Alfred Wegener Institute for Polar and Marine Research
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Seasonal increase of methane emissions linked to warming in Siberian tundra
Get PDFMethane (CH4) is a strong greenhouse gas that accelerates climate change, yet its emissions from wetlands in general and Arctic permafrost-affected wetlands in particular remain very uncertain in the global CH4 budget. Arctic CH4 sources and the expected effect of permafrost thaw on these sources have gained much attention by the public, media, policy makers, and researchers during the past decade, but neither inversion nor process-based models provide clear trends in emissions and there has not been any observational evidence for increasing CH4 emissions from Arctic permafrost ecosystems.Here, we provide this observational evidence.&#160;Based on the longest record of direct Arctic CH4 flux observations acquired since 2002 at a Siberian tundra site using the eddy covariance method, we found an increase in the early summer (June and July) CH4 emissions by 1.9 &#177; 0.7 % yr-1 since 2004 along with a strong increase in June air temperatures of 0.3 &#177; 0.1 &#176;C yr-1. Although the tundra&#8217;s maximum source strength in August has not yet changed and the overall mean annual emissions of 171.5&#8201;&#177;&#8201;12.3&#8201;mmol&#8201;m&#8722;2&#8201;yr&#8722;1 remain in the lower half of the published range, the increase in early summer methane emissions shows that atmospheric warming has begun to affect the methane flux dynamics of permafrost-affected ecosystems in the Arctic. This is especially noteworthy, given the very thick and cold continuous permafrost in the study area compared to most other observational sites.While the observed changes clearly happen in the early warm season, we also estimate 39 % of the annual emission to originate from the re-freezing and frozen period, highlighting the importance of the cold season for annual permafrost CH4 emission estimates and the substantial challenges in achieving continuous data coverage in the Arctic winter.</jats:p
Phytoplankton physiology and functional traits under artificial upwelling with varying Si:N
Get PDFIntroduction: Artificial upwelling has been discussed as a nature-based solution to fertilize currently unproductive areas of the ocean to enhance food web productivity and atmospheric CO2 sequestration. The efficacy of this approach may be closely tied to the nutrient stoichiometry of the upwelled water, as Si-rich upwelling should benefit the growth of diatoms, who are key players for primary production, carbon export and food web efficiency. Methods: With a mesocosm experiment in subtropical waters, we assessed the physiological and functional responses of an oligotrophic phytoplankton community to artificial upwelling under varying Si:N ratios (0.07-1.33). Results: Deep water fertilization led to strongly enhanced primary productivity rates and net autotrophy across Si scenarios. At the community level, Si-rich upwelling50 temporarily increased primary production and consistently enhanced diatom growth, producing up to 10-fold higher abundances compared to Si-deficient upwelling. At the organism level, contrasting effects were observed. On the one hand, silicification and size of diatom cells remained unaffected by Si:N, which is surprising given the direct dependency of these traits on Si. On the other hand, diatom Chlorophyll a density and carbon density were strongly reduced and particulate matter C:N was elevated under Si-rich upwelling. Discussion: This suggests a reduced nutritional value for higher trophic levels under high Si:N ratios. Despite these strong qualitative changes under high Si, diatom cells appeared healthy and showed high photosynthetic efficiency. Our findings reveal great physiological plasticity and adaptability in phytoplankton under artificial upwelling, with Si-dependent trade-offs between primary producer quantity and quality
Food safety status of mussels from Bulgarian coast in regard of marine biotoxins
Get PDFSeafood, such as mussels is rich of essential nutrients, but it could be also a source of contaminants that may cause adverse health effects. This article aimed to identify safety status of mussels harvested from Bulgarian coast. Wild and cultivated mussels (N = 17) were collected from their breeding sites in the period throughout 2021, along the Bulgarian coast of the Black Sea. Among all six regulated marine biotoxins (domoic acid, dinophysistoxin-1 (DTX1), dino-physistoxin-2 (DTX2), azaspiracid-1 (AZA1), pectenotoxin-2 (PTX2) and yessotoxin (YTX)) were determined via high performance liquid chromatography-tandem mass spectrometry. Safety of investigated samples was assessed by calculating the human exposure to detected toxins and comparing it with the legislated acute reference doses. For calculations a body weight (66 kg) and mean portion size of 400 g, recommended by EFSA were used. The presence of only PTX2, yessotoxin and some of their analogues (PTX2-seco acid (PTX2sa) and hydroxy-YTX) was confirmed in all samples. Highest calculated exposure was to YTX – 0,00013 microgram/kg bw, which is much lower than the accepted acute reference dose of 25 microgram/kg bw. Calculated exposures to pectenotoxins were more than thousand times lower than the acute reference dose of 0,8 microgram/kg bw. Estimated results indicate that no human health risk could be expected based on the analyzed mussels. Although, no human health risk was identified, a running monitoring of marine biotoxins is important as mass proliferations of harmful microalgal are hard to predict. Thus, high levels of yessotoxins and pectenotoxins might be a certain danger to consumers. The insidiousness lies in the mechanism of action of these toxins, as it is still unknown and does not allow us to have reliable information on the symptoms and problems that it develops in humans. This work presents that in mussel samples from Bulgarian coast from 2021, low levels of marine biotoxins were detected. No human health risk might be expected if mussels were consumed
Ground-based measurements of the weather-driven sky radiance distribution in the Southern Hemisphere.
