SSP2.3

SSP2 EDI
(Paleo-)environmental reconstructions from biomineralized carbonates: From early Archaean to the present 

Carbonate (bio)minerals have played an essential role in the history of life on Earth and form one of the most important archives for past climate and environmental change. Geochemical investigations are crucial for understanding the evolution of microbial habitats and the paleobiology of carbonate biomineralizers and for assessing changes in the atmosphere-hydrosphere systems through time. With this session, we encourage contributions from sedimentology, geochemistry and biology that utilize carbonate (bio)minerals (e.g., microbialites, stromatolites, mollusk shells and foraminifera) with the aim to reconstruct paleo-environments, seasonality, seawater chemistry and paleobiology in a wide range of modern to deep time settings, including critical intervals of environmental and climate change. This includes sedimentological and biological reconstructions of palaeo-environments, theoretical or experimental studies of trace element partitioning and isotope fractionation in carbonate (bio)minerals, and studies targeting original skeletal carbonate preservation and diagenetic alteration.

Convener: Johan Vellekoop | Co-conveners: Niels de WinterECSECS, Alexandra RodlerECSECS, Sebastian ViehmannECSECS
Presentations
| Thu, 26 May, 08:30–11:05 (CEST)
 
Room -2.32/33

Presentations: Thu, 26 May | Room -2.32/33

Chairpersons: Johan Vellekoop, Niels de Winter
08:30–08:40
Foraminifera
08:40–08:45
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EGU22-5523
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ECS
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Virtual presentation
Rafał Nawrot, Michaela Berensmeier, Ivo Gallmetzer, Alexandra Haselmair, Adam Tomašových, and Martin Zuschin

Time averaging – mixing of remains of organisms separated by decades, centuries or millennia in a single sedimentary layer – affects not only paleoecological or geochronological inferences, but also the resolution of geochemical proxy records extracted from their biomineralized hardparts. Taxonomic differences in intrinsic skeletal durability are expected to produce temporal mismatch between co-occurring species, but the importance of this effect is difficult to assess due to lack of direct estimates of time averaging for many higher taxa. Moreover, burial below the taphonomic active zone and early diagenetic processes may alleviate taxonomic differences in disintegration rates in subsurface sediments.

Here, we compare time averaging across five phyla of major carbonate producers co-occurring in a sediment core from the northern Adriatic shelf. We dated individual bivalve shells, foraminiferal tests, tests and isolated plates of irregular and regular echinoids, crab claws and fish otoliths. In spite of different skeletal architecture, mineralogy and life habit, all taxa showed very similar time averaging varying from ~1800 to ~3600 yrs (interquartile age ranges). Thus, remains of echinoids and crustaceans – two groups with multi-elemental skeletons assumed to have low preservation potential – can still undergo extensive age mixing comparable to that of the co-occurring mollusk shells. Moreover, just like macrofossil assemblages, benthic foraminifera from shallow shelf settings can be time-averaged over 103 yrs, which may limit their utility as high-resolution environmental proxies. In spite of similar time averaging of the studied taxa, their median ages differed by up to ~3700 yrs, reflecting species-specific timing of seafloor colonization during the Holocene transgression.

Our results suggest that taxa of different skeletal durability can have comparable temporal resolution due to sequestration of fragile remains below the taphonomic active zone. However, significant age offsets between co-occurring species can complicate paleoecological analyses of multi-taxic fossil assemblages and make both age models and geochemical proxy records sensitive to taxon choice.

How to cite: Nawrot, R., Berensmeier, M., Gallmetzer, I., Haselmair, A., Tomašových, A., and Zuschin, M.: Multiple phyla, one time resolution? Time averaging in benthic foraminifera, mollusk, echinoid, crustacean and otolith fossil assemblages, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5523, https://doi.org/10.5194/egusphere-egu22-5523, 2022.

