Author's personal copy
C, debilis C.debilisbloom debilis15C F.kerguelensis Figure 4
4. Statistical Analysis
4.1. Correlations between radionuclides and organic particles
The Pearson’s correlation coefficients are presented in Table IV. 210Popart/diss was positively correlated with the TEPpart but not with POC or CSP (ŇtŇ 2.571 rejects Ho). 210Pb did not present particle affinity for any of the organic particles studied here.234Thpart/diss was strongly correlated with POC and TEPpart.
4.2. Linear regressions analysis
In surface waters the variations of 234Thpart/diss, were well explained by POC (R2 = 0.72), whereas POC only accounted for much less of the variations in 210Popart/diss (R2 = 0.15) and
210Pbpart/diss (R2 = 0.28; Fig. 7 a-c). Both parameters, R2 and a suggest that 234Th had an affinity
for POC and that it was high (a = 1.27E-2); whereas the relationship between 210Po or 210Pb and POC was unclear, due to the very low R2 values.
At the more particle-producing stations influenced by the presence of ice (stations 178 and 193) POC explained about 65 % of the variations in 234Thpart/diss, and 75% in 210Popart/diss
(Figure 7 d-f). The slopes of the regressions between 234Thpart/diss and POC were not significantly different in productive conditions. However, the relationship with POC became apparent for 210Popart/diss (R2 = 0.74) Both parameters, R2 and a suggest that in particle-rich conditions (Fig. 7 d-f), the affinity of 234Th for POC remained as high as in particle poor conditions whereas 210Po seemed to trace POC well in particle-rich conditions only.
TEPpart explained best the variations (R2=0.92) in 210Popart/diss and 210Pbpart/diss (R2=0.80; Fig.
8a). 234Thpart/diss variations were less well explained by TEPpart (R2=0.67). However, 234Th exhibited the highest affinity for TEPpart (a = 2.27E-2 ± 2.59E-3), which was 2.2-3.5 times greater than with 210Po (a = 8.11E-3 ±8.42E-4).
The smaller fraction of TEP, 1>TEP>0.2μm, explained both 210Popart/diss (R2 =0.62) and
210Pbpart/diss (R2 = 0.74; Fig. 8b) distributions well; whereas there was no relation with 234Th (R2 < 0.001). The affinity of 210Po for 1>TEP>0.2μm was the highest (a = 1.47E-2) and ~ 2 times higher than that for TEPpart.
When CSP was plotted against 210Popart/diss, 210Pbpart/diss or 234Thpart/diss, none of the parameters describing CSP exhibited a R2 higher than ca. 12%.
DISCUSSION
Since a couple of decades, the empirical 234Th flux approach has been applied as a carbon flux proxy. A similar approach uses 210Po to estimate carbon fluxes, as well or in parallel with 234Th. Several authors reported that deeper insight was needed in the study of the affinity of 210Po and 234Th for POC in order to ultimately determine which tracer to use under specific circumstances (Friedrich and Michiel Rutgers van der Loeff, 2002; Murray et al., 2005; Stewart et al., 2007a, b, 2010; Verdeny, 2009). In our study, in the surface waters (<200 m) 234Th generally exhibited a higher affinity for POC (R2=0.72, a=0.0127) than 210Po (R2=0.15, a=0.0028). We will now investigate the parameters possibly influencing the affinity of these two radioisotopes for POC, looking at the phytoplankton composition and finally putting special emphasis on exopolymers.
First, we compare our data set with the only other one investigating 210Po and 234Th distributions as a function of POC in the Southern Ocean (Friedrich and Rutgers van der Loeff, 2002). The authors did not specifically compare the affinities of 210Po and 234Th for POC but used 234Th and 210Po to model the composition of the settling particles. They concluded that 210Po traced POC better; while 234Th traced biogenic silica (BSi) better. In their study, like in ours, 234Th had in general a higher affinity (R2 = 0.69; a=0.0021) than
210Po (R2 =0.59; a=0.0013) for POC (calculated from data in Friedrich and Rutgers van der Loeff, 2002).
