
- Paleomagnetism
- Paleoclimate/ocean reconstructions
- Antarctic climate evolution
Email christian.ohneiser@otago.ac.nz
Tel +64 3 479 7350
Google Scholar Christian Ohneiser
ORCID orcid.org/0000-0002-2781-2522
Research interests
My research focuses on reconstructing the history of Earth’s climate system and geomagnetic field from sedimentary records on timescales of 10’s to millions of years. The research involves expeditions on research ships around New Zealand and Pacific Ocean and to remote field areas in Antarctica.
I study sedimentary records and apply paleomagnetic and geochemical techniques to date sediments and reconstruct under what climatic conditions they were deposited. Recent paleoclimate studies demonstrate that past environmental changes have occurred quickly therefore we require techniques that can achieve centennial to millennial-scale correlations between sedimentary records separated by large distances and deposited millions of years ago. In parallel, environmental magnetic, geochemical and sedimentological studies can reveal changes in sediment source, erosion rate, and changes in ocean circulation such as current strength and direction.
Current research projects
Southern Ocean circulation reconstructions
Antarctica plays an important role in regulating earth’s climate. The cold ice sheets interact with the ocean and are the powerhouse for global deep circulation which controls our weather and how heat is distributed around the world.
Antarctic Bottom Water (AABW) is a major component of the global thermohaline ocean circulation. Changes in its strength modify the global heat distribution and can have a direct impact on earth’s climate. Deep waters at the Antarctic margin have warmed and freshened in recent decades, and export rates have slowed. We don’t know if this is part of the Southern Ocean’s natural variability or something new. I am working with other researchers to examine the long-term variability and sensitivity of AABW production to changes in the surface conditions. The aim is to determine the spectrum of natural (pre-industrial) AABW production variability in order to place the recent observations in a long term context. The tools we use include magnetic mineralogy and fabric studies to understand changes in deep current strength, sedimentologic studies to reconstruct ice rafted debris and organic geochemical studies to reconstruct ocean surface temperature.
Reconstruction of the Ross Ice Shelf history
The Ross Ice shelf is the largest floating ice shelf in the world but rising ocean temperatures and changing ocean circulation patterns in the Ross Embayment may cause it become unstable in the future. How quickly the ice shelf may retreat is unknown but geological reconstructions of the most recent retreat phase at the end of the last ice shelf can help put constraints on future retreat scenarios. This project uses short sediment cores collected from the Ross Embayment and from beneath the Ross Ice Shelf to date the most recent ice shelf retreat and reconstruct the oceanographic changes which have occurred since.
New Zealand paleoclimate reconstructions
We have inherited a collection of pristine minerals industry sedimentary drill cores which are unique archives of New Zealand’s climate over last 55 million years. Over this period global average temperatures have reduced dramatically in parallel with decreasing atmospheric CO2 concentrations. The aim of this project is to understand better the sensitivity of the climate system to changing atmospheric CO2 concentrations known as the ‘climate sensitivity’. At the moment we are focusing on reconstructing the Eocene Climatic Optimum (c. 50 million years ago) when atmospheric CO2 was high (c. 1000 ppm) and the climate was much warmer than today.
Research Under the Antarctic Science Platform
Global mean temperatures are increasing and will continue to do so until greenhouse gas emissions are reduced significantly. Antarctica’s ice sheet are sensitive to subtle changes in temperature and have the capability to raise global sea-level significantly. Knowing how the Antarctic ice sheet will respond in the future is essential but to determine that we need to look at environmental records of how the Antarctic ice sheets and surrounding ocean have changed in the past. The multi-institution Antarctic Science Platform project ‘Antarctic Ice Dynamics – Past, Present, and Future’ uses a range of geological and geophysical techniques to investigate past changes and present-day ice sheet behaviour.
Visit the multi-institution Antarctic Science Platform website.
Field working the Lower Taylor Valley under the Qmap 22 geological mapping expedition. Photo: Dougal Townsend.
Sediment coring beneath the Ross Ice Shelf at HWD-2 for the NZARI Ross Ice Shelf Programme. Photo: Christina Hulbe.
Sediment core sampling at Florida State University in Tallahassee.
