Conference Agenda

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Session Overview
3.03-2 Advances in paleoclimate proxy development and application
Monday, 04/Sept/2023:
3:30pm - 5:00pm

Session Chair: Amelia Jane Davies, Goethe University Frankfurt
Session Chair: David Bajnai, University of Göttingen
Location: Hall A (HFB)


3:30pm - 4:00pm
Invited Session Keynote
Topics: 3.03 Advances in paleoclimate proxy development and application

Continental or oceanic weathering processes – What controlled the Late Cretaceous lithium cycle?

Sandra J. Huber1,2, Vanessa Schlidt1,2, Jorit F. Kniest1,2, H.-Michael Seitz1,2, Jacek Raddatz1,2, Horst R. Marschall1,2, Silke Voigt1,2

1Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany; 2Frankfurt Isotope and Element Research Center (FIERCE), Goethe University Frankfurt, 60438 Frankfurt am Main, Germany

The lithium isotopic composition (δ7Li) of marine carbonates is known as a proxy for the chemical weathering intensity of silicate rocks. To evaluate the role of weathering as a sink for atmospheric CO2 during the Late Cretaceous, we generated a 20 Ma δ7Li record (86.3–66.0 Ma) using chalk from Northern Germany as an archive. The late Santonian to Maastrichtian record shows an overall increase of ~4.5‰ with superimposed increases in the late Santonian, early Campanian and across the Campanian–Maastrichtian transition.

The overall increase in δ7Li fits with the Late Cretaceous increase in seawater 87Sr/86Sr. Further, the δ7Li record strongly resembles both the evolution of deep-sea temperatures based on benthic oxygen isotopes and modeled changes in the rate of seafloor spreading. Thereby, increases of δ7Li in the early Campanian and across the Campanian–Maastrichtian transition correspond to major sea level falls, and the latter with a negative δ13C excursion.

These coherences allow three interpretative approaches: (1) Climate cooling controlled the weathering congruency and the magnitude of Li isotope fractionation by clay mineral formation on the continents. (2) Lowland exposure promoted erosion together with enhanced soil and clay formation after sea level falls. (3) A temperature-dependent fractionation during low-temperature basalt alteration affected the seawater δ7Li signal in a time, when more fresh oceanic basalts where available due to higher spreading rates. The best possible interpretation for the Late Cretaceous δ7Li record and the often-neglected aspects of basalt alteration and reverse weathering need to be further assessed and discussed.

4:00pm - 4:15pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Lithium isotope compositions of various biogenic carbonates throughout the mid-Cretaceous – Challenges of reconstructing δ7LiSW in deep time

Vanessa Schlidt1,2, Sandra Janina Huber1,2, René Hoffmann3, Ulrich Heimhofer4, Elisabetta Erba5, Cinzia Bottini5, Stefan Huck4, Hans-Michael Seitz1,2, Silke Voigt1,2

1Goethe University Frankfurt, Institute for Geosciences, Altenhöferallee 1, 60438 Frankfurt (Germany); 2FIERCE - Frankfurt Isotope & Element Research Center, Altenhöferallee 1, 60438 Frankfurt, Germany; 3Ruhr-Universität Bochum, Institute for Geology, Mineralogy and Geophysics, Universitätsstraße 150, 44801 Bochum (Germany); 4Leibniz University Hannover, Institute of Geology, Callinstraße 30, 30167 Hannover (Germany); 5Università degli Studi di Milano, Dipartimento di Scienze della Terra Ardito Desio, Via Mangiagalli 34, 0039 02 Milan (Italy)

The evolution of the seawater Lithium isotope composition (δ7LiSW) depends on the prevalent weathering regime. To reconstruct δ7LiSW, and thus, weathering congruency, two main archives are widely used: calcareous fossils and bulk carbonate sediments. Either of these archives has its strong and weak points. While carbonate sediments are prone to diagenesis and clay contamination, biogenic skeletons may exhibit strong vital effects on δ7LiSW. Here, we present δ7LiSW data for the mid-Cretaceous derived from various biogenic carbonates such as bivalves (mainly rudists), cephalopods, and brachiopods from well-known sample sites across Europe.

Additionally, we assessed the extent of taxon-specific vital effects on δ7Li for well-preserved Albian molluscs from Madagascar (Mahajanga Basin, age 110.5 +/-0.5Ma) and compared them with data for modern taxonomic groups.

Our most complete data set derives from rudist shells (mainly requieniid rudists) from the mid-Barremian to early Aptian sample locations of Sausset (Urgonian Limestone Formation, France), Ericeira (Crismina Formation, Portugal), Kanfanar (Kanfanar unit, Croatia), and Miravete (Villarova de los Pinares Formation, Spain). We compare their δ7Li compositions and trends therein with that of cotemporaneous carbonate-rich sediments. We provide preliminary δ7LiSW for several time intervals which range between 22-25‰ on average with values exceeding 30‰ in the late Barremian.

Relative to published bulk carbonate data, we observe a systematic offset for rudist-shell δ7Li values of 3-8‰ towards heavier values. We assign this offset to vital effects similar to those known for modern calcitic molluscs.

