In the biogeochemical dynamics of marine ecosystems, silicon is a major element whose role has, for a long time, been underestimated. It is however indispensable to the activity of several biomineralizing marine organisms, some of which play an essential role in the biological pump of oceanic carbon. This book presents notions indispensable to the knowledge on the silicon biogeochemical cycle in ocean systems, first of all describing the main quantitative analysis techniques and examination of the major organisms involved in the cycle. The author then moves on to study the most up-to-date processes to control the use of silicon and its regeneration in natural conditions, before mentioning the central role played by this original element in the control of all the biogeochemical cycles in the global ocean. The available information finally enables the global biogeochemical budget of silicon in the marine environment to be quantified.

Diatoms are a ubiquitous group of plankton responsible for 20-40% of oceanic primary production, and a higher fraction of organic matter export to the ocean interior. Diatoms actively transport dissolved inorganic silicon into their cells, and through the process of silicification (i.e. biogenic silica production) they build tough and intricate shells, known as frustules. With a global distribution and the ability to persist in high numerical abundances, diatoms dominate the biological cycling of Si in the oceans. The biogeochemical cycling of Si has been well studied in the coastal ocean, specifically in upwelling regions where diatoms are generally the dominant phytoplankton group. However, much less is known about the role diatoms play in the open ocean; which comprises the vast majority of the oceanic surface area. Outside of the Southern Ocean, only 11 studies (prior to 2003) directly examined surface-water Si biogeochemistry in the open ocean. Current knowledge about Si biogeochemistry in the open ocean suffers from what can only be described as gross under-sampling. This dissertation reports on the surface-water Si biogeochemistry in two open-ocean regions: the northwestern Sargasso Sea and the eastern equatorial Pacific. The three research chapters are linked by the examination of spatial or temporal variability in surface-water Si biogeochemistry. Chapters 2 and 4 examine scales of temporal variability in Si biogeochemistry in the Sargasso Sea. The results demonstrate that biogenic silica concentrations, and presumably Si biogeochemical processes, vary on daily, seasonal, multi-year (e.g. ~3-4 years), and decadal time scales. In Chapter 3 data were gathered over a ~2.6x106 km2 area (i.e. larger than the Bering Sea) in the equatorial Pacific. Within that area biogenic silica production showed little spatial or temporal variability. Additionally, the estimated contribution to new production (productivity supporting the export of organic matter to the ocean interior) by diatoms in this region was 4-10 times higher than the diatom contribution to total autotrophic biomass.

Biological processes in the oceans play a crucial role in regulating the fluxes of many important elements such as carbon, nitrogen, sulfur, oxygen, phosphorus, and silicon. As we come to the end of the 20th century, oceanographers have increasingly focussed on how these elements are cycled within the ocean, the interdependencies of these cycles, and the effect of the cycle on the composition of the earth's atmosphere and climate. Many techniques and tools have been developed or adapted over the past decade to help in this effort. These include satellite sensors of upper ocean phytoplankton distributions, flow cytometry, molecular biological probes, sophisticated moored and shipboard instrumentation, and vastly increased numerical modeling capabilities. This volume is the result of the 37th Brookhaven Symposium in Biology, in which a wide spectrum of oceanographers, chemists, biologists, and modelers discussed the progress in understanding the role of primary producers in biogeochemical cycles. The symposium is dedicated to Dr. Richard W. Eppley, an intellectual giant in biological oceanography, who inspired a generation of scientists to delve into problems of understanding biogeochemical cycles in the sea. We gratefully acknowledge support from the U.S. Department of Energy, the National Aeronautics and Space Administration, the National Science Foundation, the National Oceanic and Atmospheric Administration, the Electric Power Research Institute, and the Environmental Protection Agency. Special thanks to Claire Lamberti for her help in producing this volume.

Polar Oceanography is an integrated synthesis of the biological, physical, geological, and chemical processes that occur in the polar oceans. The book represents the first modern interdisciplinary synthesis of this field.

This is the second issue of the Research Topic: Biogeochemistry and Genomics of Silicification and Silicifiers. The first issue article collection can be found here: https://www.frontiersin.org/research-topics/5364/biogeochemistry-and-genomics-of-silicification-and-silicifiers Silicifiers are among the most important living organisms of planet Earth. They are able to take advantage of the abundance of silicon in the Earth crust to build silicified architectures, which in particular can help for protection against predators or for facilitating the penetration of light and nutrients to the cells.