Residual β activity of particulate 234Th as a novel proxy for tracking sediment resuspension in the ocean

Lin, Wen‐Wei; Chen, Liqi; Zeng, Shi; Li, Tao; Wang, Yinghui; Yu, Kefu

doi:10.1038/srep27069

Cited by 11 publications

(7 citation statements)

References 53 publications

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“…The net rate of removal of particulate 234 Th due to particle sinking (PTh) and the removal of dissolved 234 Th onto particles (JTh) were calculated for the shelf and slope stations at depths between 25 m and 200 m to facilitate comparison with prior studies of this region (Table 3), however, resuspension likely plays a role at some or all of these stations (Lin et al, 2016) (Cochran et al, 1995;Moran et al, 2005;Moran and Smith, 2000;Trimble and Baskaran, 2005;Yu et al, 2012).…”

Section: High 234 Th Export and Removal Over The Western Arctic Shelfmentioning

confidence: 99%

An investigation of basin-scale controls on upper ocean export and remineralization

Black¹

2018

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The biological carbon pump (BCP) helps to moderate atmospheric carbon dioxide levels by bringing carbon to the deep ocean, where it can be sequestered on timescales of centuries to millennia. Climate change is predicted to decrease the efficiency of the global BCP, however, the magnitude and timescale of this shift is largely uncertain and will likely impact some areas of the global ocean more significantly than others. Therefore, it is imperative that we (1) accurately quantify surface export and remineralization of particulate organic carbon (POC) via the BCP over large regions of the global ocean, (2) examine the factors controlling these POC fluxes and their variability, which includes the cycling of biologically-relevant trace metals, and (3) establish if and how the BCP is changing over time.This thesis focuses on addressing various aspects of these objectives using the 234 Th-238 U method across basin-scale GEOTRACES transects. First, the export and remineralization of POC were examined across large gradients in productivity, upwelling, community structure, and dissolved oxygen in the southeastern tropical Pacific Ocean. Although low oxygen zones are traditionally thought to have decreased POC flux attenuation relative to other regions of the global ocean and the low oxygen Pacific locations followed this pattern, regions that were functionally anoxic had enhanced attenuation in the upper 400 m. Second, trace metal export and remineralization were quantified across the Pacific transect. Because many trace metals are necessary for the metabolic functions of marine organisms and can co-limit marine productivity, the controls on the cycling of trace metals in the upper ocean were examined. Lastly, POC export was determined across two transects in the Western Arctic Ocean, where light and nutrient availability drive the biological pump. Upper ocean export estimates in the central basin did not reflect a substantial change in the biological pump compared to studies from the last three decades, however, an extensive maximum in 234 Th relative to 238 U deeper in the water column indicated that rapid vertical transport had occurred, which could suggest a more efficient biological pump in the Arctic Ocean.

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Section: High 234 Th Export and Removal Over The Western Arctic Shelfmentioning

confidence: 99%

An investigation of basin-scale controls on upper ocean export and remineralization

Black¹

2018

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“…The shallow Chukchi Shelf is not only characterized by intensive sedimentary N removal [ 15 , 49 ], but also tight pelagic–benthic coupling, namely sediment resuspension. Sediment resuspension has long been speculated over the Chukchi Shelf in summer by the observed high particle flux [ 40 ], enhanced scavenging of particle-reactive radionuclides (such as 234 Th, 210 Pb) [ 50 – 52 ], intensive sediment transport [ 53 , 54 ] as well as high turbidity [ 25 , 55 ], in the bottom waters. This phenomenon is also expected because of strong bottom currents passing through this area, especially during the ice-free season [ 22 , 23 ].…”

