Optical backscattering by calcifying algae: Separating the contribution of particulate inorganic and organic carbon fractions

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131

We examined the light-absorption properties of various samples of mineral particles suspended in water, which included pure mineral species (quartz, calcite, illite, kaolinite, and montmorillonite) and natural particulate assemblages such as desert dust originating from different locations in the Sahara. The absorption coefficient was measured in the spectral region from ultraviolet (UV) to near-infrared on particle suspensions, using a special measurement geometry that reduced the scattering error to a very small level. The concentrations of the total mass of particles in suspension, as well as the mineralogical and elemental composition of particulate samples, were also determined. For the samples of pure mineral species with negligible contamination with iron, absorption was undetectable in the visible spectral region. All of the examined natural assemblages of mixed mineral species showed a significant content of iron (5-29% by weight), and all these samples exhibited significant absorption in the UV and blue-green (400-550 nm) spectral regions. The spectral shape of absorption was similar to that determined on pure iron hydroxide suspension, with some spectral features (shoulders and changes in slope) superposed onto a general increase of absorption toward short wavelengths in the UV. The mass-specific absorption coefficient of the mineral samples, a (), obtained by normalization of the absorption coefficient to the dry-mass concentration of particles, * m showed a significant positive correlation with Fe content. No such relationship was found for other elements present in particles. The range of a () values covered more than an order of magnitude (from Ͻ0.1 to ϳ1 m 2 g Ϫ1 near * m 400 nm), but the normalization of absorption coefficient to iron concentration led to a considerable reduction in variability among the samples. The iron-specific absorption coefficient, a (), varied from ϳ1 to 4 m 2 (g Fe) Ϫ1* Fe near 400 nm for the natural mixtures of mineral species. Although iron was a major pigmenting agent, its concentration could explain only part of variability observed in the absorption properties of mineral particles.The application of pigment-bleaching methods, in combination with spectrophotometric measurements of marine particles retained on filters, makes it possible to determine experimentally the approximate contributions of phytoplankton and nonalgal particles to light absorption in the ocean (Doucha and Kubin 1976;Kishino et al. 1985;Tassan and Ferrari 1995). With this approach, several studies have documented the variations in the spectral absorption coefficient of nonalgal particles, a NAP (), in various marine environments. The contribution of a NAP to the total particulate absorption in the upper (photic) layer of the ocean can vary widely with location, time of year, and light wavelength. It is on the order of tens of percent in the blue spectral region and can reach nearly 100% in extreme cases (e.g., Nelson and Guarda 1995;Babin et al. 2003). The spectrum of

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confidence: 99%

Variations in the mass‐specific absorption coefficient of mineral particles suspended in water

Babin

Stramski

2004

140

131

“…Much of the previous research on the influence of light, nutrients, and temperature on phytoplankton optical properties was focused on absorption, fluorescence, or both (e.g., Kiefer 1973;Sosik and Mitchell 1994;Moore et al 1995). Studies of light scattering by phytoplankton have typically been undertaken with no simultaneous measurements of absorption (e.g., Volten et al 1998;Balch et al 1999) or with little regard for the effects of growth conditions (e.g., Bricaud et al 1988;Ahn et al 1992). Few studies that included concurrent determinations of absorption and scattering by phytoplankton under varying growth conditions showed significant varia-…”

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confidence: 99%

Effects of temperature, nitrogen, and light limitation on the optical properties of the marine diatom Thalassiosira pseudonana

Stramski

Sciandra

Claustre

2002

104

A series of laboratory experiments were conducted to examine the optical properties of the marine diatom Thalassiosira pseudonana for a broad range of growth rates ( from 0.22 to 2 d Ϫ1 ) under temperature-, nitrogen-, and light-limited conditions. The effects of temperature and nitrogen limitation on spectral absorption cross-sections expressed on a per cell basis, a ( ), were similar. With the reduction in growth rate, a at a light wavelength ϭ 674 nm showed an equivalent decrease regardless of whether the cells were limited by temperature or nitrogen. The effect of growth irradiance was distinctively different, since a increased with light limitation. The chlorophyll a (Chl a)-specific absorption coefficient showed the opposite trends than those of a . These patterns resulted primarily from the acclimative strategies of T. pseudonana involving an increase in Chl a content in response to light limitation and a decrease in Chl a under temperature and nitrogen limitation. The scattering cross-sections,

“…Viruses likely play a significant role in the ecological control of planktonic microorganisms (Suttle and Chan 1993). Despite their high abundance, marine viruses generally have been thought to play a minor role in ocean optics because of their small scattering cross-sections (Stramski and Kiefer 1991;Balch et al 2000). Within the field of virology, however, it has long been known that bacterial viruses (bacteriophage) can rapidly lyse their hosts and, in some cases, clear turbid host cultures (Stent 1963;Lamanna et al 1973).…”

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confidence: 99%

“…Scattering from a seawater or culture media blank was always subtracted from the total scattering of experimental samples, to estimate the scattering from suspended particles. For each determination, 2,000 VSFs were sampled over a 10-s period, between 35.5Њ and 144.5Њ (Balch et al 1999. Samples were initially swirled but not subsequently mixed during this 10-s period.…”

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confidence: 99%

See 1 more Smart Citation

Fundamental changes in light scattering associated with infection of marine bacteria by bacteriophage

Balch

Vaughn

Novotny

et al. 2002

Self Cite

Abstract-Bacteria and phytoplankton are key determinants of the ocean's inherent optical properties. Despite their high abundance, marine viruses have generally been thought to play a minor role in ocean optics because of their small scattering cross-sections. Nevertheless, the role of specific viral infection on the optical properties of bacteria and phytoplankton has remained unknown (i.e., as viruses disrupt micron-sized host cells to produce submicron cell debris). Here, we used laboratory and mesocosm cultures of marine bacteria for virus infection experiments in which growth conditions and host-virus specificity were controlled. We report that the chief optical impact of viruses is associated with infection and lysis of their hosts. We quantitatively describe, for the first time, two optical changes associated with infection and lysis of marine bacteria by bacteriophage: (1) rapid, strong shifts in the magnitude and shape of the optical volume scattering function and (2) rapid production of colored dissolved organic material. Qualitatively, these changes result in nearly complete clearing of turbid host bacterial suspensions. Although some optical differences would be expected between infection of bacteria in laboratory cultures versus field populations (mainly because of differences in cell size), these results are applicable to the field, especially for dense host suspensions such as in blooms. Even in nonbloom situations, as long as the host bacteria contribute a significant amount of the total particle backscattering, we expect that virus-induced backscattering changes would be detectable by use of satellite or aircraft remote-sensing techniques.