The silica cycle is intimately linked to the carbon cycle and thus has a profound impact on climate (past, modern and future). Siliceous microorganisms produced in the water column as well as microfossils preserved in underlying sediments have been intensely used in the last two decades to document variations in the trophic web, the dynamics of the silica cycle, but also paleoclimatic changes. We propose here an interdisciplinary session (1) to bring together a range of presentations covering the use of biogenic silica (opal) and silica-producing organisms for the reconstruction of environmental and climatic conditions from both, freshwater and marine systems, and (2) to discuss recent advances and challenges of opal-based
proxies. This session aims to bring together the diverse and sometimes disparate scientific communities involved including chemical and biological oceanographers,ecologists, taxonomists, micropaleontologists and paleoclimatologists.

Session themes will focus on a range of issues including (i) technological advances in biogenic silica research, (ii) (paleo)production of siliceous organisms, including aspects of biomineralization and genetics; (iii) mechanisms and controls of Si export including opal deposition modelling, (iv) factors controlling preservation and burial of Si, (v) variations of productivity, meltwater pulses, sea-ice coverage, temperature, salinity, pH, and nutrient utilization on all timescales and (vi) major geological and evolutionary changes in the silica cycle and its components Contributions are welcome from one or more of the above themes.

Keynotes:

- Olivier Ragueneau (Institut Universitaire Européen de la Mer, Plouzane, France).

- Damien Cardinal (Department of Geology, Royal Museum for Central Africa, Tervuren, Belgium).

- Gerhard Fischer (Department of Geology, Faculty of Geosciences and MARUM, University of Bremen, Bremen, Germany)

- David Harwood (ANDRILL, Antarctic Geological Drilling, USA)

- John Rogers (Dept of Earth and Marine Sciences, The Australian National University, Canberra, Australia)