A record of diatom preservation from the AND-1B drillcore: The significance of taphofacies on diatom preservation

Abstract

Abstract The processes affecting diatom dissolution and upper water column silica recycling are understood in modern environments. However, few studies have been undertaken to understand which processes have the greatest impact on diatom preservation in sedimentary archives. Furthermore, variability in diatom dissolution in the upper water column of past oceans is rarely quantified. Here we present a record of diatom dissolution, a proxy for upper water column silica recycling, from the Pliocene of the Ross Sea. Dissolution was quantified utilizing diatoms from the AND-1B core. These data were related to previously published diatom proxies of sea surface conditions. Diatoms were found to be better preserved in intervals dominated by sea ice diatoms than intervals dominated by cosmopolitan open ocean diatoms. However, preservation was not constant in the interval dominated by cosmopolitan diatoms, implying another taphonomic control. An antiphase relationship was found between diatom-inferred water temperature and dissolution; dissolution is less during cold intervals. A weaker positive correlation was found between diatom accumulation and preservation; dissolution is lower during periods of high diatom accumulation. The relationship between diatom accumulation and preservation reflects pore water saturation; individual diatoms contributes less silica to pore water saturation. However, increased growth rate is expected to result in thinner frustules and increased dissolution. These two opposing factors explain the weakness of the observed correlation. Interestingly, these results are different from those found in other Southern Ocean sediment cores. Comparative analysis highlights the importance of taphofacies on diatom preservation in understanding diatom dissolution data.