Description: The pore-densities (PD) in the tests of 232 specimens of the shallow infaunal foraminiferal species Bolivina spissa from eight locations off the Peruvian continental margin were investigated and compared to different environmental factors as water-depth, temperature, bottom-water oxygen ([O2]BW) and nitrate concentrations ([NO3–]BW). There is a negative exponential PD-[O2]BW correlation, but at oxygen-concentrations 〉10 µmol/l PD approaches a constant value without any further correlation to [O2]BW. The PD-[NO3–]BW relationship is better constrained than that for PD-[O2]BW. We hypothesize that the pores in the tests of B. spissa largely reflect the intracellular nitrate, and to a smaller extent the oxygen respiration. We also compared PD and porosity (P) of two single B.spissa and B.seminuda specimens from the same habitat. The comparison showed that P is significantly higher in B.seminuda than in B. spissa indicating that B.seminuda is much better adapted to strong oxygen-depleted habitats than B.spissa.

Description: Due to the scarcity of information concerning the role that large foraminifera play in deep-sea carbon cycling, the response of a foraminiferal community (>250 pm) to a simulated phytodetritus sedimentation event was assessed over two weeks using sediment cores collected from a deep-fjord environment. Sediment cores were collected from similar to 700 in water depth in the Korsfjorden, western Norway, and incubated ex situ with 1 9 C-org m(2) of labile C-13-labeled Skeletonema costatum for 2, 7, and 14 days. We selectively picked (without prior staining) cytoplasm-containing foraminifera and found the foraminiferal community to be largely dominated (91%) by the deep-dwelling species Globobulimina turgida and Melonis barleeanum, as well as the shallow infaunal species 1 Hyalinea balthica. None of the >250 mu m, cytoplasm-containing fraction was involved in carbon uptake during the first 7 days. After 14 days, 3% of the foraminiferal samples possessed delta C-13 signatures indicative of carbon uptake, but the uptake was confined to the surface-living (0-2 cm) G. turgida. Foraminifera contributed 2.4% to faunal carbon uptake (foraminifera plus macrofauna) after 14 days, despite making up 24% of the combined biomass. Both the dominance of deep-infaunal species, such as G. turgida and M. barleeanum (68%), which are known to prefer degraded over more labile material, together with their large size, which often makes foraminifera respond slower to phytodetritus deposition than the more abundant, smaller-size foraminifera, are possible reasons for the retarded response observed. Overall, results from this investigation highlight that the response of large-size foraminifera to phytodetritus deposition is very slow. In addition, the results presented provide evidence that the foraminiferal response is most likely driven by differences in foraminiferal community composition and structure, with large, deep-infaunal species showing slower reactions to phytodetritus deposition compared to smaller foraminifera, metazoan meiofauna, and macrofauna.

Description: Fossil benthic foraminifera are used to trace past methane release linked to climate change. However, it is still debated whether isotopic signatures of living foraminifera from methane-charged sediments reflect incorporation of methane-derived carbon. A deeper understanding of isotopic signatures of living benthic foraminifera from methane-rich environments will help to improve reconstructions of methane release in the past and better predict the impact of future climate warming on methane seepage. Here, we present isotopic signatures (δ13C and δ18O) of foraminiferal calcite together with biogeochemical data from Arctic seep environments from c. 1200 m water depth, Vestnesa Ridge, 79° N, Fram Strait. Lowest δ13C values were recorded in shells of Melonis barleeanus, − 5.2‰ in live specimens and − 6.5‰ in empty shells, from sediments dominated by aerobic (MOx) and anaerobic oxidation of methane (AOM), respectively. Our data indicate that foraminifera actively incorporate methane-derived carbon when living in sediments with moderate seepage activity, while in sediments with high seepage activity the poisonous sulfidic environment leads to death of the foraminifera and an overgrowth of their empty shells by methane-derived authigenic carbonates. We propose that the incorporation of methane-derived carbon in living foraminifera occurs via feeding on methanotrophic bacteria and/or incorporation of ambient dissolved inorganic carbon.

Description: Marine silicate alteration plays a key role in the global carbon and cation cycles, although the timeframe of this process in response to extreme weather events is poorly understood. Here we investigate surface sediments across the Peruvian margin before and after extreme rainfall and runoff (coastal El Niño) using Ge/Si ratios and laser-ablated solid and pore fluid Si isotopes (δ 30 Si). Pore fluids following the rainfall show elevated Ge/Si ratios (2.87 µmol mol −1 ) and δ 30 Si values (3.72‰), which we relate to rapid authigenic clay formation from reactive terrigenous minerals delivered by continental runoff. This study highlights the direct coupling of terrestrial erosion and associated marine sedimentary processes. We show that marine silicate alteration can be rapid and highly dynamic in response to local weather conditions, with a potential impact on marine alkalinity and CO 2 -cycling on short timescales of weeks to months, and thus element turnover on human time scales.

Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 15. - 21. Januar 2023 „MOSES Eddy Study IV“

Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 16. - 21. Januar 2023 „MOSES Eddy Study IV“