Calibration of sediment traps and particulate organic carbon export using 234Th in the Barents Sea

doi:10.1016/S0304-4203(02)00071-3

Marine Chemistry

Volume 80, Issue 1, December 2002, Pages 11-26

https://doi.org/10.1016/S0304-4203(02)00071-3 Get rights and content

Abstract

Profiles of particulate and dissolved ²³⁴Th (t_1/2=24.1 days) in seawater and particulate ²³⁴Th collected in drifting traps were analyzed in the Barents Sea at five stations during the ALV3 cruise (from June 28 to July 12, 1999) along a transect from 78°15′N–34°09′E to 73°49′N–31°43′E. ²³⁴Th/²³⁸U disequilibrium was observed at all locations. ²³⁴Th data measured in suspended and trapped particles were used to calibrate the catchment efficiency of the sediment traps. Model-derived ²³⁴Th fluxes were similar to ²³⁴Th fluxes measured in sediment traps based on a steady-state ²³⁴Th model. This suggests that the sediment traps were not subject to large trapping efficiency problems (collection efficiency ranges from 70% to 100% for four traps). The export flux of particulate organic carbon (POC) can be calculated from the model-derived export flux of ²³⁴Th and the POC/²³⁴Th ratio. POC/²³⁴Th ratios measured in suspended and trapped particles were very different (52.0±9.9 and 5.3±2.2 μmol dpm⁻¹, respectively). The agreement between calculated and measured POC fluxes when the POC/²³⁴Th ratio of trapped particles was used confirms that the POC/²³⁴Th ratio in trap particles is representative of sinking particles. Large discrepancies were observed between calculated and measured POC fluxes when the POC/²³⁴Th ratio of suspended particles was used. In the Barents Sea, vertical POC fluxes are higher than POC fluxes estimated in the central Arctic Ocean and the Beaufort Sea and lower than those calculated in the Northeast Water Polynya and the Chukchi Sea. We suggest that the latter fluxes may have been strongly overestimated, because they were based on high POC/²³⁴Th ratios measured on suspended particles. It seems that POC fluxes cannot be reliably derived from thorium budgets without measuring the POC/²³⁴Th ratio of sediment trap material or of large filtered particles.

Introduction

Particle fluxes are usually measured by sediment traps to estimate particle abundance and particle sinking speed. Variations of the quantity and presumably of the quality of particulate matter (including particulate organic carbon i.e. POC) recovered in a trap reflect the characteristics of the surface water dynamics and biomass composition. However, hydrodynamic effects and swimmers might seriously bias trapping efficiency Buesseler, 1991, Gardner, 1996. Therefore, the use of traps alone is not sufficient to estimate correctly particle fluxes. Independent measurements of vertical flux from ²³⁴Th activities in the water column can be used to calibrate the sediment trap catchment efficiency (Buesseler, 1991). This method is based on the fact that ²³⁸U (half-life 4.5×10⁹ years) has a conservative behavior in the ocean, whereas its daughter product, ²³⁴Th (half-life t_1/2=24.1 days), is highly particle-reactive and hence sticks to all particle surfaces. From the ²³⁴Th deficiency (relative to ²³⁸U) in surface waters, we can predict the particulate ²³⁴Th flux exported from these waters Coale and Bruland, 1985, Coale and Bruland, 1987. By comparing this flux with ²³⁴Th measurement in a trap, we can estimate if the trap collects ²³⁴Th-bearing particles quantitatively (Gardner, 1996). The particulate organic carbon export can be derived if the ratio POC/²³⁴Th is known. However, the relationships between POC and ²³⁴Th are not well understood.