08:45–08:50
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EGU22-3933
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ECS
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On-site presentation
Johanna Schmidt, Daniel Herwartz, Anna Saupe, Jassin Petersen, and Patrick Grunert

Benthic foraminifera provide key information for the reconstruction of ocean bottom currents. In the Iberian Margin Contourite Drift System, abundances of a distinct group of benthic foraminifera are controlled by the strength and nutrient load of bottom currents. This so-called elevated epifauna (EEF) comprises highly specialized suspension feeding benthic foraminifera attached to elevated substrates as an adaptation to strong bottom currents. Schönfeld (2002) demonstrated a direct relation between EEF abundances and Mediterranean Outflow Water strength at the Iberian Margin in modern surface samples and established EEF abundances as a bottom current proxy. Faunal and geochemical data from Pliocene-Pleistocene contourites drilled during IODP Exp. 339 in the Gulf of Cádiz, however, showed a poor correlation of EEF abundances with other bottom current proxy data, indicating a bias by depositional or taphonomic processes.

The tectonically active Iberian Margin is characterized by a complex depositional environment shaped by alongslope and downslope transport. Taphonomic processes linked to transport and loss of foraminiferal tests during early fossilization potentially bias fossil EEF abundances in marine slope sediments and may result in overestimation of bottom current speeds. Our understanding of these taphonomic processes is still rather poor. Stable oxygen and carbon isotope ratios from foraminiferal tests in Pleistocene contourites and turbidites can be used to identify allochthonous tests and provide insights into the extent of downslope transport at the Iberian Margin. The aim of this study is to quantify the effects of taphonomic processes on fossil foraminiferal assemblages and to establish an improved EEF proxy method. The improved method will provide researchers with a reliable, well-calibrated and easily applicable tool for bottom current reconstruction.

 

Reference: Schönfeld, J. (2002). A new benthic foraminiferal proxy for near-bottom current velocities in the Gulf of Cadiz, northeastern Atlantic Ocean. Deep Sea Research Part I: Oceanographic Research Papers, 49(10), 1853-1875.

How to cite: Schmidt, J., Herwartz, D., Saupe, A., Petersen, J., and Grunert, P.: Understanding the taphonomic bias on the benthic foraminiferal bottom current proxy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3933, https://doi.org/10.5194/egusphere-egu22-3933, 2022.

08:50–08:55
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EGU22-6379
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ECS
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On-site presentation
Aline Mega, Emília Salgueiro, Andreia Rebotim, Antje Voelker, Joana Cruz, Eva Calvo, and Fatima Abrantes

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.

08:55–09:00
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EGU22-8021
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ECS
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Highlight
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On-site presentation
Ana Alves, Matthieu Buisson, Pascale Louvat, Claire Rollion-Bard, Franck Bassinot, Eva Moreno, Guillaume Paris, Benoit Caron, Giulia Del Manzo, Anne Le Friant, and Annachiara Bartolini

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.

09:00–09:05
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EGU22-2822
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ECS
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Presentation form not yet defined
Theresa Nohl, Rafał Nawrot, Adam Tomašových, and Martin Zuschin

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.

09:05–09:10
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EGU22-3356
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ECS
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Presentation form not yet defined
kamran Muhammad, Frontalini Fabrizio, Xi Dangpeng, Papazzoni Cesare Andrea, Mirza Kamran, Akbar Ghulam, Jiang Tian, and Wan Xiaoqiao

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.

09:10–09:15
Sclerochronology
09:15–09:25
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EGU22-6504
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solicited
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Highlight
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Virtual presentation
Damien Huyghe, Marc de Rafelis, Laurent Emmanuel, Mathieu Daëron, Loïc Marlot, and Franck Lartaud

In the context of the current global warming, it is crucial to acquire new paleoclimatic data around past analogues. For decades, bivalve shells have constituted one of the most common supports for paleoclimatic archives based on stable isotope approaches to constrain the seasonal gradient of temperature. One of the key points to conduct this kind of project reliably is to constrain precisely what the analyzed organisms do record and what it is possible to restore from their analysis? Thus, the prerequisite for any (paleo)climatic study is to determine the rhythms that govern the biomineralization of the analyzed organisms. Additionally, it is essential to verify the significance of their geochemical signal.

Thus, in this work, we present results combining a sclerochronological and geochemical approach applied to oyster shells. The shells were cultivated in sites from the French Atlantic coast where the environmental conditions (temperature, salinity, ...) were measured continuously during two years. The shells were chemically labeled (Mn2+) in order to obtain a precise time frame within each shell that can be revealed under cathodoluiminescence.

