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Mid-water oceanic depths in coastal upwelling regions often contain oxygen deficient waters, called oxygen minimum zones (OMZs). These hypoxic ( 60 i M O2) conditions can have adverse effects on ecosystems, as many organisms cannot survive in low O2 conditions. This study investigated the OMZ in the topographically isolated Santa Monica Basin (SMB), California, a recipient of high nutrient input. The last survey of this area ~35 years ago, reported a pervious 350 year expansion of the SMB OMZ. In order to assess the OMZ since the last evaluation, sediment cores from 12 stations were retrieved by a multicorer from O2-ventilated (60 M O2) to near-anoxia (~4 M O2) regions along two depth-transects ranging from water depths between 71 and 907 m. The sediment porewater and supernatant water of the cores were analyzed for sulfate (SO42-), nitrate (NO3-), phosphate (PO43-), ammonium (NH4+), total sulfide, dissolved iron (Fe (II)), total alkalinity (TA) and bacterial sulfate reduction. The two deepest stations (907 and 893 meters, ~5 i M O2) exhibited down-core accumulation of NH4+ and TA, while also displaying enhanced rates of sulfate reduction close to the sediment surface; these patterns are all evidence of low oxygen conditions in the overlying water column. Shallower stations upslope (starting at 777 m water depth) featured increasing signs of bioturbation and bioirrigation effects in the geochemical profiles of NH4+, TA, PO43- and Fe (II). Low sulfate reduction rates (areal rates range from 0.13-0.86 mmol m-2 d-1) were detected at all stations. These results were compared with data separate from this thesis, including: 210Pb lamination analyses, the presence and activity of macrofauna at the seafloor, and iron speciation analyses. According to the stations sampled, we could not identify a definite spreading or reduction of the OMZ at the seafloor since the last survey of the SMB was done ~35 years ago.
This volume examines the deep sea ecosystem from a variety of perspectives. The initial chapters examine the deep-sea floor, the deep pelagic environment and the more specialised chemosynthetic environments of hydrothermal vents and cold seeps. These environments are examined from the perspective of the relationship of deep-sea animals to their physico-chemical environment. Later chapters examine the biogeography of the main deep oceans (Atlantic, Pacific and Indian) with particular attention to the downward flux of surface-derived organic matter and how this drives the processes within the deep-sea ecosystem. The peripheral deep seas including the polar seas and the marginal deep seas (inter alia the Mediterranean, Red, Caribbean and Okhotsk seas) are explored in the same context. The final chapters examine the processes occurring in the deep sea and include an analysis of why the deep sea has high species diversity, how the fauna respond to organic input and how species have adapted reproductive activity in the deep sea. The volume concludes with an analysis of the anthropogenic impact on the deep sea.
Compound-specific carbon isotopic (delta 13C and delta 14C) data are reported for lipid biomarkers isolated from Santa Monica Basin (SMB) and Santa Barbara Basin (SBB) surface sediments. These organic compounds represent phytoplanktonic, zooplanktonic, bacterial, archaeal, terrestrial, and fossil carbon sources. The lipids include long-chain n-alkanes, fatty acids (as FAMEs), n-alcohols, C(30) mid-chain ketols and diols, sterols, hopanols, and ether-linked C(40)-biphytanes of Archaca. The data show that the carbon source for most of the biomarkers is marine euphotic zone primary production or subsequent heterotrophic consumption of this biomass. Two lipid classes represent exceptions to this finding. Delta 14C values for the n-alkanes are consistent with mixed fossil and contemporary terrestrial plant sources. The archaeal isoprenoid data reflect chemoautotrophic growth below the euphotic zone. The biomarker class most clearly representing marine phytoplanktonic production is the sterols. It is suggested, therefore, that the sterols could serve as paleoceanographic tracers for surface-water DIC. The isotopic data are used to construct two algebraic models. The first calculates the contributions of fossil and modern vascular plant carbon to SMB n-alkanes. This model indicates that the delta 14C of the modern component is +235% (post-bomb) or 0% (pre-bomb). The second model uses these values to determine the origin of sedimentary TOC. The results are comparable to estimates based on other approaches and suggest that approx. 60% of SMB TOC is of marine origin, modern terrestrial and fossil sources contribute approx. 10% each, and the remaining approx. 20% is of unknown origin.
Provides an extraordinary case study of a classic marine petroleum system in the prolific oil basins of California. Based on results from the Cooperative Monterey Organic Chemistry Study, the volume examines paleoenvironmental conditions, organic-matter deposition, source-rock characteristics, thermal maturation, and oil generation in the Monterey Formation.
This book is a natural extension of the SCOPE (Scientific Committee of Problems on the Environment) volumes on the carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) biogeochemical cycles and their interactions (Likens, 1981; Bolin and Cook, 1983). Substantial progress in the knowledge of these cycles has been made since publication of those volumes. In particular, the nature and extent of biological and inorganic interactions between these cycles have been identified, positive and negative feedbacks recognized and the relationship between the cycles and global environmental change preliminarily elucidated. In March 1991, a NATO Advanced Research Workshop was held for one week in Melreux, Belgium to reexamine the biogeochemical cycles of C, N, P and S on a variety of time and space scales from a holistic point of view. This book is the result of that workshop. The biogeochemical cycles of C, N, P and S are intimately tied to each other through biological productivity and subsequently to problems of global environmental change. These problems may be the most challenging facing humanity in the 21 st century. In the broadest sense, "global change" encompasses both changes to the status of the large, globally connected atmospheric, oceanic and terrestrial environments (e. g. tropospheric temperature increase) and change occurring as the result of nearly simultaneous local changes in many regions of the world (e. g. eutrophication).