Measurement Of Diatom Oxygen Isotopes From The Guaymas Basin Using A Sediment Trap Time Series

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Carbonate fossils are found abundantly in marine sediments throughout the world. However, there are a number of regions such as high latitude areas, coastal upwelling zones and the deep ocean below the CCD, where carbonates are poorly preserved or absent. The dominant microfossils found in these regions are typically from plankton that secrete biogenic opal, such as diatoms. Traditional methods for measuring the δ18O of biogenic opal are difficult and hazardous in comparison to measurements of carbonate minerals. This difficulty has resulted in a paucity of published diatom oxygen isotope data. We have developed a new microfluorination technique (Menicucci et al., 2013) that permits rapid analyses of diatom oxygen isotopes using easily accessible continuous flow IRMS systems. Utilizing this technique we have analyzed a set of sediment trap diatom samples collected in the Guaymas Basin (GB, 27o53’N, 111o40’W), Gulf of California. The GB sediment time series is moored at approximately 500m water depth. Samples analyzed were collected in the late fall/early winter (1993, 1994, and 1996). Diatom δ18O ranged between 35 and 36.2‰ (VSMOW) (n=7). Measured δ18O was converted to water column temperature yielding temperatures with the relationship by Labeyrie (1974) between 22-27oC. Five of these samples yielding a narrow temperature range between 25-27oC. Our data suggest the diatom δ18O data does not track sea surface temperatures through the year, but instead are representative of mixed later temperatures during diatom bloom conditions (i.e. peak opal flux, occurring in mid November). These data may indicate diatom opal collected from the GB experienced slow decent through the pycnocline prior to collection sedimentation on the basin floor. Therefore diatom opal δ18O at this location appears to have a seasonally bias. Refs: Menicucci, A.J., Matthews, J., and Spero, H.J., 2013, Oxygen Isotope Analyses of Biogenic Opal and Quartz Using a Novel Microfluorination Technique. Rapid Communications in Mass Spectrometry. v. 27. p. 1873-1881. Labeyrie, L.D., 1974, New approach to surface seawater palaeotemperatures using 18O/16O ratios in silica of diatom frustules. Nature. v. 248. p. 40-42.

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Presented at the 2013 AGU Fall Meeting in San Francisco, CA