ALBERT

Description: We present new high-resolution snow depth data on Arctic sea ice derived from airborne microwave radar measurements from the IceBird campaigns of the Alfred Wegener Institute (AWI) together with a new retrieval method using signal peakiness based on an intercomparison exercise of colocated data at different altitudes. We aim to demonstrate the capabilities and potential improvements of radar data, which were acquired at a lower altitude (200 ft) and slower speed (110 kn) and had a smaller radar footprint size (2-m diameter) than previous airborne snow radar data. So far, AWI Snow Radar data have been derived using a 2-18-GHz ultrawideband frequency-modulated continuous-wave (FMCW) radar in 2017-2019. Our results show that our method in combination with thorough calibration through coherent noise removal and system response deconvolution significantly improves the quality of the radar-derived snow depth data. The validation against a 2-D grid of in situ snow depth measurements on level landfast first-year ice indicates a mean bias of only 0.86 cm between radar and ground truth. Comparison between the radar-derived snow depth estimates from different altitudes shows good consistency. We conclude that the AWI Snow Radar aboard the IceBird campaigns is able to measure the snow depth on Arctic sea ice accurately at higher spatial resolution than but consistent with the existing airborne snow radar data of NASA Operation IceBridge. Together with the simultaneous measurements of the total ice thickness and surface freeboard, the IceBird campaign data will be able to describe the whole sea-ice column on regional scales.

Description: The West Antarctic Ice Sheet (WAIS) is one of the largest potential sources of future sea-level rise, with glaciers draining the WAIS thinning at an accelerating rate over the past 40 years. Due to complexities in calibrating palaeoceanographic proxies for the Southern Ocean, it remains difficult to assess whether similar changes have occurred earlier during the Holocene or whether there is underlying centennial- to millennial-scale forcing in oceanic variability. Archaeal lipid-based proxies, specifically glycerol dialkyl glycerol tetraether (GDGT; e.g. TEX86 and TEXL86), are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL)-GDGTs, representing (recently) living archaeal populations in suspended particulate matter (SPM) from the Amundsen Sea and the Scotia Sea. SPM samples from the Amundsen Sea were collected from up to four water column depths representing the surface waters through to Circumpolar Deep Water (CDW), whereas the Scotia Sea samples were collected along a transect encompassing the sub-Antarctic front through to the southern boundary of the Antarctic Circumpolar Current. IPL-GDGTs with low cyclic diversity were detected throughout the water column with high relative abundances of hydroxylated IPL-GDGTs identified in both the Amundsen and Scotia seas. Results from the Scotia Sea show shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean. Indicating that the physicochemical parameters of these water masses determine changes in IPL-GDGT distributions. The Amundsen Sea results identified GDGTs with hexose-phosphohexose head groups in the CDW, suggesting active GDGT synthesis at these depths. These results suggest that GDGTs synthesised at CDW depths may be a significant source of GDGTs exported to the sedimentary record and that temperature reconstructions based on TEX86 or TEXL86 proxies may be significantly influenced by the warmer waters of the CDW.

Description: In this paper we analyze how oceanic circulation affects sediment deposition along a sector of the Ross Sea continental margin, between the Iselin Bank and the Hillary Canyon, and how these processes evolved since the Late Miocene. The Hillary Canyon is one of the few places around the Antarctic continental margin where the dense waters produced onto the continental shelf, mainly through brine rejection related to sea ice production, flow down the continental slope and reach the deep oceanic bottom layer. At the same time the Hillary Canyon represents a pathway for relatively warm waters, normally flowing along the continental slope within the Antarctic Slope Current, to reach the continental shelf. The intrusion of warm waters onto the continental shelf produces basal melting of the ice shelves, reduces their buttressing effect and triggers instabilities of the ice sheet that represent one of the main uncertainties in future sea level projections. For this study we use seismic, morpho-bathymetric and oceanographic data acquired in 2017 by the R/V OGS Explora. Seismic profiles and multibeam bathymetry are interpreted together with age models from two drilling sites (U1523 and U1524) of the International Ocean Discovery Program (IODP) Expedition 374. Oceanographic data, together with a regional oceanographic model, are used to support our reconstruction by showing the present-day oceanographic influence on sediment deposition. Regional correlation of the main seismic unconformities allows us to identify eight seismic sequences. Seismic profiles and multibeam bathymetry show a strong influence of bottom current activity on sediment deposition since the Early Miocene and a reduction in their intensity during the mid-Pliocene Warm Period. Oceanographic data and modelling provide evidence that the bottom currents are related to the dense waters produced on the Ross Sea continental shelf and flowing out through the Hillary Canyon. The presence of extensive mass transport deposits and detachment scarps indicate that also mass wasting participates in sediment transport. Through this integrated approach we regard the area between the Iselin Bank and the Hillary Canyon as a Contourite Depositional System (ODYSSEA CDS) that offers a record of oceanographic and sedimentary conditions in a unique setting. The hypotheses presented in this work are intended to serve as a framework for future reconstructions based on detailed integration of lithological, paleontological, geochemical and petrophysical data.

