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The Brown Bank Formation (BB Fm) is a clay‐rich sedimentary unit that is distributed over a large area in the southern North Sea. It is easily recognisable in 2D acoustic reflection profiles, forming sets of subparallel high‐amplitude reflections. Previous studies have provided only fragmentary information on the facies, and a variety of interpretations on the depositional environment and age of the BB Fm. In this study we combine high‐resolution 2D acoustic reflection profiles and multiproxy sedimentological, geochemical and geochronological analyses of three vibrocores, to provide a detailed description and a new age assessment for the BB Fm at its type locality, adjacent to the Brown Bank ridge. At the study site, the BB Fm shows morphologically well‐preserved submarine sand dunes, deposited in a high‐energy shelf setting, overlain by organic‐rich silty clays that were deposited under lower‐energy conditions in an increasingly compartmentalised marginal marine environment. Elevated terrestrial organic input shows that the Rhine–Meuse delta was situated relatively close‐by. Luminescence ages indicate that the sediments of the BB Fm in our cores were deposited during the Weichselian Odderade interstadial (MIS5a, ca. 80 ka) and earliest parts of the Early Pleniglacial (MIS4, ca. 70 ka), which is later than previously reported in the literature. [ABSTRACT FROM AUTHOR]

The TEX86 paleothermometer has been extensively used to reconstruct past sea water temperatures, but it remains unclear which export depths the proxy represents. Here we used a novel approach to better constrain the proxy recording depths by investigating paleotemperature proxies (TEX86, U37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$, RI−OH and RI−OH′) from two pairs of proximal (<12 km apart) cores from Chilean and Angola margins, respectively. These cores are from steep continental slopes and lower shelves, which leads to a substantial difference in water depth between them despite being closely located. Surprisingly, the deep and the shallow U37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$ records at the Chilean margin show dissimilarities, in contrast to the similar records from the Angola margin, which may be due to post‐depositional alteration at the former sites. In contrast, the TEX86 records were statistically indistinguishable between the sites at both the locations, even though the GDGT [2]/[3] ratio suggests GDGTs derived from potentially different archaeal communities residing at different depths. A short‐lived difference between the TEX86 records is observed during the last glacial period at the Angola margin, possibly due to a contribution of Antarctic Intermediate Waters to the deep site. Modelling suggests that the TEX86 source signal at our core sites reaches its peak abundance at water depths shallower than 350 m. The RI−OH and RI−OH′ records show similar variability as the TEX86 records, although regional differences in their absolute temperature estimates exist. Our approach using proximal sediment cores at steep slopes appears useful to constrain the export depth of organic proxy signals for paleo‐reconstructions. Key Points: Source signal of TEX86 proxy is likely derived from depths shallower than 350 m at Chilean and Angola marginsOH‐GDGT based proxies show similar variability as TEX86 records, but show regional differences in their absolute temperature estimatesU37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$ proxy signal may be impacted by post‐depositional changes or lateral transport even for closely located cores [ABSTRACT FROM AUTHOR]

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A new matrix‐matched reference material has been developed – NFHS‐2‐NP (NIOZ Foraminifera House Standard‐2‐Nano‐Pellet) – with element mass fractions, and isotope ratios resembling that of natural foraminiferal calcium carbonate. A 180–355 µm size fraction of planktic foraminifera was milled to nano‐particles and pressed to pellets. We report reference and information values for mass fractions of forty‐six elements measured by six laboratories as well as for 87Sr/86Sr (three laboratories), δ13C, δ18O (five laboratories) and 206,207,208Pb/204Pb isotope ratios (one laboratory) determined by ICP‐MS, ICP‐OES, MC‐ICP‐MS, isotope ratio mass spectrometry, WD‐XRF and TIMS. Inter‐ and intra‐pellet elemental homogeneity was tested using multiple LA‐ICP‐MS analyses in two laboratories applying spot sizes of 60 and 70 µm. The LA‐ICP‐MS results for most of the elements relevant as proxies for palaeoclimate research show RSD values < 3%, demonstrating a satisfactory homogeneous composition. Homogeneity of 87Sr/86Sr ratios of the pellet was verified by repeated LA‐MC‐ICP‐MS by two laboratories. Information values are reported for Pb isotope ratios and δ13C, δ18O values. The homogeneity for these isotope systems remains to be tested by LA‐MC‐ICP‐MS and secondary‐ion mass spectrometry. Overall, our results confirm the suitability of NFHS‐2‐NP for calibration or monitoring the quality of in situ geochemical techniques. [ABSTRACT FROM AUTHOR]