Core Scanning X-ray Fluorescence Analysis of Ocean Drilling Program Core 1101 at the IODP core repository in College Station Texas.
Research facilities
The Department of Geology has growing and complementary research capability which includes an analytical core repository, organic geochemical research facility and a paleomagnetic research facility. Additional facilities listed here.
The Otago Paleomagnetic Research Facility
The Department of Geology contains a state of the art magnetic research facility which include a superconducting magnetometer for measuring continuous and discrete samples and a vibrating sample magnetometer.
Postgraduate research opportunities
Are you interested in joining us for postgraduate study on sedimentary successions and paleoenvironmental reconstructions? We have several project opportunities waiting for you. The University of Otago offers scholarships to local and international students which cover tuition and provide a competitive stipend. For more information visit the Otago scholarships web page or email me for more information.
Sediment sampling At the Hogg Glacier, Antarctica.
The RV Joides Resolution at night in Honolulu before departing on IODP Expedition 320.
Teaching
- EAOS 111 Earth and Ocean Science
- OCEN 201 The Marine Environment
- GEOL 261 Geophysics of the Earth
- GEOL 361 Geophysics of the Earth
- GEOL 276 Geological Resources for a Sustainable New Zealand
- GEOL 376 Geological Resources for a Sustainable New Zealand
- GEOL 344 Advanced Field Studies*
- GEOL 421 Sedimentary and Basin Studies
- GEOL 431 Geophysics
- GEOL 471 Advanced Topics in Geophysics 2*
* Course Coordinator
Publications
Perkins, E. J., Gorman, A. R., Tidey, E. J., Wilson, G. S., Ohneiser, C., Moy, C. M., Riesselman, C. R., Gilmer, G., & Ross, B. S. (2020). High-resolution seismic imaging reveals infill history of a submerged Quaternary fjord system in the subantarctic Auckland Islands, New Zealand. Quaternary Research, 93(1), 255-266. doi: 10.1017/qua.2019.58
Ohneiser, C., Wilson, G. S., Beltran, C., Dolan, A. M., Hill, D. J., & Prebble, J. G. (2020). Warm fjords and vegetated landscapes in early Pliocene East Antarctica. Earth & Planetary Science Letters, 534, 116045. doi: 10.1016/j.epsl.2019.116045
Stevens, C., Hulbe, C., Brewer, M., Stewart, C., Robinson, N., Ohneiser, C., & Jendersie, S. (2020). Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting. PNAS, 117(29), 16799-16804. doi: 10.1073/pnas.1910760117
Beltran, C., Golledge, N. R., Ohneiser, C., Kowalewski, D. E., Marie-Alexandrine, S., Hageman, K. J., Smith, R., Wilson, G. S., & Mainié, F. (2020). Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31. Quaternary Science Reviews, 228, 106069. doi: 10.1016/j.quascirev.2019.106069
Ohneiser, C., & Tapia, C. (2020). Diagenesis of magnetic minerals at the Southwest Pacific DSDP Site 277. New Zealand Journal of Geology & Geophysics, 63(2), 250-261. doi: 10.1080/00288306.2019.1665075
Journal - Research Article
Perkins, E. J., Gorman, A. R., Tidey, E. J., Wilson, G. S., Ohneiser, C., Moy, C. M., Riesselman, C. R., Gilmer, G., & Ross, B. S. (2020). High-resolution seismic imaging reveals infill history of a submerged Quaternary fjord system in the subantarctic Auckland Islands, New Zealand. Quaternary Research, 93(1), 255-266. doi: 10.1017/qua.2019.58
