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.

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.

Oceans account for 50% of the anthropogenic CO2 released into the atmosphere. During the past 15 years an international programme, the Joint Global Ocean Flux Study (JGOFS), has been studying the ocean carbon cycle to quantify and model the biological and physical processes whereby CO2 is pumped from the ocean's surface to the depths of the ocean, where it can remain for hundreds of years. This project is one of the largest multi-disciplinary studies of the oceans ever carried out and this book synthesises the results. It covers all aspects of the topic ranging from air-sea exchange with CO2, the role of physical mixing, the uptake of CO2 by marine algae, the fluxes of carbon and nitrogen through the marine food chain to the subsequent export of carbon to the depths of the ocean. Special emphasis is laid on predicting future climatic change.

This Volume belongs to a series on Oceanography. It is designed so that it can be read on its own, or used as a supplement in oceanogrphy courses. After a brief introduction to sea-floor sediments, the book shows how the activities of marine organisms cycle nutrients and other dissolved constituents within the oceans, and influence the rates at which both solid and dissolved material is removed to sediments. It goes on to review the carbonate system and shows how sediments that come from continental areas may be transported to the deep sea, explores what sea-floor sediments have taught us about the history of the oceans, and describes the biological and chemical processes that continue long after sediments have been deposited on the deep sea-floor. * Covers the basics on the occurrence, distribution, and cycling of chemical elements in the ocean * Features full-color photographs and beautiful illustrations throughout * Reader-friendly layout, writing, and graphics * Pedagogy includes chapter summaries, chapter questions with answers and comments at the end of the book; highlighted key terms; and boxed topics and explanations * Can be used alone, as a supplement, or in combination with other Open University titles in oceanography

Marine dissolved organic matter (DOM) is a complex mixture of molecules found throughout the world's oceans. It plays a key role in the export, distribution, and sequestration of carbon in the oceanic water column, posited to be a source of atmospheric climate regulation. Biogeochemistry of Marine Dissolved Organic Matter, Second Edition, focuses on the chemical constituents of DOM and its biogeochemical, biological, and ecological significance in the global ocean, and provides a single, unique source for the references, information, and informed judgments of the community of marine biogeochemists. Presented by some of the world's leading scientists, this revised edition reports on the major advances in this area and includes new chapters covering the role of DOM in ancient ocean carbon cycles, the long term stability of marine DOM, the biophysical dynamics of DOM, fluvial DOM qualities and fate, and the Mediterranean Sea. Biogeochemistry of Marine Dissolved Organic Matter, Second Edition, is an extremely useful resource that helps people interested in the largest pool of active carbon on the planet (DOC) get a firm grounding on the general paradigms and many of the relevant references on this topic. Features up-to-date knowledge of DOM, including five new chapters The only published work to synthesize recent research on dissolved organic carbon in the Mediterranean Sea Includes chapters that address inputs from freshwater terrestrial DOM

The Pacific Arctic region is experiencing rapid sea ice retreat, seawater warming, ocean acidification and biological response. Physical and biogeochemical modeling indicates the potential for step-function changes to the overall marine ecosystem. This synthesis book was coordinated within the Pacific Arctic Group, a network of international partners working in the Pacific Arctic. Chapter topics range from atmospheric and physical sciences to chemical processing and biological response to changing environmental conditions. Physical and biogeochemical modeling results highlight the need for data collection and interdisciplinary modeling activities to track and forecast the changing ecosystem of the Pacific Arctic with climate change.

Focuses on the ocean's role in the global biogeochemical cycling of selected elements and the impact of humans on the transport of these elements. Among the topics covered are the chemical composition of seawater from the perspectives of elemental speciation and the impact of solutes on water's physical behavior; biogeochemical phenomena which control accumulation and preservation of marine sediments; marine chemistry of radioactive and stable isotopes; seawater pollution. Contains many examples as well as steady-state models to aid readers in understanding this relatively young, growing and complex science.