Deep‐seabed polymetallic nodule mining can have multiple adverse effects on benthic communities, such as permanent loss of habitat by removal of nodules and habitat modification of sediments. One tool to manage biodiversity risks is the mitigation hierarchy, including avoidance, minimization of impacts, rehabilitation and/or restoration, and offset. We initiated long‐term restoration experiments at sites in polymetallic nodule exploration contract areas in the Clarion‐Clipperton Zone that were (i) cleared of nodules by a preprototype mining vehicle, (ii) disturbed by dredge or sledge, (iii) undisturbed, and (iv) naturally devoid of nodules. To accommodate for habitat loss, we deployed >2000 artificial ceramic nodules to study the possible effect of substrate provision on the recovery of biota and its impact on sediment biogeochemistry. Seventy‐five nodules were recovered after eight weeks and had not been colonized by any sessile epifauna. All other nodules will remain on the seafloor for several years before recovery. Furthermore, to account for habitat modification of the top sediment layer, sediment in an epibenthic sledge track was loosened by a metal rake to test the feasibility of sediment decompaction to facilitate soft‐sediment recovery. Analyses of granulometry and nutrients one month after sediment decompaction revealed that sand fractions are proportionally lower within the decompacted samples, whereas total organic carbon values are higher. Considering the slow natural recovery rates of deep‐sea communities, these experiments represent the beginning of a ~30‐year study during which we expect to gain insights into the nature and timing of the development of hard‐substrate communities and the influence of nodules on the recovery of disturbed sediment communities. Results will help us understand adverse long‐term effects of nodule removal, providing an evidence base for setting criteria for the definition of "serious harm" to the environment. Furthermore, accompanying research is needed to define a robust ecosystem baseline in order to effectively identify restoration success. Integr Environ Assess Manag 2022;18:682–696. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: Adverse effects on benthic communities as expected from deep‐seabed polymetallic nodule mining call for the application of the mitigation hierarchy—including restoration measures once feasibility and positive effects have been proven.We initiated long‐term restoration experiments at sites in polymetallic nodule exploration contract areas in the Clarion‐Clipperton Zone that were (i) cleared of nodules by a preprototype mining vehicle, (ii) disturbed by dredge or sledge, (iii) undisturbed, and (iv) naturally devoid of nodules.We deployed >2000 artificial ceramic nodules to study the possible effect of substrate provision on recovery of biota and its impact on sediment biogeochemistry, and loosened sediment with a metal rake to test the feasibility of sediment decompaction to facilitate soft‐sediment recovery.Due to expected slow recovery rates and the need for detailed characterization of baseline conditions, we expect to gain conclusive knowledge on long‐term adverse effects of nodule removal and on the effectiveness of restoration measures in the next 30 years. [ABSTRACT FROM AUTHOR]

