Oxygen Isotope Analyses From Guaymas Basin Sediment Trap Diatoms

The Guaymas Basin (GB, 27º53’N, 111º40’W), located in the central Gulf of California is an evaporative basin, with sea surface temperatures (SST) varying between ~30 ^o C during summer and ~15 ^o C during winter. Productivity is controlled primarily by seasonal upwelling that starts in the fall (early November) and extends into the spring. We are using a new microfluorination method (Menicucci et al., 2013) to analyze diatom samples for their oxygen isotopic composition from a GB sediment trap, that was moored at approximately 500m water depth, just above the anoxic zone. The trap collected samples every 2 weeks between 1990-98 as part of a long term program to study the relationship between sediment fluxes and climate forcing in the Gulf of California. Samples from 1996-1997 with the highest observed opal fluxes (fall through summer) have been processed and are currently being analyzed for diatom δ ¹⁸ O.

We will present diatom oxygen isotope data from a full year of samples, where sufficient material is available. Based on preliminary data, we hypothesize that the diatoms in the sedimentary record are heavily influenced by seasonal productivity differences at this location, and likely represent a record of water column variability that is biased towards the bloom periods. Variability through time is thought to be related to the timing of upwelling and seasonal temperature variability in the chlorophyll maximum. The required time to for sinking frustules to reach the seafloor is also thought to be a contributing factor, imparting a time-lag from time of death to sedimentation. δ ¹⁸ O data will be converted to temperature using existing calibrations and directly compare to previously published SST records.