HR: 0800h
AN: PP51A-0582    [Abstracts]
TI: The Potential of Ikaite to Record the Oceanic Evolution of ?18O
AU: * Rickaby, R E
EM: rosr@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences, Parks Road, Oxford, Ox OX1 3PR United Kingdom
AU: Shaw, S
EM: sams@earth.ox.ac.uk
AF: Oxford University, Department of Earth Sciences, Parks Road, Oxford, Ox OX1 3PR United Kingdom
AU: Bennitt, G
EM: gemma.bennitt@st-edmund-hall.oxford.ac.uk
AF: Oxford University, Department of Earth Sciences, Parks Road, Oxford, Ox OX1 3PR United Kingdom
AU: Kennedy, H A
EM: h.a.kennedy@bangor.ac.uk
AF: University of Wales, Bangor, School of Ocean Sciences, Menai Bridge, Anglesey, LL59 5AB United Kingdom
AU: Lennie, A
EM: a.lennie@dl.ac.uk
AF: CCLRC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD United Kingdom
AB: Despite the importance of sea level for understanding past climates, paleoceanographers struggle to construct a continuous and definitive record of oceanic δ¹⁸O over millennial timescales. Here, we explore the possibility that ikaite, a hydrated form of calcium carbonate which forms monoclinic crystals made of CaCO₃.6H₂O units linked together by hydrogen bonds, may record the δ¹⁸O of the water from which it precipitates. Naturally occurring samples of ikaite have been found in the Ikka Fjord in Greenland where the crystals grow into huge chimneys around cold water springs at a temperature of 3°C, and ephemeral occurrences are also noted in alkaline lakes such as Mono Lake, California. The stability field of ikaite suggests that it should not exist at normal ocean temperatures and pressures. Nonetheless, the presence of ikaite has been recognised increasingly in areas such as the Bransfield Strait, Sea of Okhotsk, the Laptev Sea and the Lower Zaire Deep Sea fan, where sediments rich in organic carbon are characterised by high alkalinity and the presence of sulphate or phosphate which inhibits calcite precipitation. Whilst the presence and isotopic composition of glendonite, a pseudomorph of ikaite has been used as a key environmental indicator in the geological record, ikaite from recent ocean sediments has never been preserved for geochemical analysis. We have performed a series of laboratory growth experiments of ikaite under controlled conditions of alkalinity and temperature, from waters with a range of δ¹⁸O. Our results demonstrate that, in accordance with theory, the crystal bound waters in ikaite are isotopically heavier than the ambient water. Further a simple linear relationship with a non-zero intercept exists between the δ¹⁸O of the hydration waters of ikaite, and the waters from which the crystal precipitated. These data provide a firm foundation for application of this methodology to reconstruct oceanic δ¹⁸O from ikaite in Pleistocene sediments.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4924 Geochemical tracers
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005