SSP2.3

The Holocene, the current interglacial period covering the last ~11.5 ky, is generally characterized by warm sea surface temperatures (SSTs), high atmospheric CO₂ levels, and low ocean productivity in some regions. However, previous studies showed that the oceanographic conditions across the Holocene are highly variable, whereby regional patterns, such as in upwelling regions, are still poorly known.

The Portuguese margin is under influence of the Canary Eastern Boundary Upwelling System and is characterized by seasonal upwelling associated with cold waters and high primary productivity during spring-summer. During this period, are present the southward flowing, relatively cool and nutrient rich offshore Portugal Current (PC), and the nearshore Portuguese Coastal Current (PCC). During the fall-winter months, the PCC is substituted by the warm and nutrient poor Iberian Polar Current.

Considering that the planktonic foraminifera (PF) fauna is affected by water temperature and food availability, the present study reconstructs the Portuguese margin temperature and productivity, through a transfer function, across the Holocene using the PF fauna, at two sites under different oceanographic conditions: Shak-03-6K (37⁰42.45’N, 10⁰29.542’W, 3735m) recovered on the Sines margin and core MD03-2699 (39°02.20′N, 10°39.63′W, 1895m) from the Estremadura spur.

The fauna analysis at the Estremadura core revealed a total of 27 species and an estimated average summer SST of 18.9 °C. At the Sines core, we found 25 species, and a Holocene average SST of 21.2 °C. Our Holocene record starts with warm SSTs (above 20 °C) at both sites, followed by a cold event (starting at 10.5 ky), when the SST record at the Estremadura site abruptly dropped by 13 ºC, while at the Sines site the observed cooling was only 2 ºC. Two additional cold events, at 8.2 ky (~16 °C) and 5.2 ky (17.5 ºC) occurred during the Holocene Thermal Optimum (HTO, from 9.5 to 5.5 ky) at the Estremadura Site. According to previous studies, these short cold events are well marked in the North Atlantic, possibly caused by freshwater input from the melting Laurentide ice sheet. During these events, the relative abundance of polar and subpolar species (N. pachyderma and T. quinqueloba) increased, while the PC related species (N. incompta and G. inflata) decreased. However, this period is the warmest period of the Holocene when global glaciers reached their minimum volume extend, and in both sites the subtropical and tropical species increased.

During the Late Holocene (~4.2 ky to present), the SSTs at both sites remained constantly warm, with a high abundance of G. bulloides at the transition of HTO and this period. A feature that, most probably reflects enhanced upwelling influence, mainly at the Estremadura site. In fact, the Estremadura site records higher productivity than the Sines site, as that site is under a stronger influence of upwelling events and riverine nutrient supply from the Tagus River. Furthermore, occasional incursions of cold waters from the North are clearly marked on the Estremadura site, located close to the limit between subtropical and transitional surface and subsurface waters.

How to cite: Mega, A., Salgueiro, E., Rebotim, A., Voelker, A., Cruz, J., Calvo, E., and Abrantes, F.: Holocene temperature and productivity variability at the Portuguese margin - evidence from planktonic foraminifera faunas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6379, https://doi.org/10.5194/egusphere-egu22-6379, 2022.

The Toba volcano super-eruption on the island of Sumatra occurred about 74,000 years ago^[1], close to the transition between interglacial Marine Isotope Stage (MIS) 5 and glacial MIS 4. This eruption, called Youngest Toba Tuff (YTT), is currently described as the largest cataclysmic eruption of the Quaternary. However, the impact of this super-eruption on climate is widely debated and its effects on the ocean remains poorly understood.

The aim of this work is to estimate its impact on oceanic pH at a site near the eruption center. To do so, we measured δ¹¹B values (pH proxy) on monospecific samples of planktonic foraminifera Globigerinoides ruber and Pulleniatina obliquiloculata from sediment core BAR94-25 (Andaman Sea) using a recently developed method at the Institut de Physique du Globe de Paris (IPGP)^[2]. G. ruber is a species that thrives preferentially in surface waters, while P. obliquiloculata lives at the thermocline. Therefore, δ¹¹B measurements on their shells can reconstruct pH variations in surface and thermocline waters, respectively.

