scholarly journals The export flux of particulate organic carbon derived from <sup>210</sup>Po∕<sup>210</sup>Pb disequilibria along the North Atlantic GEOTRACES GA01 transect: GEOVIDE cruise

2019 ◽  
Vol 16 (2) ◽  
pp. 309-327 ◽  
Author(s):  
Yi Tang ◽  
Nolwenn Lemaitre ◽  
Maxi Castrillejo ◽  
Montserrat Roca-Martí ◽  
Pere Masqué ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
North Atlantic ◽  
Study Region ◽  
Vertical Advection ◽  
Export Flux ◽  
The North ◽  
Iberian Basin ◽  
Poc Export ◽  
The North Atlantic

Abstract. The disequilibrium between 210Po activity and 210Pb activity in seawater samples was determined along the GEOTRACES GA01 transect in the North Atlantic during the GEOVIDE cruise (May–June 2014). A steady-state model was used to quantify vertical export of particulate 210Po. Vertical advection was incorporated into one version of the model using time-averaged vertical velocity, which had substantial variance. This resulted in large uncertainties for the 210Po export flux in this model, suggesting that those calculations of 210Po export fluxes should be used with great care. Despite the large uncertainties, there is no question that the deficits of 210Po in the Iberian Basin and at the Greenland Shelf have been strongly affected by vertical advection. Using the export flux of 210Po and the particulate organic carbon (POC) to 210Po ratio of total (> 1 µm) particles, we determined the POC export fluxes along the transect. Both the magnitude and efficiency of the estimated POC export flux from the surface ocean varied spatially within our study region. Export fluxes of POC ranged from negligible to 10 mmol C m−2 d−1, with enhanced POC export in the Labrador Sea. The cruise track was characterized by overall low POC export relative to net primary production (export efficiency < 1 %–15 %), but relatively high export efficiencies were seen in the basins where diatoms dominated the phytoplankton community. The particularly low export efficiencies in the Iberian Basin, on the other hand, were explained by the dominance of smaller phytoplankton, such as cyanobacteria or coccolithophores. POC fluxes estimated from the 210Po∕210Pb and 234Th∕238U disequilibria agreed within a factor of 3 along the transect, with higher POC estimates generally derived from 234Th. The differences were attributed to integration timescales and the history of bloom events.

scholarly journals The export flux of particulate organic carbon derived from <sup>210</sup>Po / <sup>210</sup>Pb disequilibria along the North Atlantic GEOTRACES GA01 (GEOVIDE) transect

2018 ◽  
Author(s):  
Yi Tang ◽  
Nolwenn Lemaitre ◽  
Maxi Castrillejo ◽  
Montserrat Roca-Martí ◽  
Pere Masqué ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
North Atlantic ◽  
Net Primary Production ◽  
Study Region ◽  
Export Flux ◽  
The North ◽  
Poc Export ◽  
The North Atlantic ◽  
Vertical Export

Abstract. The disequilibrium between 210Po activity and 210Pb activity in seawater samples was determined along the GEOTRACES GA01 transect in the North Atlantic during the GEOVIDE cruise (May–June 2014). A steady-state model was used to quantify vertical export of particulate 210Po. The deficits of 210Po in the Iberian Basin and at the Greenland Shelf were strongly affected by vertical advection. Using the export flux of 210Po and the particulate organic carbon (POC) to 210Po ratio on total (> 1 µm) particles, we determined the POC export fluxes along the transect. Both the magnitude and efficiency of the estimated POC export flux from the surface ocean varied spatially within our study region. Export fluxes of POC ranged from negligible to 10 mmol C m−2 d−1, with enhanced POC export in the Labrador Sea. The cruise track was characterized by overall low POC export relative to net primary production (export efficiency 

scholarly journals High variability of particulate organic carbon export along the North Atlantic GEOTRACES section GA01 as deduced from <sup>234</sup>Th fluxes

2018 ◽  
Vol 15 (21) ◽  
pp. 6417-6437 ◽  
Author(s):  
Nolwenn Lemaitre ◽  
Frédéric Planchon ◽  
Hélène Planquette ◽  
Frank Dehairs ◽  
Debany Fonseca-Batista ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
North Atlantic ◽  
Size Fraction ◽  
Material Surface ◽  
The North ◽  
Poc Export ◽  
The North Atlantic ◽  
Iberian Margin