Ohneiser, C., & Tapia, C. (2020). Diagenesis of magnetic minerals at the Southwest Pacific DSDP Site 277. New Zealand Journal of Geology & Geophysics, 63(2), 250-261. doi: 10.1080/00288306.2019.1665075
Beltran, C., Golledge, N. R., Ohneiser, C., Kowalewski, D. E., Marie-Alexandrine, S., Hageman, K. J., Smith, R., Wilson, G. S., & Mainié, F. (2020). Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31. Quaternary Science Reviews, 228, 106069. doi: 10.1016/j.quascirev.2019.106069
Stevens, C., Hulbe, C., Brewer, M., Stewart, C., Robinson, N., Ohneiser, C., & Jendersie, S. (2020). Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting. PNAS, 117(29), 16799-16804. doi: 10.1073/pnas.1910760117
Ohneiser, C., Wilson, G. S., Beltran, C., Dolan, A. M., Hill, D. J., & Prebble, J. G. (2020). Warm fjords and vegetated landscapes in early Pliocene East Antarctica. Earth & Planetary Science Letters, 534, 116045. doi: 10.1016/j.epsl.2019.116045
Jovane, L., Florindo, F., Acton, G., Ohneiser, C., Sagnotti, L., Strada, E., … Wilson, G. S., … Passchier, S. (2019). Miocene glacial dynamics recorded by variations in magnetic properties in the ANDRILL‐2A drill core. Journal of Geophysical Research: Solid Earth, 124, 2297-2312. doi: 10.1029/2018JB016865
Ohneiser, C., Yoo, K.-C., Albot, O. B., Cortese, G., Riesselman, C., Lee, J. I., … Bollen, M., … Beltran, C., … Wilson, G. S. (2019). Magneto-biostratigraphic age models for Pleistocene sedimentary records from the Ross Sea. Global & Planetary Change, 176, 36-49. doi: 10.1016/j.gloplacha.2019.02.013
Tapia, C. A., Grant, G. R., Turner, G. M., Sefton, J. P., Naish, T. R., Dunbar, G., & Ohneiser, C. (2019). High-resolution magnetostratigraphy of mid-Pliocene (3.3-3.0 Ma) shallow-marine sediments, Whanganui Basin, New Zealand. Geophysical Journal International, 217(1), 41-57. doi: 10.1093/gji/ggz004
Cole, R. P., Ohneiser, C., White, J. D. L., Townsend, D. B., & Leonard, G. S. (2019). Paleomagnetic evidence for cold emplacement of eruption-fed density current deposits beneath an ancient summit glacier, Tongariro volcano, New Zealand. Earth & Planetary Science Letters, 522, 155-165. doi: 10.1016/j.epsl.2019.07.004
Gangl, S. K., Moy, C. M., Stirling, C. H., Jenkyns, H. C., Crampton, J. S., Clarkson, M. O., Ohneiser, C., & Porcelli, D. (2019). High-resolution records of Oceanic Anoxic Event 2: Insights into the timing, duration and extent of environmental perturbations from the palaeo-South Pacific Ocean. Earth & Planetary Science Letters, 518, 172-182. doi: 10.1016/j.epsl.2019.04.028
Martin, A. P., Ohneiser, C., Turnbull, R. E., Strong, D. T., & Demler, S. (2018). Soil magnetic susceptibility mapping as a pollution and provenance tool: An example from southern New Zealand. Geophysical Journal International, 212(1), 1225-1236. doi: 10.1093/gji/ggx484
Ohneiser, C., & Wilson, G. S. (2018). Eccentricity-paced Southern Hemisphere glacial-interglacial cyclicity preceding the middle Miocene climatic transition. Paleoceanography & Paleoclimatology, 33, 795-806. doi: 10.1029/2017PA003278
Grant, G. R., Sefton, J. P., Patterson, M. O., Naish, T. R., Dunbar, G. B., Hayward, B. W., … Ohneiser, C., & Turner, G. M. (2018). Mid- to late Pliocene (3.3–2.6 Ma) global sea-level fluctuations recorded on a continental shelf transect, Whanganui Basin, New Zealand. Quaternary Science Reviews, 201, 241-260. doi: 10.1016/j.quascirev.2018.09.044