The Dacian Basin was uniquely situated to record late Miocene hydrological changes that influenced depositional environments and faunal dispersal patterns in Central Eurasia's mega‐lake Paratethys. Differences between the high strontium isotope ratio (87Sr/86Sr) of the waters from Lake Pannon and local Carpathian rivers and low 87Sr/86Sr of the Eastern Paratethys (Black Sea ‒ Caspian Sea) allow a thorough investigation of connectivity and water fluxes in the transient Dacian Basin. We present a detailed 87Sr/86Sr record for the Dacian Basin, which provides an exceptional record of basin connectivity from the latest Tortonian (ca. 7.7 Ma) until the early Pleistocene (ca. 1.8 Ma). Data show that a late Tortonian transgression (7.6–7.4 Ma) started with an incursion of Eastern Paratethys waters into the Dacian Basin, after which local rivers became the dominant source for the mostly freshwater environments of the early Messinian. The regional Maeotian‐Pontian transitional interval (6.3–5.9 Ma) records a second incursion of Eastern Paratethys waters, but this time with an additional marine (Mediterranean) influx coinciding with a short‐lived salinity incursion. During the Messinian Salinity Crisis of the Mediterranean, the Dacian Basin progressively connected with the Eastern Paratethys (5.9–5.5 Ma), after which it became restricted during the peak Mediterranean lowstand (5.5 Ma) and filled with Lake Pannon and local river water (5.5–5.3 Ma). During the Plio‐Pleistocene, the Dacian Basin reconnected with the, at that time isolated, Black Sea, which shows similar 87Sr/86Sr as in the Last Glacial Maximum. Plain Language Summary: The late Miocene Dacian Basin (western appendix of the Black Sea) was uniquely situated to record hydrological changes that influenced environments and faunal dispersal patterns in Central Eurasia's mega‐lake Paratethys. We used strontium isotopes from the Dacian Basin to track the moments of changing connections with Paratethys and the open ocean, via the Mediterranean. We found that at 7.6–7.4 Ma, an invasion of Eastern Paratethys waters provoked the so‐called Maeotian transgression. Afterward local rivers became the dominant source for the mostly freshwater environments, interrupted at 6.1 Ma by an influx of marine, salty water from Mediterranean. During the Messinian Salinity Crisis (5.9–5.3 Ma), when the Mediterranean suffered from an interrupted connectivity to the Atlantic Ocean, the Dacian Basin progressively connected with the Eastern Paratethys (Black Sea and Caspian Sea). At the peak of Messinian Salinity Crisis in the Mediterranean (5.5 Ma), the Dacian Basin became restricted and filled with Lake Pannon and local river water (5.5–5.3 Ma). During the Plio‐Pleistocene (between 5.3 and 1.8 Ma), the Dacian Basin reconnected with the, at that time isolated, Black Sea, providing a situation similar to the one during the Last Glacial Maximum. Key Points: The early Maeotian transgression (7.6–7.4 Ma) started with an incursion of Eastern Paratethys (i.e., Black Sea) waters into the Dacian BasinThe Maeotian‐Pontian transition (6.3–5.9 Ma) records a second incursion of Eastern Paratethys followed by a short influx of marine (Mediterranean) watersThe Bosphorian transgression at ca. 5.5 Ma was probably related to the increased influence of Pannonian and local river water in the Dacian Basin [ABSTRACT FROM AUTHOR]

Deep‐sea sponge grounds are hotspots of benthic biomass and diversity. To date, very limited data exist on the range of environmental conditions in areas containing deep‐sea sponge grounds and which factors are driving their distribution and sustenance. We investigated oceanographic conditions at a deep‐sea sponge ground located on an Arctic Mid‐Ocean Ridge seamount. Hydrodynamic measurements were performed along Conductivity‐Temperature‐Depth transects, and a lander was deployed within the sponge ground that recorded near‐bottom physical properties as well as vertical fluxes of organic matter over an annual cycle. The data demonstrate that the sponge ground is found at water temperatures of −0.5°C to 1°C and is situated at the interface between two water masses at only 0.7° equatorward of the turning point latitude of semi‐diurnal lunar internal tides. Internal waves supported by vertical density stratification interact with the seamount topography and produce turbulent mixing as well as resuspension of organic matter with temporarily very high current speeds up to 0.72 m s−1. The vertical movement of the water column delivers food and nutrients from water layers above and below toward the sponge ground. Highest organic carbon flux was observed during the summer phytoplankton bloom period, providing fresh organic matter from the surface. The flux of fresh organic matter is unlikely to sustain the carbon demand of this ecosystem. Therefore, the availability of bacteria, nutrients, and dissolved and particulate matter, delivered by tidally forced internal wave turbulence and transport by horizontal mean flows, likely plays an important role in meeting ecosystem‐level food requirements. Plain Language Summary: Sponge grounds are important ecosystems in the deep‐sea that can be compared to tropical reefs. To date, very limited data exist on the range of environmental conditions in areas where deep‐sea sponges and their accompanying fauna are found. In this study, we investigated environmental conditions at a deep‐sea sponge ground located on the summit of an Arctic seamount. Measurements of the water around the seamount and close to the sponge ground were performed recording near‐bottom physical properties as well as the food supply over an annual cycle. At the summit of the seamount, the water flow interacts with the seamount itself, which produces turbulent mixing with temporarily high current speeds. At the same time, water movements around the seamount deliver food and nutrients from water layers above and below toward the sponge ground. Fresh food from the surface water was delivered only during one major event in the summer phytoplankton bloom period. The amount of food sinking from the surface is unlikely to sustain the energetic demands of this ecosystem. Therefore, the availability of other food resources such as bacteria, dissolved and particulate matter and their delivery by water movements likely play an important role in meeting ecosystem‐level food requirements. Key Points: Long‐term study at a deep‐sea sponge ground provides environmental ranges known to support spongesHydrodynamic processes deliver water with different beneficial characteristics from above and below toward the sponge groundBenthic organisms receive only a small amount of food sinking from the surface waters, which is likely not sustaining their energy demand [ABSTRACT FROM AUTHOR]