Description: The Data Science Symposium at Haus der Wissenschaft on 8/9 November 2021 in Bremen was the 6th Symposium in this series since 2017.

Description: Currently, little is known about the population identity of fin whales (Balaenoptera physalus) in Antarctic waters but initial analyses of acoustic recordings from the Southern Ocean (SO) have shown that fin whale calls differ between regions, possibly representing different fin whale populations. In the Atlantic Sector of the Southern Ocean, the typical fin whale 20-Hz song is often accompanied by simultaneous higher frequency (HF) component at around 89Hz or 99Hz. However, the distribution of these call types throughout the area and whether there is a clear spatial separation between these call types is so far unknown. In this study fin whale calls were examined between two locations, the Greenwich Meridian and Elephant Island across the Weddell Sea (from 2009, 2011, 2013, and 2015) to gain further insights into the connections between fin whales in this region. The HF call component was found to be significantly (p-value 〈 2.2e^-16) unique in its frequency at the two locations with 99Hz (97.14Hz ± 3.19) at Greenwich Meridian and 86Hz (86.26Hz ± 1.36) at Elephant Island. The inter-pulse interval (IPI) of both low frequency (LF) (20-Hz) and HF calls were also found to differ between geographic regions, with a median IPI of 14.5 seconds at Elephant Island and median IPI around 10 seconds at Greenwich Meridian. Variation in song IPIs were also investigated between geographic locations, Elephant Island was determined to have a majority singlet song type and Greenwich Meridian was found to have mostly triplet songs. The occurrence of HF and LF calls showed a strong positive correlation, indicating that both call components are produced simultaneously. The characteristic elements for fin whale calls examined in this study all indicate that the fin whale calls recorded at Elephant Island and Greenwich Meridian belong to two distinct acoustic populations. An understanding of how potentially distinct fin whale stocks utilize different geographic regions is fundamental for management and conservation measures aiming to improve the conservation status of this vulnerable species.

Description: Salt marshes, along with seagrass and mangroves, are known to be globally important carbon sinks. Salt marsh plants absorb CO2 from the air. Through photosynthesis, they use the carbon to build plant parts such as leaves and roots, i.e. organic biomass. Salt marsh plants produce a considerable amount of belowground biomass. This organic matter is persistent and only decays over a long period of time. Over time, some of the carbon-containing biomass is permanently buried in the marsh soil. Here, conditions are usually favourable for the preservation of the organic material, which can lead to carbon storage for thousands of years. In this way, salt marshes absorb CO2 from the air and store it as organic carbon in the soil - a mechanism that removes CO2 from the atmosphere and counteracts climate change. In addition, salt marshes act as a filter and trap for sediment and organic material that enters the salt marsh from outside. When water levels are high, salt marshes are flooded and the salt marsh plants literally fish out sediment and organic material from the water above them. Organic material in particular also contains carbon, which is then deposited in the salt marsh and later stored in the soil. The accumulation of carbon from sources outside the salt marsh also contributes to the role of salt marshes as carbon sinks.

