Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EqPac program

Buesseler, Ken O.; Andrews, James W.; Hartman, M. C.; Belastock, Rebecca A.; Chai, Fei

doi:10.1016/0967-0645(95)00043-p

Cited by 221 publications

(137 citation statements)

References 23 publications

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“…Moran et al 1993, Buesseler et al 1995. A recent modeling study, however, suggests that physical adsorption-aggregation can explain observed variations in POC/ 234 Th with particle size (Burd et al 1999).…”

Section: Discussionmentioning

confidence: 96%

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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Section: Discussionmentioning

confidence: 96%

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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“…In order to produce a more efficient (e.g. Buesseler et al, 1995) and homogeneous (e.g. Herranz et al, 2006) counting geometry, 228 Ra analysis was performed on fibers of the A column that had been compressed into a disk geometry 65 mm in diameter and~5 mm thick in a metal canister.…”

Section: Radium Isotope Analysismentioning

confidence: 99%

Relationships between radium and radon occurrence and hydrochemistry in fresh groundwater from fractured crystalline rocks, North Carolina (USA)

et al. 2009

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a b s t r a c t a r t i c l e i n f oNaturally-occurring radionuclides (uranium, radium, and radon), major dissolved constituents, and trace elements were investigated in fresh groundwater in 117 wells in fractured crystalline rocks from the Piedmont region (North Carolina, USA). Chemical variations show a general transition between two water types: (1) slightly acidic (pH 5.0-6.0), oxic, low-total dissolved solids (TDS) waters, and (2) near neutral, oxic to anoxic, higher-TDS waters. The uranium, radium, and radon levels in groundwater associated with granite (Rolesville Granite) are systematically higher than other rock types (gneiss, metasedimentary, and metavolcanic rocks). Water chemistry plays a secondary role on radium and radon distributions as the 222 Rn/ 226 Ra activity ratio is correlated with redox-sensitive solutes such as dissolved oxygen and Mn concentrations, as well as overall dissolved solids content including major divalent cations and Ba. Since 224 Ra/ 228 Ra activity ratios in groundwater are close to 1, we suggest that mobilization of Ra and Rn is controlled by alpha recoil processes from parent nuclides on fracture surfaces, ruling out Ra sources from mineral dissolution or significant long-distance Ra transport. Alpha recoil is balanced by Ra adsorption that is influenced by redox conditions and/or ion concentrations, resulting in an approximately one order of magnitude decrease (~20,000 to~2000) in the apparent Ra distribution coefficient between oxygensaturated and anoxic conditions and also across the range of dissolved ion concentrations (up to~7 mM). Thus, the U and Th content of rocks is the primary control on observed Ra and Rn activities in groundwater in fractured crystalline rocks, and in addition, linked dissolved solids concentrations and redox conditions impart a secondary control.

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“…Beginning with the earliest applications, differences in C / 234 Th were found between samples and between studies depending on the different particle collection devices used, such as sediment traps, filtration from ocean sample bottles, or in situ filtration using pumps and size fractionated particle sampling (Buesseler et al, 1995;Murray et al, 1996). Regional differences and changes with depth and season were also evident.…”

Section: Introductionmentioning

confidence: 99%

An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy

et al. 2006

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Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234 Th activity distribution (in order to calculate 234 Th fluxes) and an estimate of the C / 234 Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / 234 Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / 234 Th either increases or is relatively invariant with increasing particle size (size classes N 1 to 100s Am). Observations also suggest that C / 234 Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234 Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2-3). We recommend sampling for C / 234 Th from a standard depth of 100 m, or at least one depth below www.elsevier.com/locate/marchem the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234 Th profiles and C / 234 Th samples during the course of longer observation periods to better sample temporal variations in both 234 Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column. D

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Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EqPac program

Cited by 221 publications

References 23 publications

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

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

Relationships between radium and radon occurrence and hydrochemistry in fresh groundwater from fractured crystalline rocks, North Carolina (USA)

An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy

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