47242 research outputs found
Sort by
Cerium occurs as cerium-phosphate clusters around bioapatite nanocrystals in deep-sea sediments
No full textDeep-sea mud is rich in rare-earth elements, primarily found in fluorapatite, a mineral deposit that forms over hundreds of thousands to millions of years through the accumulation of fish remains. After fish die, biogenic apatite captures rare earth elements from seawater on the seafloor and from pore waters during the diagenesis process. The conventional model for rare earth element enrichment suggests that they are incorporated into the bioapatite crystal structure through solid-state diffusion. However, our data reveal that cerium atoms are instead precipitated within an amorphous layer surrounding bioapatite nanocrystals, as shown by high-energy-resolution X-ray absorption spectroscopy and transmission electron microscopy. Computational simulations further support this finding, predicting that cerium atoms cluster on the surface of fluorapatite. These results suggest that the fluorapatite-water interface plays a crucial role in the enrichment of cerium, as well as other rare earth elements, in marine sediments. (Figure presented.
The distribution and isotopomeric characterization of nitrous oxide in the Eastern Gotland Basin (central Baltic Sea)
No full textNitrous oxide (N2O) is a greenhouse gas with a global warming potential ~300 times that of carbon dioxide. Coastal areas are important sources of N2O to the atmosphere but the biogeochemical pathways of N2O production and consumption are not well understood. We measured the concentrations and nitrogen (N) and oxygen (O) stable isotopes (d15N and d18O) of N2O in the Baltic Sea to constrain the sources and sinks of N2O in this system. Further, we used the intramolecular 15N variation or the site preference (SP) as additional tracer. Samples were taken at 7 stations during a cruise with R/V Elisabeth Mann Borgese to the Eastern Gotland Basin (central Baltic Sea) in May/June 2019. The isotope signatures of N2O accumulation in the oxycline reflected production predominantly via ammonia oxidation. In the waters where hydrogen sulfide (H2S) was detected, active N2O consumption was implied by pronounced decrease in N2O levels in tandem with enrichments in δ15Nbulk, δ18O and SP. High site preference values of N2O observed in suboxic waters of the stations where H2S buildup was minimal to non-detectable point to the possibility of non-canonical denitrification pathways mediated by fungi or abiotically. A sedimentary source of N2O was observed in those stations, which resulted in a decoupling of the δ15Nbulk and δ18O of N2O. Our results reveal that transient oxygenation events have the potential to modify the N cycling within the oxic-anoxic interface even if for shorter time scales
Ocean Cleanup
No full textUnsere Meere ersticken in Plastik. Ändert sich nichts, werden im Jahr 2040 bis zu 29 Millionen Tonnen Plastikabfälle jährlich in den Ozeanen enden, schätzt die Deutsche Stiftung Meeresschutz, und verdeutlicht: Damit könnte man auf jedem Meter Küstenlinie der Welt 50 Kilogramm Plastikmüll abladen. Was also tun? Ein junger Niederländer hatte vor einigen Jahren eine Idee, die seitdem für weltweite Aufmerksamkeit sorgt: An riesigen Barrieren soll sich in den Ozeanen der Plastikmüll stauen und dann weggesammelt werden.
Klingt einfach, hat aber seine Tücken. Denn natürlich sammeln sich nicht nur die Müllmengen an den Barrieren, sondern auch Meerestiere. Außerdem sehen Meeresbiologen eine Gefahr, dass das gesamte Ökosystem an der Meeresoberfläche gestört wird. Demnach gibt immer mehr Studien, wonach viele Kleinstlebewesen auf den an der Wasseroberfläche treibenden Plastikteilchen leben.
