scholarly journals High mercury accumulation in deep-ocean hadal sediments

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hamed Sanei ◽  
Peter M. Outridge ◽  
Kazumasa Oguri ◽  
Gary A. Stern ◽  
Bo Thamdrup ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Marine Sediments ◽  
Hot Spots ◽  
Deep Ocean ◽  
Mercury Accumulation ◽  
Preliminary Estimate ◽  
High Mercury ◽  
Mercury Fluxes ◽  
Hg Accumulation

AbstractOcean sediments are the largest sink for mercury (Hg) sequestration and hence an important part of the global Hg cycle1. Yet accepted global average Hg flux data for deep-ocean sediments (> 200 m depth) are not based on measurements on sediments but are inferred from sinking particulates2. Mercury fluxes have never been reported from the deepest zone, the hadal (> 6 km depth). Here we report the first measurements of Hg fluxes from two hadal trenches (Atacama and Kermadec) and adjacent abyssal areas (2–6 km). Mercury concentrations of up to 400 ng g−1 were the highest recorded in marine sediments remote from anthropogenic or hydrothermal sources. The two trench systems differed significantly in Hg concentrations and fluxes, but hadal and abyssal areas within each system did not. The relatively low recent mean flux at Kermadec was 6–15 times higher than the inferred deep-ocean average1,3, while the median flux across all cores was 22–56 times higher. Thus, some hadal and abyssal sediments are Hg accumulation hot-spots. The hadal zone comprises only ~ 1% of the deep-ocean area, yet a preliminary estimate based on sediment Hg and particulate organic carbon (POC) fluxes suggests total hadal Hg accumulation may be 12–30% of the estimate for the entire deep-ocean. The few abyssal data show equally high Hg fluxes near trench systems. These results highlight a need for further research into deep-ocean Hg fluxes to better constrain global Hg models.

scholarly journals Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates

2013 ◽  
Vol 10 (9) ◽  
pp. 14861-14885 ◽  
Author(s):  
K. Schmidt ◽  
C. L. De La Rocha ◽  
M. Gallinari ◽  
G. Cortese
Keyword(s):  
Calcium Carbonate ◽  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Deep Ocean ◽  
Simple Experiment ◽  
Surface Ocean

Abstract. Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d−1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

scholarly journals Preservation of terrestrial organic carbon in marine sediments off shore Taiwan: mountain building and atmospheric carbon dioxide sequestration

2013 ◽  
Vol 1 (1) ◽  
pp. 177-206
Author(s):  
S.-J. Kao ◽  
R. G. Hilton ◽  
K. Selvaraj ◽  
M. Dai ◽  
F. Zehetner ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Organic Carbon ◽  
Marine Sediments ◽  
Atmospheric Carbon Dioxide ◽  
Climatic Variability ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Terrestrial Biosphere ◽  
Atmospheric Carbon ◽  
Carbon Dioxide Co2

Abstract. Geological sequestration of atmospheric carbon dioxide (CO2) can be achieved by the erosion of organic carbon (OC) from the terrestrial biosphere and its burial in long-lived marine sediments. Rivers on mountain islands of Oceania in the western Pacific have very high rates of OC export to the ocean, yet its preservation offshore remains poorly constrained. Here we use the OC content (Corg, %), radiocarbon (Δ14Corg) and stable isotope (δ13Corg) composition of sediments offshore Taiwan to assess the fate of terrestrial OC. We account for rock-derived fossil OC to assess the preservation of OC eroded from the terrestrial biosphere (non-fossil OC) during flood discharges (hyperpycnal river plumes) and when river inputs are dispersed more widely (hypopycnal). The Corg, Δ14Corg and δ13Corg of marine sediment traps and cores indicate that during flood discharges, terrestrial OC is transferred efficiently to the deep ocean and accumulates offshore with little evidence for terrestrial OC loss. In marine sediments fed by dispersive river inputs, the Corg, Δ14Corg and δ13Corg are consistent with mixing of marine OC and terrestrial OC and suggest that efficient preservation of terrestrial OC (> 70%) is also associated with hypopycnal delivery. Re-burial of fossil OC is pervasive. Our findings from Taiwan suggest that erosion and marine burial of terrestrial non-fossil OC may sequester > 8 TgC yr−1 across Oceania, a significant geological CO2 sink which requires better constraint. We postulate that mountain islands of Oceania provide strong link between tectonic uplift and the carbon cycle, one moderated by the climatic variability that controls terrestrial OC delivery to the ocean.