The Barents Sea is an arctic shelf sea of the eastern North Atlantic, which supports one of the most productive marine ecosystems in the Arctic region (Wassmann et al., 1999). The annual estimates of primary production range from 18 to 73 g C m⁻² year⁻¹ between the northern and the southern part of the Barents Sea (Wassmann and Slagstad, 1993). This region is characterized by large regional differences in hydrographic conditions and ice coverage Loeng, 1991, Loeng et al., 1997. Atlantic water flowing into the Barents Sea from south–west and Arctic water entering from north–east are separated by the Polar Front. The northern, central and eastern Barents Sea is periodically ice covered. The marginal ice zone (MIZ) is a unique frontal system (Wassmann et al., 1999). During late spring and early summer, the ice melt gives rise to a stratified and nutrient-rich euphotic zone. It is followed by a phytoplankton bloom (Slagstad and Wassmann, 1997). Temporal and spatial variability of vertical flux of biogenic matter is important to understand elemental dynamics and food webs in the ocean Legendre, 1990, Smetacek et al., 1984, Wassmann, 1991. The dynamics of this flux and the composition of the exported production were investigated during previous studies along a section in the central Barents Sea during the 1984–1993 period (Wassmann and Slagstad, 1993). Along this south–north transect, the zonal structure of the Barents Sea with its main water masses (Atlantic water, the Polar Front, the ice edge and Arctic water) was investigated (Andreassen and Wassmann, 1998). Physical processes may also influence the dynamics of the vertical flux in the Barents Sea through their impact on ice coverage, ice melt, stabilization, advection and retention of zooplankton Slagstad and Wassmann, 1997, Wassmann and Slagstad, 1993.

We present water column measurements of dissolved and particulate ²³⁴Th and ²³⁴Th collected in sediment traps at five stations representing different trophic features corresponding to different ice coverage conditions and different water masses (Arctic and Atlantic waters). These results are used to calibrate sediment traps, to quantify POC export in this region and to compare these estimates with direct POC export estimates.

Section snippets

Sample collection

Samples were collected onboard RV “Jan Mayen” from June 28, 1999 to July 12, 1999, during ALV3 cruise (Arctic Light and Heat), along a transect in the central Barents Sea. The sampling area was from 78°15′N–34°09′E to 73°49′N–31°43′E (Fig. 1). Heading for the north, we tried to penetrate as deep as possible into the MIZ. Along this south–north section, POC in small particles, nutrients and plankton were measured during short stations. When the northernmost station was reached (78°N), we

Hydrography

The main water masses encountered along the transect are identified with the temperature section (Fig. 2a). Atlantic water was predominant in the south and in the center of the section. It was divided in two branches which penetrated the Barents Sea from the south–west. The South Barents Atlantic-derived Water (SBAW) was 4–7 °C while the North Barents Atlantic-derived Water (NBAW) was colder at 2–4 °C. On the Sentralbanken, a specific water mass (Sentralbanken Water i.e. SW) of Arctic origin

Origins of ²³⁴Th/²³⁸U disequilibrium

As ²³⁴Th is highly particle-reactive and sticks to all particle surfaces, the loss of ²³⁴Th (i.e. ²³⁴Th/²³⁸U disequilibrium) from surface waters is a direct indication of the removal rate of sinking particulate matter. Coale and Bruland (1985) showed that there is a link between ²³⁴Th removal rates and new production in the open ocean. However, other mechanisms can also explain a ²³⁴Th/²³⁸U disequilibrium. ²³⁴Th/²³⁸U disequilibrium throughout the water column has been previously observed in the

Conclusion

Measurements of ²³⁴Th depth profiles in the Barents Sea indicate that ²³⁴Th/²³⁸U disequilibrium is present in July in the entire sampling area. This is due to the high concentrations of biogenic matter in the water column. The ²³⁴Th method confirms the accuracy of sediment traps in the Barents Sea. This allows to compare POC fluxes estimated with ²³⁴Th model and measured POC fluxes in sediment traps. We suggest that high POC fluxes previously reported in the Arctic Ocean during the summer based

Acknowledgements

It is a pleasure to acknowledge the sedimentation group of the Norwegian College of Fishery Science in Tromsø. We are specially grateful to C. Wexels Riser, C. Svensen and M. Reigstad for their cooperation and assistance during the cruise ALV3 and the visit of L. Coppola during 1 month in the lab. We thank F. Lyard for sharing his expertise for the barotropic calculations. We wish also to acknowledge the officers and the crew of the R/V Jan Mayen for their efforts in sampling. J. Dunne, M.

