ALBERT

Description: The seabed plays a key role in the marine carbon cycle as a) the terminal location of aerobic oxidation of organic matter, b) the greatest anaerobic bioreactor, and c) the greatest repository for reactive organic carbon on Earth. We compiled data on the oxygen uptake of marine sediments with the objective to understand the constraints on mineralization rates of deposited organic matter and their relation to key environmental parameters. The compiled database includes nearly 4000 O 2 uptake data and is available as supplementary material. It includes also information on bottom water O 2 concentration, O 2 penetration depth, geographic position, water depth, and full information on the data sources. We present the different in situ and ex situ approaches to measure the total oxygen uptake (TOU) and the diffusive oxygen uptake (DOU) of sediments and discuss their robustness towards methodological errors and statistical uncertainty. We discuss O 2 transport through the benthic and diffusive boundary layers, the diffusion- and fauna-mediated O 2 uptake, and the coupling of aerobic respiration to anaerobic processes. Five regional examples are presented to illustrate the diversity of the seabed: Eutrophic seas, oxygen minimum zones, abyssal plains, mid-oceanic gyres, and hadal trenches. A multiple correlation analysis shows that seabed O 2 uptake is primarily controlled by ocean depth and sea surface primary productivity. The O2 penetration depth scales with the DOU according to a power law that breaks down under the abyssal ocean gyres. The developed multiple correlation model was used to draw a global map of seabed O2 uptake rates. Respiratory coefficients, differentiated for depth regions of the ocean, were used to convert the global O 2 uptake to organic carbon oxidation. The resulting global budget shows an oxidation of 212 Tmol C yr − 1 in marine sediments with a 5-95% confidence interval of 175-260 Tmol C yr − 1 . A comparison with the global flux of particulate organic carbon (POC) from photic surface waters to the deep sea, determined from multiple sediment trap studies, suggests a deficit in the sedimentation flux at 2000 m water depth of about 70% relative to the carbon turnover in the underlying seabed. At the ocean margins, the flux of organic carbon from rivers and from vegetated coastal ecosystems contributes greatly to the budget and may even exceed the phytoplankton production on the inner continental shelf.

Description: ARTICLE INFO Keywords: Amazonia GDGT Amazon River Biomarkers Compound-specific isotopes N-Alkanes Paleoclimate proxies Plant waxes ABSTRACT Lipid biomarker proxies from terrigenous sediments have been extensively used to understand variations in paleoenvironmental conditions, but many of the mechanisms affecting these proxies during riverine transport are still poorly understood. Here, we analyze glycerol dialkyl glycerol tetraether (GDGT) distributions and n-alkane isotopic compositions of soils and sediments from the Amazon River Basin. Our dataset includes suspended sediments of the Amazon River and its main tributaries, as well as soils and sediments of the Xingu River, a large clearwater tributary draining the easternmost part of the Amazon River Basin. Our sampling design aimed at understanding the processes behind spatially distinct GDGT distributions and n-alkane isotopic signatures across lowland Amazonia. Gradual changes in the fractional abundances of isoprenoid GDGTs and in 5- and 6- methyl branched GDGT ratios in suspended sediments of the Amazon River towards its mouth suggest that riverine production is an increasingly important control on the distribution of GDGTs in the lower parts of the system, while values from the western parts are more in line with a dominant soil sourcing. In the Xingu River, indices based on the fractional abundances of branched GDGTs and long-chain n-alkanes demonstrate a strong contri- bution of terrestrial organic material during the high-water season and an important aquatic component during low-water season. Meanwhile, average stable carbon (δ13C) and hydrogen (δD) isotopic signatures of long-chain n-alkanes in soils, riverbed and suspended sediments of the Xingu River are similar and reinforce the relatively conservative behaviour of these proxies within large river systems. The average compound-specific δ13C signa- tures of sediments in the Xingu River are within the expected range for C3 vegetation and do not seem to capture the signals from the nearby deforested areas. n-Alkanes δD signals in the Xingu Basin are similar to values ob- tained in the Amazon River mouth and indicate that n-alkanes sourced from easternmost Amazonian lowlands may predominate over signals from western areas.

Description: Here we present dense acoustic and swath bathymetry data sets as well as geological age constraints that allow a new view on past glacial processes at the Siberian termination of Lomonosov Ridge in the Arctic Ocean between 81° and 84° 20′ N. Here, the seabed is marked by three sets of streamlined glacial lineations observed at present water depths of ~760 m to 1250 m. The shallower streamlined glacial lineations were likely formed during MIS 6 and the deeper ones during MIS 12. Other observations include recessional moraines and pockmarks on a flattened ridge crest. In the subsurface, an acoustically transparent unit above well stratified strata is interpreted as subglacial diamicton overlying pre-glacial sediments at an erosional contact. Furthermore, the diamicton is interpreted to have been deposited as lenses in glacially-eroded proximal settings. In contrast, some parts of the seafloor and subsurface show no glacial overprint in water depths as shallow as 819 m. To explain these findings, we propose that the Siberian termination of Lomonosov Ridge was covered by an ice mass of spatial and temporal variable thickness between ~780 to ~1250 m, that was likely composed of sea ice and thick icebergs calved from ice shelves.