Predicting which marine systems are close to abrupt transitions into oxygen‐deficient conditions ("anoxia") is notoriously hard but important—as rising temperatures and coastal eutrophication drive many marine systems toward such tipping points. Rapid oxic‐to‐anoxic transitions occurred regularly within the eastern Mediterranean Sea on (multi)centennial time scales, and hence, its sedimentary archive allows exploring statistical methods that can indicate approaching tipping points. The here presented high‐resolution reconstructions of past oxygen dynamics in the Mediterranean Sea reveal that early‐warning signals in these deoxygenation time series occurred long before fast transitions to anoxia. These statistical indicators (i.e., rise in autocorrelation and variance) are hallmarks of so‐called critical slowing down, signaling a steady loss of resilience of the oxygenated state as the system approaches a tipping point. Hence, even without precise knowledge of the mechanisms involved, early‐warning signals for widespread anoxia in marine systems are recognizable using an appropriate statistical approach. Plain Language Summary: As a result of rising temperatures and input of excess nutrients to coastal regions, today's oceans and seas are losing oxygen. In the geological past, large‐scale anoxic events have occasionally triggered mass extinction events, and the current loss of oxygen in the marine realm has increased worries about such events happening again. Predicting these rapid transitions to anoxia has been nearly impossible until now. By studying past large‐scale anoxic events in the Mediterranean Sea, we show, however, that before a fast transition to anoxia, there are early‐warning signals recognizable in deoxygenation time series. These early‐warning signals make it potentially possible to develop an approach to forecast rapid transitions to anoxia in areas sensitive for fast deoxygenation. Key Points: Deoxygenation events in the eastern Mediterranean Sea show tipping point behavior at which the system abruptly shifted to an anoxic stateRise in variance and autocorrelation ("early‐warning signals") in deoxygenation proxies generally signal an upcoming transition to anoxiaFirst empirical proof that these statistical indicators are applicable to marine systems sensitive to fast deoxygenation [ABSTRACT FROM AUTHOR]

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long‐term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low‐latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea. Key Points: The middle Eocene Labrador Sea was characterised by warm, low‐salinity surface watersWe find two phases of superimposed sea surface warming and subtropical plankton incursions, including the Middle Eocene Climatic OptimumBottom water stable carbon and oxygen isotope ratios indicate isolated basin [ABSTRACT FROM AUTHOR]

X-ray fluorescence (XRF) scanning of marine sediment has the potential to yield near-continuous and high-resolution records of elemental abundances, which are often interpreted as proxies for paleoceanographic processes over different time scales. However, many other variables also affect scanning XRF measurements and convolute the quantitative calibrations of element abundances and comparisons of data from different labs. Extensive interlab comparisons of XRF scanning results and calibrations are essential to resolve ambiguities and to understand the best way to interpret the data produced. For this study, we sent a set of seven marine sediment sections (1.5meach) to be scanned by seven XRF facilities around the world to compare the outcomes amidst a myriad of factors influencing the results. Results of raw element counts per second (cps) were different between labs, but element ratios were more comparable. Four of the labs also scanned a set of homogenized sediment pellets with compositions determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (MS) to convert the raw XRF element cps to concentrations in two ways: a linear calibration and a log-ratio calibration. Although both calibration curves are well fit, the results show that the log-ratio calibrated data are significantly more comparable between labs than the linearly calibrated data. Smaller-scale (higher-resolution) features are often not reproducible between the different scans and should be interpreted with caution. Along with guidance on practical calibrations, our study recommends best practices to increase the quality of information that can be derived from scanning XRF to benefit the field of paleoceanography. [ABSTRACT FROM AUTHOR]

