ALBERT

Beschreibung: Large quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub-pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea-ice is likely to increase wind speeds and seaair exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea-air methane flux is higher during melting in seasonally ice-covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.

Beschreibung: A thorough and reliable assessment of changes in sea surface water temperatures (SSWTs) is essential for understanding the effects of global warming on long-term trends in marine ecosystems and their communities. The first long-term temperature measurements were established almost a century ago, especially in coastal areas, and some of them are still in operation. However, while in earlier times these measurements were done by hand every day, current environmental long-term observation stations (ELTOS) are often fully automated and integrated in cabled underwater observatories (UWOs). With this new technology, year-round measurements became feasible even in remote or difficult to access areas, such as coastal areas of the Arctic Ocean in winter, where measurements were almost impossible just a decade ago. In this context, there is a question over what extent the sampling frequency and accuracy influence results in long-term monitoring approaches. In this paper, we address this with a combination of lab experiments on sensor accuracy and precision and a simulated sampling program with different sampling frequencies based on a continuous water temperature dataset from Svalbard, Arctic, from 2012 to 2017. Our laboratory experiments showed that temperature measurements with 12 different temperature sensor types at different price ranges all provided measurements accurate enough to resolve temperature changes over years on a level discussed in the literature when addressing climate change effects in coastal waters. However, the experiments also revealed that some sensors are more suitable for measuring absolute temperature changes over time, while others are more suitable for determining relative temperature changes. Our simulated sampling program in Svalbard coastal waters over 5 years revealed that the selection of a proper sampling frequency is most relevant for discriminating significant long-term temperature changes from random daily, seasonal, or interannual fluctuations. While hourly and daily sampling could deliver reliable, stable, and comparable results concerning temperature increases over time, weekly sampling was less able to reliably detect overall significant trends. With even lower sampling frequencies (monthly sampling), no significant temperature trend over time could be detected. Although the results were obtained for a specific site, they are transferable to other aquatic research questions and non-polar regions.

Beschreibung: Modular Observation Solutions of Earth Systems (MOSES) is a novel observation system that is specifically designed to unravel the impact of distinct, dynamic events on the long-term development of environmental systems. Hydrometeorological extremes such as the recent European droughts or the floods of 2013 caused severe and lasting environmental damage. Modeling studies suggest that abrupt permafrost thaw events accelerate Arctic greenhouse gas emissions. Short-lived ocean eddies seem to comprise a significant share of the marine carbon uptake or release. Although there is increasing evidence that such dynamic events bear the potential for major environmental impacts, our knowledge on the processes they trigger is still very limited. MOSES aims at capturing such events, from their formation to their end, with high spatial and temporal resolution. As such, the observation system extends and complements existing national and international observation networks, which are mostly designed for long-term monitoring. Several German Helmholtz Association centers have developed this research facility as a mobile and modular “system of systems” to record energy, water, greenhouse gas, and nutrient cycles on the land surface, in coastal regions, in the ocean, in polar regions, and in the atmosphere—but especially the interactions between the Earth compartments. During the implementation period (2017–21), the measuring systems were put into operation and test campaigns were performed to establish event-driven campaign routines. With MOSES’s regular operation starting in 2022, the observation system will then be ready for cross-compartment and cross-discipline research on the environmental impacts of dynamic events.

Beschreibung: Highlights • Nutrient and carbon fluxes are key processes in land-ocean interactions. • We sampled along the river-estuary-ocean system according to travel time of water. • The river was autotrophic with phytoplankton growth, high pH and oxygen concentration, and CO2 undersaturation. • Phytoplankton died off in the estuary causing low pH and oxygen concentration, CO2 supersaturation, and nutrient release. • The approach is suitable to investigate single events such as hydrological extremes. Nutrient and carbon dynamics within the river-estuary-coastal water systems are key processes in understanding the flux of matter from the terrestrial environment to the ocean. Here, we analysed those dynamics by following a sampling approach based on the travel time of water and an advanced calculation of nutrient fluxes in the tidal part. We started with a nearly Lagrangian sampling of the river (River Elbe, Germany; 580 km within 8 days). After a subsequent investigation of the estuary, we followed the plume of the river by raster sampling the German Bight (North Sea) using three ships simultaneously. In the river, we detected intensive longitudinal growth of phytoplankton connected with high oxygen saturation and pH values and an undersaturation of CO2, whereas concentrations of dissolved nutrients declined. In the estuary, the Elbe shifted from an autotrophic to a heterotrophic system: Phytoplankton died off upstream of the salinity gradient, causing minima in oxygen saturation and pH, supersaturation of CO2, and a release of nutrients. In the shelf region, phytoplankton and nutrient concentrations were low, oxygen was close to saturation, and pH was within a typical marine range. Over all sections, oxygen saturation was positively related to pH and negatively to pCO2. Corresponding to the significant particulated nutrient flux via phytoplankton, flux rates of dissolved nutrients from river into estuary were low and determined by depleted concentrations. In contrast, fluxes from the estuary to the coastal waters were higher and the pattern was determined by tidal current. Overall, the approach is appropriate to better understand land-ocean fluxes, particularly to illuminate the importance of these fluxes under different seasonal and hydrological conditions, including flood and drought events.