Figure 9 compares the affinities of 210Po and 234Th for POC in the two Antarctic studies. The biological conditions during the investigation of Friedrich and Rutgers van der Loeff differed appreciably from ours. Friedrich and Rutgers van der Loeff encountered four distinct trophic conditions in the region of the PF (Figure 9): a Corethron sp. (a); a Corethron sp. + Fragilariopsis sp. (b) and a Fragilariopsis sp. (c) bloom as well as an area where non-siliceous organisms (heterotrophic flagellates, zooplankton, salps, fecal pellets) dominated (d). During ANTXXIV-3, samples were taken in late fall and most of the stations exhibited low particles concentrations (e). Two ice-influenced blooms (f), rich in particles that had not yet led to export (Rutgers van der Loeff et al., this issue), were encountered. Moreover, we removed any zooplankton found on our particlate samples in order to focus on organic matter coming from phytoplankton, bacteria and their exsudates. This likely caused the highest affinities of both 210Po and 234Th for POC (steeper a, Fig. 9) observed in our study compared to the data from Friedrich and Rutgers van der Loeff. The bulk of biominerals fragments and phytoplankton we encountered yielded small volume to surface area ratios (V: SA), thus
increasing radionuclides bound to particles (see Fig. 2 in Buesseler et al., 2006) with little changes in POC concentrations.
There were good relationships between the distribution of 210Po and POC (R2 > 0.59), except in the (e) low particles concentration setting (R2 = 0.17). The interruption of the dominance of silicified organisms (transition from settings( a, b, c to d) affected how
210Popart/diss and POC were related (decrease of R2 from 0.92 to 0.59) but also the distribution of 210Po onto POC (increase of a from 1.29.10-3 to 3.12. 10-3) . 210Po may track better the POC from non-silicified organisms because it can adsorb onto the cell and be absorbed into it;
whereas 234Th is only particle-reactive. The biogenic silica probably prevents, at least partially, 210Po to associate with organisms cells.
In contrast, POC explained well the distribution of 234Th (R2 >0.68), excepted when non-siliceous organisms were dominant (R2 = 0.20). The distribution of 234Th onto POC was positively enhanced in presence of biogenic silica (a higher in (a, b, c) vs. (d) conditions up to a certain degree of silicification. Indeed, at the setting up of the dominance of Fragilariopsis sp. in (c), both R2 (R2 (a) = 0.90 vs. R2(c) = 0.48) and a values (a(a) = 2.57.10-3 vs. a(c) = 7.14.10-4) dropped compared to values in (a).
Thus, in most cases in the Atlantic sector of the SO, dominated by diatoms, 234Th seems better suited to trace POC; whereas the efficiency of 210Po as POC tracer seems compromised by the presence of biogenic silica. However, as soon as non-siliceous particles occur, the we suggest 210Po to be a better tracer. Other studies indicate that the later statement may differ in more oligotrophic areas of the ocean. In the low productive central equatorial Pacific, Murray et al. 2005 and Murray et al., 1996 stated that 234Th had an higher selectivity for particles (not POC specifically) than 210Po; based on distribution coefficients, Kd. 210Popart was related to POC (R2 = 0.64), but no correlation coefficient was given for
234Th. Based on their results and on other studies, they concluded that the affinity of 210Po for POC was higher than that of 234Th. Two other studies focused on both radioisotopes in oligotrophic areas. In the Mediterranean Sea (Stewart et al., 2007a,b) 210Po and 234Th exhibited a similar affinity for POC (ȡ = 0.68 and 0.64 for 210Popart and 234Thpart vs. POC, respectively). At the BATS site (Stewart et al., 2010) 210Po was always very well related to POC (R2 0.80), which was also true for 234Th (R2 >0.88), except in non-bloom conditions (R2 = 0.47).
Finally, taken together, all results (Table V) suggest that in the Southern Ocean, in areas that are dominated by large diatoms, 234Th is the better tracer for sinking POC; whereas in oligotrophic conditions, which are dominated by smaller, less silicified cells and detritus,
210Po and 234Th seem similarly appropriate. Finally, when ‘naked’ cells are dominant, 210Po would be the best choice. Thus, we suggest that the trophic conditions of an ecosystem are a critical factor determining whether 210Po or 234Th is most suitable to study POC fluxes.