scholarly journals Export fluxes in a naturally fertilized area of the Southern Ocean, the Kerguelen Plateau: seasonal dynamic reveals long lags and strong attenuation of particulate organic carbon flux (Part 1)

2014 ◽  
Vol 11 (12) ◽  
pp. 17043-17087 ◽  
Author(s):  
M. Rembauville ◽  
I. Salter ◽  
N. Leblond ◽  
A. Gueneugues ◽  
S. Blain
Keyword(s):  
Organic Carbon ◽  
Southern Ocean ◽  
Particulate Organic Carbon ◽  
Sediment Trap ◽  
Time Lag ◽  
Deep Ocean ◽  
Biomass Accumulation ◽  
Companion Paper ◽  
Kerguelen Plateau ◽  
Poc Flux

Abstract. A sediment trap moored in the naturally iron-fertilized Kerguelen plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth current speeds were low (∼10 cm s−1) and primarily tidal-driven (M2 tidal component) providing favorable hydrodynamic conditions for the collection of flux. Particulate organic carbon (POC) flux was generally low (<0.5 mmol m−2 d−1) although two episodic export events (<14 days) of 1.5 mmol m−2 d−1 were recorded. These increases in flux occurred with a 1 month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 ± 4.4 mmol m−2 yr−1 was relatively low considering the shallow deployment depth, but similar to deep-ocean (>2 km) fluxes measured from similarly productive iron-fertilized blooms. Comparison of the sediment trap data with complementary estimates of biomass accumulation and export indicate that ∼90% of the flux was lost between 200 and 300 m. We hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for rapid flux attenuation and the High Biomass Low Export regime characterizing the Kerguelen bloom. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

scholarly journals Not all calcite ballast is created equal: differing effects of foraminiferan and coccolith calcite on the formation and sinking of aggregates

2014 ◽  
Vol 11 (1) ◽  
pp. 135-145 ◽  
Author(s):  
K. Schmidt ◽  
C. L. De La Rocha ◽  
M. Gallinari ◽  
G. Cortese
Keyword(s):  
Calcium Carbonate ◽  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Deep Ocean ◽  
Simple Experiment ◽  
Surface Ocean

Abstract. Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking calcite particles like coccoliths and large, rapidly sinking calcite like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added calcite ballast. The foraminiferan tests, which sank as fast as 700 m d−1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foram-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the rolling tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast – different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.

scholarly journals Global Ocean Particulate Organic Carbon Flux Merged with Satellite Parameters

2016 ◽  
Author(s):  
Colleen B. Mouw ◽  
Audrey Barnett ◽  
Galen A. McKinley ◽  
Lucas Gloege ◽  
Darren Pilcher
Keyword(s):  
Time Series ◽  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Net Primary Production ◽  
Mixed Layer Depth ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Sediment Traps ◽  
Global Ocean ◽  
Carbon Export

Abstract. Particulate organic carbon (POC) flux estimated from POC concentration observations from sediment traps and 234Th are compiled across the global ocean. The compilation includes six time series locations: CARIACO, K2, OSP, BATS, OFP and HOT. Efficiency of the biological pump of carbon to the deep ocean depends largely on biologically mediated export of carbon from the surface ocean and its remineralization with depth, thus biologically related parameters able to be estimated from satellite observations were merged at the POC observation sites. Satellite parameters include: net primary production, percent microplankton, sea surface temperature, photosynthetically active radiation, diffuse attenuation coefficient at 490 nm, euphotic zone depth, as well as, climatological mixed layer depth. 85 % of the observations across the globe are concentrated in the Northern Hemisphere with 44 % of the data record overlapping the satellite record. Time series sites accounted for 36 % of the data. 71 % of the data is measured at ≥ 500 m with the most common deployment depths between 1000 and 1500 m. This dataset is valuable for investigations of CO2 drawdown, carbon export, remineralization, and sequestration. The compiled data can be freely accessed at doi:10.1594/PANGAEA.855600.