Section: Discussionmentioning

confidence: 99%

“…Although turbidity was not concurrently measured, the resuspended sediments were directly tracked in the same cruise. Based on a novel proxy of residual β activity of particulate 234 Th, Lin et al [ 25 ] distinguished the resuspended particles provided by benthic sediment from the biogenic particles produced by photosynthesis, and demonstrated the visible sediment resuspension event over the Chukchi Shelf during summer 2012. Strong mixing of water column was also evident during our cruise by the homogeneous distribution of salinity (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The benthic environment of the Chukchi Sea is highly dynamic. Strong current, summer cyclone, and tides commonly induce sediment resuspension in this region [ 22 – 25 ]. It is easy to speculate that anaerobic microbes might be stirred up from bottom and exert their metabolism when attached onto marine aggregates, where suboxic micro-niches exist.…”

Section: Introductionmentioning

confidence: 99%

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A potential nitrogen sink discovered in the oxygenated Chukchi Shelf waters of the Arctic

et al. 2017

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The western Arctic Shelf has long been considered as an important sink of nitrogen because high primary productivity of the shelf water fuels active denitrification within the sediments, which has been recognized to account for all the nitrogen (N) removal of the Pacific water inflow. However, potentially high denitrifying activity was discovered within the oxygenated Chukchi Shelf water during our summer expedition. Based on 15N-isotope pairing incubations, we estimated denitrification rates ranging from 1.8 ± 0.4 to 75.9 ± 8.7 nmol N2 L−1 h−1. We find that the spatial pattern of denitrifying activity follows well with primary productivity, which supplies plentiful fresh organic matter, and there was a strong correlation between integrated denitrification and integrated primary productivity. Considering the active hydrodynamics over the Chukchi Shelf during summer, resuspension of benthic sediment coupled with particle-associated bacteria induces an active denitrification process in the oxic water column. We further extrapolate to the whole Chukchi Shelf and estimate an N removal flux from this cold Arctic shelf water to be 12.2 Tg-N year−1, which compensates for the difference between sediment cores incubation (~ 3 Tg-N year−1) and geochemical estimation based on N deficit relative to phosphorous (~ 16 Tg-N year−1). We infer that dynamic sediment resuspension combined with high biological productivity stimulates intensive denitrification in the water column, potentially creating a nitrogen sink over the shallow Arctic shelves that have previously been unrecognized.

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“…Radionuclides participate in environmental processes such as weathering, sedimentation, resuspension, etc. [1]. Consequently, many studies have measured radionuclide concentrations in various environmental matrices, such as the crust, rocks, sandy beaches, building materials, and the atmosphere [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Gross Alpha and Gross Beta Activity Concentrations in the Dust Fractions of Urban Surface-Deposited Sediment in Russian Cities

2021

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Studies of gross alpha and gross beta activity in road- and surface-deposited sediments were conducted in three Russian cities in different geographical zones. To perform radiation measurements, new methods were applied which allow dealing with low mass and low volume dust-sized (2–100 μm) samples obtained after the size fractionation procedure. The 2–10 μm fraction size had the highest gross beta activity concentration (GB)—1.32 Bq/g in Nizhny Novgorod and Rostov-On-Don, while the 50–100 μm fraction size was most prominent in Ekaterinburg. This can be attributed to the presence of radionuclides that are transferred through natural and anthropogenic processes. The highest gross alpha activity concentration (GA) in fraction sizes was found in Rostov-on-Don city within the 50–100 μm range—0.22 Bq/g. The fraction sizes 50–100 μm have a higher gross alpha activity concentration than 2–10 μm and 10–50 μm fraction sizes due to natural partitioning of the main minerals constituting the urban surface-deposited sediment (USDS). Observed dependencies reflect the geochemical processes which take place during the formation and transport of urban surface sediments. Developed experimental methods of radiation measurements formed the methodological base of urban geochemical studies.

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Residual β activity of particulate 234Th as a novel proxy for tracking sediment resuspension in the ocean

Cited by 11 publications

References 53 publications

An investigation of basin-scale controls on upper ocean export and remineralization

An investigation of basin-scale controls on upper ocean export and remineralization

A potential nitrogen sink discovered in the oxygenated Chukchi Shelf waters of the Arctic

Gross Alpha and Gross Beta Activity Concentrations in the Dust Fractions of Urban Surface-Deposited Sediment in Russian Cities

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