Description: This is the first study presenting temporal changes of the macrofauna biodiversity along the bathymetric gradient from the shelf to abyssal depths in the eastern Fram Striat. In this region, between 2004 and 2008, a significant increase in surface water temperature was observed due to the transport of Atlantic water from lower latitudes and was defined as a Warm Water Anomaly (WWA). Effects of the WWA in the eastern Fram Strait were observed across the entire food web, from the pelagic to the deep seafloor. The material for our study was collected before (in 2000) and after the WWA (in 2010 and 2017) at station depths ranging from 203 m to 5561 m. Samples of macrofauna and surface sediments were collected with use of a box corer to analyze species composition and functional traits, and environmental characteristics in sediments. We explore the influence of environmental changes on the structure (species composition and diversity) and functioning (functional trait composition and diversity) of macrofauna communities. An increase of primary production in surface waters during and after the WWA was reflected in a higher food availability at the seafloor from shelf to abyssal depths. Warming induced environmental changes led to an increase of macrofauna density and taxonomic diversity at all water depths. Macrofauna species composition significantly changed after the WWA. At all study sites, macrofauna functional diversity increased after the warm period. Functional trait composition changed significantly along the bathymetric transect. Despite changes in the taxonomic composition, macrofauna communities at the shallowest stations showed high functional redundancy, i.e., trait composition remained unchanged after the WWA. At water depths below 1500 m, where functional redundancy was significantly lower, functional trait composition changed significantly after the WWA. Our results suggest that macrofauna communities on the shelves are more resistant to environmental changes compared to deep-sea assemblages in the eastern Fram Strait.

Description: Microplastics (MP) have been recorded in various environments around the globe. For a better understanding of distribution patterns and for providing a basis for risk assessments, detailed data on MP concentrations and polymer compositions are required. This study investigated the effluents of two German wastewater treatment plants (WWTP) monthly over one year, in order to better understand their temporal input of MP into the receiving river systems. MP item data down to 11 μm were obtained by means of Fourier Transform Infrared (FTIR) spectroscopy under the application of an improved polymer database. Complementary mass data were obtained by pyrolysis gas chromatography–mass spectrometry (Py-GC/MS) (for one WWTP). Both FTIR and Py-GC/MS analysis revealed a homogeneous polymer composition over the year, with a general dominance of polyolefins. Elevated MP item and mass concentrations (maximum: 3 × 104 items m−3 and 3.8 × 103 μg m−3) were observed during winter months and were accompanied by either heavy rainfall (increased discharge and total organic carbon) or elevated turbidity values. These observations emphasize the need for the assessment of background parameters in future MP monitoring studies. By providing monthly data over one year on MP items and masses in WWTP effluents, this study helps enhancing the understanding of temporal MP dynamics and can act as a valuable reference point for future assessments.

Description: Some of the highest microplastic concentrations in marine environments have been reported from the Fram Strait in the Arctic. This region supports a diverse ecosystem dependent on high concentrations of zooplankton at the base of the food web. Zooplankton samples were collected during research cruises using Bongo and MOCNESS nets in the boreal summers of 2018 and 2019. Using FTIR scanning spectroscopy in combination with an automated polymer identification approach, we show that all five species of Arctic zooplankton investigated had ingested microplastics. Amphipod species, found in surface waters or closely associated with sea ice, had ingested significantly more microplastic per individual (Themisto libellula: 1.8, Themisto abyssorrum: 1, Apherusa glacialis: 1) than copepod species (Calanus hyperboreus: 0.21, Calanus glacialis/finmarchicus: 0.01). The majority of microplastics ingested were below 50 μm in size, all were fragments and several different polymer types were present. We quantified microplastics in water samples collected at six of the same stations as the Calanus using an underway sampling system (inlet at 6.5 m water depth). Fragments of several polymer types and anthropogenic cellulosic fibres were present, with an average concentration of 7 microplastic particles (MP) L−1 (0–18.5 MP L−1). In comparison to the water samples, those microplastics found ingested by zooplankton were significantly smaller, highlighting that the smaller-sized microplastics were being selected for by the zooplankton. High levels of microplastic ingestion in zooplankton have been associated with negative effects on growth, development, and fecundity. As Arctic zooplankton only have a short window of biological productivity, any negative effect could have broad consequences. As global plastic consumption continues to increase and climate change continues to reduce sea ice cover, releasing ice-bound microplastics and leaving ice free areas open to exploitation, the Arctic could be exposed to further plastic pollution which could place additional strain on this fragile ecosystem.

Description: This dataset contains PISM simulation results of the Antarctic Ice Sheet based on code release v1.0-paleo-ensemble (https://doi.org/10.5281/zenodo.3574033). PISM is the open-source Parallel Ice Sheet Model developed mainly at UAF, USA and PIK, Germany. See documentation in https://www.pism.io. These are additional netCDF data from the same ensemble simulations already stored in doi:10.1594/PANGAEA.909728. 1) 1000-year snapshots since 125000 years before present, of ice thickness, bed topography, change in bed topography, floating/grounded mask, surface elevation, basal melt rate and vertically averaged velocity magnitude (SIA+SSA) (16GB) 2) 5000-year snapshots since 125000 years before present, SSA velocity components in x and y direction (8GB)