Mercury isotopes track the cause of carbon perturbations in the Ediacaran ocean

Geology ◽  
2020 ◽  
Author(s):  
Haifeng Fan ◽  
Xuewu Fu ◽  
Jack F. Ward ◽  
Runsheng Yin ◽  
Hanjie Wen ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Carbon Isotope ◽  
Marine Sediments ◽  
South China ◽  
South Australia ◽  
Deep Ocean ◽  
Isotope Data ◽  
Carbonate Carbon ◽  
Terrestrial Input

The unusual carbon biogeochemical cycling that occurred in the Ediacaran (ca. 635–541 Ma) ocean may have been critical for ocean oxygenation and Ediacaran life evolution. However, the triggers of the peculiar Ediacaran carbonate carbon isotope (δ13Ccarb) excursions are not well understood. Because mercury (Hg) has a strong affinity for organic carbon, we measured Hg isotope compositions (δ202Hg and Δ199Hg) from Ediacaran marine sediments of South China and South Australia to better understand the causes of the Ediacaran δ13Ccarb excursions. During two local positive δ13Ccarb excursions in the Doushantuo Formation, gradually decreasing Δ199Hg and increasing δ202Hg trends are primarily ascribed to enhanced terrestrial input. Decreasing δ202Hg in both the Doushantuo and Wonoka Formations during the latter part of the Shuram negative δ13Ccarb excursion demonstrates the significant, and potentially widespread, contribution of upwelling Hg associated with dissolved organic carbon (Hg-DOC) from the open deep ocean. New Hg isotope data also suggest that a large Hg-DOC reservoir may have been present in the open ocean continuously from the early to mid–late Ediacaran Period (ca. 635–551 Ma), buffering ocean oxygenation at that time.

scholarly journals Attenuation of sinking particulate organic carbon flux through the mesopelagic ocean

2015 ◽  
Vol 112 (4) ◽  
pp. 1089-1094 ◽  
Author(s):  
Chris M. Marsay ◽  
Richard J. Sanders ◽  
Stephanie A. Henson ◽  
Katsiaryna Pabortsava ◽  
Eric P. Achterberg ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Atmospheric Carbon Dioxide ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Length Scale ◽  
Deep Sea Sediment ◽  
The North ◽  
Labile Fraction ◽  
Poc Flux

The biological carbon pump, which transports particulate organic carbon (POC) from the surface to the deep ocean, plays an important role in regulating atmospheric carbon dioxide (CO2) concentrations. We know very little about geographical variability in the remineralization depth of this sinking material and less about what controls such variability. Here we present previously unpublished profiles of mesopelagic POC flux derived from neutrally buoyant sediment traps deployed in the North Atlantic, from which we calculate the remineralization length scale for each site. Combining these results with corresponding data from the North Pacific, we show that the observed variability in attenuation of vertical POC flux can largely be explained by temperature, with shallower remineralization occurring in warmer waters. This is seemingly inconsistent with conclusions drawn from earlier analyses of deep-sea sediment trap and export flux data, which suggest lowest transfer efficiency at high latitudes. However, the two patterns can be reconciled by considering relatively intense remineralization of a labile fraction of material in warm waters, followed by efficient downward transfer of the remaining refractory fraction, while in cold environments, a larger labile fraction undergoes slower remineralization that continues over a longer length scale. Based on the observed relationship, future increases in ocean temperature will likely lead to shallower remineralization of POC and hence reduced storage of CO2 by the ocean.

scholarly journals Export fluxes in a naturally iron-fertilized area of the Southern Ocean – Part 1: Seasonal dynamics of particulate organic carbon export from a moored sediment trap

