Daniel Birgel’s research while affiliated with Hamburg University and other places

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Publications (183)


(A) Map of the Caribbean region with location of Great Blue Hole. (B) Satellite image of Lighthouse Reef atoll offshore Belize. (C) Aerial photograph of Great Blue Hole, taken with drone from 500 m distance in 200 m height, looking east towards windward reef margin. Note supply boat at eastern rim of blue hole and coring platform at blue hole centre (location of corehole BH8). Diameter of Great Blue Hole is 320 m. For a cross‐section, see Figure 16C.
(A) Simplified log of core BH8 with sedimentary units, absolute age data and representative core photographs. (B) Section from the lower, dark‐coloured unit A deposited in a cenote environment with faintly visible lamination; core depth of 29.22–29.38 cm. (C) Example from middle mangrove‐swamp unit B with slightly visible annual layering and darker event beds; core depth of 25.40–25.56 m. (D) Section from the upper marine unit C with greenish annually layered background sediments and lighter coloured event beds; core depth of 1.19–1.35 m.
(A) Carbonate content, (B) relative percentages of carbonate phases along core BH8 (ARA = aragonite; HMC = high‐magnesium calcite; LMC = low‐magnesium calcite) and (C) water and total organic carbon (TOC) contents along core BH8.
Selected element (Si, S, Ti, Fe) plots along core BH8. cps, counts per second.
SEM images of core material from core catcher samples of core BH8. (A) Foraminiferal (probably Triloculina) tests (F), tunicate spicules (T) and shell fragments produced by boring sponges (S). Marine unit C; core depth of 9.74–10.0 m. (B) Foraminiferal (probably Quinqueloculina) tests (F), tunicate spicules (T) and fragment of sponge needle (SP). Marine unit C; core depth of 9.74–10.0 m. (C) Abundant coccoliths, crystals of aragonite needles and nanograins. Marine unit C; core depth of 9.74–10.0 m. (D) Aragonite needles and nanograins. Marine unit C; core depth of 19.9–20.0 m. (E) Presumed fragment of Halimeda platelet in centre consists of aragonite needles. Marine unit C; core depth of 19.4–20.0 m. (F) Planktonic foraminiferal (probably Globigerinoides) tests (F), tunicate spicules (T) and shell fragments (S) excavated by boring sponges. Mangrove‐swamp unit B; core depth of 28.01–28.04 m.

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Late Pleistocene to Holocene sedimentation in the Great Blue Hole (Lighthouse Reef, Belize): Results from a 30 m long core
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June 2025

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95 Reads

Eberhard Gischler

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Annika Wiegand

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Jörn Peckmann

The Great Blue Hole is a prominent flooded karst sinkhole, located in the lagoon of Lighthouse Reef atoll off the coast of Belize. Short cores recovered from varved bottom sediments have been used in previous studies as climate and cyclone archives covering as much as the past ca 1.7 ka BP. A new 30 m long sediment core, encompassing the entire Holocene and the latest Pleistocene, allows a reconstruction of the development of this geoscientifically significant site in the light of the postglacial and Holocene sea‐level rise. The sedimentary succession in the core is tripartite. The lowermost sedimentary unit A (30.0–28.6 m) comprises grey‐brown to black organic‐rich carbonate sediments, which contain freshwater snails (Pyrgophorus), tropical forest pollen (Myrtaceae) and a low‐diversity dinocyst assemblage. The intermediate unit B (28.6–24.65 m) is a dark greyish‐green to greyish‐brown, weakly laminated carbonate silt, which comprises marine fossils, that is, euryhaline foraminifera (Elphidium) and Halimeda (codiacean algal) platelets. Unit B contains abundant red mangrove (Rhizophora) pollen and a dinocyst assemblage indicating high productivity in surface waters. The uppermost unit C (24.65–0 m) is an annually layered buff and light green carbonate silt with abundant marine fossils. A total of 574 intercalated, coarser‐grained and lighter‐coloured event (storm) beds usually rich in Halimeda and coral fragments were identified in unit C. Fully marine conditions, including trophic seasonality, are also indicated by the dinocyst spectrum. The pollen spectrum derives from a variety of trees (largely pine, oak, podocarp), shrubs and herbs. The sedimentary succession represents the transition from an initial terrestrial cenote phase on a vegetated limestone island (unit A: 12.5–7.2 ka BP), via a subsequent restricted marine phase on an initially flooded carbonate platform with mangrove swamps (unit B: 7.2–5.7 ka BP), to a fully marine phase in an open, well‐circulated atoll lagoon (unit C: 5.7–0 ka BP).