We selected the interval from 258 to 355 cm, corresponding to an age between 57 and 82 ka. This interval contains two clearly visible tephra layers corresponding to the YTT, at the transition from MIS 5 to MIS 4, and to a post-YTT explosive activity during MIS 4. These layers are correlated with a significant decrease in carbonate content (CaCO₃). Our results indicate a complex pH response during the two concerned volcanic episodes. Thermocline seawater doesn’t show significant pH decrease during the volcanic episodes compared to the overall signal recorded throughout the studied interval. Conversely, surface seawater shows a much more important pH decrease during part of the volcanic episodes than during the all studied interval. Such decrease in pH during the transition to a glacial state is particularly surprising because an increase in pH, due to the global reduction in atmospheric CO₂, is rather expected, as shown by previous foraminifera δ¹¹B records^[3].

The coupling of CaCO₃ and pH decrease during tephra levels suggests acidification in the Andaman Sea as a consequence of the Toba volcanic eruptive activity. The seawater surface seems much more sensitive to pH changes than the thermocline zone. However, the reduction of carbonate in the two tephra layers may also be due to dilution from ash falling into the sediment. Other analyses, such as measuring the variation of calcification intensity in planktonic foraminifera, are therefore necessary to better interpret these paleo-pH data.

[1] Storey et al., 2012, PNAS, 109 (46), 18684-18688

[2] Buisson et al., 2021, JAAS, 36, 2116-2131

[3] Foster et al., 2008, EPSL, 271, 254-266

How to cite: Alves, A., Buisson, M., Louvat, P., Rollion-Bard, C., Bassinot, F., Moreno, E., Paris, G., Caron, B., Del Manzo, G., Le Friant, A., and Bartolini, A.: Impacts of the Toba super-eruption on the pH of the Andaman Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8021, https://doi.org/10.5194/egusphere-egu22-8021, 2022.

Variations in sediment supply are known to potentially alter the concentration of fossils or to mix up components of different environments or stratigraphic ages. The combination of shifts in sediment supply rates, sediment transport, bioturbation, erosion, and accommodation space can, controlled by the eustatic sea-level, lead to systematic changes in the extend of time averaging and consequently temporal resolution of the fossil record. The effect of this bias on fossil occurrence patterns is well studied, though less emphasis has been paid to its potential influence on the observed record of geochemical proxies, which are extracted from these fossils. To assess this potential bias in geochemical proxies we analysed δ¹³C and δ¹⁸O values from ¹⁴C- and amino-acid dated Holocene Corbula gibba shells from the Northern Adriatic Sea, covering the transgression and sea level highstand since the last deglaciation. As the fossil assemblages in transgressive deposits are typically more time-averaged compared to highstand strata, and thus capture larger absolute age span,  the range of δ¹³C and δ¹⁸O values should be higher in the transgressive core sections. However, our initial results suggest that while the age range indeed increases with sediment depth, the carbon and oxygen isotopic ranges decrease, with a few exceptions. This could be caused by higher variation or higher pace of environmental change during deposition of highstand strata, or by increased homogenisation due to the increased time of exposition to diagenetic fluids with sediment depth.

How to cite: Nohl, T., Nawrot, R., Tomašových, A., and Zuschin, M.: Time averaging, stratigraphic disorder and geochemical proxy records: cautionary tale from the Holocene stratigraphic record of the Adriatic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2822, https://doi.org/10.5194/egusphere-egu22-2822, 2022.

In the Potwar Basin (Pakistan, Eastern Neotethys), the Paleocene-Eocene transition has been investigated and the changes in larger benthic foraminiferal (LBF) assemblages have been compared with the carbon isotope excursion (CIE). The ~5‰ negative CIE is here used to place the exact position of the Paleocene-Eocene boundary that falls in the base of the Shallow Benthic Zone (SBZ) 5. The boundary between the SBZ 5 and 6 corresponds to the early stages of the CIE recovery phase, which is characterized by the disappearance of the some typical Paleocene lamellar-perforate LBF genera such as Miscellanea, Kathina, and possibly Ranikothalia. In the Potwar Basin, some species of Daviesina and Glomalveolina also disappeared at the base of SBZ 6. At the same time, the genus Orbitolites and some species of Alveolina, Nummulites, miliolids, and Assilina appeared and led to the larger foraminiferal extinction and origination (LFEO) event.

