International ECR diatomists: Luca Pellegrino - From Italy to Japan

Luca Pellegrino – Dipartimento di Scienze della Terra (Università degli Studi di Torino)

 

I am an Italian PhD student in the Earth Sciences Department of the University of Torino (Italy). You can find more information of how I got into diatoms here: http://youngisdr.blogspot.com/2020/01/how-i-got-into-diatoms-luca-pellegrino.html

I spent three months, from December 2018 to the end of February 2019, doing intensive research in Japan, at the Department of Earth and Environmental Sciences of Yamagata University, supervised by Professor Richard Jordan (hereafter Ric J) and flanked by his fantastic students, in order to improve my knowledge about the late Miocene diatom assemblages of the Mediterranean region. I worked in a perfectly equipped micropaleontological lab, surrounded by enthusiastic students and researchers, such as the silicoflagellate-expert Hideto Tsutsui. I was free to consult Ric’s huge library, full of useful references for diatom identification. Many times Ric complained to me about the unusual ‘gaps’ appearing in his book shelves …

Ric’s library, the most organized part of his office, is full of inspiring books and journals.

The work in Ric’s lab started in the early morning, with a coffee kindly prepared by Kazuki-san, a young and promising nannofossil-researcher who helped me a lot in almost every aspect of my Japanese daily-life. The material we studied was from different Upper Miocene localities of the Mediterranean region. The sediment was routinely processed through a standard acid cleaning procedure, then filtered with the aid of a vacuum pump. The filter was then cut, mounted on aluminium stubs and subsequently gold-coated for SEM investigation. A wonderful world, made up of diatoms and other tiny, glassy microfossils (e.g., radiolarians, variously shaped sponge spicules, ebridians, silicoflagellates), therefore appeared under our astonished eyes. A never-ending surprise, and just in some tens of mm²… The best training in diatom taxonomy I can desire!

After a day spent on the SEM, a coffee break with Kazuki and Kenta

A common diatom on our filters was Thalassionema nitzschioides. The Mediterranean Upper Miocene diatomites are full of this planktonic marine araphid pennate. Since it presents a wide sternum in the middle of two rows of areolae, it recalls to me the pattern of cinematographic films, especially if it is broken and lacks its apices. It ranges in size from 10 to 110 µm, and is a cosmopolitan species thriving in nutrient-rich waters, forming zig-zag, star- or fan-shaped colonies of cells joined by mucilage (Hallegraeff, 1986; Round et al., 1990; Hasle and Syvertsen, 1997). Once the nutrient pool is exhausted, the T. nitzschioides blooms collapse: aggregated by the abundant mucilage produced, the needle-like cells rapidly sink towards the seafloor, where they can create oozes of pristine frustules (e.g., Bull and Kemp, 1996; Dickens and Barron, 1998). Intriguingly, in other late Miocene diatom-bearing world localities T. nitzschioides is generally very abundant, if not dominant (e.g., Dickens and Owen, 1998). Why was this diatom so widespread during the late Miocene? What was the main trigger for the nutrient enrichment of the Mediterranean and other oceans? Improved oceanic circulation (possibly related to the late Neogene global cooling; e.g., Dickens and Owen, 1999)? Volcanism (linked to the Neogene geodynamic reconfigurations; e.g., Taliaferro, 1933)? Continental erosion (related to active tectonic uplift and boosted monsoonal precipitations; e.g., Filippelli, 1997)? This is a hitherto open question, and in order to better address it, beside models and interpretations we absolutely need a detailed documentation of the whole diatom assemblage preserved in diatomites, combining micropaleontological, sedimentological and geochemical data.

Left: SEM photomicrograph of a specimen of Thalassionema nitzschioides. Note the areolation pattern and the wide sternum. Right: SEM photomicrograph of an almost monospecific diatom ooze dominated by T. nitzschioides (from Bull and Kemp, 1996).

Of course, beside diatom research, these three months have been a full immersion into the fascinating Japanese culture. Yamagata is surrounded by mountains where breathtaking shrines, such as scenic Yamadera, have been built centuries ago. A bit of fatigue during the ascension is always well rewarded by the sight and the suggestive silence that you can enjoy once you have reached the summit. By the way, a bath in the hot springs (onsen) and a good Japanese dinner watered down by the local sake, will definitely restore you, especially during the winter time, particularly tough in this region of Japan. Otherwise, you can choose a relaxing boat trip along the river, immerse in the nature and by rejoiced by boat driver songs.

Yamadera Temple: entrance and panoramic view once you have reached the summit

University entrance during a National holiday. Winter in Yamagata is cold and very, very, very snowy…

Eating and drinking in a typical Japanese restaurant…

A relaxing boat trip along the Mogami River, with the funny boat driver singing traditional japanese songs…

Last but not least, the accommodation for international students and researchers was very comfortable, clean and cheap, just 15-20 minutes distance from the University by walk.

The international student dormitory

Ric and his students (especially Kazuki, Kenta, Yuki, Takeshi and Nao) gave me the extraordinary opportunity to improve my knowledge about a microscopic world of organisms that flourished, sank and accumulated millions of years ago, originating the enigmatic successions outcropping almost everywhere in the Mediterranean region.

I strongly encourage students to visit Ric’s labs in Yamagata, where you will find one of the last ‘Victorian’ approaches to micropaleontology (‘fascinated by everything, focused on nothing’), with guys working on coccolithophorids, silicoflagellates, parmales, chysophytes, ebridians, siliceous dinoflagellates, sponge spicules, sea cucumbers, as well as diatoms. All of this, surrounded by a cloud of funny and motivated students, always available to welcome you in the crazy research of the past oceans paleobiodiversity.

References

• ·         Bull, D., Kemp, A.E.S., 1996. Composition and origins of laminae in late Quaternary and Holocene sediments from the Santa Barbara Basin. In: Kemp, A.E.S. (Ed.), Paleoclimatology and Paleoceanography from Laminated Sediments. Geological Society Special Publication 116, 143-156.
• ·         Dickens, G.R., Barron, J.A., 1998. A rapidly deposited pennate diatom ooze in Upper Miocene-Lower Pliocene sediment beneath the North pacific polar front. Marine Micropaleonology 31, 177-182.
• ·         Dickens, G.R., Owen, R.M., 1999. The Latest Miocene-Early Pliocene biogenic bloom: a revised Indian Ocean perspective. Marine Geology 161, 75-91.
• ·         Filippelli, G.M., 1997. Intensification of the Asian monsoon and a chemical weathering event in the Late Miocene-Early Pliocene: implications for Late Neogene climate change. Geology 25, 27-30.
• ·         Hallegraeff, G.M., 1986. Taxonomy and morphology of the marine plankton diatoms Thalassionema and Thalassiothrix. Diatom Research 1 (1), 57-80.
• ·         Hasle, G.R., Syvertsen, E.E., 1997. Marine diatoms. In: Tomas, C.R. (Ed.), Identifying Marine Phytoplankton. Academic Press, 858 pp.
• ·         Round, F.E., Crawford, R.M., Mann, D.G., 1990. The diatoms. Biology and morphology of the genera. Cambridge University Press, 747 pp.
• ·         Taliaferro, N.L., 1933. The relation of volcanism to diatomaceous and associated siliceous sediments. In: Bull. Dep. Geol. Sci. 23 (1). University of California Press, pp. 1–55.