A review of present techniques and methodological advances in analyzing 234Th in aquatic systems

Loeff, Michiel M. Rutgers van der; Sarin, M.M.; Baskaran, M.; Benitez-Nelson, Claudia R.; Buesseler, Ken O.; Charette, Matthew A.; Dai, Minhan; Gustafsson, Örjan; Masqué, Pere; Morris, Paul J.; Orlandini, K.A.; Baena, Alessia Rodriguez y; Savoye, Nicolas; Schmidt, Sabine; Turnewitsch, Robert; Vöge, Ingrid; Waples, James T.

doi:10.1016/j.marchem.2005.10.012

Cited by 126 publications

(65 citation statements)

References 99 publications

(111 reference statements)

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“…Three seawater profiles were taken at the central station on 3, 12 and 17 February (C91, C128, C140, respectively). In addition, replicates of deep samples (2500 m) were collected for calibration purposes (Rutgers van der Loeff et al, 2006). The samples were processed according to the MnO 2 co-precipitation technique (Buesseler et al, 2001b), using 230 Th as a chemical yield tracer .…”

Section: Total 234 Th and 238 Umentioning

confidence: 99%

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Roca‐Martí

Puigcorbé

Iversen

et al. 2017

Deep Sea Research Part II: Topical Studies in Oceanography

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a b s t r a c tCarbon fixation by phytoplankton plays a key role in the uptake of atmospheric CO 2 in the Southern Ocean. Yet, it still remains unclear how efficiently the particulate organic carbon (POC) is exported and transferred from ocean surface waters to depth during phytoplankton blooms. In addition, little is known about the processes that control the flux attenuation within the upper twilight zone. Here, we present results of downward POC and particulate organic nitrogen fluxes during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean in summer 2012. We used thorium-234 ( 234 Th) as a particle tracer in combination with drifting sediment traps (ST). Their simultaneous use evidenced a sustained high export rate of 234 Th at 100 m depth in the weeks prior to and during the sampling period. The entire study area, of approximately 8000 km 2 , showed similar vertical export fluxes in spite of the heterogeneity in phytoplankton standing stocks and productivity, indicating a decoupling between production and export. The POC fluxes at 100 m were high, averaging 26 715 mmol C m À 2 d À 1 , although the strength of the biological pump was generally low. Only o 20% of the daily primary production reached 100 m, presumably due to an active recycling of carbon and nutrients. Pigment analyses indicated that direct sinking of diatoms likely caused the high POC transfer efficiencies ( $ 60%) observed between 100 and 300 m, although faecal pellets and transport of POC linked to zooplankton vertical migration might have also contributed to downward fluxes.

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Section: Total 234 Th and 238 Umentioning

confidence: 99%

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Roca‐Martí

Puigcorbé

Iversen

et al. 2017

Deep Sea Research Part II: Topical Studies in Oceanography

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“…Isolation and purification of dissolved 234 Th ( 234 Th D ) were carried out on board a ship within 24 h after seawater collection, using an anion-exchange procedure. Activities of 234 Th and chemical efficiencies, based on 229 Th, were determined in the lab using a single γ-counting (Rutgers van der Loeff et al, 2006;Schmidt and Reyss, 2000). Standards used for the calibration of the γ detector were International Atomic Energy Agency reference materials (RGU-1).…”

Section: Th Activitiesmentioning

confidence: 99%

Particle export during a bloom of Emiliania huxleyi in the North-West European continental margin