Get PDFThe angular distribution of the sky radiance determines the energy generation of solar power technologies as well as the ultraviolet (UV) doses delivered to the biosphere. The sky-diffuse radiance distribution depends on the wavelength, the solar elevation, and the atmospheric conditions. Here, we report on ground-based measurements of the all-sky radiance at three sites in the Southern Hemisphere across a transect of about 5,000 km: Santiago (33°S, a mid-latitude city of 6 million inhabitants with endemic poor air quality), King George Island (62°S, at the northern tip of the Antarctic Peninsula, one of the cloudiest regions on Earth), and Union Glacier (79°S, a snow-covered glacier in the vast interior of Western Antarctica). The sites were strategically selected for studying the influence of urban aerosols, frequent and thick clouds, and extremely high albedo on the sky-diffuse radiance distribution. Our results show that, due to changing site-specific atmospheric conditions, the characterization of the weather-driven sky radiance distribution may require ground-based measurements
Fractures in glaciers—Crack tips and their stress fields by observation and modeling
Get PDFAbstractHigh‐resolution optical camera systems are opening new opportunities to study fractures in ice. Here, we present data obtained from the Modular Aerial Camera System camera system operated onboard of Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) polar aircraft in northeast Greenland in 2022. In addition, we are using optical and radar satellite imagery. The study area is the 79°N Glacier (Nioghalvfjerdsbræ, 79NG), an outlet glacier of the Northeast Greenland Ice Stream. We found that crack tips are exhibiting additional isolated cracks ahead of the main crack. Subsequent crack propagation is starting from those isolated cracks, leading to an advance of the crack, with bridges between crack faces. The bridges provide information of the episodic crack propagation. Fractures have typically a length scale of kilometers and the distance of crack faces is in the order of meters to tenths of meters. Fracture modes will be inferred from stress fields computed by an inverse modeling approach using the Ice Sheet and Sea Level System Model. To this end, a surface velocity field derived from satellite remote sensing is used for the optimal control method that constrains model parameters, for example, basal friction coefficient or rheology.</jats:p
Coastal permafrost was massively eroded during the Bølling-Allerød warm period
Get PDFThe Bølling-Allerød interstadial (14,700–12,900 years before present), during the last deglaciation, was characterized by rapid warming and sea level rise. Yet, the response of the Arctic terrestrial cryosphere during this abrupt climate change remains thus far elusive. Here we present a multi-proxy analysis of a sediment record from the northern Svalbard continental margin, an area strongly influenced by sea ice export from the Arctic, to elucidate sea level - permafrost erosion connections. We show that permafrost-derived material rich in biospheric carbon became the dominant source of sediments at the onset of the Bølling-Allerød, despite the lack of direct connections with permafrost deposits. Our results suggest that the abrupt temperature and sea level rise triggered massive erosion of coastal ice-rich Yedoma permafrost, possibly from Siberian and Alaskan coasts, followed by long-range sea ice transport towards the Fram Strait and the Arctic Ocean gateway. Overall, we show how coastal permafrost is susceptible to large-scale remobilization in a scenario of rapid climate variability
Long-Term Effects of Cold Atmospheric Plasma-Treated Water on the Antioxidative System of Hordeum vulgare
Get PDFFacing climate change, the development of innovative agricultural technologies securing food production becomes increasingly
important. Plasma-treated water (PTW) might be a promising tool to enhance drought stress tolerance in plants.
Knowledge about the effects of PTW on the physiology of plants, especially on their antioxidative system on a long-term
scale, is still scarce. In this work, PTW was applied to barley leaves (Hordeum vulgare cv. Kosmos) and various constituents
of the plants’ antioxidative system were analyzed 30 days after treatment. An additional drought stress was performed
after foliar PTW application followed by a recovery period to elucidate whether PTW treatment improved stress tolerance.
Upon PTW treatment, the Total Antioxidant Capacity (TAC) in leaves and roots was lower in comparison to deionized water
treated plants. In contrast, PTW treatment caused a higher content of chlorophyll, quantum yield and total ascorbate content
in leaves compared to deionized water treated plants. After additional drought application and subsequent recovery period,
an enhancement of values for TAC, contents of malondialdehyde, glutathione as well as activity of ascorbate peroxidase
indicated a possible upregulation of antioxidative properties in roots. Hydrogen peroxide and nitric oxide might mediate
abiotic stress tolerance and are considered as key components of PTW
New microalgae media formulated with completely recycled phosphorus originating from agricultural sidestreams
Get PDFThis study investigated the impact of struvite as a sustainable phosphorus source on the growth and phycocyanin production by the blue-green alga Arthrospira platensis. Three modified growth media were compared to the typical SAG-spirul culture media. CS(+) refers to the completely recycled struvite from bovine urine as a phosphate source, while S(-) and S(+) refer to commercially available struvite as a phosphate source. On media with (+), a pre-treatment was conducted to evaporate NH4, as it negatively affects cell growth and functions of the photosynthetic apparatus at high concentrations, and to release phosphate due to the low solubility of struvite in water. For each medium, three cultures were cultivated in Erlenmeyer flasks for a duration of 42 days. Results showed that no statistically significant negative effect of struvite was found on the growth rates. However, C-phycocyanin (CPC-P) in CS(+) and S(+) was significantly higher compared to CPC-P in untreated growth media. The study hypothesized that low concentrations of NH3 remaining after the pre-treatment of struvite could have a positive impact on phycocyanin accumulation, as an energy efficient and quick nitrogen source for A. platensis