The LFEO event represents the late response of the LBF to the abrupt environmental perturbation induced by the Paleocene-Eocene Thermal Maximum (PETM). At the Duleram section (Potwar Basin), the pre-PETM phase is characterized by highly stable and oligotrophic conditions, as revealed by the dominance of large, K-strategists LBF genera (e.g., Miscellanea, Ranikothalia, and Daviesina). At the onset of the PETM, an increased nutrient supply led to establishment of more eutrophic conditions and a collapse of the oligotrophic LBF with the rise of more nutrient-tolerant, small-sized LBF (e.g., glomalveolinids). At the post-PETM phase, stable oligotrophic conditions were re-established, as revealed by the dominance of new K-strategists LBF genera (Alveolina, Nummulites, and Assilina).

As the changes in the LBF assemblages match well with the CIE changes, we can use them as proxies to infer the variations from stable oligotrophic to eutrophic marine conditions during the PETM event in the Eastern Neotethys.

How to cite: Muhammad, K., Fabrizio, F., Dangpeng, X., Cesare Andrea, P., Kamran, M., Ghulam, A., Tian, J., and Xiaoqiao, W.: Larger Foraminiferal Extinction and Origination Event during the Paleocene-Eocene Thermal Maximum in the Potwar Basin (Eastern Neotethys), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3356, https://doi.org/10.5194/egusphere-egu22-3356, 2022.

Bivalve shells are accretionary biogenic carbonates that yield a record of the organisms’ life history, also with respect to the physiological response to the ambient environmental conditions. This is reflected by variations in the shells’ growth bands, their chemical composition, and morphological features, making them useful tools in paleobiology and paleoenvironmental reconstructions. Corbula gibba is an abundant bivalve species in the Adriatic Sea that is commonly used to resolve questions in age determinations, paleoenvironmental reconstructions and sequence stratigraphic studies [1,2]. Nevertheless, a detailed analysis of its response in growth bands and chemical signatures to environmental variations is currently missing. This study evaluates growth increments and chemical variations in Corbula gibba shells. The shells have been collected alive from the Western Adriatic Sea between Senigallia and Ancona to shed light on the reliability of the Corbula gibba as an archive for (paleo)environmental information. Mutvei's solution has been used [3] to stain the alternating dark and light bundles in the shell, enhancing the visualization of growth increments. High-resolution elemental profiles have been acquired across the outer shells layer using the non-destructive Micro X-ray fluorescence (µ-XRF) technique [4]. The results are compared to available climatic information for Ancona and indicate that Corbula gibba shells record detailed temporal changes in the environment such as tidal fluctuations caused by lunar cycle.

[1] Tomašových, A., Gallmetzer, I., Haselmair, A., Kaufman, D., Vidović, J., & Zuschin, M. (2017). Stratigraphic unmixing reveals repeated hypoxia events over the past 500 yr in the northern Adriatic Sea. Geology, 45 (4), 363-366.

[2] Tomašových, A., Gallmetzer, I., Haselmair, A., Kaufman, D., Kralj, M., & Cassin, D. et al. (2018). Tracing the effects of eutrophication on molluscan communities in sediment cores: outbreaks of an opportunistic species coincide with reduced bioturbation and high frequency of hypoxia in the Adriatic Sea. Paleobiology, 44 (4), 575-602.

[3] Schöne, B., Dunca, E., Fiebig, J., & Pfeiffer, M. (2005). Mutvei's solution: An ideal agent for resolving microgrowth structures of biogenic carbonates. Palaeogeography, Palaeoclimatology, Palaeoecology, 228 (1-2), 149-166.

[4] de Winter, N.J., Sinnesael, M., Makarona, C., Vansteenberge, S., Claeys, P., (2017). Trace element analyses of carbonates using portable and micro-X-ray fluorescence: performance and optimization of measurement parameters and strategies. Journal of Analytical Atomic Spectrometry, 32, 1211–1223.

How to cite: Strafella, P., Al Fudhaili, N., de Winter, N., López Correa, M., Teichert, S., Scarcella, G., and Nohl, T.: Sclerochronological insights into the environmental response of Corbula gibba from the Adriatic Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9165, https://doi.org/10.5194/egusphere-egu22-9165, 2022.

