Environment shallow water

For example, the many deepwater fields located in the Gulf of Mexico are of Tertiary age and are comprised of complex sand bodies which were deposited in a deepwater turbidite sequence. The BP Prudhoe Bay sandstone reservoir in Alaska is of Triassic/ Cretaceous age and was deposited by a large shallow water fluvial-alluvial fan delta system. The Saudi Arabian Ghawar limestone reservoir is of Jurassic age and was deposited in a warm, shallow marine sea. Although these reservoirs were deposited in very different depositional environments they all contain producible accumulations of hydrocarbons, though the fraction of recoverable oil varies. In fact, these three fields are some of the largest in the world, containing over 12 billion barrels of oil each ... 

STROMATOLITE. A term that has been generally applied to variously shaped (often domal), laminated, calcareous sedimentary structures formed in a shallow-water environment under the influence of a mat or assemblage of sediment-binding blue-green algae that trap fine (silty) detritus and precipitate calcium carbonate and that commonly develop colonies or irregular accumulations of a constant shape, but with little or no... 

Our ability to predict changes in the biogeochemistry of estuaries and lagoons, as well as other shallow water organic-rich environments, is tied to our ability to quantitatively model the dynamics of microbially-mediated energetic changes closely associated with degradation processes and their chemical end products. 

The protobranch mollusc, Solemya reidi, is a shallow water bivalve which lives in very high sulfide environments and maintains an autotrophic mode of nutrition via symbiotic sulfur oxidizing bacteria located in the gills (5Q). It can... 

Several types of anoxic environment harbor H2S along the periphery of the bulk ocean, but in order to exist in oxic waters more than a few hours of mixing removed from these isolated localities, the sulfides must be kinetically supported. They have generally been ignored in the open sea, because no internal sources nave been known for them. In an early paper on trace metals, for example, Krauskopf (21 restricted metal sulfide interactions to anoxic basins. Ostlund and Alexander (2) later determined an oxidation lifetime of about half an hour in Or saturated seawater, and noted that sulfide generated in sediments was expected to reach the atmosphere only from very shallow waters (< a few meters). With no sources between the sea bottom and surface, the sulfides were presumed absent from most of the sea. This sentiment is echoed almost to the present (1). 

At this stage in the development of the subject of the geochemistry of sedimentary carbonates, we have dealt primarily with the mineralogy and basic physical chemistry of the carbon system and some of its important phases. In the following chapters, this information and additional data and interpretations are utilized to explain the behavior of sedimentary carbonates in shallow water and deep marine environments, and during early and late diagenesis. The... 

It is convenient to divide the deposition of carbonates in marine sediments into those being deposited in shallow (shoal) water (water depths of a few hundred meters or less) and those being deposited in deep sea sediments, where the water depth is on the order of kilometers. The primary reasons for this division are the differing sources, dominant mineralogies, and accumulation processes operative in these environments. Shoal water carbonates are the topic of Chapter 5. Naturally, there are "grey" areas of intermediate characteristics between these two extremes, such as continental slopes and the flanks of carbonate banks and atolls. 

In this chapter and the following, shoal-water ("shallow-water") carbonate sediments, and the seawaters they form from, are examined. Emphasis is on the biogeochemical processes affecting carbonate materials in this global marine environment, not on the general sedimentology of shoal-water carbonate deposits. The latter subject is discussed in innumerable publications such as "Carbonate Depositional Environments" (Scholle et al., 1983), to which the reader is referred. 

This sulfate reduction reaction in anoxic carbonate sediments has potential importance for carbonate dissolution in shallow-water, marine environments, but its global significance remains a question. An observation of interest is that even complete sulfate reduction returns the saturation state of the water to only about half its original value. Thus the sulfate reduction reaction by itself may not promote carbonate precipitation and partial sulfate reduction may result in carbonate dissolution. 

Thus, processes leading to their chemical stabilization resemble those occurring in both the shallow-water and the deep-sea environment. 

Sulfate reduction is the terminal microbial process in anaerobic sediments, when S042- is not limiting, leading to the formation hydrogen sulfide (H2S). This process has been shown to be particularly important in the cycling of S and C chemistry of highly productive shallow-water subtidal and salt marsh environments. 

In the marine environment, cyanobacteria are emerging as contributors to HABs, especially in tropical environments however, their impact is likely more pronounced on the ecological structure of shallow-water reef systems than on human populations. But in some locations, such as the East Coast of Australia, extensive blooms of Lyngbya majuscula, which produce the hepatotoxic lyngbyatoxins, have influenced human health. Nevertheless, some populations of this same species from elsewhere in the world do produce neurotoxic natural products, as reviewed in the latter part of... 

Nakata, H., Kannan, K., Nasu, T., Cho, H.-S., Sinclair, E., Takemura, A. Perfluorinated contaminants in sediments and aquatic organisms collected from shallow water and tidal flat areas of the Ariake Sea. Japan environmental fate of perfluorooctane sulfonate in aquatic ecosystems. Environ. Sci. TechnoL, 40 4916 921 (2006). 

The development of a convenient field assay for N2 fixation in the late 1960s (Stewart et al, 1967 Hardy et al, 1968) which was rapidly adapted for marine studies (see Capone 1983, 1993), led to a flurry of field efforts in a range of open ocean and shallow water and benthic marine environments. We wiU first summarize some of the recent advances and insights relative to N2 fixation in benthic marine environments, move on to the water column, summarize the controls on N2 fixation and comment on the broader, biogeochemical impacts of N2 fixation. 

In benthic environments, ranging from the rhizosphere of shallow water macrophyte communities such as Zostera, Thalassia and Spartim hundreds of different diazotrophic strains have been isolated, and these are typically microaerophyUic or anaerobic, and often are sulfate respiring bacteria. These diazotrophs make significant contributions to the nitrogen economy of their respective plant communities. 

A wide range of groundwater chemistry has been recorded in crystalline rock environments. Shallow groundwaters (usually <200 m) are dominantly Ca-Na-HCOa formed by the interaction of atmospherically recharged meteoric water with the soil and shallow bedrock. These waters are fresh with dilute dissolved loads and young, as indicated by the presence of tritium. Occasionally, saline intrusions from adjacent seawater bodies or upwelhng of deeper saline fluids can influence the chemistry of shallow groundwaters. 

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