References (42)

Andersson, P.S.Ö.G., Roos, P., Broman, D., Toneby, A., 2000. Particle mediated surface water export: comparison of...
I.J Andreassen et al.
Vertical flux of phytoplankton and particulate biogenic matter in the marginal ice zone of the Barents Sea in May 1993
Mar. Ecol., Prog. Ser.
(1998)
R Arraes-Mescoff
The behavior of Al, Mn, Ba, Sr, REE and Th isotopes during in vitro degradation of large marine particles
Mar. Chem.
(2001)
M.P Bacon et al.
Removal of thorium-234 by scavenging in the bottom nepheloid layer of the ocean
Earth Planet. Sci. Lett.
(1989)
M.P Bacon et al.
Export flux of carbon at the equator during EqPac time-series cruises estimated from ²³⁴Th measurements
Deep-Sea Res., Part II
(1996)
K.O Buesseler
Do upper-ocean sediment traps provide an accurate record of particle flux?
Nature
(1991)
K.O Buesseler et al.
Carbon and nitrogen export during the JGOFS North Atlantic Bloom Experiment estimated from ²³⁴Th:²³⁸U disequilibria
Deep-Sea Res.
(1992)
K.O Buesseler et al.
A three dimensional time-dependent approach to calibrating sediment trap fluxes
Glob. Biogeochem. Cycles
(1994)
K.O Buesseler et al.
Regional estimates of the export flux of particulate organic carbon derived from thorium-234 during the JGOFS EQPAC Program
Deep-Sea Res., Part II
(1995)
K.O Buesseler
Upper ocean export of particulate organic carbon in the Arabian Sea derived from thorium-234
Deep-Sea Res.
(1998)

M.A Charette et al.

Rates of particle scavenging and particulate organic carbon export estimated using ²³⁴Th as a tracer in the subtropical and equatorial Atlantic Ocean

Deep-Sea Res., Part II

(1999)

M.A Charette et al.

²³⁴Th as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean

Deep-Sea Res., Part II

(1999)

J.H Chen et al.

²³⁸U–²³⁴U and ²³²Th in seawater

Earth Planet. Sci. Lett.

(1986)

K.H Coale

Labyrinth of doom: advice to minimize the “swimmer” component in sediment trap collections

Limnol. Oceanogr.

(1990)

K.H Coale et al.

²³⁴Th:²³⁸U disequilibria within the California current

Limnol. Oceanogr.

(1985)

K.H Coale et al.

Oceanic stratified euphotic zone as elucidated by ²³⁴Th:²³⁸U disequilibria

Limnol. Oceanogr.

(1987)

J.K Cochran et al.

Thorium-234/Uranium-238 disequilibrium as an indicator of scavenging rates and particulate organic carbon fluxes in the Northeast Water Polynya Greenland

J. Geophys. Res.

(1995)

S Falk-Petersen

Physical and ecological processes in the marginal ice zone of the northern Barents Sea during the summer melt period

J. Mar. Syst.

(2000)

N.S Fisher et al.

Accumulation of Th, Pb, U and Ra in marine phytoplankton and its geochemical significance

Limnol. Oceanogr.

(1987)

Gardner, W.D., 1996. Sediment trap technology and sampling in surface waters. Report of the sediment trap workshop, 1st...

L Legendre

The significance of microalgal blooms for fisheries and for the export of particulate organic carbon in oceans

J. Plankton Res.

(1990)

Cited by (80)

