Diatoms in northeast Pacific surface sediments as paleoceanographic proxies

Fossil diatom total abundances (# valves/g) in 54 surface-sediment samples from the northeast (NE) Pacific Ocean reflect the position of high primary production associated with coastal upwelling and that possible biases associated with dilution or dissolution are small. Diatom species assemblages, defined by Q-mode factor analysis in 30 samples with abundant diatoms, are related to modern oceanographic properties. Five statistical assemblages, given by five specific diatom species and/or groups, are related to upwelling (Chaetoceros spores), subtropical (Thalassionema nitzschioides), subarctic (Rhizosolenia hebetata), transitional (Neodenticula seminae) and freshwater (freshwater diatoms) ecological environments. These factors are significantly correlated with primary productivity, temperature, nutrient concentrations and salinity, although the strongest relationship is that between diatom assemblages and productivity. However, it is not possible to distinguish between coastal and open-ocean (curl-driven) upwelling based on Chaetoceros spores relative percentages by themselves or on the floral factors.