The results of the sclerochronological study indicate that oysters mineralize their shells with a rhythmicity following tidal cycles (2 calcite increments / day). A lunar and seasonal cyclicity is also highlighted. High resolution geochemical measurements (d18O) confirm that oysters can reliably reproduce seasonal temperature variations, even if geochemical drifts are observed during the first year of growth due to a very high growth rate. We also tested the new ∆47thermometer for these mollusks. Our results are consistent with a strong correlation between seawater temperature and ∆47 for all samples except for the juvenile samples that also exhibited an isotopic disequilibrium for the d18O. This correlation is consistent with earlier calibrations reprocessed in the recent I-CDES metrological scale, adding to the evidence that many different types of carbonates conform to statistically indistinguishable relationships between ∆47 and crystallization temperature.

Finally, these results are applied to reconstruct the paleoclimatic evolution around a hyperthermal event that occurred 40 Ma ago, the Middle Eocene Climatic optimum.

How to cite: Huyghe, D., de Rafelis, M., Emmanuel, L., Daëron, M., Marlot, L., and Lartaud, F.: What do oyster shells tell us about paleoclimatology?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6504, https://doi.org/10.5194/egusphere-egu22-6504, 2022.

09:25–09:30
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EGU22-2137
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ECS
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Virtual presentation
Niels J. de Winter, Rob Witbaard, Ilja Kocken, Inigo A. Müller, and Martin Ziegler

Understanding the response of Earth’s climate to perturbations requires accurate and detailed reconstructions of past climate states (e.g. Tierney et al., 2020). The clumped isotope thermometer has the potential to constrain the formation temperatures of carbonates independent from the (isotopic) composition of the precipitation fluid and regardless of the origin (e.g. taxonomy) of the carbonate producer (e.g. Anderson et al., 2020), making it an ideal tool for paleoclimate reconstructions. Unfortunately, it is still not fully certain whether the clumped isotope composition of different carbonate minerals (e.g. calcite, aragonite, dolomite) responds similarly to changes in formation temperatures or variations in the temperature at which the acid reaction takes place during analyses (e.g. Guo et al., 2009; Müller et al., 2017). This uncertainty complicates the application of clumped isotope thermometry to biogenic aragonite shells of bivalves and gastropods, as well as to chemically precipitated travertines and speleothems.

To solve part of these issues, we present a new dataset consisting of clumped isotope measurements on aragonitic Arctica islandica bivalves grown at precisely controlled temperatures (1.1±0.2°C - 18±0.3°C). We compare our data with preexisting clumped isotope calibration datasets spanning a wide temperature range and containing both aragonite and calcite samples. Our clumped isotope data with well-defined formation temperatures allows us to constrain small but important differences between previously published calibration datasets and sheds light on the temperature dependence of clumped isotope composition of aragonites. We use these new insights into the clumped isotope thermometer at low temperatures to produce seasonally resolved paleotemperature reconstructions from excellently preserved aragonitic bivalves from the Pliocene Warm Period, a valuable analogue for future climate under intermediate greenhouse gas emission scenarios (SSP2-4.5; Meinshausen et al., 2020).

References

Anderson et al. GRL 48, e2020GL092069, https://doi.org/10.1029/2020GL092069, 2021.

Guo et al. GCA, 73, 7203–7225, https://doi.org/10.1016/j.gca.2009.05.071, 2009.

Meinshausen et al. GMD 13, 3571–3605, https://doi.org/10.5194/gmd-13-3571-2020, 2020.

Müller et al. Chem. Geol., 449, 1–14, https://doi.org/10.1016/j.chemgeo.2016.11.030, 2017.

Tierney et al. Science 370, https://doi.org/10.1126/science.aay3701, 2020.

How to cite: de Winter, N. J., Witbaard, R., Kocken, I., Müller, I. A., and Ziegler, M.: Clumped isotope analyses on biogenic aragonites and their use in paleoclimate reconstructions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2137, https://doi.org/10.5194/egusphere-egu22-2137, 2022.

