Seasonal changes in thorium scavenging and particle aggregation in the western Arctic Ocean

Lepore, Kate; Moran, S. Bradley

doi:10.1016/j.dsr.2007.03.001

Cited by 16 publications

(21 citation statements)

References 65 publications

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“…Higher POC/ 234 Th ratios were observed during the summer and in areas with greater absolute POC flux from the photic zone (Table ). Furthermore, during summer and in higher flux environments, POC/ 234 Th ratios decreased with depth (Figures ), which may reflect a combination of preferential remineralization of POC, decay of particle‐bound 234 Th, or particle aggregation and disaggregation [ Buesseler et al ., ; Burd et al ., ; Lepore and Moran , ].…”

Section: Resultsmentioning

confidence: 99%

Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export

Baumann

Moran

Lomas

et al. 2013

J. Geophys. Res. Oceans

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[1] Particulate organic carbon (POC) export fluxes and net primary production (NPP) rates are used to assess seasonal patterns in the export ratio (e-ratio ¼ POC export/NPP) in relation to proximity of the sea-ice edge near the shelf break of the eastern Bering Sea during [2008][2009][2010]. POC fluxes were relatively low in April (4.6 6 1.6, trap, and 5.7 6 4.3 mmol C m À2 d À1 , 234 Th-derived) and increased in May-early June (19.9 6 13.3 and 17.0 6 8.8 mmol C m À2 d À1 ). POC export reached a maximum in mid-June-mid-July (30.0 6 12.6 and 48.1 6 17.4 in 2009; 33.1 6 27.6 and 57.0 6 68.4 mmol C m À2 d À1 in 2010) and decreased by late July (13.1 6 4.7 and 14.1 6 8.0 mmol C m À2 d À1 ). NPP rates were relatively high and export fluxes low near the ice-edge in spring leading to e-ratios <0.25. In early summer, POC export exceeded NPP at individual stations and resulted in e-ratios >1, which is attributed to a temporal decoupling, or offset, of spring NPP and export during summer. While these observations reveal a seasonal progression in POC export and the e-ratio, there is no direct relationship to sea-ice proximity. Furthermore, based on a water column-sediment 234 Th budget, the off-shelf export of POC during springsummer is estimated to be 24 6 35 mmol C m À2 d À1 , which represents an off-shelf e-ratio of 0.07 and 0.21 for contemporaneous seasonally averaged daily rates of NPP and 0.17 and 0.52 for historical monthly averaged daily rates of NPP. An implication is that off-shelf POC transport may represent a seasonal net sink for CO 2 in this and other polar shelf regions.

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Section: Resultsmentioning

confidence: 99%

Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export

Baumann

Moran

Lomas

et al. 2013

J. Geophys. Res. Oceans

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“…It is analogous to the model proposed by Bacon et al (1985), with the addition of the remineralization of small particles leading to the release of small particulate material to solution. The resulting model is identical to that applied in subsequent analyses of Th and particle measurements on oceanic samples (e.g., Murnane et al, 1990Murnane et al, , 1994Murnane et al, , 1996Cochran et al, 1993Cochran et al, , 2000Murnane, 1994;Lepore and Moran, 2007). The interested reader is invited to consult these references for a discussion of the model assumptions.…”

Section: Methodsmentioning

confidence: 95%

“…Present-day knowledge about sorption reactions and particle processes in the ocean stems largely from measurements of particle-reactive metals, in particular thorium. Estimates of rate constants of Th and particle cycling have been obtained from such measurements at various locations in the world oceans, e.g., in the North Pacific (Nozaki et al, 1981;Nozaki et al, 1987;Murnane et al, 1990;, the Equatorial Pacific , the Panama Basin (Bacon and Anderson, 1982), the Arctic Ocean Lepore and Moran, 2007), the North Atlantic (Cochran et al, 1993;Murnane et al, 1994Murnane et al, , 1996, the Ross Sea (Cochran et al, 2000), the Indian Ocean near Kerguelen Islands (Venchiarutti et al, 2008), and the Drake Passage (Venchiarutti et al, 2011). These estimates range over several orders of magnitude and suffer generally from very large uncertainties ( Fig.…”

Section: Introductionmentioning

confidence: 99%

What can paired measurements of Th isotope activity and particle concentration tell us about particle cycling in the ocean?

Marchal

Lam

2012

Geochimica et Cosmochimica Acta

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“…Disequilibria between 228 Th and 228 Ra have been interpreted in terms of scavenging removal in the GEOSECS (Li et al, ) and JGOFS (Luo et al, ) ocean chemistry campaigns. Only a few studies have derived 228 Th deficit‐based particulate fluxes (Lepore & Moran, ; Okubo et al, ). This is because the low open ocean abundance of sediment‐sourced 228 Ra (half‐life 5.8 years) makes it challenging to measure this nuclide and its daughter 228 Th with sufficient accuracy.…”

Section: Introductionmentioning

confidence: 99%

Flux of Particulate Elements in the North Atlantic Ocean Constrained by Multiple Radionuclides

Hayes

Black

Anderson

et al. 2018

Global Biogeochemical Cycles

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Sinking particles strongly regulate the distribution of reactive chemical substances in the ocean, including particulate organic carbon and other elements (e.g., P, Cd, Mn, Cu, Co, Fe, Al, and 232Th). Yet, the sinking fluxes of trace elements have not been well described in the global ocean. The U.S. GEOTRACES campaign in the North Atlantic (GA03) offers the first data set in which the sinking flux of carbon and trace elements can be derived using four different radionuclide pairs (238U:234Th ;210Pb:210Po; 228Ra:228Th; and 234U:230Th) at stations co‐located with sediment trap fluxes for comparison. Particulate organic carbon, particulate P, and particulate Cd fluxes all decrease sharply with depth below the euphotic zone. Particulate Mn, Cu, and Co flux profiles display mixed behavior, some cases reflecting biotic remineralization, and other cases showing increased flux with depth. The latter may be related to either lateral input of lithogenic material or increased scavenging onto particles. Lastly, particulate Fe fluxes resemble fluxes of Al and 232Th, which all have increasing flux with depth, indicating a dominance of lithogenic flux at depth by resuspended sediment transported laterally to the study site. In comparing flux estimates derived using different isotope pairs, differences result from different timescales of integration and particle size fractionation effects. The range in flux estimates produced by different methods provides a robust constraint on the true removal fluxes, taking into consideration the independent uncertainties associated with each method. These estimates will be valuable targets for biogeochemical modeling and may also offer insight into particle sinking processes.

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Seasonal changes in thorium scavenging and particle aggregation in the western Arctic Ocean

Cited by 16 publications

References 65 publications

Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export

Seasonal decoupling of particulate organic carbon export and net primary production in relation to sea-ice at the shelf break of the eastern Bering Sea: Implications for off-shelf carbon export

What can paired measurements of Th isotope activity and particle concentration tell us about particle cycling in the ocean?

Flux of Particulate Elements in the North Atlantic Ocean Constrained by Multiple Radionuclides

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