Electronic Supplemental Material for:
Evidence for microbial attenuation of particle flux in the Amundsen Gulf and Beaufort Sea: elevated hydrolytic enzyme activity on sinking aggregates
C.T.E. Kellogg, S.D. Carpenter, A.A. Renfro, A. Sallon, C. Michel, J.K. Cochran, and J.W. Deming
Contents
Appendix 1 (page 2)
Table S1 (page 3)
Table S2 (page 4)
Appendix 1:
POC flux estimate method comparison: 234Th deficit vs. Free-drifting particle interceptor traps
The 234Th fluxes determined at 100 m from the integrated deficit of 234Th with respect to its parent 238U in the water column were lower by factors of 3–7 than those determined from free-drifting particle interceptor trap samples (Tables S1, S2), except at the shallowest of the five stations where comparative data were available (station 416). Differences between POC fluxes measured in traps and those calculated from water column 234Th deficits were also evident (Table S1). Previous similar comparisons in the North Water and in the Mackenzie Shelf/Cape Bathurst Polynya had shown relatively good agreement between these methods in the upper 50 m, but at greater depths (75–100 m) offsets were evident: trap fluxes were less than those calculated from water column 234Th profiles (Amiel et al. 2002; Amiel 2007). Reasons for discrepancies between these two estimates of flux, explained extensively elsewhere (Savoye et al. 2006; Buesseler et al. 2007; Cochran et al. 2009), include hydrodynamic biases in free-drifting traps, the effects of lateral advection and non-steady state processes on the water column 234Th profiles. Bloom dynamics can produce non-steady state conditions for 234Th profiles because sinking 234Th fluxes must be maintained for some time to approach a steady-state deficit of this radionuclide in the water column. Similarly, after the sinking flux of 234Th is attenuated, deficits can persist in the water column (Cochran et al. 2009). Our data suggest that bloom dynamics at least partially accounted for the differences observed between water column and trap 234Th fluxes. Integrated primary production (0–100 m; Table 2) correlated inversely with water column 234Th deficits (Table S2; r2 = 0.5); i.e., stations with highest primary production had lowest Th deficits. These stations may have been in earlier stages of bloom, such that the sinking flux of POC and 234Th had not operated long enough to develop as large a 234Th deficit in the water column compared to stations where primary production had peaked and the sinking flux of POC (and 234Th) was well established.
Comparison of POC fluxes measured in traps with those calculated from water column 234Th deficits also showed differences between values determined by the two approaches (Table S2). In the latter case, we derived POC fluxes from water column 234Th deficits using the conventional approach of multiplying the deficit (integrated to 100 m) by the POC/234Th ratio measured on large filterable particles at 100 m, assuming that they represent settling material (Buesseler et al. 2006). The variation in POC/234Th measured in trap material at 100 m was substantially less than that in > 70-μm filterable particles and the trap POC flux was generally comparable to or greater than the Th-derived POC flux (except at station 1208; Table S2). We used the trap POC fluxes for comparative analyses with integrated EEA. The collection of particles by in situ filtration or free-drifting particle interceptor trap deployments represents a snapshot of the particle (and POC) distributions and fluxes in time, making comparisons with short-term EEA assays seem appropriate; however, the importance of EEA in mobilizing POC in the photic zone pertains, even if POC fluxes obtained from water column 234Th deficits are considered.
