Direct optical assessment of large amorphous aggregates (marine snow) in the deep ocean

Honjo, Susumo; Doherty, Kenneth W.; Agrawal, Y. C.; Asper, Vernon

doi:10.1016/0198-0149(84)90073-6

Cited by 148 publications

(56 citation statements)

References 17 publications

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“…We observed a range of 1 l-350 mm3 liter--l with upper mixed layer means of 43 mm3 liter-* . Photographic systems that image large volumes of seawater per frame (> 600 liters) such as those of Honjo et al (1984) 01 ' Asper et al (1992) tend to report surface-water abundances of marine snow about 1 order of magnitude lower than ours, probably due to the lower resolution that is the result of imaging a large volume.…”

Section: Aggregate Abundancementioning

confidence: 92%

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Accumulation of marines now at density discontinuities in the water column

MacIntyre

Alldredge

Gotschalk

1995

Limnology & Oceanography

238

206

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The vertical distribution of marine snow-aggregated particles > 0.5 mm in diameter-was strongly correlated with density discontinuities in the upper 100 m of the water column at 33 stations off central California. Eighty-seven percent of peaks in aggregate abundance were associated with density discontinuities in which . . . . . . . N* (the Brunt-Vaisala frequency) exceeded 1.25 x lop4 s-~ (N = 6 cph). For 56% of the peaks, N2 exceeded 2.5 x 1O-4 s2 (N = 9 cph). Absolute abundances of aggregates increased from a mean of 38.7+ 18.3 aggregates liter' above peaks to 59.3k26.0 aggregates liter-' within peaks. Accumulations of aggregates could result from sinking into denser water if sinking rates were reduced by at least 20% due to slow equilibrium of either interstitial water or mucus within the floes with the surrounding, higher density water. However, our observed increases in ct were insufficient to cause such slowing for floes whose porosity was 99% or less; such floes comprised a significant proportion of aggregates in the observed peaks. However, larger floes of moderate to high porosity were likely to decelerate as they encountered denser water and could even become neutrally or negatively buoyant for changes in ur such as we observed. Equilibration times of the interstitial water of these generally larger floes ranged from hundreds of seconds up to 3 h. Results of a random walk simulation of particle motion indicated that turbulence was likely to cause localized accumulations of aggregates and to increase particle aggregation. Because we found subcritical values of the Richardson number (an indicator of turbulent mixing) at the top of regions of peak abundance but not at the base, for 68% of the peaks observed, we infer that turbulence may contribute to the accumulation of the smaller floes. Occurrence of strong shear and deviations of temperature and salinity profiles from typical patterns suggest that at least 23% of these aggregate peaks were associated with horizontal intrusions.

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Section: Aggregate Abundancementioning

confidence: 92%

“…Measurement of particle abundance and size-Vertical profiles of the abundance and size distribution of marine snow were obtained by photographing the aggregates present in slabs of illuminated seawater (0.78 liters in total volume) with either a still camera system or a video camera system, both modified from the design of Honjo et al (1984).…”

Section: Methodsmentioning

confidence: 99%

Accumulation of marines now at density discontinuities in the water column

MacIntyre

Alldredge

Gotschalk

1995

Limnology & Oceanography

238

206

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“…Even within the open ocean, particlerich microenvironments like marine snow have been shown to be important in the cycling of materials and energy in oceanic systems (Knauer et al 1982, Honjo et al 1984, Pilskaln & Honjo 1987, Alldredge et al 1993. Protistan grazers are known to be an important component of such microenvironments (Caron et al 1986, Alldredge & Silver 1988.…”

Section: Discussionmentioning

confidence: 99%

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Barbeau¹,

Kujawinski²,

Moffett³

2001

Aquat. Microb. Ecol.