Patterson, M. O., McKay, R., Naish, T., Bostock, H. C., Dunbar, R., Ohneiser, C., … Wilson, G., & Caballero-Gill, R. (2018). A Southwest Pacific perspective on long-term global trends in Pliocene-Pleistocene stable isotope records. Paleoceanography & Paleoclimatology, 33(7), 825-839. doi: 10.1029/2017pa003269
Levy, R., Harwood, D., Florindo, F., Sangiorgi, F., Tripati, R., von Eynatten, H., … and SMS Science Team, including Ohneiser, C., Riesselman, C., & Wilson, G. (2016). Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene. PNAS, 113(13), 3453-3458. doi: 10.1073/pnas.1516030113
Beltran, C., Ohneiser, C., Hageman, K. J., & Scanlan, E. (2016). Evolution of the southwestern Pacific surface waters during the early Pleistocene. New Zealand Journal of Geology & Geophysics, 59(4), 514-521. doi: 10.1080/00288306.2016.1195756
von Lichtan, I., White, J. D. L., Manville, V., & Ohneiser, C. (2016). Giant rafted pumice blocks from the most recent eruption of Taupo volcano, New Zealand: Insights from palaeomagnetic and textural data. Journal of Volcanology & Geothermal Research, 318, 73-88. doi: 10.1016/j.jvolgeores.2016.04.003
Ohneiser, C., Florindo, F., Stocchi, P., Roberts, A. P., DeConto, R. M., & Pollard, D. (2015). Antarctic glacio-eustatic contributions to late Miocene Mediterranean desiccation and reflooding. Nature Communications, 6, 8765. doi: 10.1038/ncomms9765
Ohneiser, C., Wilson, G. S., & Cox, S. C. (2015). Characterisation of magnetic minerals from southern Victoria Land, Antarctica. New Zealand Journal of Geology & Geophysics, 58(1), 52-65. doi: 10.1080/00288306.2014.990044
Yamamoto, Y., Yamazaki, T., Acton, G. D., Richter, C., Guidry, E. P., & Ohneiser, C. (2014). Palaeomagnetic study of IODP Sites U1331 and U1332 in the equatorial Pacific: Extending relative geomagnetic palaeointensity observations through the Oligocene and into the Eocene. Geophysical Journal International, 196(2), 694-711. doi: 10.1093/gji/ggt412
Brachfeld, S., Pinzon, J., Darley, J., Sagnotti, L., Kuhn, G., Florindo, F., Wilson, G., Ohneiser, C., … Joseph, L. (2013). Iron oxide tracers of ice sheet extent and sediment provenance in the ANDRILL AND-1B drill core, Ross Sea, Antarctica. Global & Planetary Change, 110, 420-433. doi: 10.1016/j.gloplacha.2013.09.015
Guidry, E. P., Richter, C., Acton, G. D., Channell, J. E. T., Evans, H. F., Ohneiser, C., … Yamazaki, T. (2013). Oligocene-Miocene magnetostratigraphy of deep-sea sediments from the Equatorial Pacific (IODP Site U1333). Geological Society, London, Special Publications, 373, 13-27. doi: 10.1144/sp373.7
Ohneiser, C., Acton, G., Channell, J. E. T., Wilson, G. S., Yamamoto, Y., & Yamazaki, T. (2013). A middle Miocene relative paleointensity record from the Equatorial Pacific. Earth & Planetary Science Letters, 374, 227-238. doi: 10.1016/j.epsl.2013.04.038
Channell, J. E. T., Ohneiser, C., Yamamoto, Y., & Kesler, M. S. (2013). Oligocene-Miocene magnetic stratigraphy carried by biogenic magnetite at sites U1334 and U1335 (equatorial Pacific Ocean). Geochemistry, Geophysics, Geosystems, 14(2), 265-282. doi: 10.1029/2012gc004429
Wilson, G. S., Levy, R. H., Naish, T. R., Powell, R. D., Florindo, F., Ohneiser, C., … Riesselman, C., … Wise, S. (2012). Neogene tectonic and climatic evolution of the Western Ross Sea, Antarctica: Chronology of events from the AND-1B drill hole. Global & Planetary Change, 96-97, 189-203. doi: 10.1016/j.gloplacha.2012.05.019