Recent work suggested a marked impact of the Pliensbachian-Toarcian boundary event on marine invertebrate communities [1]. This event resulted in a decrease in belemnite body size in assemblages as well as the dominant species in the Toarcian GSSP [2], but it remains unclear to what degree this lilliput effect reflects changes in growth and reproductive strategies [3, 4]. Increments in the concentric calcitic layers of the belemnite rostrum indicate their growth, where their width variation is reflecting the changes in the surrounding conditions (e.g., temperature). The preservation of these calcitic layers has been assessed using the micro X-ray fluorescence (µ-XRF) heatmap. Combining sclerochronological analysis and high-resolution elemental records from the rostrum yields valuable insights into the influence of the environmental changes on the organisms’ physiological and morphological features. Six specimens of two belemnite species (Catateuthis longiforma and Passaloteuthis bisculcata) were analysed from three different stratigraphic levels (before, during and after the Pliensbachian-Toarcian boundary) in the Peniche section of the Lusitanian Basin in Portugal. The current research aims to investigate a) whether there are any differences in the environmental preferences seen within the species across the Pliensbachian-Toarcian boundary. b) Whether there are any environmental differences between the three ontogenetic (juvenile, neanic and adult) stages of the two species. Point-by-point µ-XRF [5] line scans across the rostrum widest part produced high-resolution (25 µm) trace element profiles. From across the two sides of the apical growth line in the rostrum; symmetrical trace elemental records (e.g., Sr/Ca, Mg/Ca, and S/Ca) can be interpreted as environmental proxies across the different stratigraphic levels of the Pliensbachian-Toarcian boundary. The variation of the trace elemental records throughout the different ontogenetic stages reveals how the ontogenetic trajectory affects the belemnites sensitivity to changes on the ambient conditions.

[1] Morten, S., & Twitchett, R. (2009). Palaeogeography, Palaeoclimatology, Palaeoecology, 284 (1-2).

[2] Rita, P., Nätscher, P., Duarte, L., Weis, R., & De Baets, K. (2019). Royal Society Open Science, 6 (12).

[3] Nätscher, P. S., Dera, G., Reddin, C. J., Rita, P., & De Baets, K. (2021). Scientific Reports, 11(10).

[4] Rita, P., Nätscher, P., Duarte, L. V., Weis, R., & De Baets, K. (2019). Royal Society open science, 6 (12).

[5] de Winter, N.J., Sinnesael, M., Makarona, C., Vansteenberge, S., Claeys, P., (2017). Journal of Analytical Atomic Spectrometry, 32, 1211–1223.

How to cite: al-Fudhaili, N., de Winter, N., Kaskes, P., Claeys, P., and De Baets, K.: Belemnite growth dynamics and trace elemental composition across the Pliensbachian-Toarcian boundary event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-590, https://doi.org/10.5194/egusphere-egu22-590, 2022.

The carbonate shell of rhynchonelliformean brachiopods is a relevant archive of seawater temperature / δ¹⁸O for the Phanerozoic. However, its application to investigate seasonality is under-exploited despite its wide employment to reconstruct the chemical conditions of past oceans. Indeed studies of brachiopod sclerogeochemistry are still rare compared to some other biogenic archives. In order to better understand if ontogenetic time-series faithfully record the seasonal variability of the surrounding environment, we investigated the incorporation of δ¹⁸O in the shell (δ¹⁸O_shell) of a modern temperate brachiopod species, Calloria inconspicua, living in the intertidal zone of Otago Harbor (New Zealand).  After reconstructing the life history and ontogenetic age using morphological features of the valves, carbonate samples were collected from the inner fibrous layer along the maximum growth axis with a sub-millimetric resolution. Databases provided environmental parameters of seawater for comparison, and time-series of δ¹⁸Ofor equilibrium calcite (δ¹⁸O_eq) were estimated using salinity and temperature data. Results reveal that maxima and minima of δ¹⁸O_shell are well related to morphological markers highlighting yearly growth steps. The count of yearly cycles allowed an estimate of the timing of shell secretion and comparison with the estimated δ¹⁸O_eq of the surrounding environment.

