Measuring the Production of Marine

Strickland, J. D. H., 1960. Measuring the production of marine phytoplankton. Bulletin ofthe Fisheries Research Board of Canada, 122, 1-172. 

The subject of marine photosynthesis and its measurement is becoming highly complicated and cannot be discussed in any detail in the present manual. The topic has been reviewed fully by Strickland (Measuring the Production of Marine Phytoplankton, Bull. Fish. Res. Bd. Canada, No. 122, 1960) or, more recently, the chapter by Strickland (Riley and Skirrow [ed.] Chemical Oceanography, Academic Press, 1965) and the review of Eppley and Strickland (M. Droop [ed.] Advances in Microbiology of the Sea, Vol. I, Academic Press, 1968). 

In a benchmark study, Olson (1981a) used improved N tracer methods to measure the production of N02, independently from NOs and NH4, as weU as the simultaneous uptake of NOs and NH4+ in a variety of marine habitats. He found... 

The geochemistry of marine sediments is a major source of information about the past environment. Of the many measurements that provide such information, those of the U-series nuclides are unusual in that they inform us about the rate and timescales of processes. Oceanic processes such as sedimentation, productivity, and circulation, typically occur on timescales too short to be assessed using parent-daughter isotope systems such as Rb-Sr or Sm-Nd. So the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides (principally or the U-series nuclides. This makes the U-series nuclides powerful allies in the quest to understand the past ocean-climate system and has led to their widespread application over the last decade. 

Enzyme Decay. Moffett and Zafiriou (I) differentiated catalase- and peroxidase-mediated decay in coastal (marine) waters by using lsO-labeled H202 and 02, and by determining the labeled end products. Equation 13 shows that the products of catalase decomposition are H20 and 02. In contrast, peroxidase decomposition results in the formation of H20 without 02. From the measurement of the relative amount of labeled products it is possible to determine the contribution of both enzymes in the decay of the H202. In the coastal water, 65-80% of the decomposition was attributed to catalase and the rest to peroxidase (I). These studies are the first to use this technique. The approach should be extended to freshwater ecosystems to see if the same pattern would be found. 

Reduced Sulfur Compounds in Marine Sediments. To determine the applicability of the bimane-HPLC technique to measure reduced sulfur compounds in sediment porewater samples, we compared the results of the methylene blue method of Cline (26). the DTNB procedure of Ellman (28) and the bimane-HPLC procedure outlined above. Cores included came from a Spartina foliosa marsh in Mission Bay (near San Diego, California), and an evaporation pond for the production of salt in south San Diego Bay (Table I). 

Figure 1. Transformations in the ocean and overlying atmosphere which lead to the production of sulfate from a marine biogenic source (dark arrows). DMS is produced in the ocean after the uptake of seawater sulfate by phytoplankton and the production and breakdown of DMSP. Sulfate formation occurs after DMS is transferred across the sea-air interface and undergoes atmospheric oxidation. The S S values for the individual sulfur pools are indicated in the boxes and measured or estimated discriminations (D) are indicated above the arrows. Clearly, data for the remote atmosphere are limited.

Specifically we wished to measure the rate of reaction of OH with MSA to enable modelling calculations of the stability of MSA in aerosol droplets. The one reported measurement of this rate (2), using pulse radiolysis techniques, 3.2 x 109 M 1 s 1, is fast enough to suggest that this reaction pathway could be an important sink for MSA. This is of interest in explaining an apparent discrepancy that exists between laboratory and field studies of tne oxidation of dimethyl sulfide. Although a number of laboratory studies (6-9 ) show that MSA is the major stable product, and SO2 a minor one, field observation suggest MSA is only a minor (10%) fraction (2) of total non-sea-salt sulfur in marine aerosols. Two possible rationalizations of this are that i) MSA is subject to further reaction in marine aerosols and ii) other reaction pathways of dimethyl sulfide, or perhaps other non-methylated sulfur compounds should be considered. 

Also at issue is the preservation of marine biodiversity that relates, in turn, to chemical diversity. As stated previously, discoveries to date reflect a small percentage of the resources available. Measures must be taken to ensure sustainable use of these resources. Alternative renewable sources need to be identified to supply pharmacological evaluation. Due to the critical nature of this aspect of marine natural products drug discovery, several alternative approaches are discussed in detail. 

Recent advances in chemoinformatics have greatly enhanced the utility of these resources and many are now accessible via the Internet.28 CHEMnet-BASE (www.chemnetbase.com) provides online access to a variety of databases including the Dictionary of Natural Products and the Dictionary of Marine Natural Products, although full access through CHEMnetBASE requires a subscription. The Chemical Structure Lookup Service (http //cactus.nci.-nih.gov/lookup) is an open access database and incorporates information from more than 80 databases on over 27 million structures. PubChem (http //pub-chem.ncbi.nlm.nih.gov/) is another open access database that also links bioassay data to each structure. Measures such as the US National Institutes of Health (NIH) Public Access Policy Mandate should increase the amount of openly accessible information available on the Internet and facilitate dissemination of information. 

The numerator of the right side is the product of measured total concentrations of calcium and carbonate in the water—the ion concentration product (ICP). If n = 1 then the system is in equilibrium and should be stable. If O > 1, the waters are supersaturated, and the laws of thermodynamics would predict that the mineral should precipitate removing ions from solution until n returned to one. If O < 1, the waters are undersaturated and the solid CaCOa should dissolve until the solution concentrations increase to the point where 0=1. In practice it has been observed that CaCOa precipitation from supersaturated waters is rare probably because of the presence of the high concentrations of magnesium in seawater blocks nucleation sites on the surface of the mineral (e.g., Morse and Arvidson, 2002). Supersaturated conditions thus tend to persist. Dissolution of CaCOa, however, does occur when O < 1 and the rate is readily measurable in laboratory experiments and inferred from pore-water studies of marine sediments. Since calcium concentrations are nearly conservative in the ocean, varying by only a few percent, it is the apparent solubility product, and the carbonate ion concentration that largely determine the saturation state of the carbonate minerals. 

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