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Fig. 1. Study area, historical storm record, and mechanisms of tempestite sedimentation. (A) Map of circum-caribbean region (89) with important tc-frequency archives (yellow stars): Florida (26), Yucatán Peninsula (28, 29), Belize (30, 31, 34, 67, 69), Bahamas (3, 20, 32, 33, 35-37), and Puerto Rico (58) and a conceptual scheme of the itcZ summer position (105). the red pin points to the study site. (B) the position of the GBh (encircled) on an open access ASteR satellite image of lighthouse Reef (https://asterweb.jpl.nasa.gov) supplied by Japan Space Systems and U.S/Japan ASteR Science teAM (nASA/Meti/AiSt/). (C) Aerial view of the GBh taken from an UAv (unmanned aerial vehicle/drone) showing the coring platform at site Bh8 (17° 18.572′ n, 87° 32.060′ W) and a support boat within the sinkhole structure. Photo: e.G. (D) Selected tc pathways from the historical record (2022-1950 ce) passing over the study site within a 100-km diameter circle. Storm track maps were downloaded from https://coast.noaa.gov/hurricanes/ and compared with the international Best track Archive for climate Stewardship-iBtrAcS (49). (E) Mechanisms of event-layer (tempestite) formation in the GBh.
Fig. 3. 5700-year-long reconstruction of southwestern Caribbean TC frequency. (A) Obliquity and precession changes, which lead to a gradual modification of solar insolation in high latitudes and tropical regions, respectively (107). (B) Southward itcZ migration during the holocene, reconstructed from titanium contents of cariaco Basin sediments (53) along with proxy-based global and 30° to 0° n mean surface temperatures (MSt) (108). (C) Sedimentary units in core composite Bh8 with their paleoenvironmental interpretation combined with a modeled relative sea-level curve (RSl) of lighthouse Reef (47) that explains two stages of a varying site sensitivity starting at 7.2 ka B.P. (boundary unit A/B) and 5.7 ka B.P. (boundary unit B/c), respectively. (D) 5700-year-long tc-frequency reconstruction in a 50-year counting window, with the tc frequency for the 21st century based on an extrapolation of nine event-layer counts from 2000 to 2022 ce, showing a long-term trend of increase and shortterm fluctuations. increased and decreased cyclone activities, with >5.1 and <5.1 tcs per 50 years, are indicated by red and blue coloring of the bars, respectively, and the smoothed 50-year tc-frequency reconstruction is shown by the bold black curve. (E) comparison of our smoothed 50-year tc reconstruction with the enSO intensity (57) and prominent holocene cold (light blue) and warm (light red) phases: hcO, holocene climate Optimum; Mht, mid-holocene transition; PcP, Piora cold Period; SWP, Sumerian Warm Period; BAc, Bronze Age cold; MiWP, Minoan Warm Period; iAc, iron Age cold; RWP, Roman Warm Period; dAc, dark Ages cold; MWP, Medieval Warm Period; liA, little ice Age; and iW, industrial Warmth. For coloring, please consider the online version of the manuscript.
Fig. 4. Comparison of multi-millennial TC-frequency records. Multi-millennial tc-frequency records from the GBh, Puerto Rico (58), the Bahamas (3), and Florida (26), covering up to the past 5700 years. Active and calm phases are separated by site-specific thresholds (red lines) and highlighted for the GBh record in gray (for coloring, please refer to the online version of the manuscript). the black dashed lines are linear regressions (SlR), demonstrating long-term trends in the data. All the raw data for the reanalysis of the Puerto Rico, Bahamas, and Florida records originate from the nOAA paleoclimate database. it was taken into account that their age models have a different reference point (calibrated years B.P. 1950). the tc-frequency plots were generated processing a three-point moving average step plot using the software package PASt.v.4.08.
Fig. 5. Reconstruction of Atlantic TC frequency from 850 to 2000 CE and regional comparison. (A) A multisite sedimentary-based Atlantic Basin compilation (gray shading) (68) is provided besides the tc-frequency curve from this study (green). (B) Regional comparison between our tc-frequency reconstruction from the GBh (green) and the adjacent cenote Muyil record (29) over common era times. tc-frequency plots were generated processing a three-point moving average step plot using the software package PASt.v.4.08. Active and calm phases have been defined by calculating site-specific thresholds (red lines) for storm activity: 6.7 ± 2.6 tcs (GBh) and 3.0 ± 1.3 tcs (cenote Muyil) per 50-year counting window. Both records show overlapping intervals (gray) of enhanced south-western tc frequency (600 to 800 ce, 900 to 1400 ce, and 1800 ce-modern) and a mutual calm phase from 1400 to 1800 ce.
An annually resolved 5700-year storm archive reveals drivers of Caribbean cyclone frequency