09:30–09:35
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EGU22-3472
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ECS
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Virtual presentation
Pengchao Zhou, Hong Yan, Shi Ge, Chengcheng Liu, Luo Fan, Han Tao, Guozhen Wang, Hanfeng Wen, Nanyu Zhao, John Dodson, Yue Li, and Weijian Zhou

Seasonal climate variability is an important component of the climate system, and has a significant impact on ecosystems and social systems. However, the temporal resolution of most proxy-based paleoclimate records is limiting to fully understand the past seasonal changes. Here we used high-precision monthly resolution Sr/Ca records of three Tridacna squamosa from northern SCS to reconstruct the SST seasonality during three-time windows of the middle Holocene. The results suggested that the SST seasonality in northern SCS during the middle Holocene (3.21 ± 0.98℃) was smaller than that for recent decades (1994-2004 AD, 4.32 ± 0.59℃). The analysis of modern instrumental data showed that the SST seasonality in northern SCS was dominated by the winter SST, which was deeply influenced by the intensity of EAWM. Strong EAWM usually resulted in cooler winter SST and a larger SST seasonality in northern SCS. The reconstructed Holocene EAWM records showed that the EAWM strengthened from the middle to late Holocene, which could be demonstrated by our reconstruction of a smaller SST seasonality during the middle Holocene in northern SCS. This study highlighted that the Sr/Ca ratios of Tridacna shells can be used as a potential high-resolution indicator of past seasonal climate changes.

How to cite: Zhou, P., Yan, H., Ge, S., Liu, C., Fan, L., Tao, H., Wang, G., Wen, H., Zhao, N., Dodson, J., Li, Y., and Zhou, W.: Sea surface temperature seasonality in northern South China Sea during the middle Holocene derived from high resolution Sr/Ca ratios of Tridacna shells, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3472, https://doi.org/10.5194/egusphere-egu22-3472, 2022.

09:35–09:40
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EGU22-4634
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ECS
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On-site presentation
Nina Wichern, Niels de Winter, Martin Ziegler, Andrew Johnson, Maartje Hamers, and Stijn Goolaerts

Obtaining temperature data from the mid-Piacenzian warm period (mPWP) is a key factor in understanding the coming changes brought upon by anthropogenic climate change. The mPWP, a high-CO2 world with a paleogeography similar to modern times, has been used to validate and improve model retrodictions, which in turn enables assessing the prediction strength of these models1. For the first time, stable isotope analysis has been applied to the extinct tellinid bivalve Angulus benedeni benedeni, originating from the mid-Piacenzian of the Lillo Formation of Belgium in the southern North Sea basin. Multi-annual oxygen isotope records with a seasonal resolution obtained from its shell indicate that this species could live for up to a decade and formed monthly growth increments. From this oxygen isotope record, a clumped-isotope-based mean annual temperature of 12.6 ± 3.6°C was reconstructed. This is 2.1°C warmer than today2,3, 2.6°C warmer than the pre-industrial North Sea2, and in line with global Pliocene temperature estimates of +2-4°C compared to the pre-industrial climate4,5. The pristine nature of the aragonitic shell material was verified through electron backscatter diffraction analysis (EBSD), and backed up by light microscopy, X-ray diffraction, and X-ray fluorescence. The various microstructures as obtained from the EBSD maps have been described, and they provide a template of pristine A. benedeni benedeni material to which potentially altered shells may be compared. The bivalve A. benedeni benedeni is suitable for high resolution isotope-based paleoclimatic reconstruction and it can be used to unravel the marine conditions in the Pliocene North Sea basin at a seasonal scale, yielding enhanced insight into imminent western European climate conditions.

  • 1Dowsett, H. J. et al. Assessing confidence in Pliocene sea surface temperatures to evaluate predictive models. Nature Climate Change 2, 365–371 (2012). https://doi.org/10.1038/NCLIMATE1455
  • 2Emeis, K.-C. et al. The North Sea — A shelf sea in the Anthropocene. Journal of Marine Systems 141, 18–33 (2015). https://doi.org/10.1016/j.jmarsys.2014.03.012
  • 3Locarnini, R. A. et al. World Ocean Atlas 2018, Volume 1: Temperature. NOAA Atlas NESDIS 81. A. Mishonov, Technical Editor. 52pp. (2019). https://www.ncei.noaa.gov/access/world-ocean-atlas-2018/
  • 4Dowsett, H. J. et al. Sea surface temperature of the mid-Piacenzian ocean: a data-model comparison. Scientific reports 3, 1–8 (2013). https://doi.org/10.1038/srep02013
  • 5Haywood, A. M. et al. The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity. Clim. Past 16, 2095–2123 (2020). https://doi.org/10.5194/cp-16-2095-2020

How to cite: Wichern, N., de Winter, N., Ziegler, M., Johnson, A., Hamers, M., and Goolaerts, S.: The potential of high-resolution stable isotope records in the bivalve Angulus benedeni benedeni's shells to investigate Pliocene seasonality, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4634, https://doi.org/10.5194/egusphere-egu22-4634, 2022.