Moreover, the presence of highly silicified organisms and lithogenic material would greatly affect the affinity of 210Po and 234Th for POC, respectively. In our study the diagenetic state of the POM seems to especially influence 234Th.
Likely, not only the V: SA ratios and the degree of silification of the phytoplankton were different between these studies but also probably the reactivity of the OM. In an attempt to identify specific compounds of the OM controlling the affinity of 210Po, 210Pb and 234Th for particles, we studied two different exopolymers: TEP, rich in acidic polysaccharides and CSP, rich in proteins.
210Po is known to preferentially bind to proteinaceous material, especially S-enriched amino acids such as Methionin, both intracellulary and extracellulary (Stewart et al., 2005;
2007, 2008). However, we found no correlation between CSP, proteinaceous gel-particles, and 210Po, even though we used a large range of parameters to describe the CSP particles.
Several reasons may explain this result.
On one hand, 210Po may accumulate in intracellular proteins other than those forming CSP exsudates and remain in the cells. This is further supported by the fact that 210Po seems to be especially released during phytoplankton cell breakdown (Kadko, 1993). On the other hand, 210Po may bind extracellularly to CSP which have a high turnover rate. In that case the
210Po-enriched CSP fraction (rich in sulfur compounds, like methionine) could be rapidly degraded and the 210Po transferred to the microbial loop and the dissolved phase. Turnover time of CSP is unknown but bacteria can absorb and accumulate 210Po (Burnett et al., 1995).
The fact that no affinity between 234Th and the CSP was observed as well emphasizes differences in reactivity between the CSP and TEP. Possibly CSP are less surface active and do not scavenge trace elements to the same degree as TEP.
TEP and their precursors are well correlated with 234Th in different particle size fractions (Santschi et al, 2003, Passow et al. 2006). In our study, particle affinity of 210Po and
210Pb for TEP are shown in natural samples for the first time. All three radiotracers, 210Po,
210Pb and 234Th presented affinity for the bigger size fraction of TEP, independently of the depth or the sampled region. The high affinity of 210Po for TEP could be attributed to the
fraction of higly surface-active carbohydrates composing TEP and strongly enriched in sulfate groups (Mopper et al., 1995; Zhou et al., 1998).
However, only 210Po and 210Pb were related to the smaller 1>TEP>0.2μm fraction. The fact that in our study 234Th bound to large TEP but not to smaller ones is striking. Indeed, following the line of the Brownian-pumping model (Honeyman and Santschi 1989) it could be interpreted as a decoupling between the adsorption of 234Th onto colloids and the coagulation of these colloids into particles. We did not specifically determine colloidal TEP though but rather a bacteria-enriched (1 - 0.2 μm) fraction of TEP. During our cruise in fall, the bacteria may have hydrolized the colloidal polymers to which 234Th and 210Po are adsorbed and fractionated them: 210Po preferentially absorbed into the bacteria cells and 234Th released to the dissolved pool.
The high affinity of these radioisotopes for TEP suggests that the presence of TEP may introduce artifacts in flux estimates. TEP can account for a significant fraction of POC, up to 100% (Engel, A., and U. Passow, 2001), and in our study ~ 40% on average. If all radiotracers bind well to TEP, a high fraction of TEP in POC would increase the fraction of the radioisotopes on POC, resulting in a miscalculation of POC flux if the POC/Ypart method is used. Indeed, TEP can be neutrally or positively buoyant (Azetsu-Scott & Passow, 2004;
Mari, 2008) thus they are not necessarily exported with the rest of the POC. Depending on the composition of POC (e.g. distribution of the radionuclides onto particles) and on how much TEP accounts for the POC, flux estimates would be over- or underestimated.
ACKNOWLEDGMENTS
We would like to acknowledge and thank our coworkers Pinghe Cai and Michiel Rutgers van der Loeff, who kindly provided a large part of the 234Th data and supported this study.