March 2025

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210 Reads

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2 Citations

Science Advances

Predictions of tropical cyclone (TC) frequencies are hampered by insufficient knowledge of their natural variability in the past. A 30-m-long sediment core from the Great Blue Hole, a marine sinkhole offshore Belize, provides the longest available, continuous, and annually resolved TC-frequency record. This record expands our understanding, derived from instrumental monitoring (73 years), historical documentations (173 years), and paleotempestological records (2000 years), to the past 5700 years. A total of 694 event layers were identified. They display a distinct regional trend of increasing storminess in the southwestern Caribbean, which follows an orbitally driven shift in the Intertropical Convergence Zone. Superimposed short-term variations match Holocene climate intervals and originate from solar irradiance–controlled sea-surface temperature anomalies and climate phenomena modes. A 21st-century extrapolation suggests an unprecedented increase in TC frequency, attributable to the Industrial Age warming.


An Anaerobic Microbial Community Mediates Epigenetic Native Sulfur and Carbonate Formation During Replacement of Messinian Gypsum at Monte Palco, Sicily

March 2025

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85 Reads

Geobiology

The microbially mediated replacement of sulfate‐bearing evaporites by authigenic carbonate and native sulfur under anoxic conditions is poorly understood. Sulfur‐bearing carbonates from the Monte Palco ridge (Sicily) replacing Messinian gypsum were therefore studied to better characterize the involved microorganisms. The lack of (1) sedimentary bedding, (2) lamination, and (3) significant water‐column‐derived lipid biomarkers in the secondary carbonates implies replacement after gypsum deposition (epigenesis). Allochthonous clasts from the older Calcare di Base and the younger Trubi Formation within these carbonates further evidence epigenetic formation. The sulfur‐bearing carbonates are significantly ¹³ C‐depleted (δ ¹³ C as low as −51‰), identifying methane as a major carbon source. The ¹⁸ O‐enrichment of the carbonates (δ ¹⁸ O as high as 5.4‰) probably reflects precipitation from ¹⁸ O‐enriched fluids transported along adjacent faults or precipitation in a closed system with very little water. Native sulfur with variable ³⁴ S‐enrichment (δ ³⁴ S as high as 18.9‰), a relatively small maximum offset (12.3‰) between the sulfate source (gypsum) and native sulfur, and high δ ³⁴ S values of carbonate‐associated sulfate (as high as 61.1‰) suggest a high conversion to native sulfur in a (semi‐)closed system, with insignificant sulfate removal. Anaerobic methanotrophic archaea (ANME) apparently affiliated with the ANME‐1 clade mediated secondary mineral formation as evidenced by the biomarker inventory, which contains abundant ¹³ C‐depleted isoprenoids including sn3 ‐hydroxyarchaeol as the sole hydroxyarchaeol isomer and glycerol dibiphytanyl glycerol tetraethers (GDGTs). A series of various, tentatively identified ¹³ C‐depleted non‐isoprenoidal dialkyl glycerol diethers (DAGEs), 10me‐C 16 fatty acid, hydroxy C 16 fatty acids, and cyclopropyl‐C 17:0ω7,8 fatty acid agree with sulfate‐reducing bacteria participating in the anaerobic oxidation of methane. Specific conditions during gypsum replacement, unlike those at marine methane seeps, are reflected by the occurrence of ¹³ C‐depleted lipids such as lycopane, 9me‐C 17 fatty acid, and novel DAGEs. As a response to a confined environment probably characterized by high sulfate concentrations, sulfidic conditions, and elevated salinity, ANMEs and sulfate‐reducing bacteria apparently adapted their membrane compositions to cope with such stressors.