Are all sediment traps created equal? An intercomparison study of carbon export methodologies at the PAP-SO site
2020, Progress in Oceanography
Sinking particulate flux out of the upper ocean is a key observation of the ocean’s biological carbon cycle. Particle flux in the upper mesopelagic is often determined using sediment traps but there is no absolute standard for the measurement. Prior to this study, differing neutrally-buoyant sediment trap designs have not been deployed simultaneously, which precludes meaningful comparisons between flux data collected using these designs.
The aim of the study was to compare a suite of modern methods for measuring sinking carbon flux out of the surface ocean. This study compared samples from two neutrally buoyant drifting sediment trap designs, and a surface tethered drifting sediment trap, which collected sinking particles alongside other methods for sampling particle properties, including in situ pumps and ²³⁴Th radionuclide measurements. Samples were collected at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) site in the Northeast Atlantic Ocean (49°N, 16.5°W).
Neutrally-buoyant conical traps appeared to collect lower absolute fluxes than neutrally-buoyant, or surface-tethered cylindrical traps, but compositional ratios of sinking particles indicated collection of similar material when comparing the conical and cylindrical traps. In situ pump POC:²³⁴Th ratios generally agreed with trap ratios but conical trap samples were somewhat depleted in ²³⁴Th, which along with sinking particle size distribution data determined from gel traps, may imply under-sampling of small particles. Cylindrical trap POC fluxes were of similar magnitude to ²³⁴Th-derived POC fluxes while conical POC fluxes were lower. Further comparisons are needed to distinguish if differences in particle flux magnitude are due to conical versus cylindrical trap designs. Parallel analytical determinations, conducted by different laboratories, of replicate samples for elemental fluxes and gel trap particle size distributions were comparable. This study highlights that the magnitude of particle fluxes and size spectra may be more sensitive than the chemical composition of particle fluxes to the instrumentation used. Only two deployments were possible during this study so caution should be taken when applying these findings to other regions and export regimes. We recommend that multiple methodologies to measure carbon export should be employed in field studies, to better account for each method’s merits and uncertainties. These discrepancies need further study to allow carbon export fluxes to be compared with confidence across laboratory, region and time and to achieve an improved global understanding of processes driving and controlling carbon export.
Distribution of 210Pb and 210Po in the Arctic water column during the 2007 sea-ice minimum: Particle export in the ice-covered basins
2018, Deep-Sea Research Part I: Oceanographic Research Papers
²¹⁰Pb and ²¹⁰Po are naturally occurring radionuclides that are commonly used as a proxy for particle and carbon export. In this study, the distribution of the ²¹⁰Po/²¹⁰Pb pair was investigated in the water column of the Barents, Kara and Laptev Seas and the Nansen, Amundsen and Makarov Basins in order to understand the particle dynamics in the Arctic Ocean during the 2007 sea-ice minimum (August–September). Minimum activities of total ²¹⁰Pb and ²¹⁰Po were found in the upper and lower haloclines (approx. 60–130 m), which are partly attributed to particle scavenging over the shelves, boundary current transport and subsequent advection of the water with low ²¹⁰Pb and ²¹⁰Po activities into the central Arctic. Widespread and substantial (> 50%) deficits of ²¹⁰Po with respect to ²¹⁰Pb were detected from surface waters to 200 m on the shelves, but also in the basins. This was particularly important in the Makarov Basin where, despite very low chlorophyll-a levels, estimates of annual new primary production were three times higher than in the Eurasian Basin. In the Nansen, Amundsen and Makarov Basins, estimates of annual new primary production correlated with the deficits of ²¹⁰Po in the upper 200 m of the water column, suggesting that in situ production and subsequent export of biogenic material were the mechanisms that controlled the removal of ²¹⁰Po in the central Arctic. Unlike ²¹⁰Po, ²³⁴Th deficits measured during the same expedition were found to be very small and not significant below 25 m in the basins (Cai et al., 2010), which indicates, given the shorter half-life of ²³⁴Th, that particle export fluxes in the central Arctic would have been higher before July–August in 2007 than later in the season.
Zooplankton fecal pellets, marine snow, phytodetritus and the ocean's biological pump
2015, Progress in Oceanography