2015 ◽  
Vol 12 (11) ◽  
pp. 3153-3170 ◽  
Author(s):  
M. Rembauville ◽  
I. Salter ◽  
N. Leblond ◽  
A. Gueneugues ◽  
S. Blain
Keyword(s):  
Organic Carbon ◽  
Southern Ocean ◽  
Particulate Organic Carbon ◽  
Sediment Trap ◽  
Time Lag ◽  
Deep Ocean ◽  
Companion Paper ◽  
Grazing Pressure ◽  
Carbon Export ◽  
Poc Flux

Abstract. A sediment trap moored in the naturally iron-fertilized Kerguelen Plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth, current speeds were typically low (~ 10 cm s−1) and primarily tidal-driven (M2 tidal component). Although advection was weak, the sediment trap may have been subject to hydrodynamical and biological (swimmer feeding on trap funnel) biases. Particulate organic carbon (POC) flux was generally low (< 0.5 mmol m−2 d−1), although two episodic export events (< 14 days) of 1.5 mmol m−2 d−1 were recorded. These increases in flux occurred with a 1-month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 ± 4.4 mmol m−2 yr−1 was low considering the shallow deployment depth but comparable to independent estimates made at similar depths (~ 300 m) over the plateau, and to deep-ocean (> 2 km) fluxes measured from similarly productive iron-fertilized blooms. Although undertrapping cannot be excluded in shallow moored sediment trap deployment, we hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for the low POC flux beneath the base of the winter mixed layer. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

scholarly journals Preservation of terrestrial organic carbon in marine sediments offshore Taiwan: mountain building and atmospheric carbon dioxide sequestration

2014 ◽  
Vol 2 (1) ◽  
pp. 127-139 ◽  
Author(s):  
S.-J. Kao ◽  
R. G. Hilton ◽  
K. Selvaraj ◽  
M. Dai ◽  
F. Zehetner ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Organic Carbon ◽  
Marine Sediments ◽  
Atmospheric Carbon Dioxide ◽  
Climatic Variability ◽  
Deep Ocean ◽  
Terrestrial Biosphere ◽  
Holocene Sediments ◽  
Co2 Sink ◽  
Atmospheric Carbon

Abstract. Geological sequestration of atmospheric carbon dioxide (CO2) can be achieved by the erosion of organic carbon (OC) from the terrestrial biosphere and its burial in long-lived marine sediments. Rivers on mountain islands of Oceania in the western Pacific have very high rates of OC export to the ocean, yet its preservation offshore remains poorly constrained. Here we use the OC content (Corg, %), radiocarbon (Δ 14Corg) and stable isotope (δ13Corg) composition of sediments offshore Taiwan to assess the fate of terrestrial OC, using surface, sub-surface and Holocene sediments. We account for rock-derived OC to assess the preservation of OC eroded from the terrestrial biosphere and the associated CO2 sink during flood discharges (hyperpycnal river plumes) and when river inputs are dispersed more widely (hypopycnal). The Corg, Δ14Corg and δ 13Corg of marine sediment traps and cores indicate that during flood discharges, terrestrial OC can be transferred efficiently down submarine canyons to the deep ocean and accumulates offshore with little evidence for terrestrial OC loss. In marine sediments fed by dispersive river inputs, the Corg, Δ14Corg and δ 13Corg are consistent with mixing of terrestrial OC with marine OC and suggest that efficient preservation of terrestrial OC (>70%) is also associated with hypopycnal delivery. Sub-surface and Holocene sediments indicate that this preservation is long-lived on millennial timescales. Re-burial of rock-derived OC is pervasive. Our findings from Taiwan suggest that erosion and offshore burial of OC from the terrestrial biosphere may sequester >8 TgC yr−1 across Oceania, a significant geological CO2 sink which requires better constraint. We postulate that mountain islands of Oceania provide a strong link between tectonic uplift and the carbon cycle, one moderated by the climatic variability which controls terrestrial OC delivery to the ocean.

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