ALBERT

Description: The data set was used to predict soil organic carbon and soil moisture in the vertical as well as horizontal domain, i.e. volumetrically, by using a weighted conditioned Latin Hypercube Sampling design for selecting the calibration samples and the geophysical covariates derived from electromagnetic induction (EMI) and a gamma-ray spectrometer with different intercoil spacings and, thus, different penetration depths and footprints of the signal. The study site is an agricultural field of 58 ha about 70 km north of Leipzig, Saxony-Anhalt, Germany. Present soil types are Gleysols and Gleyic Cambisols consisting of alluvial loam (loam and clay)over Holocene sediments of fluvial sand (LAGB, 2014). The geophysical measurements were recorded with three EMI sensors (EM38-DD, Geonics Limited, ON, CA; CMD-Explorer and CMD-Mini-Explorer, both GF Instruments, CZ) and a gamma-ray spectrometer (GS CAR, GF Instruments, CZ) in August 2016. EMI sensors measure the apparent electric conductivity (ECa in mSm-1). All EMI sensors captured 5 records s-1 in any dipole orientation. The gamma-ray spectrometer is equipped with a 4l NaI(Tl)-crystal and automatic peak-stabilization to measure the concentration of potassium (40K), uranium (238U) and thorium (232Th). The device has 512 channels with an energy range from 100 keV to 3 MeV. Measurements were captured every 5 seconds. 40K, 238U and 232Th were measured as counts per second. The concentration of 40K (in %) and 238U and 232Th (both in ppm) was calculated corresponding to the decay rate at specific energy levels. The concentration of 40K, 238U and 232Th was used to calculate the dose rate (nGyh 1; IAEA, 2003). For determination of soil organic carbon, the samples were dried at 40 °C for 24 h, sieved (〈2 mm), ground and root fragments were removed. Total carbon was determined with dry combustion using an ELTRA CHS-580A Helios analyser (ELTRA GmbH, GER). Soil moisture was measured gravimetrically with drying at 90 °C for 24 h.

Description: Methane is a very effective greenhouse gas, but the role of the Polar Regions in the methane budget and its sources there is subject to discussion. The sparse surface network data and satellite data indicate significant source regions above the polar oceans. The remotely piloted quadrocopter ALICE was developed for taking air samples to study methane isotopic composition related to different polar atmospheric boundary layer conditions above sea ice and open water (German Research Foundation, DFG, grant No. LA2907/8-1, DA 2907/5-1). Adapted to rough polar conditions the quadrocopter carries twelve 100 ml glass bottles for air sampling and sensors for air temperature, humidity, irradiation and surface temperature up to 1000 m above ground. The samples can be taken by opening the evacuated glass bottles at any point of the trajectory, at predefined positions or manually triggered by the operator. The quadrocopter is a tool to get vertical profiles of air samples easier than with other methods. The initially tested prototype was field operated for the first time during Polarstern cruise PS109 (ARK-XXXI/4) in September/October 2017. A scientific case study was done at rewetted peatland area at Zarnekow (Northeast Germany), by probing the atmosphere above this known methane source during the morning transition at one day in late spring 2018 and at one day in early autumn 2018 (Lampert et al., https://www.atmos-meas-tech-discuss.net/amt-2019-111/) The data set includes 5 flights of the initial operational field testing during the PS109 expedition and two days of surveying a rewetted peatland area at Zarnekow. In the PANGAEA data set, different parameters characterizing the measurement system, the meteorological conditions and the air sampling system are provided: Time of the measurements, coordinates and altitude of the quadrocopter based on global navigation satellite systems (GNSS) and barometric pressure, three-dimensional velocity of the quadrocopter, raw data of air temperature and humidity measured by several temperature and humidity sensors, surface temperature, upward and downward solar radiation, and the pressure inside the twelve glass bottles, to control at which altitude the sample was taken. For the Zarnekow data set, the methane isotopic composition of each sample is included, as well as the corresponding sampling altitude. Methane concentration and methane isotopic composition for additional water samples are provided in Lampert et al. (2019).