The “biological pump” is the process by which photosynthetically-produced organic matter in the ocean descends from the surface layer to depth by a combination of sinking particles, advection or vertical mixing of dissolved organic matter, and transport by animals. Particulate organic matter that is exported downward from the euphotic zone is composed of combinations of fecal pellets from zooplankton and fish, organic aggregates known as “marine snow” and phytodetritus from sinking phytoplankton. Previous reviews by Turner and Ferrante (1979) and Turner (2002) focused on publications that appeared through late 2001. Since that time, studies of the biological pump have continued, and there have been >300 papers on vertical export flux using sediment traps, large-volume filtration systems and other techniques from throughout the global ocean. This review will focus primarily on recent studies that have appeared since 2001. Major topics covered in this review are (1) an overview of the biological pump, and its efficiency and variability, and the role of dissolved organic carbon in the biological pump; (2) zooplankton fecal pellets, including the contribution of zooplankton fecal pellets to export flux, epipelagic retention of zooplankton fecal pellets due to zooplankton activities, zooplankton vertical migration and fecal pellet repackaging, microbial ecology of fecal pellets, sinking velocities of fecal pellets and aggregates, ballasting of sinking particles by mineral contents, phytoplankton cysts, intact cells and harmful algae toxins in fecal pellets, importance of fecal pellets from various types of zooplankton, and the role of zooplankton fecal pellets in picoplankton export; (3) marine snow, including the origins, abundance, and distributions of marine snow, particles and organisms associated with marine snow, consumption and fragmentation of marine snow by animals, pathogens associated with marine snow; (4) phytodetritus, including pulsed export of phytodetritus, phytodetritus from Phaeocystis spp., picoplankton in phytodetritus, the summer export pulse (SEP) of phytodetritus in the subtropical North Pacific, benthic community responses to phytodetritus; (5) other components of the biological pump, including fish fecal pellets and fish-mediated export, sinking carcasses of animals and macrophytes, feces from marine mammals, transparent exopolymer particles (TEP); (6) the biological pump and climate, including origins of the biological pump, the biological pump and glacial/interglacial cycles, the biological pump and contemporary climate variations, and the biological pump and anthropogenic climate change. The review concludes with potential future modifications in the biological pump due to climate change.
234Th-derived surface export fluxes of POC from the Northern Barents Sea and the Eurasian sector of the Central Arctic Ocean
2012, Deep-Sea Research Part I: Oceanographic Research Papers
Citation Excerpt :
Given projections of relatively large changes to the Arctic hydrography, plankton ecology and carbon system due to climate change, there is a call for greater spatial and temporal coverage in observations of upper ocean carbon export in large areas of the Arctic Ocean (e.g., Wassmann et al., 2004; Cai et al., 2010; Wassmann, 2011). Studies to date have mainly been confined to either the Barents Sea region of the extensive Eurasian shelf (e.g., Andreassen and Wassmann, 1998; Wassmann, 2002; Olli et al., 2002; Coppola et al., 2002; Wassmann, 2004; Lalande et al., 2008; Lalande et al., 2009; Reigstad et al., 2011), or to the more narrow western Arctic (North American) shelves and neighboring Canada Basin (e.g., Hargrave et al., 1994; Moran et al., 1997, 2005; Moran and Smith, 2000; Chen et al., 2003; Baskaran et al., 2003; Trimble and Baskaran, 2005; Lalande et al., 2007; Fahl and Nöthig, 2007; Lepore and Moran, 2007; Cai et al., 2010). The broad picture of Arctic Ocean surface-ocean POC export that is emerging is that the studied shelf/slope waters exhibit higher export fluxes than the perennially ice-covered central basins, consistent with elevated primary production and inefficient recycling in these Arctic shelf/ Marginal Ice Zone (MIZ) regions.
Settling-based surface ocean export of particulate organic carbon (POC) in the western Eurasian sector of the Arctic Ocean was investigated from the marginal ice zone (MIZ) of the northern Barents Sea to the North Pole area. Upper ocean profiles of POC were combined with corresponding dissolved and particulate ²³⁴Th activities measured with a low-volume at-sea direct beta counting protocol to constrain the ²³⁴Th-derived POC export in July and August of 2001 to 6−32 mmol m⁻² d⁻¹ for the Barents Sea MIZ dropping to 2–6 mmol m⁻² d⁻¹ for multi-year-ice (MYI) covered central Arctic stations in Nansen, Amundsen and Makarov basins. Secular equilibrium between ²³⁴Th and ²³⁸U activities in intermediate to deep waters in the Amundsen Basin (n=10) demonstrated that the at-sea measurement protocol was functioning satisfactorily. There was no distinction in POC export efficiency between the MIZ and the MYI-covered interior basins with an average ratio between ²³⁴Th-derived POC export and primary production (so-called ThE ratio) of 44%. A projected increase in primary production with retreat in areal extent of sea ice is thus likely to yield increased POC sequestration in the Arctic Ocean interior.