Probing large paleoenvironmental variability during the Messinian-Zanclean transition in the Northern Apennines (Maccarone section), Italy, via multivariate statistical analysis on lipid biomarker-based proxies

January 2025

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115 Reads

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1 Citation

Palaeogeography Palaeoclimatology Palaeoecology

Quantitative reconstruction of paleoenvironmental and paleoclimatic changes that lack modern analogues is inherently challenging. A notable example of extreme paleoenvironmental transformation occurred in the Mediterranean Basin at the Messinian–Zanclean boundary (5.33 Ma), marked by the transition from the terminal Lago-Mare phase of the Messinian salinity crisis to the re-establishment of normal marine conditions starting with Zanclean. Despite its significance, the paleoenvironmental conditions of the Lago-Mare phase remain unresolved due to the conflicting fossil record, including both freshwater to brackish assemblages and marine microfossils. In this study, we applied a multivariate statistical approach to interpret a large dataset of terrestrial and aquatic biomarker indices from the Maccarone section in northern Italy. This analytical method was specifically tailored to address complexities associated with records originating from highly dynamic and contrasting, transitional environments (i.e., from lacustrine to marine) bringing the advantage of using statistical techniques to identify features that a traditional, visual, observation of complex array of proxies is unable to identify. Cluster analysis reveals a stepwise evolution of environmental conditions throughout the Messinian–Zanclean transition, while redundancy analysis indicates a sudden shift in the water column structure from stratified to well-mixed conditions at the Messinian–Zanclean boundary. Additionally, a gradual change is inferred in terrestrial vegetation, reflecting a progressive reconfiguration of coastal environments following the Zanclean marine transgression, with inland migration of the coastline and a decrease in wetland aquatic plant indicators.


Seep carbonate from the Yam Seep area; m = microcrystalline aragonite, pa = pink aragonite, ca = clear aragonite
A, B Polished rock samples showing the paragenetic sequence of microcrystalline aragonite, pink aragonite, and clear aragonite. C Thin section scan showing the mineral paragenesis. D Photomicrograph highlighting textural differences between pink and clear aragonite cement. E Same image as in (D) under UV light; fluorescence image.
Growth rates of pink and clear aragonite cement based on uranium/thorium (²³⁰Th/U) dating; m = microcrystalline aragonite, pa = pink aragonite, ca = clear aragonite; gray arrows and inserted numbers show the approximate area of sampling on the polished rock slabs
Black arrows within the graphs denote the growth direction of cements, and values indicate mean growth rates assuming constant growth along the transects. A, B Clear aragonite showing nearly identical growth rates. C, D Pink aragonite growth rates. Note the different scales for age and distance.
Schematic cartoon of precipitation modes of pink and clear aragonite cement
A Ascent of methane-rich fluids enables the formation of gas hydrates in open cracks and voids within lithified host sediment (microcrystalline aragonite) and leads to methane emissions to the seafloor. B Detailed view of the black box in (A): Methane seepage-derived fluid mixes with seawater in open fractures of lithified host sediment, enabling SD-AOM mediated by microbial consortia that form biofilms on fracture walls. C In situ mineralization of biofilms after Dupraz et al.16, where calcium and carbonate ions precipitate carbonate coatings on EPS within the mat. Biofilm growth continues after mineralization, producing layer upon layer of mineralized biofilm resulting in pink aragonite cement. D Diffusion of calcium and carbonate ions towards the locus of clear aragonite precipitation without in situ biofilm mineralization, leading to the formation of clear botryoidal aragonite cement. No scale implied, see text for details.
Marine carbon burial enhanced by microbial carbonate formation at hydrocarbon seeps