Methane emissions from peat bogs are mitigated by methanotrophs, which live in symbiosis with peat moss (e.g. Sphagnum). Here, we investigate the influence of temperature and resultant changes in methane fluxes on Sphagnum and methanotroph‐related biomarkers, evaluating their potential as proxies in ancient bogs. A pulse‐chase experiment using 13C‐labelled methane in the field clearly showed label uptake in diploptene, a biomarker for methanotrophs, demonstrating in situ methanotrophic activity in Sphagnum under natural conditions. Peat cores containing live Sphagnum were incubated at 5, 10, 15, 20 and 25°C for two months, causing differences in net methane fluxes. The natural δ13C values of diploptene extracted from Sphagnum showed a strong correlation with temperature and methane production. The δ13C values ranged from −34‰ at 5°C to −41‰ at 25°C. These results are best explained by enhanced expression of the methanotrophic enzymatic isotope effect at higher methane concentrations. Hence, δ13C values of diploptene, or its diagenetic products, potentially provide a useful tool to assess methanotrophic activity in past environments. Increased methane fluxes towards Sphagnum did not affect δ13C values of bulk Sphagnum and its specific marker, the C23n‐alkane. The concentration of methanotroph‐specific bacteriohopanepolyols (BHPs), aminobacteriohopanetetrol (aminotetrol, characteristic for type II and to a lesser extent type I methanotrophs) and aminobacteriohopanepentol (aminopentol, a marker for type I methanotrophs) showed a non‐linear response to increased methane fluxes, with relatively high abundances at 25°C compared to those at 20°C or below. Aminotetrol was more abundant than aminopentol, in contrast to similar abundances of aminotetrol and aminopentol in fresh Sphagnum. This probably indicates that type II methanotrophs became prevalent under the experimental conditions relative to type I methanotrophs. Even though BHP concentrations may not directly reflect bacterial activity, they may provide insight into the presence of different types of methanotrophs. [ABSTRACT FROM AUTHOR]

The Baltic Sea, a dynamic, marginal marine basin, experienced a number of large changes in salinity during the Holocene as a result of fluctuations in global and local sea level related to melting of glacial ice sheets and subsequent isostatic rebound. These changes likely had pronounced effects on the species composition of haptophytes, a common phytoplankton group found in the Baltic Sea. This dynamic environment provides the ideal setting to study how species change impacts distribution and hydrogen isotope ratios of long‐chain alkenones (δ2HC37), haptophyte‐specific biomarkers. Here we analyzed the aforementioned parameters in Holocene sediments covering the contrasting hydrological phases of the Baltic Sea. Alkenone distributions changed with different Baltic Sea salinity phases, suggesting that species shifts coincide with salinity change. δ2HC37 values show two major shifts: one in the middle of the freshwater Ancylus Lake phase (10.6 to 7.7 ka) and a second at the transition from the brackish Littorina Sea phase (7.2 to 3 ka) into the fresher Modern Baltic (3 ka to the present). The first shift represents a significant enrichment of 50‰, which cannot be explained by salinity or species changes only. At this time, the isotopically depleted ice sheets had melted, and only the relatively enriched freshwater source remained. The second shift, coincident with a change in distribution, is likely caused by a change in species composition alone. These findings show that hydrogen isotope ratios of long‐chain alkenones, combined with their relative distribution, can be used to reconstruct changes in source water. Plain Language Summary: Algae record information about the water they grow in, for example, if the water is from the ocean or freshwater sources. This information is preserved in organic compounds and can be elucidated by measuring the stable hydrogen isotope composition of these molecules. The Baltic Sea is particularly suited to study hydrological changes preserved in organic compounds because it maintains a connection with the North Sea, encompassing a range of ocean to freshwater habitats, and this connection has fluctuated over time causing large salinity changes. We investigated hydrological changes in the Baltic Sea over the last 11,000 years. In the older part of the record, a major shift in isotopes of algal compounds occurred without a shift in the algal population. We interpret this as the melting of the last remnants of glacial‐aged ice at this time, leading to an abrupt shift to other freshwater sources. In the younger parts of the record, more ocean water entered the Baltic Sea, causing a change in the algal population along with isotopic change. Overall, these results contribute to our knowledge of how water source and salinity affect algal populations, which is important for understanding how ecosystems might respond to future climate change and hydrological budget. Key Points: Unusual alkenone isomers are reported for Holocene sediments from the Arkona Basin, Baltic SeaHydrogen isotope ratios of alkenones correspond to changes in source water as well as changes in species and salinityAlkenone distributions show mixing of different haptophyte groups, which changed with well‐established Baltic Sea phase shifts [ABSTRACT FROM AUTHOR]