Beschreibung: 1) Bei Untersuchungen zu Methodik der quantitativen Erfassung von SRB (Sulfatreduzierenden Bakterien) erwies sich die Methode der MPN (most propable number) mit dem Medium nach Widdel als die Methode der Wahl. Zur Dispergieren der Bakterien von dem Sediment und dem Periostrakum der Muschel Arctica islandica erwiesen sich Ultraschall und Magnetrührer als vorteilhaft. 2) Im Verlauf der Untersuchungen ergab sich eine zeitliche Abhängigkeit der MPN-Werte von der Inkubationsdauer. Diese war durch den K50-wert gekennzeichnet, definiert als die Zeit in Tagen, die benötigt wird 50% des Endwertes der Keimzahlbestimmung nach 8 Wochen zu erreichen. Unterschiedliche K50-werte werden durch einen unterschiedlichen physiologischen Zustand der Ausgangskultur und damit auch mit unterschiedlicher Stoffwechselaktivität erklärt. 3) Keimzahlbestimmungen in der Kieler Bucht von Acetat, Laktat, Succinat, Propionat und Ethanol verwertenden SRB im Sediment und dem Periostrakum der Muschel A.islandica in dem Zeitraum März bis September 1989 ergaben keine eindeutigen Hinweise auf eine Anreicherung der SRB auf dem Periostrakum der Muschel. Je nach Anreicherungssubstrat und Datum der Probennahme waren im Sediment oder auf dem Periostrakum höhere Abundanzen zu finden. Maximale Keimzahlen der Laktat verwertenden SRB lagen bei 5 x 104/cm3 auf dem Periostrakum, für Acetat wurden maximale Keimzahlen von nur 1 x 103 auf dem Periostrakum erzielt werden. Demgegenüber wurden maximal 1 x 104/cm3 Succinat verwertende SRB auf dem Periostrakum und Sediment nachgewiesen. Bei der Betrachtung der Summe der Acetat, Laktat und Succinat verwertenden SRB zeigten sich deutliche saisonale Schwankungen. Ein erstes Maximum wurde im März registriert, gefolgt von einem Kleineren im Mai und einem Herbstmaximum in September. Diese Schwankungen folgten um 2 bis 3 Wochen verzögert den Werten der Primärproduktion. Es zeigte sich die Tendenz einer Anreicherung von SRB auf dem Periostrakum der Muschel zu Zeiten mit niederen Keimzahlen. 4) Hälterungexperimente zur Bedeutung der Ausscheidung organischer Säuren (Acetat, Propionat und Succinat) durch eine gärende A. islandica auf die SRB zeigten keinen Einfluß auf die Abundanzen und K50-werte der Acetat und Laktat verwertenden SRB. Keimzahlbestimmungen der Succinat verwertenden SRB ergaben gleiche Abundanzen auf Periostrakum und im umgebenden Sediment, aber unterschiedliche K50-Werte. Die epizoischen SRB wiesen dabei niedrigere K50-Werte auf als die Sedimentbakterien. Es wird postuliert, daß die epizoischen Succinat verwertenden SRB eine höhere Aktivtät und eine höhere Substrataffinitat aufweisen als die SRB aus dem umgebenden Sediment. Die epizoischen SRB können somit als copiotroph von den oligotrophen SRB aus dem Sediment unterschieden werden.