The authors would like to thank S. Ebert and C. Lorenzen for assistance in the lab. We are more than greatful to the captain of the RV Polarstern, Kap. S. Schwarz, as well as to the crew of Polarstern during ANTXXIV-3 for their dedication, support and kindness. Their expertise is most valuated. Many thanks should go to Dr. E. Fachbach, our chief scientist, for his diplomacy and kindness. Prof. H de Baar has been most suportive during the cruise and should be thanked for the organization of this special issue. Finally, many thoughts go to the NIOZ team and to the LEGOS team for the path undertaken together.
MR thanks the Alfred Wegner Institute, the Marie Curie Early Stage Training program and the Max Planck Institute for Marine Microbiology for their support.
REFERENCES
Alderkamp, A-C. et al.,. Photoacclimation of natural phytoplankton assemblages in the photic zone of the Southern Ocean. submitted to L&O.
Alldredge, A. L., Passow, U., & Logan, B. E. (1993). The abundance and significance of a class of large, transparent organic particles in the ocean. Deep-Sea Research I, 40:
1131–1140.
Bacon, M.P. and Anderson, R.F., 1982. Distribution of thorium isotopes between dissolved and particulate forms in the deep sea. Journal of Geophysical Research, 87: 2045-2056 Bacon, M.P., Spencer, D.W. and Brewer, P.G., 1976. 210Pb/226Ra and 210Po/210Pb
disequilibria in seawater and suspended particulate matter. Earth and Planetary Science Letters, 32(2): 277-296
Baskaran, M. and Santschi, P.H., 1993. The role of particles and colloids in the transport of radionuclides in coastal environments of Texas. Marine Chemistry, 43(1-4): 95-114.
Bathmann, U.V., Scharek, R., Klaas, C., Dubischar, C.D. and Smetacek, V., 1997. Spring development of phytoplankton biomass and composition in major water masses of the Atlantic sector of the Southern Ocean. Deep Sea Research Part II: Topical Studies in Oceanography, 44(1-2): 51-67.
Boyd, P.W., Trull, T.W., 2007. Understanding the export of biogenic particles in oceanic waters: is there consensus?. Progress in Oceanography 72, 276–312.
Buesseler, K.O., 1998. The decoupling of production and particulate export in the surface ocean. Global Biogeochemical Cycles, 12(2): 297-310.
Buesseler, K.O. et al., 2006. An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of 234Th as a POC flux proxy.
Marine Chemistry, 100(3-4): 213-233.
Burnett, W. C. et al., 1995. Microbiology and radiochemistry of phosphogypsum. Final report. Florida Institute of Phosphate Research, pp. 1-225.
Cai, P., Dai, M., Lv, D. and Chen, W., 2006. An improvement in the small-volume technique for determining thorium-234 in seawater. Marine Chemistry, 100(3-4): 282-288.
Clegg, S.L. and Whitfield, M., 1991. A generalized model for the scavenging of trace metals in the open ocean - II: Thorium scavenging. Deep Sea Research, 38(1): 91-120.
Cochran, J.K., Bacon, M.P., Krishnaswami, S. and Turekian, K.K., 1983. 210Po and210Pb distributions in the central and eastern Indian Ocean. Earth and Planetary Science Letters, 65(2): 433-452.
Cochran, J.K. et al., 2009. Time-series measurements of 234Th in water column and sediment trap samples from the northwestern Mediterranean Sea. Deep Sea Research Part II:
Topical Studies in Oceanography, 56(18): 1487-1501
Engel, A., & Passow, U. (2001). Carbon and nitrogen content of transparent exopolymer particles (TEP) in relation to their Alcian Blue adsorption. Marine Ecology Progress Series, 219, 1–10.
Fahrbach et al. This issue
Fleer, A.P., Bacon, M.P., 1984. Determination of lead-210 and polonium-210 in seawater and marine particulate matter. Nuclear Instruments and Methods in Physics Research 223:
243–249.
Flynn, W.W., 1968. The determination of low levels of polonium-210 in environmental materials. Analytica Chimica Acta 43: 221–227.