During the last glacial period, climate conditions in the North Atlantic region were determined by the alternation of relatively warm interstadials and relatively cool stadials, with superimposed rapid warming (Dansgaard‐Oeschger) and cooling (Heinrich) events. So far little is known about the impact of these rapid climate shifts on the seasonal variations in sea surface temperature (SST) within the North Atlantic region. Here, we present a high‐resolution seasonal SST record for the past 152 kyrs derived from Integrated Ocean Drilling Program "Shackleton" Site U1385, offshore Portugal. Assemblage counts of dinoflagellates cysts (dinocysts) in combination with a modern analog technique (MAT), and regression analyses were used for the reconstructions. We compare our records with previously published SST records from the same location obtained from the application of MAT on planktonic foraminifera. Our dinocyst‐based reconstructions confirm the impression of the Greenland stadials and interstadials offshore the Portuguese margin and indicate increased seasonal contrast of temperature during the cold periods of the glacial cycle (average 9.0 °C, maximum 12.2 °C) with respect to present day (5.1 °C), due to strong winter cooling by up to 8.3 °C. Our seasonal temperature reconstructions are in line with previously published data, which showed increased seasonality due to strong winter cooling during the Younger Dryas and the Last Glacial Maximum over the European continent and North Atlantic region. In addition, we show that over longer time scales, increased seasonal contrasts of temperature remained characteristic of the colder phases of the glacial cycle. Key Points: New high‐resolution dinocyst‐based summer and winter SST record from IODP "Shackleton" Site U1385 for the last 150 kyrs is presentedDinocyst‐based SST confirms the D‐O cycles and HEs at Site U1385Increased seasonal contrast of SST (up to 12 degree C) during cold periods of the glacial cycle related to strong winter cooling is shown [ABSTRACT FROM AUTHOR]

Reconstructing millennial‐ to centennial‐scale climate variability for the Eemian—an interval with estimated sea surface temperatures ~0.5 °C warmer than "preindustrial"—requires records with high temporal resolution. Sapropel S5 sediments, deposited under anoxic conditions in the Eastern Mediterranean Sea, offer the rare opportunity to assess multicentennial climate variability during this time. Here we present high‐resolution S5 piston core data from the Nile delta region. Specifically, we focus on Ba/Ti, Br/Ti, and Mo/Ti, as they are proxies for paleo‐productivity, marine organic carbon, and sediment anoxia, respectively. A high correlation between our Ba/Ti values in core 64PE‐406‐E1 and well‐dated Ba records of nearby cores (LC21 and ODP967) was found. We, therefore, tuned our data to these cores obtaining an initial age model. A time‐frequency analyses indicated significant frequency content in the multicentennial band, although the frequency components drifted over time. Assuming spectral simplicity, we corrected for sedimentation rate changes on a multicentennial time scale. This novel approach grants a higher‐resolution age model. The resulting variability in sedimentation rate is similar to records of monsoon variability, indicating a possible link between sedimentation at the core location and low‐latitude monsoon variability, linked via the River Nile. Moreover, the periodicities found in the sapropel time series are similar to the frequency content of total solar irradiance and sunspot records known for the Holocene, at least at high frequencies (~50–150 years). Hence, our data suggest cyclic intrasapropel variability, at least during the deposition of sapropel S5, may be linked to solar cycles. Key Points: Mediterranean Sea sediments record multicentennial variability in productivity and anoxia (Ba/Ti, Br/Ti, and Mo/Ti) during sapropel S5We corrected our time series for changes in sedimentation rate on a multicentennial time scale, by using "spectral simplicity"Sedimentation covaries with monsoon variability during S5, while multicentennial variability may be linked to solar variability [ABSTRACT FROM AUTHOR]