234Th in different size classes of sediment trap collected particles from the Northwestern Pacific Ocean
2012, Geochimica et Cosmochimica Acta
²³⁴Th, a surface area specific particle-reactive radionuclide has been used to estimate particulate organic carbon (POC) export fluxes, based on the POC/²³⁴Th ratio of sinking particles and the ²³⁴Th flux, in the ocean. The POC/²³⁴Th ratios from large particles (>50 μm) are conventionally considered to represent sinking particles (collected by sediment traps), but this assumption has not been thoroughly tested. More recently, Hung and Gong (2010) separated sinking particles from the northern South China Sea (where diatoms are the most dominant group) using different Nitex screens and found that small (<50 μm) sinking particles dominate the bulk ²³⁴Th and POC flux. However, the size distribution of sinking particles has seldom been measured in picoplankton-dominated oligotrophic and upwelling conditions. Here we used Nitex screens to separate sinking particles in oligotrophic and upwelling regions. Additionally, images of selected bulk sinking particles (not subject to sequential filtration) were directly taken by scanning electron microscopy (SEM) to determine the size distribution of sinking particles. Within the trap-collected ²³⁴Th pool in the upwelling area, the 1–10 and 10–50 μm fractions had, on average, the highest amounts of ²³⁴Th, while POC did not show significant variations among the different size fractions. In the oligotrophic region, the 10–50 and 1–10 μm fractions had, on average, the highest amounts of ²³⁴Th, while the >150 and 10–50 μm had elevated shares of POC. Results thus demonstrate that ²³⁴Th was mainly carried by the smaller (<50 μm) sinking particles (∼70–80% of the total). SEM images of bulk sinking particles demonstrate that sinking particles contained abundant diatom cells, fecal pellets, detritus and small particle aggregates, mostly smaller than 50 μm. These images show that particles smaller than 50 μm indeed can account for a major fraction of the bulk sinking particles in open ocean regions. While the sequentially size-fractionated filtration might have influenced the original size distribution of sinking particles to some extent, the results provide new and consistent data which suggest that the contribution of particles smaller than 50 μm to the sinking ²³⁴Th flux can be a major fraction of the total sinking flux of this isotope, and thus, particles smaller than 50 μm cannot be ignored because the POC/²³⁴Th ratio that is often used is that of large (>50 μm) particles obtained from pump systems, not traps.
Seasonal succession of net primary productivity, particulate organic carbon export, and autotrophic community composition in the eastern Bering Sea
2012, Deep-Sea Research Part II: Topical Studies in Oceanography
Seasonal patterns in the partitioning of phytoplankton carbon during receding sea ice conditions in the eastern Bering Sea water column are presented using rates of ¹⁴C net primary productivity (NPP), phototrophic plankton carbon content, and POC export fluxes from shelf and slope waters in the spring (March 30–May 6) and summer (July 3–30) of 2008. At ice-covered and marginal ice zone (MIZ) stations on the inner and middle shelf in spring, NPP averaged 76±93 mmol C m⁻² d⁻¹, and in ice-free waters on the outer shelf NPP averaged 102±137 mmol C m⁻² d⁻¹. In summer, rates of NPP were more uniform across the entire shelf and averaged 43±23 mmol C m⁻² d⁻¹ over the entire shelf. A concomitant shift was observed in the phototrophic pico-, nano-, and microplankton community in the chlorophyll maximum, from a diatom dominated system (80±12% autotrophic C) in ice covered and MIZ waters in spring, to a microflagellate dominated system (71±31% autotrophic C) in summer. Sediment trap POC fluxes near the 1% PAR depth in ice-free slope waters increased by 70% from spring to summer, from 10±7 mmol C m⁻² d⁻¹ to 17±5 mmol C m⁻² d⁻¹, respectively. Over the shelf, under-ice trap fluxes at 20 m were higher, averaging 43±17 mmol C m⁻² d⁻¹. POC export over the shelf and slope estimated from ²³⁴Th deficits averaged 11±5 mmol C m⁻² d⁻¹ in spring and 10±2 mmol C m⁻² d⁻¹ in summer. Average e-ratios calculated on a station-by-station basis decreased by ∼30% from spring to summer, from 0.46±0.48 in ice-covered and MIZ waters, to 0.33±0.26 in summer, though the high uncertainty prevents a statistical differentiation of these data.