January 2025

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235 Reads

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1 Citation

Some of the carbon removed from Earth’s surface is stored within authigenic carbonate in marine sediments. Methane seeps are crucial sites of global marine carbon cycling sustaining microbial activity, enabling carbonate formation and the transfer of methane-derived carbon to the geosphere. Carbon sequestration rates depend on carbonate precipitation rates, which can be accelerated by mat-forming microorganisms that are ubiquitous at methane seeps and other Earth surface environments today. We investigate a 5-m-long drill core from an active methane seep at 1350 m water depth in the South China Sea with an exceptional abundance of pink and clear aragonite cement derived from the sulfate-driven anaerobic oxidation of methane, yet both cements precipitated under different conditions. Phase-specific ²³⁰Th/U-based ages, lipid biomarker compositions, and calcium isotope data suggest that pink aragonite is a product of in situ biofilm mineralization. First estimated precipitation rates of these individual cements in the seep carbonates range from 0.04 cm/ka for clear aragonite to 1.0 cm/ka for pink aragonite, suggesting an up to 25-fold increase in precipitation rates associated with biofilm mineralization. These results provide first kinetic constraints for future quantitative carbon cycle models, emphasizing the role of biofilms in accelerating carbon sequestration in marine authigenic carbonates.




(a) Map showing the study locations in the central Arabian Sea along the 64° E transect during SSD-068 (December 2019). The low-level atmospheric jet (Findlater Jet) is depicted with a dashed white arrow, and the boundary of the oxygen minimum zone (OMZ) (0.5 mmol L⁻¹ O2 concentration) is displayed with a dashed black line. (b) Average SST (2017–2020) values depicting spatial variability among the sampling stations from north to south. (c) Average Chl a values derived from the satellite for the period 2017–2020 over the Arabian Sea, indicating that average phytoplankton biomass remains higher on an annual scale for the stations in the north compared to the south.
The distribution of total inorganic carbon (TIC %) (a), total organic carbon (TOC %) (b), total nitrogen (TN %) (c), alkenone-based sea surface temperature (SST °C) (d), brassicasterol (e), dinosterol (f), dinostanol (g), C37 alkenones (h), cholesterol (i), cholestanol (j), radiolarians (k), and diatom frustules (l) along the 64° E transect in the central Arabian Sea.
The bubble plot shows the relative percentage of diatom frustules of major species (>3 % of total abundance) from surface sediment samples (average of 0–0.5 cm and 0.5–top 1 cm) along the 64° E transect in the central Arabian Sea. Individual contributions from centric and pennate diatoms <3 % are summed as “others”. The colours denote the specific phytoplankton taxa as indicated by coloured closed circles at the bottom of the panel.
RDA biplot showing the interrelationship between the key parameters shown in blue (diatom frustules, biomarkers, radiolarians) and the bulk sedimentary parameters indicated in red (TOC, TN, TIC, TOC : TN, SST). The names of the diatom genera are marked as “Sp.” and are mentioned in the top left of the panel. Axis 1 and Axis 2 explain nearly 97.2 % of the variability.
The schematic shows the spatial variability in particle flux along the 64° E transect in the central Arabian Sea.
Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea

October 2024

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371 Reads

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2 Citations

The central Arabian Sea, a unique tropical basin, is profoundly impacted by monsoon wind reversal affecting its surface circulation and biogeochemistry. Phytoplankton blooms associated with high biological productivity and particle flux occur in the northern part of the central Arabian Sea due to summer-monsoon-induced open-ocean upwelling and winter convection. The core oxygen minimum zone (OMZ) at intermediate water depths is another important feature of the northern central Arabian Sea and fades southward. In this study, we attempt to interlink how these factors collectively impact phytodetrital export to the sediment. Short sediment core-top (1 cm) samples representing the recent particle flux signatures were analysed from five locations (21 to 11° N; 64° E) in the central Arabian Sea. Previously, we used core-top (0–0.5 cm) samples and observed a trend between diatom frustule abundance and diversity with bulk sedimentary parameters indicating a spatial variability in phytodetrital export to the sediment. To verify this observation further, lipid biomarkers of key phytoplankton groups and a sea surface temperature (SST) proxy have been analysed in addition to diatom frustules. The C37 alkenone-based SST proxy indicated cooler SST (27.6 ± 0.25 °C) in the north (21–15° N) mostly due to upwelling (summer) and convective mixing (winter). Warmer SSTs (+0.4 °C) are measured in the south, which usually remains nutrient-poor. This trend was consistent with satellite-derived average SST values (2017–2020). Lipid biomarker analysis suggests that dinoflagellates were likely to be the highest contributor, as indicated by dinosterol and its degradative product dinostanol, followed by brassicasterol and C37 alkenone, likely representing diatoms and coccolithophores, respectively. The north, which largely experiences periodic phytoplankton blooms and is influenced by the thick OMZ, revealed the highest contents of organic matter, diatom frustules (diversity and abundance), dominated by large, thickly silicified cells (e.g. Coscinodiscus and Rhizosolenia) and phytoplankton lipid biomarkers, as well as lower contents of zooplankton biomarkers (cholesterol and cholestanol). In contrast, relatively smaller chain-forming centric (e.g. Thalassiosira) and pennate (e.g. Pseudo-nitzschia, Nitzschia, Thalassionema) diatom frustules along with lower phytoplankton lipid biomarker contents were found in the south, where zooplankton biomarkers and silicious radiolarians were more abundant. The possible impacts of the OMZ on particle flux related to the phytoplankton community, including zooplankton grazing and other factors, have been discussed.



Citations (63)


... Therefore, it was the aim of this study to recover a complete sedimentary package at the bottom of the Great Blue Hole to fill the described gaps in knowledge and to provide a continuous Holocene and late Pleistocene climate and storm archive. The latter was recently compiled by Schmitt et al. (2025). This study focuses on the sedimentology and palaeontology of the new 30 m long core. ...

Reference:

Late Pleistocene to Holocene sedimentation in the Great Blue Hole (Lighthouse Reef, Belize): Results from a 30 m long core
An annually resolved 5700-year storm archive reveals drivers of Caribbean cyclone frequency

Science Advances

... This finding is consistent with previous research (Chu et al., 2005;Wang et al., 2015). Notably, this relationship is not readily discernible from the univariate plots in Fig. 5A and B. In fact, it becomes apparent only when the value of the C 37 /C 38 ratio significantly deviates from those typical of marine associations which may compromise SST interpretation (Pilade et al., 2023(Pilade et al., , 2025. ...

Probing large paleoenvironmental variability during the Messinian-Zanclean transition in the Northern Apennines (Maccarone section), Italy, via multivariate statistical analysis on lipid biomarker-based proxies
  • Citing Article
  • January 2025

Palaeogeography Palaeoclimatology Palaeoecology

... For example, diatoms are present during both the summer [34] and winter monsoons [35]. Recent investigations [36] have shown that certain diatoms, such as Coscinodiscus and Rhizosolenia, both found in the Arabian Gulf along the coastline of Qatar, are major contributors to bloom formation and dominate the flux of biogenic silica [37]. The impact of these blooms on marine life was recently examined in detail by Al-Thani and Yasseen [5]. ...

Sedimentary organic matter signature hints at the phytoplankton-driven biological carbon pump in the central Arabian Sea

... However, an opposite trend was observed in the northern Gulf of Mexico for RI-OHʹ due to high abundance of OH-isoGDGT-0 in the riverbank sediments and soils (Figs. 3 and 4,Supplementary Fig. 2). This discrepancy might be attributed to regional differences in the source organisms producing these compounds, such as methanogenic archaea (Guan et al., 2024). Further studies, including stable carbon isotope analysis, are needed to confirm methanogenic contributions to OH-isoGDGTs. ...

Hydroxylated GDGTs-0 in marine methane seep environments: A putative indicator for archaeal methanogenesis
  • Citing Article
  • August 2024

Organic Geochemistry

... In marine sediments not affected by seepage, pyrite formed by OSR typically reveals low δ 34 S values (Wortmann et al., 2001;Canfield and Teske, 1996); organic matter contents and sedimentation rates have been shown to affect the sulfur stable isotope composition of pyrite (e.g., Pasquier et al., 2017;Jørgensen, 2021). In contrast, many studies reported 34 S enriched authigenic pyrite from modern seep environments (Peckmann et al., 2001;Lin et al., 2016aLin et al., , 2017aLin et al., , 2018Lin et al., , 2024Wu et al., 2019;Miao et al., 2021), with 34 S enrichment apparently caused by higher rates of sulfate reduction compared to OSR (Deusner et al., 2014), low sulfate replenishment , and quantitative conversion of seawater sulfate to sulfide (Borowski et al., 2013). Since pyrite formationstrictly speaking, the formation of iron mono sulfide minerals and their subsequent conversion into pyriteis a cumulative process in seep environments, occurring at different stages of diagenesis, the sulfur isotope composition of the resultant composite pyrite reflects the mixture of pyrite forming under changing environmental conditions. ...