Friedrich, J. and Rutgers van der Loeff, M.M., 2002. A two-tracer (210Po-234Th) approach to distinguish organic carbon and biogenic silica export flux in the Antarctic
Circumpolar Current. Deep Sea Research Part I: Oceanographic Research Papers, 49(1): 101-120.
Geibert, W. and R. Usbeck (2004). "Adsorption of thorium and protactinium onto different particle types: experimental findings." Geochimica et Cosmochimica Acta 68(7):
1489-1501.
Guo, L., Hung, C.-C., Santschi, P.H. and Walsh, I.D., 2002. 234Th scavenging and its relationship to acid polysaccharide abundance in the Gulf of Mexico. Marine Chemistry, 78(2-3): 103-119.
Hewes, C. D. and O. Holm-Hansen (1983). "A method for recovering nanoplankton from filters for identification with the microscope: The filter-transfer-freeze (FTF) technique." Limnology and Oceanography 28(2): 389-394.
Honeyman BD, Santschi PH (1989) A Brownian-pumping model for oceanic trace metal scavenging: Evidence from Th isotopes. Journal of Marine Research 47: 951-992 Honjo, S., Manganini, S.J., Cole, J.J., 1982. Sedimentation of biogenic matter in the deep
ocean. Deep-Sea Research Part A 29, 609–625.
Kim, G. and Church, T.M., 2001. Seasonal biogeochemical fluxes of Th-234 and Po-210 in the upper Sargasso Sea: Influence from atmospheric iron deposition. Global Biogeochemical Cycles, 15(3): 651-661.
Klatt, O., Fahrbach, E., Hoppema, M., Rohardt, G. (2005). "The transport of the Weddell Gyre across the Prime Meridian". Deep-Sea Research II 52 (3-4): 513–528.
Klunder et al., this issue. Distributions and sources of dissolved iron over a prime meridian transect in the Southern Ocean. This issue
Lochte, K., Bjørnsen, P.K., Giesenhagen, H. and Weber, A., 1997. Bacterial standing stock and production and their relation to phytoplankton in the Southern Ocean. Deep Sea Research Part II: Topical Studies in Oceanography, 44(1-2): 321-340.
Long, R. A. and F. Azam (1996). "Abundant protein-containing particles in the sea." Aquatic Microbial Ecology 10(3): 213-221.
Mari, X. and M. Robert (2008). "Metal induced variations of TEP sticking properties in the southwestern lagoon of New-Caledonia." Marine Chemistry 110(1): 98-108.
Mari, X. (1999). Carbon content and C:N ratio of transparent exopolymeric particles (TEP) produced by bubbling exudates of diatoms. Marine Ecology Progress Series 183: 59–
71.
Mari, X. and A. Burd (1998). "Seasonal size spectra of transparent exopolymeric particles (TEP) in a coastal sea and comparison with those predicted using coagulation theory."
Marine Ecology Progress Series 163(0): 63-76.
Martin, W.R. and Sayles, F.L., 1987. Seasonal cycles of particle and solute transport processes in nearshore sediments: 222Rn/226Ra and 234Th/238U disequilibrium at a site in Buzzards Bay, MA. Geochimica et Cosmochimica Acta, 51(4): 927-943
Middag, R., De Baar, H.J.W., Laan, P., Van Ooijen, J., this issue. Dissolved Manganese in the Southern Ocean.
Mopper, K. et al., 1995. The role of surface-active carbohydrates in the flocculation of a diatom bloom in a mesocosm. Deep Sea Research Part II: Topical Studies in Oceanography, 42(1): 47-73.
Murray, J.W., Paul, B., Dunne, J.P. and Chapin, T., 2005. 234Th, 210Pb, 210Po and stable Pb in the central equatorial Pacific: Tracers for particle cycling. Deep Sea Research Part I: Oceanographic Research Papers, 52(11): 2109-2139.