Description: This dataset contains the collection of available published paired Uk'37 and Tex86 records spanning multi-millennial to multi-million year time scales, as well as a collection of Mg/Ca-derived temperatures measured in parallel on surface and subsurface dwelling foraminifera, both used in the analyses of Ho and Laepple, Nature Geoscience 2016. As the signal-to-noise ratios of proxy-derived Holocene temperatures are relatively low, we selected records that contain at least the last deglaciation (oldest sample 〉18kyr BP).

Description: Documentation of sediment cores from RV Polarstern cruise ANT-IX/3 to the Weddell Sea.

Description: Sedimentation and the early diagenetic processes have been studied in surface sediments from the NE-Greenland shelf and continental slope. I have used these data together with geochemical and sedimentological investigations from seven long sediment cores from the NE- and E-Greenland continental margin between 80' and 72' N for reconstructing the paleoenvironmental history of the East- Greenland-Current (ff).

Description: The mode and vigor of the global oceanic circulation critically depend on the salinity of (sub)surface water masses advected to the loci of deep-water formation. Within the Atlantic meridional overturning circulation (AMOC), an important supplier of high-salinity waters is the Mediterranean Outflow Water (MOW), discharging into the North Atlantic via the Strait of Gibraltar. Despite its importance for the North Atlantic salinity budget, the long-term dynamics of MOW production have remained poorly understood. Here we present high-resolution records of bottom-current velocity from three drill sites within the Gulf of Cádiz that document a persistent low-latitude forcing of MOW flow speed over the past ~150 k.y. We demonstrate that the African monsoon is the predominant driver of orbital-scale MOW variability via its influence on the freshwater budget of the eastern Mediterranean Sea. Consequently, MOW formation fluctuates in concert with orbital precession overprinted by centennial-scale oscillations of high-latitude origin. We further document that Northern Hemisphere summer insolation minima stimulate maximal injection of MOW-derived salt into the North Atlantic, likely strengthening the intermediate AMOC branch. The direct coupling of MOW dynamics to low-latitude climate forcing represents a hitherto neglected process for propagating (sub)tropical climate signals into the high northern latitudes.

Description: Paleostudies of the Indonesian Throughflow (ITF) are largely based on temperature and salinity reconstructions of its near surface component, whereas the variability of its lower thermocline flow has rarely been investigated. We present a multi-proxy record of planktonic and benthic foraminiferal d18O, Mg/Ca-derived surface and lower thermocline temperatures, X-ray fluorescence (XRF)-derived runoff and sediment winnowing for the past 130 ka in marine sediment core SO18471. Core SO18471, retrieved from a water depth of 485 m at the southern edge of the Timor Strait close to the Sahul Shelf, sits in a strategic position to reconstruct variations in both the ITF surface and lower thermocline flow as well as to investigate hydrological changes related to monsoon variability and shelf dynamics over time. Sediment winnowing demonstrates that the ITF thermocline flow intensified during MIS 5d-a and MIS 1. In contrast during MIS 5e, winnowing was reduced and terrigenous input increased suggesting intensification of the local wet monsoon and a weaker ITF. Lower thermocline warming during globally cold periods (MIS 4 - MIS 2) appears to be related to a weaker and contracted thermocline ITF and advection of warm and salty Indian Ocean waters.

Description: Limited information on the East Antarctic Ice Sheet (EAIS) geometry during Marine Isotope Stage 3 (MIS 3; 60-25 ka) restricts our understanding of its behaviour during periods of climate and sea level change. Ice sheet models forced by global parameters suggest an expanded EAIS compared to the Holocene during MIS 3, but field evidence from East Antarctic coastal areas contradicts such modelling, and suggests that the ice sheet margins were no more advanced than at present. Here we present a new lake sediment record, and cosmogenic exposure results from bedrock, which confirm that Rauer Group (eastern Prydz Bay) was ice-free for much of MIS 3. We also refine the likely duration of the Last Glacial Maximum (LGM) glaciation in the region. Lacustrine and marine sediments from Rauer Group indicate the penultimate period of ice retreat predates 50 ka. The lacustrine record indicates a change from warmer/wetter conditions to cooler/drier conditions after ca. 35 ka. Substantive ice sheet re-advance, however, may not have occurred until much closer to 20 ka. Contemporary coastal areas were still connected to the sea during MIS 3, restricting the possible extent of grounded ice in Prydz Bay on the continental shelf. In contrast, relative sea levels (RSL) deduced from field evidence indicate an extra ice load averaging several hundred metres thicker ice across the Bay between 45 and 32 ka. Thus, ice must either have been thicker immediately inland (with a steeper ice profile), or there were additional ice domes on the shallow banks of the outer continental shelf. Further work is required to reconcile the differences between empirical evidence of past ice sheet histories, and the history predicted by ice sheet models from far-field temperature and sea level records.

