When the oceans were 20 metres higher: revealing past and future climates

Dr Christina Riesselman, geologist, University of Otago, Dunedin

2015 L'Oréal-UNESCO For Women in Science Fellow Christina Riesselman (Credit: L'Oréal New Zealand)

Three million years ago Earth was much as it is today – familiar continents, animals, and carbon dioxide levels. But temperatures were higher and sea levels were also about 20 metres higher. Today, a billion people live on land less than 20 metres above sea level, and carbon dioxide levels are rising.

Working on the Antarctic ice shelf and at sea Dr Christina Riesselman collects sediment cores from hundreds of metres under the sea floor and reads the climate history of millennia past using the microscopic fossilised fish teeth and diatomic algae she finds in the cores.

Christina will use her L’Oréal-UNESCO For Women in Science Fellowship to turn her focus to the end of the last Ice Age around 10,000 years ago. 2014 was the hottest year on record, but was it the hottest year since the end of the last ice age? Christina’s research could answer that question and help us understand and plan for the impact of our planet’s rapidly changing climate.

Christina is a geologist at the University of Otago in Dunedin.

Christina’s parents are both scientists and she was determined not to follow them. So she went to university intending to be a writer. But, the experiences of a Rocky Mountains childhood, visits to Yellowstone National Park, and a great geology lecturer combined to capture Christina’s interests.

From the University of Nebraska-Lincoln she went to the non-profit Joint Oceanographic Institutions in Washington DC, then Stanford, and the US Geological Survey, ending up in Otago in 2013 having been drawn south by a series of Antarctic expeditions.

In essence Christina is piecing together the climate record of past millennia. She does that with the help of ships like the JOIDES Resolution, one of the flagships of the International Ocean Discovery Program. The JOIDES Resolution is, for Christina, “Like a space shuttle for geoscientists.” It can lower a drill bit kilometres down under the Southern Ocean and then drill into the ocean floor and bring up sediment cores that hold the record of past climate going back millions of years.

 Video at 1080p and overlay without sound available for download here. 

Christina cracks these cores open to reveal the cycle of life and death in prehistoric Antarctica. The sediments contain the glass-like shells of diatoms, microscopic plants that form a large part of the plankton in the Southern Ocean. And these fossils can tell us much about the iciness, temperature, and chemistry of the oceans in which they grew.

“Sometimes I’ll crack open a core and there is a 3 cm layer representing a single year. I can see the retreat of the sea ice, the algae growing in spring and summer and then the return of the ice in winter,” says Christina. Other cores have taken her back to the time of the dinosaurs.

But her focus to date has been on sediment cores some three million years old. These are from an era when life on Earth was much as it is now with similar carbon dioxide levels to those in the atmosphere today as a result of human activity. But, there was one critical difference: temperatures were higher, the Antarctic ice sheets had retreated, and as a result the oceans were about 20 metres higher than they are today.

Christina will use her L’Oréal-UNESCO Fellowship to study more recent sediment cores that carry East Antarctica’s climate record of the past 11,000 years. This is a period of rapid climate change as the Earth came out of the last ice age and sea levels rose to their modern levels.

“What we’re learning about past climate will help us better understand the changes that we’re making to the planet right now, and help us plan for the future,” says Christina.

2015 L’Oréal-UNESCO For Women in Science New Zealand Fellow Christina Riesselman (Credit: L’Oréal New Zealand)
2015 L’Oréal-UNESCO For Women in Science New Zealand Fellow Christina Riesselman (Credit: L’Oréal New Zealand)


2011PhD (geological and environmental sciences), Stanford University, USA
2001Bachelor of Arts (English and geology), University of Nebraska-Lincoln, USA

Career highlights, awards, fellowships, grants

2015Korea Polar Research Institute sediment coring expedition (ANA05B), Ross Sea, Antarctica
2015Project leader for Ministry of Business, Innovation and Employment funded Past Antarctic Climate programme
2015Co-principal Investigator, New Zealand Antarctic Research Institute grant
2014Organiser and facilitator, Dual Careers in Academia panel and workshop for early career scientists, Goldschmidt2014, Sacramento, USA
2013Principal Investigator, Royal Society of New Zealand Marsden Fund, Windows onto warmer worlds: Sea ice, nutrient utilization, and primary production on the Wilkes Land margin, Antarctica
2013TRACERS modern process cruise (NBP13-02), Ross Sea, Antarctica
2014Invited contributor, A multiproxy approach to the reconstruction of Pliocene climate workshop, Barcelona, Spain
2013Invited presentation, Geological Society of Washington, Cosmos Club, Washington DC, USA
2011–2013Mendenhall Postdoctoral Fellowship, U.S. Geological Survey
2011Invited presentation, International Symposium on the Antarctic Earth Sciences, Edinburgh, UK
2011Invited presentation, University School of Earth and Environment, Earth Surface Science Institute, Leeds, UK
2012Invited presentation, American Geophysical Union, San Francisco, USA
2005ARCS Foundation Fellowship
2007ANDRILL Southern McMurdo Sound project, McMurdo Station, Antarctica
2007-2009Graduate Research Fellowship, ANDRILL
2002Antarctic expedition, AntarcticaNZ/ANDRILL site survey, Ross Ice Shelf, Antarctica
2001Chancellor’s Scholar, University of Nebraska, USA

Top five publications

Riesselman CR, Dunbar RB (2013) Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica, Palaeogeography, Palaeoclimatology, Palaeoecology 369:136–153. (Impact factor 3.035, 2 citations)

McKay R, Naish T, Carter L, Riesselman C, Sjunneskog C, Winter D, Dunbar R, Sangiorgi F, Warren C, Pagani M, Schouten S, Willmott V, Levy R, DeConto R, Powell R (2012) Antarctic and Southern Ocean influences in global Late Pliocene cooling, Proceedings of the National Academy of Sciences 109(17): 6423–6428. (Impact factor 10.727, 29 citations)

Dowsett HJ, Robinson MM, Haywood AM, Hill DJ, Dolan AM, Stoll DK, Chan W-L, Abe-Ouchi A, Chandler MA, Rosenbloom NA, Otto-Bliesner BL, Braggs FJ, Lunt DJ, Foley KM, Riesselman CR (2012) Assessing confidence in Pliocene sea surface temperatures to evaluate predictive models, Nature Climate Change 2:365–371. (Impact factor 15.327, 41 citations)

Cook CP, van de Flierdt T, Williams T, Hemming SR, Iwai M, Kobayashi M, Jimenez-Espejo FJ, Escutia C, González JJ, Khim B-K, McKay RM, Passchier S, Bohaty SM, Riesselman CR, Tauxe L, Sugisaki S, Galindo AL, Patterson MO, Sangiorgi F, Pierce EL, Brinkhuis H, IODP Expedition 318 Scientists (2013) Dynamic behaviour of the East Antarctic Ice Sheet during Pliocene warmth, Nature Geoscience 6:765–769. (Impact factor 13.93, 19 citations)

Tortell PD, Payne CD, Li Y, Trimborn S, Rost B, Smith W, Riesselman C, Dunbar R, Sedwick P, DiTullio G (2008) Response of Southern Ocean phytoplankton to CO2, Geophysical Research Letters 35:L04605. (Impact factor 4.41, 81 citations)