4:15pm - 4:30pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Temporal and spatial distribution of modern ostracod species of Lago Enriquillo (SW Dominican Republic)

Christopher Berndt1, Torsten Haberzettl1, Lilly Biedermann1, Michael Ernst Böttcher1,2,3, Berenice Matias Marte de Reyes4, Edwin Garcia Cocco4, Claudia Wrozyna1

1University Greifswald, Germany; 2Geochemistry & Isotope Biogeochemistry, Leibniz IOW, Germany; 3Interdisciplinary Faculty, University of Rostock, Germany,; 4Servicio Geológico Nacional, Santo Domingo, Dominican Republic

Understanding modern species´ ecological preferences and distribution are prerequisites for their application as proxies in paleoenvironmental reconstructions. This knowledge is, however, missing for the majority of tropical species. In order to contribute to close this gap we characterize the ostracod fauna of Lago Enriquillo in the Dominican Republic. Located in the Main Development Region of North Atlantic tropical storms it has experienced rapid water level fluctuations in the past that are assumed to be related to storm activities. This highlights the relevance of the lake for reconstructions of changes in precipitation and storm activity. Living ostracods inhabiting Lago Enriquillo were analyzed in March and September (dry and rainy season) 2022 with the aim to understand their temporal and spatial distribution and changes in morphological characteristics (valve size). Lago Enriquillo is a warm (27.8-33.8°C), mesohaline (43.7-46.3 psu) and generally slightly alkaline lake (pH: 7.5-8.1) with a max. water depth of 25 m. The spatially variable ostracod fauna is composed of Cyprideis similis, Perissocytheridea cribrosa and Thalassocypria sarbui. The three species reflect the lake’s seasonality differently in terms of their morphology and population structure. C. similis occurred continuously but is smaller in spring than in autumn. P. cribrosa inhabits the lake only in autumn and shows a distinct distribution dominating littoral areas with seasonal freshwater inflow. T. sarbui forms larger populations only in spring and forms only tentative size clusters. Their occurrence is restricted to water depths above (temporary) minima of oxygen (below 10 – 14 m).

4:30pm - 4:45pm
Topics: 3.03 Advances in paleoclimate proxy development and application

High resolution study of Glycymeris sp. shells from high energy event layers of the Cadiz Bay – a sclerochronological record for the onset of the Dark Ages Period

Alexandra Németh

Research Centre for Astronomy and Earth Sciences, Budapest, Hungary

Driving factors of shell growth of sub-fossil Glycymeris nummaria shells deposited by high energy events into layers at the Atlantic coast of the Iberian Peninsula were investigated by stable isotope analysis and analysing their growth patterns.

High energy events deposited layers of cockles along the coast of Cádiz Bay during the Roman Period (313 ± 114 AD) and the Dark Ages (648 ± 108 AD) (Gutiérrez-Mas, 2011). The climate fluctuation of the region between these two periods was largely investigated by analysing sediment cores from the pro-deltas on the Iberian margin (e.g. Bartels-Jónsdóttir et al., 2015), Glycymeris shells, however can provide seasonal data of temperature change and the seasonality in chemical characteristics of the marine ecosystems. Comparing the paleotemperature data reconstructed from oxygen isotope ratios of seasonally sampled shell carbonate indicates no significant cooling for the ‘Dark Ages Cold Period’ (DACP) for the Cádiz Bay. The seasonality of carbon isotope ratios however showed distinct changes between the Roman Period and the DACP. Seasonal maxima of δ13C values were twice as higher during the DACP which indicates seasonally intensified biological fractionation connected to enhanced primary productivity. This agrees with other studies implying intensified coastal upwelling during the DACP along the Iberian Peninsula, while they observe no significant cooling of the sea surface (Bartels-Jónsdottir et al. 2015). This case study adds to the growing number of evidence that the DACP can not be interpreted as a Europe-wide cooling event as it affected southern regions differently.

4:45pm - 5:00pm
Topics: 3.03 Advances in paleoclimate proxy development and application

Triple oxygen isotope measurements of air CO2 around Göttingen

David Bajnai, Tammo Freese, Andreas Pack

University of Göttingen, Germany

The triple oxygen isotope composition (δ18O and ∆’17O) of atmospheric CO2 provides valuable information about CO2 sources and carbon exchange fluxes between atmospheric reservoirs [1-2]. For example, stratospheric CO2 has a large positive 17O-anomaly due to photochemical processes. The ∆’17O of tropospheric CO2 is primarily influenced by carbonic anhydrase-catalyzed oxygen isotope exchange between air CO2 and water in vegetation, resulting in an air CO2 ∆’17O mainly governed by the isotope composition of local meteoric water. Additionally, CO2 from fossil fuel combustion processes shows a negative 17O-anomaly inherited from the isotope composition of atmospheric O2 [3].

Starting in April 2023, we conducted automated triple oxygen isotope measurements of air CO2 in Göttingen using tunable infrared laser direct absorption spectroscopy (TILDAS; Aerodyne, USA) coupled with a custom-built inlet system. The internal error of the ∆’17O measurements was < 10 ppm and of the δ18Omeasurements < 0.01‰.

In this report, we present our initial results and discuss the contribution of various reservoirs to the ∆’17O of atmospheric CO2 in Göttingen. We also examine daily and seasonal variations observed in our data.

[1] G. Koren et al., J. Geophys. Res. Atmos. 124, 8808–8836 (2019).

[2] M. E. G. Hofmann et al., Geochim. Cosmochim. Acta. 199, 143–163 (2017).

[3] B. Horváth, M. E. G. Hofmann, A. Pack, Geochim. Cosmochim. Acta. 95, 160–168 (2012).