formations form a main source of IRD in HLs and hence infer an active role of the Hudson Strait paleo-ice flow in these events

Permafrost-carbon mobilization in Beringia caused by deglacial meltwater runoff, sea-level rise and warming

During the last deglaciation (18–8 kyr BP), shelf flooding and warming presumably led to a large-scale decomposition of permafrost soils in the mid-to-high latitudes of the Northern Hemisphere. Microbial degradation of old organic matter released from the decomposing permafrost potentially contributed to the deglacial rise in atmospheric CO2 and also to the declining atmospheric radiocarbon contents (Δ14C). The significance of permafrost for the atmospheric carbon pool is not well understood as the timing of the carbon activation is poorly constrained by proxy data. Here, we trace the mobilization of organic matter from permafrost in the Pacific sector of Beringia over the last 22 kyr using mass-accumulation rates and radiocarbon signatures of terrigenous biomarkers in four sediment cores from the Bering Sea and the Northwest Pacific. We find that pronounced reworking and thus the vulnerability of old organic carbon to remineralization commenced during the early deglaciation (~16.8 kyr BP) when meltwater runoff in the Yukon River intensified riverbank erosion of permafrost soils and fluvial discharge. Regional deglaciation in Alaska additionally mobilized significant fractions of fossil, petrogenic organic matter at this time. Permafrost decomposition across Beringia's Pacific sector occurred in two major pulses that match the Bølling-Allerød and Preboreal warm spells and rapidly initiated within centuries. The carbon mobilization likely resulted from massive shelf flooding during meltwater pulses 1A (~14.6 kyr BP) and 1B (~11.5 kyr BP) followed by permafrost thaw in the hinterland. Our findings emphasize that coastal erosion was a major control to rapidly mobilize permafrost carbon along Beringia's Pacific coast at ~14.6 and ~11.5 kyr BP implying that shelf flooding in Beringia may partly explain the centennial-scale rises in atmospheric CO2 at these times. Around 16.5 kyr BP, the mobilization of old terrigenous organic matter caused by meltwater-floods may have additionally contributed to increasing CO2 levels

Reasons for downtimes of the AWI-MICADAS.

In November 2016, the first MICADAS manufactured by Ionplus AG was delivered and installed at the Alfred-Wegener-Institute (AWI), Germany. After one year of establishing the instrument and preparation methods, we started routine operation for scientific purposes in January 2018. In the talk, we will present varying reasons for technically related downtimes of the MICADAS_15 and solutions to reduce them. We will also present an outlook of wishes for future applications

Late Pleistocene to Holocene variations in marine productivity and terrestrial material delivery to the western South Atlantic

Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8 degrees S, 44.3 degrees W, 840-m water depth). The organic proxies were classified into "terrestrial-source" and "marine-source" groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the South Brazil Bight may respond to warmer and dryer climate conditions.Peer reviewe

Deglacial release of petrogenic and permafrost carbon from the Canadian Arctic impacting the carbon cycle

AbstractThe changes in atmospheric pCO2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide Ice Sheet retreat. Glacial-retreat-induced physical erosion of bedrock has mobilized petrogenic carbon, as revealed by sedimentary records of radiocarbon dates and thermal maturity of organic carbon from the Canadian Beaufort Sea. Additionally, coastal erosion during the meltwater pulses 1a and 1b has remobilized pre-aged carbon from permafrost. Assuming extensive petrogenic organic carbon oxidation during the glacial retreat, a model-based assessment suggests that the combined processes have contributed 12 ppm to the deglacial CO2 rise. Our findings suggest potentially positive climate feedback of ice-sheet retreat by accelerating terrestrial organic carbon remobilization and subsequent oxidation during the glacial-interglacial transition.</jats:p

Fossil organic carbon utilization in marine Arctic fjord sediments by subsurface micro-organisms

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 timescale