text: The silicon cycle has gained increasingly in scientific attention the past decade for several reasons:
  Firstly, the modern marine silica cycle is widely believed to be dominated by diatoms for the fixation and export of particulate matter (including organic carbon), from the euphotic zone to the deep ocean, via a process known as the biological pump.  As a result, diatoms, and other silica-secreting organisms, play a crucial role in the global carbon cycle, and have the ability to affect atmospheric CO concentrations on a variety of time scales, by sequestering CO in the ocean. This connection between biogenic silica and organic carbon, together with the significantly higher preservation potential of biogenic siliceous compounds, compared to organic carbon, makes opal accumulation records very interesting for paleoceanography and paleoclimatology.
  Secondly, biogenic silica accumulation on the sea floor contains lot of information about where in the ocean export production has occurred on time scales ranging from hundreds to millions of years. For this reason, opal deposition records provide valuable information regarding large-scale oceanographic reorganizations in the geological past, as well as paleoproductivity.
  Thirdly, the mean oceanic residence time for silicate is approximately 10,000–15,000 yr. This relative short residence time, makes oceanic silicate concentrations and fluxes sensitive to glacial/interglacial perturbations, and thus an excellent proxy for evaluating climate changes.
  Increasingly, isotope ratios of oxygen (O:O) and silicon (Si:Si) are analysed from biogenic silica preserved in lake and marine sediments to derive records of past climate change and nutrient cycling (De La Rocha, 2006; Leng and Barker, 2006). This is a particularly valuable approach considering the role of diatoms in global carbon cycling. In addition, isotope analyses from BSi are useful for tracing past climate changes in regions such as in the Southern Ocean, where few biogenic carbonates are preserved.