Ohneiser, C., & Wilson, G. (2012). Revised magnetostratigraphic chronologies for New Harbour drill cores, southern Victoria Land, Antarctica. Global & Planetary Change, 82-83, 12-24. doi: 10.1016/j.gloplacha.2011.11.007
Pälike, H., Lyle, M. W., Nishi, H., Raffi, I., Ridgwell, A., Gamage, K., … Beltran, C., … Ohneiser, C., … Zeebe, R. E. (2012). A Cenozoic record of the equatorial Pacific carbonate compensation depth. Nature, 488(7413), 609-614. doi: 10.1038/nature11360
Levy, R., Cody, R., Crampton, J., Fielding, C., Golledge, N., Harwood, D., … Ohneiser, C., Wilson, G., … Winter, D. (2012). Late Neogene climate and glacial history of the Southern Victoria Land coast from integrated drill core, seismic and outcrop data. Global & Planetary Change, 80-81, 61-84. doi: 10.1016/j.gloplacha.2011.10.002
Passchier, S., Browne, G., Field, B., Fielding, C. R., Krissek, L. A., Panter, K., … and ANDRILL-SMS Science Team, including Ohneiser, C., Palin, M., Riesselman, C., & Wilson, G. (2011). Early and middle Miocene Antarctic glacial history from the sedimentary facies distribution in the AND-2A drill hole, Ross Sea, Antarctica. Geological Society of America Bulletin, 123(11-12), 2352-2365. doi: 10.1130/B30334.1
Frank, T. D., Gui, Z., and the ANDRILL SMS Science Team, including Ohneiser, C., Palin, M., Riesselman, C., & Wilson, G. (2010). Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica. Geology, 38(7), 587-590. doi: 10.1130/G30849.1
Naish, T., Powell, R., Levy, R., Wilson, G., Scherer, R., Talarico, F., … Ohneiser, C., … Riesselman, C., … Williams, T. (2009). Obliquity-paced pliocene west antarctic ice sheet oscillations. Nature, 458(7236), 322-328. doi: 10.1038/nature07867
Field, B. D., Crundwell, M. P., Lyon, G. L., Mildenhall, D. C., Morgans, H. E. G., Ohneiser, C., Wilson, G. S., … Chanier, F. (2009). Middle Miocene paleoclimate change at Bryce Burn, southern New Zealand. New Zealand Journal of Geology & Geophysics, 52(4), 321-333. doi: 10.1080/00288306.2009.9518461
Acton, G., Crampton, J., Di Vincenzo, G., Fielding, C. R., Florindo, F., Hannah, M., … Ohneiser, C., … Riesselman, C., … Wilson, G. S., … and the ANDRILL-SMS Science Team. (2008-2009). Preliminary integrated chronostratigraphy of the AND-2A core, ANDRILL Southern McMurdo Sound Project, Antarctica. Terra Antartica, 15(1-2), 211-220.
Ohneiser, C., Wilson, G. S., Field, B. D., & Crundwell, M. P. (2008). A new high-resolution, middle Miocene magnetostratigraphy from western Southland, New Zealand. New Zealand Journal of Geology & Geophysics, 51(3), 261-274. doi: 10.1080/00288300809509864
Acton, G., Florindo, F., Jovane, L., Lum, B., Ohneiser, C., Sagnotti, L., … Wilson, G. S., and the ANDRILL-SMS Science Team. (2008). Palaeomagnetism of the AND-2A Core, ANDRILL southern McMurdo Sound Project, Antarctica. Terra Antartica, 15(1), 193-210.
Wilson, G. S., Florindo, F., Sagnotti, L., & Ohneiser, C. (2007). Palaeomagnetism of the AND-1B core, ANDRILL McMurdo Ice Shelf Project, Antartica. Terra Antartica, 14(3), 289-296.
Wilson, G. S., Levy, R., Browne, G., Cody, R., Dunbar, N., Florindo, F., … Ohneiser, C., … and the ANDRILL-MIS Science Team. (2007). Preliminary integrated chronostratigraphy of the AND-1B core, ANDRILL McMurdo Ice Shelf Project, Antarctica. Terra Antartica, 14(3), 297-316.