Archaea are important players in marine biogeochemical cycles, and their membrane lipids are useful biomarkers in environmental and geobiological studies. However, many archaeal groups remain uncultured and their lipid composition unknown. Here, we aim to expand the knowledge on archaeal lipid biomarkers and determine the potential sources of those lipids in the water column of the euxinic Black Sea. The archaeal community was evaluated by 16S rRNA gene amplicon sequencing and by quantitative PCR. The archaeal intact polar lipids (IPLs) were investigated by ultra‐high‐pressure liquid chromatography coupled to high‐resolution mass spectrometry. Our study revealed both a complex archaeal community and large changes with water depth in the IPL assemblages. In the oxic/upper suboxic waters (<105 m), the archaeal community was dominated by marine group (MG) I Thaumarchaeota, coinciding with a higher relative abundance of hexose phosphohexose crenarchaeol, a known marker for Thaumarchaeota. In the suboxic waters (80–110 m), MGI Nitrosopumilus sp. dominated and produced predominantly monohexose glycerol dibiphytanyl glycerol tetraethers (GDGTs) and hydroxy‐GDGTs. Two clades of MGII Euryarchaeota were present in the oxic and upper suboxic zones in much lower abundances, preventing the detection of their specific IPLs. In the deep sulfidic waters (>110 m), archaea belonging to the DPANN Woesearchaeota, Bathyarchaeota, and ANME‐1b clades dominated. Correlation analyses suggest that the IPLs GDGT‐0, GDGT‐1, and GDGT‐2 with two phosphatidylglycerol (PG) head groups and archaeol with a PG, phosphatidylethanolamine, and phosphatidylserine head groups were produced by ANME‐1b archaea. Bathyarchaeota represented 55% of the archaea in the deeper part of the euxinic zone and likely produces archaeol with phospho‐dihexose and hexose‐glucuronic acid head groups. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Since available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2‐fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed. RESULTS: In a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0–97.2 kg dry weight (DW) ha−1 d−1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176–208 g kg−1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800 ppm) significantly boosted biomass production by 36–47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79–100 g kg−1 DW) and (poly)phenols (21–69 g kg−1 DW). CONCLUSIONS: By continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Dinitrogen fixation by Nostoc azollae residing in specialized leaf pockets supports prolific growth of the floating fern Azolla filiculoides. To evaluate contributions by further microorganisms, the A. filiculoides microbiome and nitrogen metabolism in bacteria persistently associated with Azolla ferns were characterized., A metagenomic approach was taken complemented by detection of N2O released and nitrogen isotope determinations of fern biomass. Ribosomal RNA genes in sequenced DNA of natural ferns, their enriched leaf pockets and water filtrate from the surrounding ditch established that bacteria of A. filiculoides differed entirely from surrounding water and revealed species of the order Rhizobiales. Analyses of seven cultivated Azolla species confirmed persistent association with Rhizobiales., Two distinct nearly full-length Rhizobiales genomes were identified in leaf-pocket-enriched samples from ditch grown A. filiculoides. Their annotation revealed genes for denitrification but not N2-fixation. 15N2 incorporation was active in ferns with N. azollae but not in ferns without. N2O was not detectably released from surface-sterilized ferns with the Rhizobiales., N2-fixing N. azollae, we conclude, dominated the microbiome of Azolla ferns. The persistent but less abundant heterotrophic Rhizobiales bacteria possibly contributed to lowering O2 levels in leaf pockets but did not release detectable amounts of the strong greenhouse gas N2O. [ABSTRACT FROM AUTHOR]

RATIONALE: Analyses of stable carbon isotope ratios (δ13C values) of organic and inorganic matter remains have been instrumental for much of our understanding of present and past environmental and biological processes. Until recently, the analytical window of such analyses has been limited to samples containing at least several μg of carbon. METHODS: Here we present a setup combining laser ablation, nano combustion gas chromatography and isotope ratio mass spectrometry (LA/nC/GC/IRMS). A deep UV (193 nm) laser is used for optimal fragmentation of organic matter with minimum fractionation effects and an exceptionally small ablation chamber and combustion oven are used to reduce the minimum sample mass requirement compared with previous studies. RESULTS: Analyses of the international IAEA CH-7 polyethylene standard show optimal accuracy, and precision better than 0.5‰, when measuring at least 42 ng C. Application to untreated modern Eucalyptus globulus (C3 plant) and Zea mays (C4 plant) pollen grains shows a ~ 16‰ offset between these species. Within each single Z. mays pollen grain, replicate analyses show almost identical δ13C values. CONCLUSIONS: Isotopic offsets between individual pollen grains exceed analytical uncertainties, therefore probably reflecting interspecimen variability of ~0.5-0.9‰. These promising results set the stage for investigating both δ13C values and natural carbon isotopic variability between single specimens of a single population of all kinds of organic particles yielding tens of nanograms of carbon. [ABSTRACT FROM AUTHOR]