Methanogenic Archaea as Catalysts for Magnetite Formation in Iron‐Rich Marine Sediments

... The crusts found in the Red Sea are reported to have formed in situ by biogenic processes, which are indicated through SEM analysis by the presence of calci ed bacterial/fungal laments and probable coccoid shaped algae and bacteria, which bind the sediment (Brachert and Dullo 1991). A recent study undertaken in a deep fore reef in western Indian, which is characterized by a high diversity and abundance of sponges, has also proven the biogenicity of microbial carbonates (Maak et al. 2024). Based on various lines of evidence, including lipid biomarkers that are speci c for sulfate reducing bacteria and the co-occurrence of lipid signatures with diverse microtextures, ie. ...

Molecular fossils in reefal carbonates and sponges of the deep fore reef of Mayotte and Mohéli, Comoro Islands, western Indian Ocean

Facies

... With an open Strait of Gibraltar, the input of Atlantic waters as underflow would promote a threefoldstratified structure of the Mediterranean, with Lago Mare freshwater on top, normal marine water at intermediate depths, and possibly denser, residual hypersaline waters at the bottom. This could explain the possible presence of normal marine water that has often been documented, especially for substage 3.2, based on paleontological (Popescu et al. 2007, Carnevale et al. 2018 and/or organic-geochemical proxies (long-chain alkenones from marine calcareous nannoplankton; Vasiliev et al. 2017, Pilade et al. 2023). Moreover, a high sea level could also easily explain the extremely homogeneous character of the stage 3 succession in terms of the number of evaporite cycles and geochemical signatures of both evaporites and fossils ( 87 Sr/ 86 Sr; see Figure 2), in either marginal or deep settings all along the Mediterranean (Roveri et al. 2014a,c;Gvirtzman et al. 2017). ...

Deciphering the termination of the Messinian salinity crisis: The alkenone record of the Miocene-Pliocene transition in the northern Mediterranean.
  • Citing Article
  • October 2023

Palaeogeography Palaeoclimatology Palaeoecology

... Observations of fibrous dolomite suggest the presence of dolomite seas, where dolomite precipitates directly from seawater [40][41][42]. It is speculated that dolomite could have formed under highly alkaline and anoxic sulfate-reducing conditions [40][41][42]. ...

Fibrous dolomite formation at a Miocene methane seep may reflect Neoproterozoic aragonite-dolomite sea conditions

... Strains have also been documented to be involved in replacing anhydrite (Ca[SO 4 ]) with authigenic carbonates (Zueblin, 1988). When either OM or methane (in conjunction with ANME) is available, bicarbonate is produced, increasing alkalinity and causing an oversaturation of calcium-and carbonate-ions; thus, forming secondary carbonate precipitates (Rouwendaal et al., 2023). If this were the case then the enrichment of Alkalinibacteraceae could be explained. ...

Two modes of gypsum replacement by carbonate and native sulfur in the Lorca Basin, SE Spain

... There is controversy in the presence of C-24 sterol methyltransferase (C 24 -SMT) in different invertebrate groups. Whereas de novo sitosterol synthesis has been demonstrated in some annelids using a noncanonical C 24 -SMT [46], to our knowledge brassicasterol synthesis was never previously reported in mollusks due to the absence of canonical C24-SMT genes in mollusks [32]. Such brassicasterol synthesis in larvae fed T (i.e., diet lacking cholesterol) and TCg support the assertion of Voogt [47] who highlighted the importance and possible role of brassicasterol in bivalves, which might replace cholesterol in some of its structural and/or physiological functions. ...

De novo phytosterol synthesis in animals
  • Citing Article
  • May 2023

Science