We found that C. inconspicua can be a robust archive for seasonal variation since it records with high fidelity the local condition of seawater in certain phases of its life. Although the application of the brachiopod shells in sclerogeochemistry and studies of past seasonality is promising, future researches should consider a few potential drawbacks which need to be taken into consideration. These include the fact that growth rate changes over the life-span and that shell is not deposited throughout the entire year (leading to under-estimation of the full seasonal range). Additionally, it is important to ensure that sampling does not sample different thickness within the shell, this returning time-averaged values. Knowledge of likely general biology, population composition, life cycle and shell structure are important prerequisites for the interetation of δ¹⁸O time-series measured on fossil brachiopod shells.

How to cite: Garbelli, C., Lamare, M. D., and Harper, E. M.: Benefits and drawbacks of employing the carbonate shell of brachiopods as an archive of δ18O seasonality: facts and clues from the living Calloria inconspicua (Sowerby, 1846), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13210, https://doi.org/10.5194/egusphere-egu22-13210, 2022.

The discovery of hydrated magnesium carbonates in a paleolake in Jezero Crater, Mars, has inspired the study of carbonates associated with lacustrine systems on Earth. Lake Salda, Turkey, contains hydromagnesite-dominated microbialites in a mafic-rock hosted terrain. This alkaline lacustrine system provides an excellent natural laboratory in which to characterize various depositional environments and biosignature preserving potential of microbialites and other magnesium carbonate deposits. Here we aim to describe the textures, mineral composition, and macroscopic morphology of hydromagnesite structures in Lake Salda. All microbialites are covered by a thick, sticky organic-rich layer dominated by diatoms and cyanobacteria. A close association of contemporary hydromagnesite precipitation with organic-rich layers in microbialites indicates biologically mediated precipitation. Microbialites around the lake exhibit a range of morphologies, including finger-like, mini columnar, domical, and structureless. The recently exposed microbialites commonly contain colloform and cerebroid structures with fine, crude lamination, vuggy and globular textures. Layered microscopic textures preserve evidence of partially mineralized filamentous bacteria that trapped detrital grains and also contain globules embedded in extracellular polymeric substances, and dense hydromagnesite. The differences in mineralogy, density, and organic preservation potential within these textures likely correspond to the depositional environment. For example, the globular textures are closely associated with the purple layers in microbialites, including the layers in the recently sampled microbialites from the deeper part of the lake (ca. 10 m). These layers may form in the presence of anoxygenic purple sulfur bacteria. Our preliminary results suggest that the textures and macroscopic structures of hydromagnesite microbialites may record and reflect relationships among carbonate minerals, environmental factors, and microbial community composition.

How to cite: Gunes, Y., Baldes, M. J., Gong, J., Bosak, T., and Balci, N.: Morphospace, composition and texture of Lake Salda microbialites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-395, https://doi.org/10.5194/egusphere-egu22-395, 2022.

Glendonites are calcite pseudomorphs, that form after the mineral ikaite. Their occurrence in sediments is typically seen as an indication of cold environmental conditions, even when found in predetermined greenhouse climates (Zhou et al., 2015). However, there is still uncertainty about the exact conditions that control glendonite formation and their occurrences are often in conflict with other temperature proxies (Price et al., 2013). Some authors have postulated that the temperature stability range of ikaite could be extended under certain chemical boundary conditions (Teichert and Luppold, 2013). One process that could possibly lead to such circumstances is methane seepage. Here we use clumped isotope thermometry to determine the formation temperature of glendonites. The analysed specimen, comes from a mud volcano, within the upper Paleocene, Basilika Formation near Sveagruva in Svalbard.

Thin section analyses and micro-X-ray fluorescence mapping of a glendonite specimen, show that the mineral is highly heterogeneous in terms of trace elemental incorporation. We sampled two distinct phases, for isotope analysis. The clumped isotope composition for both phases are relatively low, indicating apparent formation temperatures >50 degrees, which  are unrealistic values for the formation temperature of ikaite. The high Sulfur concentrations, surrounding sediments and low δ¹³C values of the glendonite are consistent with a formation and decomposition of the ikaite/glendonite caused by the activity of a methane seep. Degassing of CO₂ coupled to the methane seepage may have caused isotopic disequilibrium resulting in low clumped isotope values (Bajnai et al., 2020).

Sources

Bajnai, D., et al., 2020.: ‘Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures’, Nat Commun, 11, 4005, https://doi.org/10.1038/s41467-020-17501-0.