Abstract. In this study we report particulate organic carbon (POC) export fluxes for different biogeochemical basins in the North Atlantic as part of the GEOTRACES GA01 expedition (GEOVIDE, May–June 2014). Surface POC export fluxes were deduced by combining export fluxes of total Thorium-234 (234Th) with the ratio of POC to 234Th of sinking particles at the depth of export. Particles were collected in two size classes (>53 and 1–53 µm) using in situ pumps and the large size fraction was considered representative of sinking material. Surface POC export fluxes revealed latitudinal variations between provinces, ranging from 1.4 mmol m−2 d−1 in the Irminger basin, where the bloom was close to its maximum, to 12 mmol m−2 d−1 near the Iberian Margin, where the bloom had already declined. In addition to the state of progress of the bloom, variations of the POC export fluxes were also related to the phytoplankton size and community structure. In line with previous studies, the presence of coccolithophorids and diatoms appeared to enhance the POC export flux, while the dominance of picophytoplankton cells, such as cyanobacteria, resulted in lower fluxes. The ratio of POC export to primary production (PP) strongly varied regionally and was generally low (≤14 %), except at two stations located near the Iberian Margin (35 %) and within the Labrador basin (38 %), which were characterized by unusual low in situ PP. We thus conclude that during the GEOVIDE cruise, the North Atlantic was not as efficient in exporting carbon from the surface, as reported earlier by others. Finally, we also estimated the POC export at 100 m below the surface export depth to investigate the POC transfer efficiencies. This parameter was also highly variable amongst regions, with the highest transfer efficiency at sites where coccolithophorids dominated.

scholarly journals High variability of export fluxes along the North Atlantic GEOTRACES section GA01: Particulate organic carbon export deduced from the <sup>234</sup>Th method

2018 ◽  
Author(s):  
Nolwenn Lemaitre ◽  
Frédéric Planchon ◽  
Hélène Planquette ◽  
Frank Dehairs ◽  
Debany Fonseca-Batista ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
North Atlantic ◽  
Size Fraction ◽  
Material Surface ◽  
The North ◽  
Poc Export ◽  
The North Atlantic ◽  
Iberian Margin

Abstract. In this study, we report Particulate Organic Carbon (POC) export fluxes estimated using the 234Th-based approach in different biogeochemical basins of the North Atlantic, as part of the GEOTRACES GA01 expedition (GEOVIDE, May–June 2014). Surface POC export fluxes were deduced by combining export fluxes of 234Th with the POC to 234Th ratio of sinking particles at the depth of export. Particles were collected in two size classes (> 53 µm and 1–53 µm) using in-situ pumps and the large size fraction was considered as representative of sinking material. Surface POC export fluxes revealed latitudinal variations between provinces ranging from 1.4 mmol C m−2 d−1 in the Irminger basin where the bloom was close to its maximum peak, to 12 mmol C m−2 d−1 near the Iberian Margin where the bloom had already declined. In addition to the bloom staging, the variations of POC export fluxes were also related to the phytoplankton community structure. In line with previous studies, the presence of coccolithophorids and diatoms appeared to increase the POC export flux while stations dominated by pico-phytoplankton cells, such as cyanobacteria, were characterized by lower fluxes. The surface POC export fluxes were then compared to in-situ and satellite primary production (PP) in order to assess the export efficiency. This ratio strongly varied regionally and was generally low (≤ 14 %), except at two stations located near the Iberian margin (35 %) and within the Labrador basin (38 %), which were characterized by unusual low in-situ PP. We thus conclude that the North Atlantic during this period was not as efficient in exporting carbon from the surface, as described in recent studies. Finally, we estimated the flux of POC exported 100 m below the surface export depth in order to investigate the transfer efficiency along the section. This parameter was also highly regional-dependent but the lowest attenuation of the POC flux was observed at stations where coccolithophorids dominated.

scholarly journals Particulate barium tracing of significant mesopelagic carbon remineralisation in the North Atlantic

2018 ◽  
Vol 15 (8) ◽  
pp. 2289-2307 ◽  
Author(s):  
Nolwenn Lemaitre ◽  
Hélène Planquette ◽  
Frédéric Planchon ◽  
Géraldine Sarthou ◽  
Stéphanie Jacquet ◽  
...  
Keyword(s):  
Carbon Sequestration ◽  
North Atlantic ◽  
Deep Convection ◽  
Sediment Traps ◽  
Heterotrophic Activity ◽  
Physical Forcing ◽  
The North ◽  
Poc Export ◽  
Order Of Magnitude ◽  
The North Atlantic

Abstract. The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May–June 2014) using the particulate biogenic barium (excess barium; Baxs) proxy. Important mesopelagic (100–1000 m) Baxs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Baxs content (up to 727 pmol L−1), which was attributed to an intense bloom averaging 6 mg chl a m−3 between January and June 2014 and by an intense 1500 m deep convection in the central Labrador Sea during the winter preceding the sampling. This downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs content (391 pmol L−1), was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Baxs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation fluxes (up to 13 and 4.6 mmol C m−2 d−1, respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014.

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