Biogeochemistry process rates

Fig. 5.2 Approaches of marine biogeochemistry. Top Geochemical methods based on solute and solid phase analyses and modelling. Left Experimental methods for the analyses of process rates. Bottom Identification, quantification and characterization of the microbial populations. Right High resolution and in situ methods for the analyses of microbial populations and their microenvironment. Graphics by Niels Birger Ramsing.

Although under chemolithoautotrophic growth conditions, cell densities of only 3-5 x 10 cells per milliliter were observed, the specific rate of Fe(III) reduced per cell unit was about 10 times faster than what had been published for any other Fe(lll) reducer. This strengthens the hypothesis that microbially mediated Fe(III) reduction by obligately anaerobic thermophiles could have been an important process on early Earth, when elevated temperatures were predominant (Baross 1998 Kashefi and Lovley 2000), which includes the involvement in the formation of specific Banded Iron Formations. In light of the properties of the above Fe(lll) reducers, the theories on the origin and biogeochemistry of Banded Iron Formations should be revisited. 

Our understanding of the biogeochemistry of nitrification has advanced greatly in the past two decades. The basic patterns of distributions and rates have been discovered and are largely understood in terms of the characteristics of the organisms believed to be responsible for the process and their interactions with other components of the ocean s physical and biological systems. Unpredictable surprise discoveries that change our view of the N cycle are hkely to appear, as they have done in recent years. Nevertheless, there are some avenues of future discovery that are more easily predictable on the basis of current research. 

The study of biogeochemistry involves the descriptions of the distribution of material throughout our system and the rates at which material moves from region to region. The organization of the book is divided into three major sections. The first section, consisting of Chapters 1-5, describes the processes and characteristics that are important in all parts of the system the mix of elements present on the Earth and processes important on a cosmological scale ... 

A diversity of approaches, of which only a few examples can be discussed here, is used in marine biogeochemistry (Fig. 5.2). Among the important goals is to quantify the rate at which biological and chemical processes take place in different depth zones of the sediment. These are often fast processes for which the reactants may have turnover times in the order of days or hours or even minutes. Data on dissolved species in the pore water and on solid-phase geochemistry can be used in diagenetic models to calculate such rates, as discussed in Chapter 3 (e.g. Schulz et al. 1994). The dynamic process is then derived from the... 

When properly formulated, the combination of ocean process tracers and numerical models provides powerful tools for studying ocean biogeochemistry. At their most basic level, models are simply a mathematical statement quantifying the rates of the essential physical and biogeochemical processes. For example, advection-diffusion models are structured around coupled sets of differential equations ... 

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