Price, G., et al., 2013. Isotopic evidence for long term warmth in the Mesozoic. Sci. Rep. 3 https://doi.org/10.1038/srep01438.

Teichert, B. M. A., et al., 2013. ‘Glendonites from an Early Jurassic Methane Seep — Climate or Methane Indicators?’ Palaeogeography, Palaeoclimatology, Palaeoecology, 390, 81–93. https://doi.org/10.1016/j.palaeo.2013.03.001.

Zhou, Xiaoli, e.a, 2015. ‘Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity’. The Journal of Geology, 123, 3, 269–81. https://doi.org/10.1086/681918.

How to cite: Koenders, E., Kaskes, P., de Winter, N., Jochmann, M., van de Schootbrugge, B., and Ziegler, M.: Disequilibrium clumped isotope values in glendonites support formation linked to rapid CO2 degassing and methane seepage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12047, https://doi.org/10.5194/egusphere-egu22-12047, 2022.

Trace element compositions of carbonate microbialites are valuable proxies to reconstruct shallow water microbial environments through Earth's history. Most of the published trace element data of microbial carbonates are obtained from bulk digestion or carbonate leaching from sample powders or via in situ laser ablation analysis calibrated to external reference materials such as NIST glasses. However, due to the complex formation mechanism of microbial carbonates, huge compositional differences are associated with spatial and lithological sample heterogeneities that cannot be fully resolved with the current analytical methodologies.

Here, we describe a new method using a high-frequency laser ablation (LA) system (NWR ImageGEO193) coupled to inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) and external calibration via matrix-matched nanopowder carbonate reference materials to obtain rapid high-resolution quantitative trace element maps.

Our mapping results reveal that detrital elements such as thorium (Th), aluminium (Al), bioactive elements such as cadmium (Cd) iron (Fe) and nickel (Ni), and rare earth elements (REE) have concentration distributions that correspond with the intrinsic bio-sedimentary layering of the samples. Fully quantitative trace element maps are the foundation for follow-up research such as in situ U-Pb dating on truly authigenic carbonate phases or stable novel metal isotope analyses on individual lithified microbial layers to study bio-essential metal uptake in diverse microbial communities through deep times.

Therefore, quantitative trace element mapping via LA-ICP-TOF-MS is a promising method that can rapidly obtain the spatial geochemical characteristics of microbial carbonates.

How to cite: Jiang, Y., Hohl, S. V., and Huang, X.: Rapid quantitative trace element mapping of microbial carbonates by LA-ICP-TOF-MS: Context, results and perspectives, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9014, https://doi.org/10.5194/egusphere-egu22-9014, 2022.

Non-traditional stable isotope systematics of bioactive metals are emerging new tools for studying the biogeochemical cycling of micronutrients in sedimentary archives through deep time. In the case of Ni and Cd, their role as cofactors for biochemical reactions is directly related to enzymatic prosses essential for variable microbial communities. While methanotrophic bacteria incorporate Ni, Cd acts as a cofactor in carbonic anhydrase activity in phototrophic bacteria and matchesnutrient-like concentration patterns complementary to phosphorous in modern open ocean environments. Ba, although not acting as a cofactor in metabolic processes, is accumulated in sedimentary barite via respiration of organic matter and thus traces the extent of microbial activity and heterotrophic remineralization. All three metals follow kinetic isotopic fractionation systematics under trace element-influx limited environmental conditions, and microbial carbonates that form from a fractionated isotope pool in ambient waters have been shown to record these isotope variations through deep time.

We show a combined Ni, Cd and Ba isotope record from the ~3.0 Ga old Pongola supergroup stromatolites from the Kaapvaal Craton (S. Africa) as novel isotope-biomarkers for microbial communities. Strong positive correlated fractionation of authigenic δ¹³⁸Ba with Ba/Ca and δ¹¹²Cd with Cd/P ratios above igneous reference values reveal the presence of phototrophic and heterotrophic microbial communities building up the Pongola stromatolites.

In contrast, subdued δ⁶⁰Ni isotope fractionation close to igneous reference values either argues for less influence of methanotrophic communities or non-limited Ni influx into the microbial paleo-environment. The latter is likely linked to extensive weathering of a mafic and hence Ni rich upper crust in the Archean. Co-variation with C isotopes can only be observed with Cd isotopes underlining their potential as the most promising isotope biomarker for phototrophic activity in Archean microbial habitats. Our work aims to extend the use of heavy metals that work as cofactors in enzymatic processes and their isotope systematics in biogeochemical metal cycling in paleo-environmental reconstructions to understand better metallome evolution on Earth and beyond.

