A fluorometric method is described which provides sensitive measurements of extracted chlorophyll a free from the errors associated with conventional acidification techniques. Fluorometric optical configurations were optimized to produce maximum sensitivity to Chl a while maintaining desensitized responses from both Chl b and pheopigments. Under the most extreme Chl b:Chl a ratio likely to occur in nature (1 : 1 molar), the new method results in only a 10% overestimate of the true Chl a value, while estimates from older acidification methods are 2.5-fold low. Under conditions of high pheopigment concentrations (pheo a: Chl a = 1 : 1 molar), the new method provides Chl a estimates that are equivalent to those determined from the acidification technique. The new simple method requires a single fluorescence determination and provides adequate sensitivity for small sample sizes (<200 ml) even in the most oligotrophic marine and freshwater environments.

https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1994.39.8.1985

Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments

Methane is the most abundant organic chemical in Earth's atmosphere, and its concentration is increasing with time, as a variety of independent measurements have shown. Photochemical reactions oxidize methane in the atmosphere; through these reactions, methane exerts strong influence over the chemistry of the troposphere and the stratosphere and many species including ozone, hydroxyl radicals, and carbon monoxide. Also, through its infrared absorption spectrum, methane is an important greenhouse gas in the climate system. We describe and enumerate key roles and reactions. Then we focus on two kinds of methane production: microbial and thermogenic. Microbial methanogenesis is described, and key organisms and substrates are identified along with their properties and habitats. Microbial methane oxidation limits the release of methane from certain methanogenic areas. Both aerobic and anaerobic oxidation are described here along with methods to measure rates of methane production and oxidation experimentally. Indicators of the origin of methane, including C and H isotopes, are reviewed. We identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time. From these constraints and other data on sources and sinks we construct a list of sources and sinks, identities, and sizes. The quasi-steady state (defined in the text) annual source (or sink) totals about 310(±60) × 1012 mol (500(±95) × 1012 g), but there are many remaining uncertainties in source and sink sizes and several types of data that could lead to stronger constraints and revised estimates in the future. It is particularly difficult to identify enough sources of radiocarbon-free methane.

/pdf/biogeochemical-aspects-of-atmospheric-methane-1j0pgr75la.pdf

Biogeochemical aspects of atmospheric methane

An estimate of global net primary production in the ocean has been computed from the monthly mean near-surface chlorophyll fields for 1979-1986 obtained by the Nimbus 7 CZCS radiometer. Our model required information about the subsurface distribution of chlorophyll, the parameters of the photosynthesis-light relationship, the sun angle and cloudiness. The computations were partitioned among 57 biogeochemical provinces that were specified from regional oceanography and by examination of the chlorophyll fields. Making different assumptions about the overestimation of chlorophyll by the CZCS in turbid coastal areas, the global net primary production from phytoplankton is given as 45-50 Gt C year"1. This may be compared with current published estimates for land plants of 45-68 Gt C year"' and for coastal vegetation of 1.9 Gt C year"1.

An estimate of global primary production in the ocean from satellite radiometer data

This review shows that thermodynamic and kinetic constraints largely prevent large-scale methanogenesis in the open ocean water column. One example of open-ocean methanogenesis involves anoxic digestive tracts and fecal pellet microenvironments; methane released during fecal pellet disaggregation results in the mixed-layer methane maximum. However, the bulk of the methane in the ocean is added by coastal runoff, seeps, hydrothermal vents, decomposing hydrates, and mud volcanoes. Since methane is present in the open ocean at nanomolar concentrations, and since the flux to the atmosphere is small, the ultimate fate of ocean methane additions must be oxidation within the ocean. As indicated in the Introduction and highlighted in Table 3, sources of methane to the ocean water column are poorly quantified. There are only a small number of direct water column methane oxidation rates, so sinks are also poorly quantified. We know that methane oxidation rates are sensitive to ambient methane concentrations, but we have no information on reaction kinetics and only one report of the effect of pressure on methane oxidation. Our perspective on methane sources and the extent of methane oxidation has been changed dramatically by new techniques involving gene probes, determination of isotopically depleted biomarkers, and recent 14C-CH4 measurements showing that methane geochemistry in anoxic basins is dominated by seeps providing fossil methane. The role of anaerobic oxidation of methane has changed from a controversial curiosity to a major sink in anoxic basins and sediments. © 2007 American Chemical Society.

/pdf/oceanic-methane-biogeochemistry-12rf80pqzx.pdf

Oceanic methane biogeochemistry.

CHEMTAX - a program for estimating class abundances from chemical markers: application to HPLC measurements of phytoplankton

Estimates of the in vivo specific absorption coefficients (m2 mg'; 400-750 nm, 2 nm intervals) for the major algal pigment groups (chlorophylls, carotenoids and phycobilins) are presented. "Unpackaged" absorption coefficients were initially obtained by measuring the absorption properties of pure pigment standards spectrophotometrically and "shifting" their absorption maxima to match in vivo positions. Two approaches for estimating the phytoplankton absorption coefficient (spectral reconstruction and spectral decomposition) are compared by linear regression analysis, incorporating concurrent measurements of particulate absorption and pigmentation performed in the Sargasso Sea. Results suggest that "pigment package" effects are minimal for natural assemblages of open-oceanic phytoplankton and that accessory pigments do not always co-vary with chlorophyll a over depth and time.