Conference Contribution - Published proceedings: Full paper
Villamor, P., Barrell, D. J. A., Gorman, A., Davy, B. W., Hreinsdottir, S., Hamling, I. J., Stirling, M. W., … Holt, A., Todd, E., Denys, P., Pearson, C., Sangster, C., … Ohneiser, C., Lepine, P., & Caratori-Tontini, F. (2018). Unknown faults under cities. GNS Science Miscellaneous Series. 124. doi: 10.21420/G2PW7X
Conference Contribution - Published proceedings: Abstract
Baltar, F., De Corte, D., Ohneiser, C., Thomson, B., Greening, C., Stepanauskas, R., … Morales, S., Hulbe, C. L., … Martínez-Pérez, C. (2020). Chemoautotrophy drives plankton activity under the Ross Ice Shelf. Proceedings of the Ocean Sciences Meetings (OSM). OB44G-0761. Retrieved from https://agu.confex.com/agu/osm20/meetingapp.cgi
Beltran, C., Golledge, N. R., Ohneiser, C., Kowalewski, D. E., Sicre, M.-A., Hageman, K. J., Smith, R. O., Wilson, G. S., & Mainié, F. (2020). Rapid Antarctic ice sheet retreat under low atmospheric CO2. Proceedings of European Geosciences Union (EGU): Sharing Geoscience Online. EGU2020-12028. doi: 10.5194/egusphere-egu2020-12028
Martin, A., Dunbar, G., Hulbe, C., Ohneiser, C., Grant, G., & Brandt, S. (2020). Provenance of gravel- and sand-sized sediment from both the ice shelf and shallowest seafloor at the HWD-2b site, mid Ross Ice Shelf, Antarctica. Scientific Committee on Antarctic Research (SCAR) Open Science Conference. 1539. Retrieved from https://www.scar2020.org
Ohneiser, C. (2020). Obliquity pacing of Antarctic glaciations during the Quaternary. Proceedings of the Geoscience Society of New Zealand (GSNZ) Annual Conference. Retrieved from https://confer.eventsair.com/gsnz2020
Chorley, H., Levy, R., Naish, T., Hemming, S., Ohneiser, C., Prebble, J., … Florindo, F. (2020). Orbital-scale, glacial evolution of the Transantarctic mountains during the Miocene Climatic Optimum and its termination (˜15.5-13.8 Ma). Scientific Committee on Antarctic Research (SCAR) Open Science Conference. 615. Retrieved from https://www.scar2020.org
Ohneiser, C., Beltran, C., Hulbe, C., Moy, C., Riesselman, C., Worthington, R., & Condon, D. (2020). Obliquity pacing of Antarctic glaciations during the Quaternary. Proceedings of European Geosciences Union (EGU): Sharing Geoscience Online. EGU2020-11191. doi: 10.5194/egusphere-egu2020-11191
Brenna, M., Ohneiser, C., Gorman, A., & Palin, M. (2020). Geothermal energy from extinct volcanoes: The Dunedin experiment. 14th Annual Otago Energy Research Centre (OERC) Symposium: New Energy Futures post COVID-19. Retrieved from https://www.otago.ac.nz/oerc
Levy, R., Patterson, M., van de Flierdt, T., Espejo, F., Stocchi, P., Klages, J., … Ohneiser, C., & Flores, J.-A. (2020). The SWAIS 2C project: Sensitivity of the West Antarctic Ice Sheet in a warmer world. Scientific Committee on Antarctic Research (SCAR) Open Science Conference. 1598. Retrieved from https://www.scar2020.org
Ohneiser, C., Beltran, C., Hulbe, C., Moy, C., Riesselman, C., Worthington, R., & Condon, D. (2020). Obliquity paced oscillations of the Ross Ice Shelf during the quaternary. Scientific Committee on Antarctic Research (SCAR) Open Science Conference. 996. Retrieved from https://www.scar2020.org
Stevens, C., Hulbe, C., Brewer, M., Stewart, C., Robinson, N., Ohneiser, C., … Wilson, G., & Riesselman, C. (2019). There and back again: Oceanic connections between the grounding line and the Southern Ocean. Proceedings of the New Zealand Antarctic Science Conference: Our future in focus. (pp. 37). New Zealand Antarctic Research Institute. Retrieved from https://www.antarcticanz.govt.nz/science/new-zealand-antarctic-science-conference-2019
Jovane, L., Florindo, F., Acton, G., Ohneiser, C., Sagnotti, L., Strada, E., … Wilson, G., … Passchier, S. (2019). Miocene glacial dynamics recorded by variations in magnetic properties in the ANDRILL-2A drill core. Geophysical Research Abstracts, 21, EGU2019-5081. [Abstract]
Ohneiser, C., & Wilson, G. (2019). Eccentricity-paced Southern Hemisphere glacial-interglacial cyclicity preceding the middle Miocene climatic transition. Geophysical Research Abstracts, 21, EGU2019-2123. [Abstract]