Description: Just like salt marshes and mangroves, seagrasses are ecologically important habitats in coastal ecosystems and are also important carbon storages. Seagrasses absorb CO2 and other forms of inorganic carbon from water and air and produce organic biomass, i.e. new plant components, by means of photosynthesis. Dead parts of the seagrass plant can be buried into the deeper, oxygen-poor layers of the tidal flat sediment by current-induced sediment reallocation or burrowing activity of animals. Bacteria that are responsible for decomposing the organic material and would thus release the carbon again can hardly become active there due to the lack of oxygen. The carbon incorporated in the plant parts can thus be stored in the seabed for many centuries. In addition to this internal source, seagrasses also act as filters for sediment and organic material, which is transported into the seagrass bed from outside. Sediment and organic material may originate from deeper areas of the sea and then be transported towards the coast, or may be directly from nearby coastal vegetation. Above a seagrass bed, these components are literally fished out of the seawater near the bottom as if with a comb. In this way, new layers of sediment and organic material are continuously deposited in the seagrass meadow, leading to a further accumulation of organic material that can be stored in the seabed for up to thousands of years.

Description: The introduction of non-indigenous species may cause strong effects on biodiversity, species interactions and functioning of native soft-bottom coastal ecosystems. Especially introduced bioengineering organisms modify existing benthic habitat structures and thereby habitat-specific species interactions. In the Wadden Sea, beds of native blue mussels have been invaded by Pacific oysters Magalana gigas, which caused a large-scale shift from pure epibenthic Mytilus edulis beds to current mixed reefs of mussels and oysters. These newly developed biotic habitats may affect the occurrence of former associated key organisms and their ecological functions. In this context, we studied the grazing activity of native periwinkles Littorina littorea and the spatial distribution of M. edulis in oyster reefs in the northern Wadden Sea and explored the resulting distribution patterns of barnacle epibionts attached to oyster and mussel shells. A manipulative field experiment revealed that density of L. littorea significantly affects the recruitment success of barnacles Semibalanus balanoides on oyster shells. The highest number of barnacles recruited at periwinkle exclusion and this relationship was already known for pure blue mussel beds in the past. Barnacle epigrowth on blue mussel shells, however, changed with the new position of mussels within the oyster matrix and is nowadays lower than in former times. Our results demonstrate that introduced bioengineering organisms may alter, native biotic habitats but associated species interactions may remain the same. Additionally, it shows that native species may profit from the new structures by, for example, being less overgrown with detrimental barnacle overgrowth.

Description: The introduction of non-indigenous species may cause strong effects on biodiversity, species interactions and functioning of native coastal ecosystems. Especially introduced bioengineering organisms may fundamentally change native soft-bottom ecosystems by modifying existing benthic habitat structures and thereby habitat-specific species interactions. The introduction of Pacific oysters Crassostrea gigas into the sedimentary coastal area of the south-eastern North Sea and its preferred settlement on native blue mussel shells caused a large-scale shift from pure epibenthic Mytilus edulis beds to current mixed reefs of mussels and oysters. To investigate whether the newly developed biotic habitat affects the occurrence of associated key organisms and their ecological functions, we studied the long-term occurrence of periwinkles Littorina littorea and their grazing activity on barnacles attached to Pacific oyster shells in the northern Wadden Sea. We found no negative effects of oyster density increase on periwinkle population dynamics in the last two decades, which spans a time-period from the beginning of Pacific oyster establishment on mussel beds to oyster dominance today. A manipulative field experiment revealed that density of L. littorea significantly affects the recruitment success of barnacles Semibalanus balanoides on oyster shells. The highest number of barnacle recruited at periwinkle exclusion. Thus, snail density and resulting grazing activity may control barnacle overgrowth on oyster shells, which is known to cause detrimental effects on overgrown bivalves. The company of introduced oysters and native periwinkles in the Wadden Sea shows that alien species may find native friends in newly conquered ecosystems with mutual benefits.

Description: The number of input-output assessments focused on energy has grown considerably in the last years. Many of these assessments combine data from multi-regional input-output (MRIO) databases with energy extensions that completely or partially depict the different stages through which energy products are supplied or used in the economy. The improper use of some energy extensions can lead to double accounting of some energy flows, but the frequency with which this happens and the potential impact on the results are unknown. Based on a literature review, we estimate that around a quarter of the MRIO-based energy assessments reviewed incurred into double accounting. Using the EXIOBASE MRIO database, we also analyse the effects of double accounting in the absolute values and rankings of different countries' and products' energy footprints. Building on the insights provided by our analysis, we offer a set of key recommendations to MRIO users to avoid the double accounting problem in the future. Likewise, we conclude that the harmonisation of the energy data across MRIO databases led by experts could simplify the choices of the data users until the provision of official energy extensions by statistical offices becomes a widespread practice.