Schmidt

Harlay

Borges

et al. 2013

Journal of Marine Systems

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Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological CO 2 pump. In May 2002 a cruise was conducted on the outer shelf of the North-West European continental margin, from the north Bay of Biscay to the Celtic Sea (47.0°-50.5°N, 5.0°-11.0°W), an area where massive blooms of Emiliania huxleyi are observed annually. Biogeochemical variables including primary production, calcification, partial pressure of CO 2 (pCO 2 ), chlorophyll-a (Chl-a), particle load, particulate organic and inorganic carbon (POC, PIC) and 234 Th, were measured in surface waters to assess particle dynamic and carbon export in relation to the development of a coccolithophore bloom. We observed a marked northward decrease in Chl-a concentration and calcification rates: the bloom exhibited lower values and may be less well developed in the Goban Spur area. The export fluxes of POC and PIC from the top 80 m, determined using the ratios of POC and PIC to 234 Th of particles, ranged from 81 to 323 mg C m − 2 d − 1 and from 30 to 84 mg C m − 2 d − 1 , respectively. The highest fluxes were observed in waters presenting a well-developed coccolithophore bloom, as shown by high reflectance of surface waters. This experiment confirms that the occurrence of coccolithophores promotes efficient export of organic and inorganic carbon on the North-West European margin.

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“…In VERTIGO, particles were all collected with in-situ pumps and both elements analyzed on the exact same sample, so this ratio is not impacted by collecting POC with bottles vs. pumps, which generally show higher POC in bottle samples (Gardner et al, 2003;Liu et al, 2005;Moran et al, 1999). There is evidence of preferential sorption of dissolved 234 Th on to quartz based filters (Benitez-Nelson et al, 2001b;Rutgers van der Loeff et al, 2006), and this may be one reason that on average C/Th ratios are lower on QMAs, though there are other possibilities, such as greater Th uptake onto the higher surface:volume ratio of small particles, or greater removal of organic carbon by respiration during the generation of suspended small particles from larger sinking particles.…”

Section: Poc/mentioning

confidence: 99%

Thorium-234 as a tracer of spatial, temporal and vertical variability in particle flux in the North Pacific

Buesseler

Pike

Maiti

et al. 2009

Deep Sea Research Part I: Oceanographic Research Papers

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An extensive 234 Th data set was collected at two sites in the North Pacific: ALOHA, an oligotrophic site near Hawaii, and K2, a mesotrophic HNLC site in the NW Pacific as part of the VERTIGO (VERtical Transport in the Global Ocean) study. Total 234 Th:238 U activity ratios near 1.0 indicated low particle fluxes at ALOHA, while 234 Th: 238 U ~0.6 in the euphotic zone at K2 indicated higher particle export. However, spatial variability was large at both sites-even greater than seasonal variability as reported in prior studies. This variability in space and time confounds the use of single profiles of 234 Th for sediment trap calibration purposes. At K2, there was a decrease in export flux and increase in 234 Th activities over time associated with the declining phase of a summer diatom bloom, which required the use of non-steady state models for flux predictions. This variability in space and time confounds the use of single profiles of 234 Th for sediment trap calibration purposes. High vertical resolution profiles show narrow layers (20-30 m) of excess 234 Th below the deep chlorophyll maximum at K2 associated with particle remineralization resulting in a decrease in flux at depth that may be missed with standard sampling for 234 Th and/or with sediment traps. Also, the application of 234 Th as POC flux tracer relies on accurate sampling of particulate POC/ 234 Th ratios and here the ratio is similar on sinking particles and mid-sized particles collected by in-situ filtration (>10-50 µm at ALOHA and >5-350 µm at K2). To further address variability in particle fluxes at K2, a simple model of the drawdown of 234 Th and nutrients is used to demonstrate that while coupled during export, their ratios in the water column will vary with time and depth after export. Overall these 234 Th data provide a detailed view into particle flux and remineralization in the North Pacific over time and space scales that are varying over days to weeks, and 10's to 100's km at a resolution that is difficult to obtain with other methods.

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A review of present techniques and methodological advances in analyzing 234Th in aquatic systems

Cited by 126 publications

References 99 publications

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

High particulate organic carbon export during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean

Particle export during a bloom of Emiliania huxleyi in the North-West European continental margin

Thorium-234 as a tracer of spatial, temporal and vertical variability in particle flux in the North Pacific

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