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To characterize trace metal cycling in marine systems as mediated by heterotrophic protists, we conducted a series of laboratory experiments in 2-organism model systems consisting of bacteria and protistan grazers. Trace metal isotopes ( 59 Fe and 234 Th), 14 C, and bulk organic carbon measurements were used to follow the chemical transformation of bacterial carbon and associated trace metals by several different grazer species. Results indicate that grazers were able to cause repartitioning of Th and regeneration of Fe from bacterial prey into the dissolved phase (< 0.2 µm), even in particle-rich laboratory cultures. For both Th and Fe, protist grazing led to the formation of relatively stable dissolved and colloidal metal-organic species. Metal/carbon ratios of the particle pool in some model systems with grazers were significantly altered, indicating a decoupling of trace metal and organic carbon cycling through the grazing process. Different protist species exhibited substantial variation (up to a factor of 10) in their ability to quantitatively remobilize trace metals from bacterial prey. The implications of these findings for trace metal cycling in marine systems are discussed. KEY WORDS: Marine protists · Iron · Thorium · Organic carbon · RecyclingResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 24: 69-81, 2001 suggests that the effect of protist grazing on trace metals in the oceans is both geochemically and ecologically significant.This study presents some of the first data on the regeneration and recycling of cell-associated Fe and Th isotopes in conjunction with cellular organic carbon by heterotrophic protists in laboratory culture. Despite the widespread use of naturally occurring Th isotopes as analogues for particle-reactive species (Clegg & Whitfield 1991, Gustafsson et al. 1997) and as tracers of particulate organic carbon (POC) export from the upper ocean (e.g. Buesseler et al. 1992, Murray et al. 1996, almost nothing is known about the actual mechanism of Th cycling via protists and associated organisms of the 'microbial loop'. Very few model system studies have examined the mechanism of Fe recycling in seawater via protistan grazing (Hutchins & Bruland 1994, Chase & Price 1997. Both of these studies employed the grazer Paraphysomonas sp. In the present study several different grazer species (including Paraphysomonas) were examined in terms of Fe, Th and organic carbon remineralization.In the first experiment, a model system study, the size fractionation of Fe and Th isotopes and organic carbon was followed as a heterotrophic nanoflagellate (Cafeteria sp., a free-living flagellate 3-5 µm diameter) consumed bacterial prey. Next a sequence of experiments was conducted in order to determine the relative abilities of 3 different kinds of protists to remobilize cell-associated Fe and Th (Cafeteria sp.; Uronema sp., a benthic scuticociliate 7-15 µm in length; and Paraphysomonas imperforata, a free-living flagellate 5-7 µm in diameter, whic...

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“…Optical imaging systems such as digital cameras have been used since the 1980s to study in-situ concentrations of particles larger than tens of micron including marine snow with an equivalent spherical diameter (ESD) >500 lm (Alldredge, 1998;Davis et al, 2005;Goldthwait and Alldredge, 2006;Gorsky et al, 1992;Honjo et al, 1984;McDonnell et al, 2015;Walsh and Gardner, 1992). Since then, the technology has evolved allowing fast laboratorybased or in-situ measurements of particle size distribution from a few microns to a few millimetres.…”

Section: Optical Imaging Of Particle Abundance and Size Distributionmentioning

confidence: 99%

Optical techniques for remote and in-situ characterization of particles pertinent to GEOTRACES

Boss

Guidi

Richardson

et al. 2015

Progress in Oceanography

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a b s t r a c tField and laboratory characterization of marine particles is laborious and expensive. Proxies of particle properties have been developed that allow researchers to obtain high frequency distributions of such properties in space or time. We focus on optical techniques used to characterize marine particles in-situ, with a focus on GEOTRACES-relevant properties, such as bulk properties including particle mass, crosssectional area, particle size distribution, particle shape information, and also single particle optical properties, such as individual particle type and size. We also address the use of optical properties of particles to infer particulate organic or inorganic carbon. In addition to optical sensors we review advances in imaging technology and its use to study marine particles in situ. This review addresses commercially available technology and techniques that can be used as a proxy for particle properties and the associated uncertainties with particular focus to open ocean environments, the focus of GEOTRACES.

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Direct optical assessment of large amorphous aggregates (marine snow) in the deep ocean

Cited by 148 publications

References 17 publications

Accumulation of marines now at density discontinuities in the water column

Accumulation of marines now at density discontinuities in the water column

Remineralization and recycling of iron, thorium and organic carbon by heterotrophic marine protists in culture

Optical techniques for remote and in-situ characterization of particles pertinent to GEOTRACES

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