Und der Kieler Meeresbiologe Mark Lenz sagte uns: „Anstatt im offenen Meer unter widrigsten Bedingungen Müll einzusammeln, muss der Strom aus Plastik gestoppt werden, bevor er sich überhaupt in die Natur ergießt. Das Prinzip von Ocean Cleanup ist nicht zeitgemäß.“ Urteilt selbst
Seasonal sea ice characterized the glacial Arctic-Atlantic gateway over the past 750,000 years
No full textThe past occurrence of an extreme similar to 1-kilometer-thick Arctic Ocean-Nordic Seas ice shelf has been inferred from submarine landscape features and geochemical records, although fundamental aspects of its characteristics, impacts, and timing remain highly debated. Here, we challenge this pan-Arctic glaciation hypothesis by investigating two sites from the Arctic-Atlantic gateway (AAG) and the Nordic Seas. Suborbital to millennial-scale surface water bioproductivity changes provide no evidence for a continuous ice shelf in the AAG and the Nordic Seas over the past similar to 750,000 years. Instead, proxy data and model simulations reveal the persistent presence of seasonal sea ice cover and open water phytoplankton blooms during both glacial and interglacial times. If the AAG and Nordic Seas were ever covered by an ice shelf during these times, then it must have been a partial, or at best, a very short-lived glacial phenomenon
Changing impact of large-scale atmospheric circulation variability on the water mass exchange and circulation of the Baltic Sea during winters 1950–2022
No full textThe winter climate of northern Europe is influenced by the variability of large-scale pressure systems that control the airflow over the region, namely NAO+, NAO-, SCAND, and the Atlantic Ridge. The positive phase of the North Atlantic Oscillation (NAO+) is associated with westerly winds that bring mild and moist air to the Baltic Sea region, while the negative phase (NAO-) is characterised by easterly winds and the advection of cold, dry air. Both phases are linked to shifts in the centres of action and changes in storm track pathways. The third mode, the East Atlantic or Atlantic Ridge pattern, is structurally similar to the NAO but features a north–south dipole with anomaly centres shifted southward. This pattern reflects variations in the north–south positioning of the NAO. The fourth dominant mode, the Scandinavian, Eurasian, or Blocking pattern, influences the Baltic region by generating high-pressure conditions over Scandinavia. These conditions are typically accompanied by dry, cold weather and weak easterly winds. Severe winters in the Baltic, characterised by extensive ice cover, are often associated not only with NAO- conditions but also with blocking situations
Dissociating Gas Hydrate Beneath the Hydrate Stability Zone
No full textVast amounts of carbon are stored beneath the seafloor in the form of methane hydrate. Hydrate is stable at moderate pressure and low temperature at a depth extending several hundred meters beneath the seafloor to the base of gas hydrate stability (BGHS) often marked by bottom simulating reflections (BSRs) in seismic profiles. However, data from logging-while-drilling and coring during Integrated Ocean Discovery Program Expeditions 372 and 375 offshore New Zealand identified hydrate ∼60 m beneath the BSR. This hydrate appears to be dissociating over thousands of years following a gradual temperature increase from sediment burial modulated by changes in bottom-water temperature and sea-level fluctuations. Slow hydrate dissociation significantly buffers the release of methane and therefore, carbon through glacial cycles. Dissociating hydrate beneath the BGHS may also increase estimated global budgets of methane stored in hydrate
Influence of dumped munition on the benthic macrofauna: Relation to munition object proximity and explosive compounds content
No full textGerman waters contain around 1.6 million tons of dumped munition spread in coastal areas of the North and Baltic seas. The current study investigated the effect of sea-dumped munitions on benthic macrofauna at the WWII-era dumpsite, Haffkrug (Lübeck Bay, Baltic Sea). A total of 68 samples were taken using 0.1 m2 van-Veen grab along three transects in the southern part of the munition dumpsite, sieved through a 1 mm sieve and fixed in formalin. All taxa were identified, counted and weighted. Additionally, a set of environmental variables was analyzed, including continuous and discrete sediment parameters, obtained with multibeam echosounder (distance to individual munition items, depth and morphological derivatives) and direct sample measurement (grain size and munition compounds content). Random Forests algorithm applied to the dataset revealed that depth and, to a lesser degree, distance to munition items shaped the abundance, biomass and diversity of the benthic community. Specifically, the model predicted elevated abundance and biomass in the proximity of the munition. A possible reason for the distance influence is that munition shells and crates represent hard substrata, which is otherwise rare in the Lübeck Bay region. The modelling revealed five different benthic communities in the study area. Munition compounds in the sediment showed no significant influence on the overall structure of macrofauna. However, the abundance of at least two species – polychaete Spio goniocephala and crustacean Diastylis rathkei – were strongly positively correlated with TNT content in the sediment, although the reasons for this are unknown