09:40–09:45
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EGU22-9165
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On-site presentation
Pierluigi Strafella, Najat Al Fudhaili, Niels de Winter, Matthias López Correa, Sebastian Teichert, Giuseppe Scarcella, and Theresa Nohl

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.

09:45–09:50
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EGU22-590
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ECS
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On-site presentation
Najat al-Fudhaili, Niels de Winter, Pim Kaskes, Philippe Claeys, and Kenneth De Baets

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.

09:50–09:55
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EGU22-3955
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ECS
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On-site presentation
David Bajnai, Oliver Jäger, and Andreas Pack

The 18O/16O ratio (δ18O) and the clumped isotope composition (47) of marine carbonates are widely used proxies of Earth’s past seawater temperature. However, kinetic isotope fractionation effects occurring during carbonate precipitation and diagenesis complicate their use as climate proxies. Specifically, the failure to identify disequilibrium precipitation and post-depositional alteration in the investigated samples could lead to biased temperature estimates [1,2]. The identification of these effects using the δ18O and the 47 proxies are not straightforward. The triple oxygen isotope method, that is, the combined analyses of the 18O/16O and the 17O/16O ratios, expands the traditional oxygen (and clumped isotope) scheme by another dimension, thus providing information on the nature and extent of kinetic effects involved in carbonate formation and the subsequent diagenetic processes [2].

In this study, we measured the triple oxygen isotope composition (17O) of modern and fossil brachiopods. Brachiopods are an important group of calcifiers because they are abundant in the sedimentary archive and present since the Cambrian. We show how triple oxygen isotope analyses can help identify and disentangle kinetic effects and diagenesis and ultimately provide a more accurate palaeotemperature estimate.

[1] Bajnai et al. (2018) Sci Rep

[2] Wostbrock et al. (2020) GCA

How to cite: Bajnai, D., Jäger, O., and Pack, A.: Carbonate triple oxygen isotope analyses of brachiopod shells, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3955, https://doi.org/10.5194/egusphere-egu22-3955, 2022.

09:55–10:00
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EGU22-13210
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Virtual presentation
Claudio Garbelli, Miles D. Lamare, and Elizabeth M. Harper

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 (δ18Oshell) 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 (δ18Oeq) were estimated using salinity and temperature data. Results reveal that maxima and minima of δ18Oshell 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 δ18Oeq 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.

Coffee break
Chairpersons: Alexandra Rodler, Sebastian Viehmann
10:20–10:25
Microbialites
10:25–10:30
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EGU22-395
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ECS
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On-site presentation
Yagmur Gunes, Matthew J. Baldes, Jian Gong, Tanja Bosak, and Nurgul Balci

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.

10:30–10:35
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EGU22-1515
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ECS
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On-site presentation
Camille Thomas, Amotz Agnon, Julien Alleon, Christophe Thomazo, Johanna Marin-Carbonne, and Daniel Ariztegui

Exopolymeric Substances (EPS) form biofilms in which the vast majority of prokaryotic organisms develop and thrive. They are ubiquitous,  harbor metal and chemical species binding properties and can be the matrix for bio/orgamineralizations. Because of these properties, EPS have also been proposed as some of the most ancient traces of microbial life on Earth. They form sedimentary structures diagnostic of biological activity in some of the most ancient sedimentary rocks of the Archean. However, the metabolisms hosted by such ecosystems remain poorly understood given poor preservation and specificity of the available molecular, isotopic or fossilized signatures. Deep time paleobiological research therefore needs for new ways to unlock the history of the rare and variably preserved sedimentary rocks of these ages, by looking for new proxies that could help characterizing microbial ecosystems and better understand the co-evolution of the geosphere and the biosphere.