References
Amiel D (2007) Terrestrial and marine POC fluxes derived from 234Th distributions and d13C measurements on the Mackenzie River Shelf. Dissertation, Stony Brook University
Amiel D, Cochran JK, Hirschberg DJ (2002) Th-234/U-238 disequilibrium as an indicator of the seasonal export flux of particulate organic carbon in the north water. Deep-Sea Res Part II 49:5191-5209
Buesseler KO, Antia AN, Chen M, Fowler SW, Gardner WD, Gustafsson O, Harada K, Michaels AF, Rutgers van der Loeff, Michiel, Sarin M, Steinberg DK, Trull T (2007) An assessment of the use of sediment traps for estimating upper ocean particle fluxes. J Mar Syst 65:345-416
Buesseler KO, Benitez-Nelson CR, Moran SB, Burd A, Charette M, Cochran JK, Coppola L, Fisher NS, Fowler SW, Gardner WD, Guo LD, Gustafsson Ö, Lamborg C, Masque P, Miquel JC, Passow U, Santschi PH, Savoye N, Stewart G, Trull T (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. Mar Chem 100:213-233
Chen JH, Edwards RL, Wasserburg GJ (1986) 238U, 234U, 232Th in seawater. Earth Planet Sc Lett 80:241-251
Cochran JK, Miquel JC, Armstrong R, Fowler SW, Masqué P, Gasser B, Hirschberg D, Szlosek J, Rodriguez y Baena AM, Verdeny E, Stewart GM (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 56:1487-1501
Savoye N, Benitez-Nelson C, Burd AB, Cochran JK, Charette M, Buesseler KO, Jackson GA, Roy-Barman M, Schmidt S, Elskens M (2006) 234Th sorption and export models in the water column: A review. Mar Chem 100:234-249
Table S1 Water column 234Th data
416 / 0 / 2.00 / 1.69 / 0.85
10 / 2.01 / 2.16 / 1.07
25 / 2.11 / 1.74 / 0.83
50 / 2.23 / 1.90 / 0.85
75 / 2.30 / 1.46 / 0.63
100 / 2.34 / 1.57 / 0.67
6006 / 0 / 2.02 / 1.89 / 0.94
10 / 2.10 / 2.22 / 1.06
25 / 2.16 / 2.44 / 1.13
50 / 2.23 / 2.60 / 1.17
75 / 2.28 / 1.46 / 0.64
100 / 2.33 / 2.11 / 0.91
410 / 10 / 1.99 / 1.71 / 0.86
25 / 2.14 / 2.26 / 1.06
50 / 2.23 / 1.80 / 0.81
75 / 2.26 / 2.15 / 0.95
100 / 2.30 / 2.26 / 0.98
1208 / 2 / 2.14 / 2.09 / 0.98
10 / 2.14 / 2.44 / 1.14
25 / 2.20 / 2.47 / 1.12
50 / 2.24 / 1.98 / 0.88
75 / 2.28 / 2.07 / 0.91
100 / 2.31 / 1.76 / 0.76
421 / 5 / 1.87 / 1.47 / 0.79
10 / 1.89 / 1.48 / 0.78
25 / 2.10 / 1.85 / 0.88
50 / 2.22 / 2.35 / 1.05
75 / 2.26 / 1.78 / 0.79
100 / 2.29 / 1.91 / 0.83
†Calculated from U-salinity relationship of Chen et al. (1986)
‡Uncertainty estimated to be ± 8%
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Table S2 234Th and POC fluxes at 100 m determined from water column 234Th deficits and free-drifting particle interceptor traps
Station / Station depth (m) / Primary productivity0–100 m
(mg C m–2 d–1) / 234Th flux
(dpm m–2 d–1)† / Trap-based
234Th flux
(dpm m–2 d–1) / > 70 µm POC/234Th
(µg dpm–1)‡ / Trap
POC/234Th
(µg dpm–1)‡ / Th-derived
POC flux
(mg C m–2 d–1) / Trap
POC flux
(mg C m–2 d–1) / ThE ratio
(%)
416 / 156 / 456 (38.0)* / 1320 / 1370 / 8.4 (0.7) / 47 (3.9) / 12 (1.0)* / 64 (5.3)* / 2.6
6006 / 220 / 874 (72.8) / 200 / 1390 / 132 (11) / 55 (4.6) / 25 (2.1) / 77 (6.4) / 2.9
410 / 384 / 510 (42.5) / 470 / 1330 / 54 (4.5) / 52 (4.3) / 25 (2.1) / 68 (5.7) / 4.9
1208 / 397 / 926 (77.1) / 300 / 810 / 733 (61) / 47 (3.9) / 217 (18.1) / 37 (3.1) / 23
421 / 1142 / 178 (14.8) / 740 / 2290 / 100 (8.3) / 32 (2.7) / 74 (6.2) / 73 (6.1) / 42
* Parenthetic values in mmol C m–2 d–1
† 234Th flux at 100 m based on integrated water column 234Th deficit 0–100 m
‡ Values for pump-filtered particles > 70 µm or trapped material at 100 m; parenthetic values in μmol dpm–1
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