In-vivo absorption properties of algal pigments

An undescribed mussel (family Mytilidae), which lives in the vicinity of hydrocarbon seeps in the Gulf of Mexico, consumes methane (the principal component of natural gas) at a high rate. The methane consumption is limited to the gills of these animals and is apparently due to the abundant intracellular bacteria found there. This demonstrates a methane-based symbiosis between an animal and intracellular bacteria. Methane consumption is dependent on the availability of oxygen and is inhibited by acetylene. The consumption of methane by these mussels is associated with a dramatic increase in oxygen consumption and carbon dioxide production. As the methane consumption of the bivalve can exceed its carbon dioxide production, the symbiosis may be able to entirely satisfy its carbon needs from methane uptake. The very light (delta(13)C = -51 to -57 per mil) stable carbon isotope ratios found in this animal support methane (delta(13)C = -45 per mil at this site) as the primary carbon source for both the mussels and their symbionts.

http://science.sciencemag.org/content/sci/233/4770/1306.full.pdf

A methanotrophic marine molluscan (bivalvia, mytilidae) symbiosis: mussels fueled by gas.

Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme assays, elemental sulfur analysis, and carbon dioxide fixation studies demonstrate that vestimentiferan tube worms and three clam species contain intracellular, autotrophic sulfur bacterial symbionts. Carbon isotopic ratios of 246 individual animal tissues were used to differentiate heterotrophic (8(13)C = -14 to -20 per mil), sulfur-based (8(13)C = -30 to -42 per mil), and methane-based (8(13)C = <-40 per mil) energy sources. Mussels with symbiotic methanotrophic bacteria reflect the carbon isotopic composition of the methane source. Isotopically light nitrogen and sulfur confirm the chemoautotrophic nature of the seep animals. Sulfur-based chemosynthetic animals contain isotopically light sulfur, whereas methane-based symbiotic mussels more closely reflect the heavier oceanic sulfate pool. The nitrogen requirement of some seep animals may be supported by nitrogen-fixing bacteria. Some grazing neogastropods have isotopic values characteristic of chemosynthetic animals, suggesting the transfer of carbon into the background deep-sea fauna.

https://science.sciencemag.org/content/sci/238/4830/1138.full.pdf

Deep-sea hydrocarbon seep communities: evidence for energy and nutritional carbon sources

Recent discoveries on the northern Gulf of Mexico continental slope have altered our understanding of biological and chemical processes occurring in the deep ocean A biological community of hydrothermal vent-type organisms was recently discovered at the base of the Florida Escarpment1, where the fauna are apparently nourished by hydrogen sulphide-rich hypersaline water seeping out onto the sea floor Dense colonies of deep living chemosynthetic benthic organisms were first discovered during investigations of warm water anomalies along the axis of the Galapagos Rift in the Pacific Ocean in 19772—4, and this first discovery of clusters of clams, tube worms and other filter feeders in the immediate proximity of warm water vents has been followed by the discovery of a number of other hydrothermal vent sites, for example Guaymas Basin, East Pacific Rise at 21° N The dense population assemblages at these sites are apparently restricted to small areas of the ocean floor where hydrogen sulphide-rich water is escaping from spreading centres, but the Florida Escarpment discovery indicates that these communities can also exist on passive margins Here we report the discovery of dense biological communities associated with regions of oil and gas seepage on the Louisiana continental slope These communities of large epi- and infaunal organisms are similar to those associated with the vents of the Pacific and the hypersaline brine seeps of the Florida Escarpment Carbon isotope analyses suggest that these communities are chemosynthetic and derive their energy from hydrogen sulphide and/or hydrocarbons Similar communities may be widely distributed on the sea floor in other oil-producing regions of the ocean

Vent-type taxa in a hydrocarbon seep region on the Louisiana slope

Sediment and water samples were collected by submersible in September 1986 at 16 locations on the carbonate cap overlying a conical diapir, which was formed by the upward migration of oil and gas through a subsurface fault on the continental slope off Louisiana, USA (27°47′N; 91°30.4′W). The biological community at the site was photographed quantitatively with still and video cameras. Rigorous spatial sampling indices were maintained so that variation in chemical parameters and in the abundance of photographed organisms could be estimated within the bounds of the study site. Concentrations of extractable organic material (EOM) ranged from 0.24 to 119.26‰ in the sediment samples, while methane concentrations in the water samples were from 0.037 to 66.474 μM. The visible biological community was predominantly composed of the chemosynthetic tube worms (Vestimentifera) Lamellibrachia sp. and Escarpia sp., and an undescribed, methane-oxidizing mussel (Mytilidae: Bathymodiolus-like), as well as diverse non-chemosynthetic organisms. The ranked abundance of tube worms was significantly correlated (p<0.05) with the concentration of EOM in the sediment samples, while the abundance of mussels was significantly correlated (p<0.05) with the concentration of methane in the water samples. Tube worms and mussels both occurred in dense clusters; however, the clusters of mussels had a more restricted distribution within the study site than did clusters of tube worms. Both organisms were most abundant in the vicinity of the subsurface fault.

Robert R. Bidigare

Papers

In-vivo absorption properties of algal pigments

A methanotrophic marine molluscan (bivalvia, mytilidae) symbiosis: mussels fueled by gas.

Deep-sea hydrocarbon seep communities: evidence for energy and nutritional carbon sources

Vent-type taxa in a hydrocarbon seep region on the Louisiana slope

Gulf of Mexico hydrocarbon seep communities