View all citing articles on Scopus

View full text

Calibration of sediment traps and particulate organic carbon export using 234Th in the Barents Sea

Abstract

Introduction

Section snippets

Sample collection

Hydrography

Origins of 234Th/238U disequilibrium

Conclusion

Acknowledgements

Vertical flux of phytoplankton and particulate biogenic matter in the marginal ice zone of the Barents Sea in May 1993

Mar. Ecol., Prog. Ser.

The behavior of Al, Mn, Ba, Sr, REE and Th isotopes during in vitro degradation of large marine particles

Mar. Chem.

Removal of thorium-234 by scavenging in the bottom nepheloid layer of the ocean

Earth Planet. Sci. Lett.

Export flux of carbon at the equator during EqPac time-series cruises estimated from 234Th measurements

Deep-Sea Res., Part II

Do upper-ocean sediment traps provide an accurate record of particle flux?

Nature

Carbon and nitrogen export during the JGOFS North Atlantic Bloom Experiment estimated from 234Th:238U disequilibria

Deep-Sea Res.

A three dimensional time-dependent approach to calibrating sediment trap fluxes

Glob. Biogeochem. Cycles

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

Deep-Sea Res., Part II

Upper ocean export of particulate organic carbon in the Arabian Sea derived from thorium-234

Deep-Sea Res.

Rates of particle scavenging and particulate organic carbon export estimated using 234Th as a tracer in the subtropical and equatorial Atlantic Ocean

Deep-Sea Res., Part II

234Th as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean

Deep-Sea Res., Part II

238U–234U and 232Th in seawater

Earth Planet. Sci. Lett.

Labyrinth of doom: advice to minimize the “swimmer” component in sediment trap collections

Limnol. Oceanogr.

234Th:238U disequilibria within the California current

Limnol. Oceanogr.

Oceanic stratified euphotic zone as elucidated by 234Th:238U disequilibria

Limnol. Oceanogr.

Thorium-234/Uranium-238 disequilibrium as an indicator of scavenging rates and particulate organic carbon fluxes in the Northeast Water Polynya Greenland

J. Geophys. Res.

Physical and ecological processes in the marginal ice zone of the northern Barents Sea during the summer melt period

J. Mar. Syst.

Accumulation of Th, Pb, U and Ra in marine phytoplankton and its geochemical significance

Limnol. Oceanogr.

The significance of microalgal blooms for fisheries and for the export of particulate organic carbon in oceans

J. Plankton Res.

Calibration of sediment traps and particulate organic carbon export using ²³⁴Th in the Barents Sea

Origins of ²³⁴Th/²³⁸U disequilibrium

Export flux of carbon at the equator during EqPac time-series cruises estimated from ²³⁴Th measurements

Carbon and nitrogen export during the JGOFS North Atlantic Bloom Experiment estimated from ²³⁴Th:²³⁸U disequilibria

Rates of particle scavenging and particulate organic carbon export estimated using ²³⁴Th as a tracer in the subtropical and equatorial Atlantic Ocean

²³⁴Th as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean

²³⁸U–²³⁴U and ²³²Th in seawater

²³⁴Th:²³⁸U disequilibria within the California current

Oceanic stratified euphotic zone as elucidated by ²³⁴Th:²³⁸U disequilibria