Nick Shackleton

On January 24 of this year, Nicholas John Shackleton passed away in Cambridge, UK. Nick Shackleton was widely recognized as one of the world's great palaeoclimate scientists. He was one of the pioneers of palaeoclimatology and palaeoceanography and his work has inspired a whole generation of researchers. Among his major achievements is the reconstruction of global ice volume variation through the ice ages. His work has strongly influenced, and will continue to do so, studies of future climate change.

Following a study of physics, Nick Shackleton started his career as a PhD student in Cambridge where he developed his own sensitive mass spectrometer. He measured stable oxygen isotopes from the fossil shells of bottom dwelling as well as surface dwelling foraminifera. This approach turned out to be crucial for his discovery that changes in the ratio of heavy ¹⁸O and light ¹⁶O in ocean sediments had been caused by removal of isotopically “light” water to form the ice sheets. His 1967 seminal paper “Oxygen isotope analyses and Pleistocene temperatures re-assessed” (Nature, 215) was the first major step towards reconstructing the waxing and waning of ice sheets through glacial and interglacial times. This paper clearly stated that it was global ice volume rather than sea water temperature determining the oceans' isotopic composition.

In 1976, together with Jim Hays and John Imbrie he published his classic paper “Variations in the earth’s orbit: pacemaker of the ice ages” (Science, 194), which confirmed Milutin Milankovitch' theory of orbital control of climate change. Milankovitch stated that the climate changes globally in response to variations in the Earth's orbit around the Sun with periodicities of 100,000, 40,000 and 21,000 years. Shackleton, Hays and Imbrie found exactly these periodicities in the long climate records obtained from different ocean regions, thereby confirming the Milankovitch theory. Today, isotope stratigraphy is routinely used to date and correlate past climate changes.

Nick Shackleton's other pioneering work was in using carbon isotopes in palaeoclimate research. He recognized that the oceans' carbon isotope composition depends on the  volume of carbon stored on land. From this he could determine how the continental carbon reservoir changed from glacial to interglacial periods. In a paper published in 1983 he  demonstrated how atmospheric carbon dioxide had changed over the past 100,000 years. This appeared to be quite similar to the Vostok ice core CO₂ record.

His last, and possibly boldest contribution was an attempt to estimate the relative contributions of temperature and global ice volume to the isotopic composition of the sea water. In 2005, in analysis of ice core records and ocean sediment records, he and his co-workers could demonstrate that ice volume variations lag behind CO₂ variations. It follows that carbon dioxide plays a major role in the transition from cold to warm periods. This finding has important consequences for predictions of future climate.

At scientific conferences, summer and winter, as in normal life, Nick invariably walked around on sandals without socks, except when he performed playing clarinet in chamber music ensembles, e.g. at the International Conference of Palaeoceanography. He owned the largest private collection of historical clarinets in the world. He told Hays once that he was more famous for the clarinet than for science.

Until his retirement in 2004 he was Professor of Quaternary Palaeoclimatology and Director of the Godwin Institute of Quaternary Research in Cambridge.

In 1999, in recognition of his work and quite fitting, he received the EGS Milutin Milankovic Medal. In 2003 he was appointed Honorary Fellow of the EUG.

For a link to Nick Shackleton's old research group, Cambridge Quaternary, see http://www.quaternary.group.cam.ac.uk/