Description: Bioturbation in marine sediments has basically two aspects of interest for palaeo-environmental studies. First, the traces left by the burrowing organisms reflect the prevailing environmental conditions at the seafloor and thus can be used to reconstruct the ecologic and palaeoceanographic situation. Traces have the advantage over other proxies of practically always being preserved in situ. Secondly, for high- resolution stratigraphy, bioturbation is a nuisance due to the stirring and mixing processes that destroy the stratigraphic record. In order to evaluate the applicability of biogenic traces as palaeoenvironmental indicators, a number of gravity cores from the Portuguese continental slope, covering the period from the last glacial to the present were investigated through X-ray radiographs. In addition, physical and chemical parameters were determined to define the environmental niche in each core interval. A number of traces could be recognized, the most important being: Thalassinoides, Planolites, Zoophycos, Chondrites, Scolicia, Palaeophycus, Phycosiphon and the generally pyritized traces Trichichnus and Mycellia. The shifts between the different ichnofabrics agree strikingly well with the variations in ocean circulation caused by the changing climate. On the upper and middle slope, variations in current intensity and oxygenation of the Mediterranean Outflow Water were responsible for shifts in the ichnofabric. Larger traces such as Planolites and Thalassinoides dominated in coarse, well oxygenated intervals, while small traces such as Chondrites and Trichichnus dominated in fine grained, poorly oxygenated intervals. In contrast, on the lower slope where calm steady sedimentation conditions prevail, changes in sedimentation rate and nutrient flux have controlled variations in the distribution of larger traces such as Planolites, Thalassinoides, and Palaeophycus. Additionally, distinct layers of abundant Chondrites correspond to Heinrich events 1, 2, and 4, and are interpreted as a response to incursions of nutrient rich, oxygen depleted Antarctic waters during phases of reduced thermohaline circulation. The results clearly show that not one single factor but a combination of several factors is necessary to explain the changes in ichnofabric. Furthermore, large variations in the extent and type of bioturbation and tiering between different settings clearly show that a more detailed knowledge of the factors governing bioturbation is necessary if we shall fully comprehend how proxy records are disturbed. A first attempt to automatize a part of the recognition and quantification of the ichnofabric was performed using the DIAna image analysis program on digitized X-ray radiographs. The results show that enhanced abundance of pyritized microburrows appears to be coupled to organic rich sediments deposited under dysoxic conditions. Coarse grained sediments inhibit the formation of pyritized burrows. However, the smallest changes in program settings controlling the grey scale threshold and the sensitivity resulted in large shifts in the number of detected burrows. Therefore, this method can only be considered to be semi-quantitative. Through AMS-^C dating of sample pairs from the Zoophycos spreiten and the surrounding host sediment, age reversals of up to 3,320 years could be demonstrated for the first time. The spreiten material is always several thousands of years younger than the surrounding host sediment. Together with detailed X-ray radiograph studies this shows that the trace maker collects the material on the seafloor, and then transports it downwards up to more than one meter in to the underlying sediment where it is deposited in distinct structures termed spreiten. This clearly shows that age reversals of several thousands of years can be expected whenever Zoophycos is unknowingly sampled. These results also render the hitherto proposed ethological models proposed for Zoophycos as largely implausible. Therefore, a combination of detritus feeding, short time caching, and hibernation possibly combined also with gardening, is suggested here as an explanation for this complicated burrow.