Murray, J.W. et al., 1996. Export flux of particulate organic carbon from the central equatorial Pacific determined using a combined drifting trap-234Th approach. Deep Sea
Research Part II: Topical Studies in Oceanography, 43(4-6): 1095-1132.
Niven, S.E.H., Kepkay, P.E. and Boraie, A., 1995. Colloidal organic carbon and colloidal 234Th dynamics during a coastal phytoplankton bloom. Deep Sea Research Part II:
Topical Studies in Oceanography, 42(1): 257-273.
Orsi, A. H., T. Whithworth, and W. D. Nowlin 1995. On the meridional extent and fronts of the Antarctic circumpolar current. Deep-Sea Research Part I-Oceanographic Research Papers 42: 641-673.
Passow, U. and A. L. Alldredge (1995). "Aggregation of a diatom bloom in a mesocosm: The role of transparent exopolymer particles (TEP)." Deep Sea Research Part II: Topical Studies in Oceanography 42(1): 99-109.
Passow, U., 2002. Transparent exopolymer particles (TEP) in aquatic environments. Progress In Oceanography, 55(3-4): 287-333.
Passow, U., Dunne, J., Murray, J.W., Balistrieri, L. and Alldredge, A.L., 2006. Organic carbon to 234Th ratios of marine organic matter. Marine Chemistry, 100(3-4): 323-336.
Pike, S.M., Buesseler, K.O., Andrews, J.A., Savoye, N., 2005. Quantification of 234Th recovery in small volume sea water samples by inductively coupled plasma mass spectrometry. Journal of Radioanalytical and Nuclear Chemistry 263: 355– 360.
Pollard, R.T., Lucas, M.I., Read, J.F., 2002. Physical controls on biogeochemical zonation in the Southern Ocean. Deep Sea Research Part II 49 (18): 3931-3950.
Quigley, M.S., Santschi, P.H., Guo, L.D. and Honeyman, B.D., 2001. Sorption irreversibility and coagulation behavior of Th-234 with marine organic matter. Marine Chemistry, 76(1-2): 27-45.
Quigley, M.S., Santschi, P.H., Hung, C.C., Guo, L.D. and Honeyman, B.D., 2002. Importance of acid polysaccharides for Th-234 complexation to marine organic matter. Limnology and Oceanography, 47(2): 367-377.
Rutgers van der Loeff, M.M., Buesseler, K., Bathmann, U., Hense, I. and Andrews, J., 2002.
Comparison of carbon and opal export rates between summer and spring bloom periods in the region of the Antarctic Polar Front, SE Atlantic. Deep Sea Research Part II: Topical Studies in Oceanography, 49(18): 3849-3869.
Rutgers van der Loeff, M., Cai, P., Stimac, I., Middag, R., Klunder, M., van Heuven, S., this issue. 234Th in surface waters: distribution of particle export flux across the Antarctic Circumpolar Current and in the Weddell Sea during the GEOTRACES expedition ZERO and DRAKE. This issue
Santschi, P.H. et al., 2003. Control of acid polysaccharide production, and 234Th and POC export fluxes by marine organisms,. Geophysical Res. Lett., . 30(2): 1044, dio 10.1029/2002GL016046.
Stewart, G et al., 2010. Seasonal POC fluxes at BATS estimated from 210Po deficits. Deep Sea Research Part I: Oceanographic Research Papers, 57(1): 113-124.
Stewart, G. M., N. S. Fisher, and S. W. Fowler. Chapter 8: Bioaccumulation of U/Th isotopes in marine organisms (2008), in U/Th Series Radionuclides in Aquatic Systems, S.
Krishnaswami and J. K. Cochran, editors. Elsevier Press
Stewart, G. et al., 2007a. Comparing POC export from 234Th/238U and 210Po/210Pb
disequilibria with estimates from sediment traps in the northwest Mediterranean. Deep Sea Research Part I: Oceanographic Research Papers, 54(9): 1549-1570.
Stewart, G. et al., 2007b. Exploring the connection between 210Po and organic matter in the northwestern Mediterranean. Deep Sea Research Part I: Oceanographic Research Papers, 54(3): 415-427.
