Abstract
Measurements of diatom oxygen isotopes ( δ 18O diatom) hold the potential to provide an important additional source of palaeoceanographic information in regions depleted in carbonates. However, despite analyses of δ 18O diatom being carried out since the 1970s and the increasingly widespread use of δ 18O diatom in palaeolimnology since the 1990s, to date only a handful of studies have applied δ 18O diatom in marine reconstructions. Here the historical development and current state of affairs concerning the usage of δ 18O diatom in palaeoceanography is reviewed. This includes a summary of: 1. sample purification and analytical techniques for δ 18O diatom; 2. existing palaeoceanographic reconstructions with an emphasis on sites at which both diatoms and foraminifera have been analysed for δ 18O; 3. uncertainties associated with δ 18O diatom including the presence of isotope vital effects and secondary isotope exchanges; 4. a review of the current and future developments required to improve the reliability of δ 18O diatom based reconstructions in palaeoceanography.
Highlights
One of the most widely used palaeoceanographic techniques is the oxygen isotope analysis of foraminifera (δ18Oforam), a CaCO3 organism which fractionates oxygen either in equilibrium with the ambient seawater or with a known vital effect which can be quantitatively accounted for (e.g., Emiliani, 1955; Lisiecki and Raymo, 2007)
As increasing numbers of laboratories set up facilities to analyse δ18Odiatom, we hope that this review will re-focus attention on the potential that exists in using δ18Odiatom in palaeoceanography
At present it remains unknown to what extent these processes may alter the analysed δ18O within the -Si-O-Si layer, it would be expected that the chemical and biological dissolution of diatom frustules, in alkaline waters, would alter δ18Odiatom. Such an assumption is reinforced by a limited number of laboratory dissolution experiments carried out by Moschen et al (2006) who observed isotope deviations of up to 7‰ following the removal of the protective organic matter coating around the frustule
Summary
One of the most widely used palaeoceanographic techniques is the oxygen isotope analysis of foraminifera (δ18Oforam), a CaCO3 organism which fractionates oxygen either in equilibrium with the ambient seawater or with a known vital effect which can be quantitatively accounted for (e.g., Emiliani, 1955; Lisiecki and Raymo, 2007). Recent years have witnessed considerable advancements in the development of techniques for analysing stable isotopes in biogenic silica, including δ13C, δ15N and δ30Si as well as δ18O (e.g., De La Rocha, 2002; Robinson et al, 2004; Lücke et al, 2005; Leng and Sloane, 2008) The majority of δ18O work, has focused on diatoms (δ18Odiatom). This is due to the δ18O of other siliceous organisms being considerably less well understood. As increasing numbers of laboratories set up facilities to analyse δ18Odiatom, we hope that this review will re-focus attention on the potential that exists in using δ18Odiatom in palaeoceanography
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