How to cite: Hohl, S. V. and Viehmann, S.: Using Cd, Ba and Ni isotope systematics as novel biomarkers to decipher Archean microbial metal cycling in the ~3.0 Ga Pongola Supergroup stromatolites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6766, https://doi.org/10.5194/egusphere-egu22-6766, 2022.

Stromatolitic carbonates were formed in ancient microbial mats, and, thus, provide unique geochemical archives to reconstruct palaeo-environments in which microbial life thrived and evolved. In this study, we report the first geochemical data of Miocene stromatolites from the Oberpullendorf Basin (Austria) that were formed during the Badenian salinity crisis at the north-western coast of the Paratethys Sea. The combined approach of trace element data obtained by quadrupol ICP-MS with C-O isotopes of individual stromatolite laminae is used to reconstruct short-term variations of palaeo-environmental conditions in microbial habitats of the Oberpullendorf Basin.

Stromatolitic carbonates in the lower stromatolite units show negative δ¹³C_carb values and typical shale-normalized seawater-like rare earths and yttrium (REY_SN) patterns with positive La_SN, Gd_SN anomalies, super-chondritic Y/Ho ratios, and heavy REY_SN enrichments to light REY_SN, indicating an open marine-dominated depositional setting. Stratigraphic upwards, stromatolitic carbonates show suppressed seawater-like REY_SN signatures and increasing δ¹³C_carb values that argue for the development of a restricted environment. Seawater-like REY_SN patterns and homogenously distributed negative δ¹³C_carb values in the stratigraphic uppermost part resemble the transition to fully marine environmental conditions again. Enrichment factors of bio-essential elements (Fe, Mn, Co, Zn, Mo, W) reflect sufficient element availability during marine conditions but limitation during the development of the (semi)closed lagoon.

We show that combined REY, C isotopes, and enrichment factors of bio-essential elements bear the unique potential to reconstruct temporal changes in paleo-environments and determine the availability of bio-essential elements in microbial habitats. This approach provides the groundwork for a better understanding of the evolution and development of microbial metabolisms under severely different atmospheric-hydrospheric on planet Earth and beyond.

How to cite: Viehmann, S., Kujawa, R., Hohl, S. V., Tepe, N., Rodler, A. S., Hofmann, T., and Draganits, E.: Trace metal availability in extreme microbial habitats of the Miocene Oberpullendorf Basin, Austria, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2653, https://doi.org/10.5194/egusphere-egu22-2653, 2022.

The growth and morphology of stromatolitic carbonates, i.e., lithified microbial mats, are tightly linked to complex microbial activities. However, the role of microbial metabolism in carbonate nucleation and formation during stromatolite growth remains controversial. Magnesium isotopes are a promising tool to trace carbonate formation processes due to significant isotopic fractionations associated with carbonate precipitation. This study reports Mg isotope compositions of Holocene, ca. 4000 years old stromatolites from the Lagoa Salgada lagoon (Brazil) with different morphologic features. Petrological and C-S isotopic evidence indicates microbial metabolisms varied during the formation of morphologically different stromatolites. However, the direction and magnitude of Mg isotope fractionation between Mg-calcite and ambient fluid are relatively constant despite the changes of microbial activities in ecosystems and consistent with the typical Mg isotope behavior during abiotic calcite precipitation. As a result, we propose that microbial metabolism do not influence the dehydration pathway of aqueous Mg²⁺ into calcite lattices. Our study corroborates earlier findings indicating that metabolism-related fractionation of Mg isotopes is limited or even absent during stromatolite growth. This finding also promotes understanding of Mg isotopic records in widespread Precambrian stromatolites for reconstructing seawater chemistry in deep time.

How to cite: Hu, Z., Hohl, S., Viehmann, S., Meister, P., and Tepe, N.: Magnesium isotopes as a proxy to decode the effects of microbial metabolisms on the formation of stromatolitic carbonate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9489, https://doi.org/10.5194/egusphere-egu22-9489, 2022.