Changing climates and shifting currents in Jurassic oceans
The Jurassic Earth was very different from today - atmospheric CO2 was higher, long-term climate was warmer, and there were no permanent polar ice-caps. The supercontinent Pangea was breaking apart, leading to changes in the configuration of the landmasses, oceans, and seaways. Using geochemical signals from fossilized marine animals, a new study in Palaeo3 looked at how the ocean currents and climates changed in the European and Arctic regions during this Greenhouse period of Earth’s history.
During the Middle and Late Jurassic (ca. 175-145 Million years ago), Europe and the Boreal regions in the north formed a network of semi-restricted, relatively shallow seas which overlay continental crust. The Atlantic Ocean did not yet exist. Instead, Greenland and North America lay immediately to the west of these European shallow seaways, and to the right an ancient ocean called the Tethys (Fig. 1). The only water connection between the Boreal and European seas was the Viking Corridor, a narrow strip situated between Greenland and the Norwegian margin. Being the main location of water exchange between the Arctic and lower latitudes, this restricted seaway potentially affected global ocean heat transport and therefore global climate.
Much of our understanding of climate and ocean patterns from these times comes from looking at geochemical signals in the shells of marine organisms that lived in these seas. In particular, the internal hard parts of a group of organisms called belemnites, ancient relatives of squids and cuttlefish, are often used for this purpose. Their internal shell is made from calcium carbonate, which contains oxygen. Oxygen has both heavy and light forms (“isotopes”), the lightest with an atomic weight of 16 and the heaviest with an atomic weight of 18. The belemnites incorporated different ratios of heavy 18O and light 16O (18O/16O, referred to as “δ18O”) in their shells depending on the temperature and salinity of the seawater in which they lived. Consequently, δ18O records from belemnites were strongly influenced by changes in both ocean currents and climate.
This collaborative study used belemnite fossils collected by GEUS (Denmark) during fieldwork to eastern Greenland in the 1990s and 2000s, analyzed and interpreted at the University of Copenhagen (Denmark), University of Exeter (U.K.), and the University of Oslo (Norway).
During the Jurassic, Eastern Greenland was situated on the western margin of the Viking Corridor (Fig. 1). The belemnite fossils were analyzed to see how the δ18O of their shells changed during the Jurassic. By comparing this record to those from the Tethys and the higher latitude Boreal region (Fig. 1), some trends appeared to reflect changes in water temperature, driven by changes in global climates (as all the localities show a change in δ18O), whereas others indicated more local changes in the current directions, as evidenced by only some localities showing a change in δ18O trends (Fig. 2).
Across the Early to Middle Jurassic transition (EMJT), increases in δ18O in all localities indicate that widespread climate cooling occurred, although the timing of this appears to be offset and of variable magnitude across the western Subboreal Province and Tethys Realm (see Figs. 1 & 2). The transition from the Middle to Late Jurassic epoch saw a move to relatively heavy δ18O values in the Subboreal Province, but this trend is less pronounced in the northwest Tethys, suggesting that a change in currents occurred, whereby there was strengthening of a southward current bringing colder Boreal waters down towards the Tethys. The latest part of the Jurassic shows increases in belemnite δ18O, consistent with other studies that indicate that the Arctic became entirely isolated from the lower latitudes across the Jurassic–Cretaceous boundary (as shown in the papers Galloway et al., 2020 and Jelby et al., 2020). This study therefore demonstrates how intimately linked climate and ocean current patterns were during the Jurassic period.
Contact information: Madeleine L. Vickers, firstname.lastname@example.org
Vickers, M.L., Hougård, I.W., Alsen, P., Ullmann, C.V., Jelby, M.E., Bedington, M., and Korte, C., 2022. Middle to Late Jurassic palaeoclimatic and palaeoceanographic trends in the Euro-Boreal region: Geochemical insights from East Greenland belemnites. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 597, 111014. https://doi.org/10.1016/j.palaeo.2022.111014
(See article for full list of references used in the compilation shown in Fig. 2).
Galloway, J.M., Vickers, M.L., Price, G.D., Poulton, T., Grasby, S.E., Hadlari, T., Beauchamp, B., Sulphur, K., 2020. Finding the VOICE: organic carbon isotope chemostratigraphy of Late Jurassic–Early Cretaceous Arctic Canada. Geological Magazine 157 (10), 1643–1657. https://doi.org/10.1017/s0016756819001316
Jelby, M.E., Sliwinska, K.K., Koevoets, M.J., Alsen, P., Vickers, M.L., Olaussen, S., Stemmerik, L., 2020. Arctic reappraisal of global carbon-cycle dynamics across the Jurassic–Cretaceous boundary and Valanginian Weissert Event. Palaeogeography, Palaeoclimatology, Palaeoecology 555, 109847 https://doi.org/10.1016/j.palaeo.2020.109847
Funding for this research came from The Danish Council for Independent Research–Natural Sciences (project DFF - 7014-00142 to CK), the European Commission, Horizon 2020 Marie Skłodowska-Curie Actions (ICECAP; grant no. 101024218, to MLV), and by the Research Council of Norway through the Centres of Excellence funding scheme, project number 223272.
The CEED blog covers some behind-the-scenes about our latest research and activities. The contributors are a mix of students and staff from The Centre for Earth Evolution and Dynamics, Dept. of Geosciences, University of Oslo, Norway.