Stewart, G.M., Fisher, N.S., 2003a. Experimental studies on the accumulation of polonium-210 by marine phytoplankton. Limnology and Oceanography 48, 1193–1201.
Stewart, G.M., Fisher, N.S., 2003b. Bioaccumulation of polonium-210 in marine copepods.
Limnology and Oceanography 48, 2011–2019.
Sudre, J., Garçon, V., Provost, C., Sennechael, N., Huhn, O., Lacombe M. Multiparametric analysis of water masses across Drake Passage during ANT-XXIII/3. This issue Verdeny, E. et al., 2009. POC export from ocean surface waters by means of 234Th/238U and
210Po/210Pb disequilibria: A review of the use of two radiotracer pairs. Deep Sea Research Part II: Topical Studies in Oceanography, 56(18): 1502-1518.
Whitworth, T., Nowlin, W.D., 1987. Water Masses and Currents of the Southern-Ocean at the Greenwich Meridian. Journal of Geophysical Research 92 (C6): 6462-6476.
Zar, J. H. Biostatistical Analysis. Fifth Edition. Pearson International Edition. (1999) 944 pp.
FIGURES CAPTIONS Figure 1.
Map location of the stations sampled and of the main water fronts during ANTXXIV-3.
Figure 2.
Bathymetry, locations of the water masses encountered ans stations sampled along the Zero Meridian transect during ANTXXIV-3.
Figure 3.
Distribution of (a) 210Pototal, (b)210Podissolved and (c) 210Poparticulate activities along the Zero Meridian transect. Note the plotting problem in (c) at station 157, where data point at 50 m is not represented (3.07 dpm.100L-1).
Figure 4
Distribution of (a) 210Pbtotal, (b) 210Pbdissolved and (c) 210Pbparticulate activities along the Zero Meridian transect.
Figure 5
Distribution of POC concentrations along the Zero Meridian transect.
Figure 6
Comparison of the percentage of 210Po (a, b, c) and 210Pb (d,e, f) associated with particles in different regions: the North of PF (101 & 104), the South of PF (113, 131 & 178), the Weddell Sea (193) and the Drake Passage (250), respectively.
Figure 7
Linear regressions between POC and each radionuclide total particle affinity, (a) 210Popart/diss, (b) 210Pbpart/diss, (c) 234Thpart/diss in general and (d), (e), (f) at the ice-influenced bloom stations (178 & 193), respectively. White and black dots represent surface waters (0 – 200 m) and deep water (500 – 1000 m) samples, respectively. Only surface waters samples (white dots) are considered for the regressions.
Figure 8
Total affinity of the radionuclides for particles according to (a) TEPpart and (b) 1>TEP>0.2μm
during ANTXXIV-3.
Figure 9
Influence of the type of particles on the affinity of (a) 210Po, (b) 234Th for POC in the Southern Ocean. Note that the individual regressions for the settings (a), (b) and (c) are not shown.
