Table III:
Comparison of measured and estimated nitrogen fluxes (μmol N m−2 day−1)
| Cycle | Region | Dates | Nitrate uptake | Nitrification | Export at 90/100 m (Th) | Export at 90/100 m (SedTrap) | Remin below 50 m | PN accumulation | Mesozoo active transport | Mesozoo biomass production |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Coastal | June 23–26 | 2990 ± 525 | 2572 (86%) | 896 ± 105 (30%) | 0 (0%) | −7639 (−255%) | <32 ± 74 (<1%) | 973 ± 198 (33%) | |
| 2 | CRD Core | July 3–7 | 5813 ± 2691 | 69 ± 20 (1%) | 1206 ± 629 (21%) | 528 ± 111 (9%) | 82 (1%) | 5402 (93%) | <68 ± 34 (<1%) | 502 ± 37 (9%) |
| 3 | CRD Edge | July 8–12 | 3051 ± 866 | 8 ± 1 (0%) | 371 ± 376 (12%) | 551 ± 48 (18%) | 143 (5%) | −1869 (−61%) | <323 ± 209 (<11%) | 2075 ± 429 (68%) |
| 4 | CRD Core | July 14–18 | 3098 ± 477 | 19 ± 1 (1%) | 370 ± 113 (12%) | 404 ± 44 (13%) | 64 (2%) | −2787 (−90%) | <82 ± 32 (<3%) | 864 ± 149 (28%) |
| 5 | CRD Edge | July 19–23 | 7198 ± 1839 | 772 ± 75 (11%) | 637 ± 74 (9%) | 48 (1%) | 2810 (39%) | <341 ± 125 (<5%) | 1931 ± 168 (27%) | |
| 2 and 4 | CRD Core | July 3–18 | 4456 ± 814 | 44 ± 10 (1%) | 591 ± 251 (13%) | 489 ± 93 (11%) | 83 (2%) | −1335 (−30%) | <75 ± 31 (<2%) | 713 ± 92 (16%) |
| 2–5 | CRD | Mean | 4790 ± 2060 | 32 ± 33 (1%) | 680 ± 399 (14%) | 530 ± 96 (11%) | 84 (2%) | 889 (19%) | <203 ± 149 (<4%) | 1343 ± 779 (28%) |
Values in parentheses are the percentage of nitrate uptake. Mean ± standard deviation of repeat measurements are given when possible. Columns are: (1) cycle (Cycles 2 and 4 show results from an extended Lagrangian study during which a drifter left at the end of Cycle 2 was revisited for Cycle 4; final row is the mean of Cycles 2–5 in the CRD region), (2) region, (3) Dates, (4) vertically integrated conservative 15NO3− uptake (e.g. f-ratio capped at 1, see nitrate uptake sections in Methods and Results), (5) vertically integrated euphotic zone nitrification (Buchwald et al., in revision). (6) 234Th-derived export, (7) sediment trap-derived export, (8) estimated remineralization between 50-m depth horizon (average depth of euphotic zone) and export measurement horizon (90 or 100 m) as assessed by 234Th deficiency and an estimated rate of change of N:234Th with depth (see Discussion), (9) vertically integrated particulate nitrogen accumulation above the depth horizon used for export determined from samples taken at beginning and end of each cycle. Negative values indicate that PN concentrations were decreasing, thus exacerbating measured imbalances between new and export production (note that no standard deviation is given for these estimates because we could not quantify the portion of uncertainty associated with small errors in tracking a water parcel with our Lagrangian drift array), (10) mesozooplankton active transport estimated from day–night differences in grazing rate (see Décima et al., 2016) and assumptions about the fraction of ingested N that is excreted. Note that, since we estimated that half of all excretion occurred at depth despite the temperature-dependence of mesozooplankton excretion, this is necessarily an overestimate of active transport (see Discussion). (11) Mesozooplankton biomass production (and hence potential export to higher trophic levels, see Discussion).