Isotope offsets in marine diatom δ¹⁸O over the last 200 ka

Abstract

Previous work has suggested that a species effect may be present in diatom oxygen isotope ratios ( δ 18 Odiatom).While predominantly attributed to be a size related species effect, currently the precise mechanism remains unknown. Here, two size fractions of diatoms (38-75 μm and >100 μm) covering the last 200 ka are analysed for δ 18 O from ODP Site 882 in the North West Pacific Ocean. Synchronous variations of up to 13‰ occur in both size fractions. However, large isotope offsets (mean = 2.02‰) exist between the two fractions with no relationship between their magnitude and the overlying palaeoenvironmental conditions. In contrast to earlier work from the same site, no one size fraction is constantly higher or lower in δ 18 O relative to the other. As such, the dominant mechanism is most likely separate to the size effect previously detected. In addition, no relationship exists between the magnitude of the offsets and the species composition of the two size fractions. The presence of these isotope offsets imposes significant constraints upon the future use of δ 18 Odiatom in palaeoceanographic reconstructions and reiterates the need to extract and analyse only species and size specific diatom samples.

Oxygen isotope composition of diatoms as Late Holocene climate proxy at Two-Yurts Lake, Central Kamchatka, Russia

“…Although Swann et al (2007Swann et al ( , 2008 found a small vital effect (isotopic-species effect) in diatom oxygen isotopic composition, studies on both marine (Shemesh et al, 1995) and freshwater diatoms (Shemesh and Peteet, 1998;Rosqvist et al, 1999;Shemesh et al, 2001;Chapligin et al, 2012b), established that vital effects do not influence the isotopic composition of diatoms. As the Two-Yurts Lake contains predominantly two main diatom species (A. subarctica and S. minutulus) in the N10 μm fraction, which are consistently present throughout the core, we assume that δ…”

A 250 ka oxygen isotope record from diatoms at Lake El'gygytgyn, far east Russian Arctic

“…The diatom assemblage in the < 10 µm fraction of 40 purified samples equally distributed throughout the core was assessed by counting under light microscope (LM) , based on Morley et al, 2004, and Swann et al, 2008. Five random fields of view were selected along a transect in the middle of the slide and at least 200 valves as well as fragments were counted whenever possible.…”

“…Thus, % cont. was calculated by dividing the sample percentage of Al 2 O 3 by the Al 2 O 3 percentage from a 100 % contamination end member according to Brewer et al (2008), Swann and Leng (2008) and Mackay et al (2011). tested different contamination assessment techniques to Lake El'gygytgyn sub-surface samples and found no significant difference between this method and calculating % cont.…”

Reconstructing past atmospheric circulation changes using oxygen isotopes in lake sediments from Sweden

“…Bigler et al, 2003). Speciesspecific (vital effects) and size related differences in the oxygen isotope fractionation may exist within the δ 18 O diatom, as have been reported from marine cores (Swann et al, 2007(Swann et al, , 2008. There is currently no evidence that changes in species composition would influence δ 18 O diatom signal in lake sediments (Shemesh et al, 2001;Jones et al, 2004;Schiff et al, 2009).…”