We here attempt to describe trace metal signatures of a modern, arsenic-rich lacustrine microbial mat fueled by oxygenic and anoxygenic photosynthesis as an analog to better understand how microbial mats and their sedimentary and chemical signatures can be preserved in the Archean sedimentary record. We coupled in-situ imaging of a microbial mat from modern Dead Sea shore with SEM, Raman spectroscopy, and X-ray mapping, to (meta)genomics data and chemical analyses. Arsenic enrichments in the anoxygenic photosynthetic layer of the mat reached a 10’000-fold level, and was associated to Mg-Si-rich EPS. The latter ultimately mineralized into aragonite clusters with a co-enrichment of Sr, Mn and Mo. At the mat scale, the mineralized zone (rich in Fe, Sr and Ca from authigenic calcium carbonates and detrital clay) is clearly located above the As-enrichment layer, in association with Mn. These data support a chemically dynamic microbial mat where microbial activity, EPS chemical affinity and environmental processes lead to specific organic and mineralized chemical signatures linked to metabolic activity. Metagenomics and synchrotron-based speciation analyses shall confirm the links between elemental enrichments and the microbial metabolic pathways.

We parallel this study to a well characterized microbial system of the Archean, the stromatolitic units of the Tumbiana Lake (2.72 Ga, Pilbara, Western Australia). In this environment, microbial mat accretionary behaviour has formed limestone stromatolites harboring layered nanopyrites embedded in carbonaceous material and chlorite (Marin-Carbonne et al., 2018). C, N and S isotopes of mineral fractions have suggested a connection of photosynthetic activity, sulfate reduction and methane cycling, potentially influenced by arsenotrophy (e.g. Thomazo et al., 2009; Sforna et al., 2014; Lepot et al., 2019). This is likely the most diverse undisputed microbial environment of the Archean. Our trace-elemental mapping using PIXE suggests co-enrichment of Mo and As in association to the nanopyrite-OM layer, that could be attributed to arsenotrophic and anoxygenic photosynthetic activity, in a similar fashion than argued for in the Dead Sea mat. Simulated diagenesis experiments are planned and should be able to provide chemical insights into the transformation of microbial mats to their fossilized counterparts at the microscale, to further validate the promises of metal biosignatures for reconstructing Archean ecosystems.

How to cite: Thomas, C., Agnon, A., Alleon, J., Thomazo, C., Marin-Carbonne, J., and Ariztegui, D.: Modern activity and ancient signatures preserved by metals in microbial mats of lake environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1515, https://doi.org/10.5194/egusphere-egu22-1515, 2022.

10:35–10:40
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EGU22-12047
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ECS
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Virtual presentation
Emily Koenders, Pim Kaskes, Niels de Winter, Malte Jochmann, Bas van de Schootbrugge, and Martin Ziegler

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.

10:40–10:45
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EGU22-9014
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ECS
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Virtual presentation
Yuxiang Jiang, Simon V. Hohl, and Xiangtong Huang

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.

10:45–10:50
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EGU22-6766
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ECS
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Presentation form not yet defined
Simon V. Hohl and Sebastian Viehmann

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.

10:50–10:55
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EGU22-2653
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ECS
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Presentation form not yet defined
Sebastian Viehmann, Robert Kujawa, Simon V. Hohl, Nathalie Tepe, Alexandra S. Rodler, Thilo Hofmann, and Erich Draganits

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 δ13Ccarb values and typical shale-normalized seawater-like rare earths and yttrium (REYSN) patterns with positive LaSN, GdSN anomalies, super-chondritic Y/Ho ratios, and heavy REYSN enrichments to light REYSN, indicating an open marine-dominated depositional setting. Stratigraphic upwards, stromatolitic carbonates show suppressed seawater-like REYSN signatures and increasing δ13Ccarb values that argue for the development of a restricted environment. Seawater-like REYSN patterns and homogenously distributed negative δ13Ccarb 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.

10:55–11:00
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EGU22-9489
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ECS
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Highlight
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Presentation form not yet defined
Zhongya Hu, Simon Hohl, Sebastian Viehmann, Patrick Meister, and Nathalie Tepe

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.

11:00–11:05