*values calculated from Friedrich and Rutgers van der Loeff, 2002
**this study
Table I. Station locations and depths (m) where the different parameters were sampled during ANT XXIV-3 (PS71/...). Station no.Latitude (°S)Longitude (°)POC TEP CSP 210 Po and 210 Pb234 Th 10142.32 9.00E 25/100/500/1000 25/100 25/100 25/100/200/500/750/1000 25/100/200 10447.65 4.27E 25/100/500/750/1000 25/100/500 25/100 25/100/200/750/1000 25/100/200 11353.03 0.06E 25/100/200/500/750/1000 25/100/500 25/500 25/100/200/500/750 25/100/200 13159.00 0.00E 25/100/200/500/750/1000 25/100 25/100 25/100/200/500/750/1000 25/100/200 15065.00 0.00E 40 40 40 40 15766.52 0.06W25/45/50/100/200 25/45/50/100/200 25/45/50/100/200 17869.40 0.09W 25/100/200/500/
750/1000 25/1000 25 25/100/200/500/750/1000 25/100/200 19366.62 27.15W 50/100/200/500/
750/1000 50/100/500/1000 50/100/500 50/100/200/500/750/1000 50/100/200 22466.52 0.06W75 75 75 24157.63 60.91W75 75 75 25055.73 64.44W50/100/200/500 50/100/200/500/750/1000 50/100/200
Table II. Summary of the characteristics of the filters used for the determination and the separation of the parameters. PC=polycarbonate, QMA=quartz fiber membrane, GF/F=Glas fiber membrane, all filters were purchased at ©Whatman. PARTICULATE SAMPLES ParameterNominal pore size (μm)Type of filter Number of samples
DISSOLVED SAMPLES 210 Popart and 210 Pbpart1 PC, Ø142 mm46 Yes 234 Thpart upper 200 m1 PC, Ø142 mm19 234 Thdiss= 234 Thtotal - 234 Thpart with 234 Thtotal from RvdL et al., submitted 234 Thpart at 100 m1 QMA, Ø25 mm7 234 Thdiss= 234 Thtotal - 234 Thpart with all data from RvdL et al., submitted POC and PON 0.7 GF/F, Ø25mm 45 nd TEPpart 1 PC, Ø25 mm17 nd TEP>0.2μm 0.2 PC, Ø25 mm17 nd CSPpart 1 PC, Ø25 mm12 nd
Table III. Matrix Correlations. Selection of stations used in the calculation of Pearson’s correlation coefficients (n = 7). Cells shaded in grey indicate outliers that were removed for calculations. Matrix correlations Station Depth PS 71 / m 101 25 104 25 104 100 113 25 131 25 131 100 178 25 193 50 193 100
Table IV. Pearson’s coefficients, r, and results of the hypothesis test, t; calculated from the selection of data (Table III). The cells shaded in grey correspond to correlations where Ho:ȡ=0 (no correlation) was rejected, i.e. ŇtŇ2.571 with Į= 0.05 and n=7. POC1>TEP>0.2μmTEPpartCSPpart volumeCSPpart average area 210 Popart/diss0.74 0.46 0.87-0.08 -0.08 210 Pbpart/diss0.03 0.57 0.23 0.00 0.55 234 Thpart/diss0.94-0.02 0.860.34 -0.38
Table V. Review of studies comparing the affinity of 210 Po and 234 Th for POC. Size fraction (μm)Affinity for POC Site SamplingTime serie Depth (m) POC210 Po,234 ThIndicator used general variability Source SO Atlantic sector 47 - 57°S 3 distinct blooms Bottles 3 transects: early, middle and end spring 1997 20 - 200 0.7 1 R2 , a with part/diss ratio recalculated
234 Th > 210 Po
234 Th > 210 Po when fresh, diatom OM 234 Th >> 210 Po if highly silicified diatoms dominant 210 Po>234 Th if non-silicifed organisms dominant a Mediterranean Sea DYFAMED Non productive & 1 major flux event
Traps 4-5 days resolution: early spring to late summer 2003 200 0.7 SP ȡ with particulate activities
234 Th ~ 210 Po 210 Po = fresh, N-rich, phytoplankton OM 234 Th = degraded OM and inorganics b Pumps 3 cruises: Nov. 2006, Feb. And March 2007 75 - 500 6 filters 1-100 * Bottles idem10 - 500 nd total
Sargasso Sea BATS non-bloom semi-bloom bloom & exportTraps idem 1.8 - 4.3 days resolution 150, 200, 3000.7 SP R2 with particulate fraction of the total radionuclide (%)
234 Th ~ 210 Po
234 Th ~ 210 Po when fresh OM with dominance of aggregated picoeukaryotes 234 Th < 210 Po when old OM and inorganics c SO Atlantic sector 42 - 70°S Low particle concentration 2 blooms, 1 exported
Bottles No sampled in fall 25 - 1000 0.7 1 R2 , a with part/diss ratio 234 Th >> 210 Powhen fresh, lightly silicified diatom OM and less reactive OM d a Friedrich and Rutgers van der Loeff, 2002 b Stewart et al., 2007b c Stewart et al., 2010 d this study SP = sinking particles * each subsamples filtered onto 0.7μm for POC