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Nelson, David M; Dortch, Quay (1996): Biogenic silica in the coastal plume of the Mississippi River. PANGAEA, https://doi.org/10.1594/PANGAEA.734951, Supplement to: Nelson, DM; Dortch, Q (1996): Silicic acid depletion in the plume of the Mississippi River and limitation of Si availability to diatoms in the northern Gulf of Mexico: evidence from kinetic studies in spring and summer. Marine Ecology Progress Series, 136, 163-178, https://doi.org/10.3354/meps136163

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Abstract:
The surface distributions of dissolved silicic acid, chlorophyll and diatom abundance were measured in the plume of the Mississippi River and adjacent waters during spring (late April and early May 1993) and summer (July 1992). In spring, the time of maximum river flow, there was an intense diatom bloom with a mean diatom abundance of 1.5 x 10**7 cells/l, more than an order of magnitude higher than in summer. Mixing curves of silicic acid concentration ([Si(OH)4]) versus salinity indicate that biological uptake within the river plume removed >99% of the Si(OH)4 supplied by the river in spring and 80 to 95% in summer. In spring [Si(OH)4] was occasionally depleted to <0.2 µM-among the lowest values ever reported from the ocean-with extensive depletion to >=0.5 µM over the shelf. In summer [Si(OH)4] was less severely depleted; the lowest measured was 0.93 µM and all others were >=2.4 µM. 30Si kinetic experiments were performed during both spring and summer to measure the degree to which the rate of Si uptake by the natural diatom assemblages was limited in situ by substrate availability. In spring the dependence of the specific uptake rate (V) on extracellular [Si(OH)4] conformed much more closely to the Michaelis-Menten saturation function than has been observed in past studies. Strong dependence of V on [Si(OH)4] was observed throughout the most Si(OH)4-depleted (<0.5 µM) region, where V was limited to 12 to 45% of the diatom assemblages' maximum uptake rate (Vmax). Half-saturation concentrations for Si uptake (Ks) averaged 0.85 uM (range = 0.48 to 1.71; n = 7) in spring, with the lowest values equal to the lowest previously reported for natural diatom assemblages. There was only 1 station in summer where V was limited by [Si(OH)4], and at that station Ks was 5.3 µM-quite high in comparison with previous studies. At stations where V was limited by [Si(OH)4], in both spring and summer, Chaetoceros spp. were numerically dominant; where there was no Si limitation other diatoms, usually Skeletonema costatum, dominated. The data thus indicate strong Si limitation in spring, with diatom assemblages well adapted to low [Si(OH)4], but little or no Si limitation in summer. Historical data suggest that coastal Si(OH)4 depletion and Si limitation may be recent phenomena in the northern Gulf of Mexico, resulting from increasing [NO3-] and decreasing [Si(OH)4] in the Mississippi River during the past 30 to 50 yr.
Funding:
Fourth Framework Programme (FP4), grant/award no. MAS3970141: Silicon Cycling in the World Ocean
Coverage:
Median Latitude: 28.879821 * Median Longitude: -90.257994 * South-bound Latitude: 28.390000 * West-bound Longitude: -91.250000 * North-bound Latitude: 29.132500 * East-bound Longitude: -89.430000
Date/Time Start: 1992-07-25T08:00:00 * Date/Time End: 1993-05-01T10:55:00
Event(s):
NECOP1993-#A3 * Latitude: 29.030000 * Longitude: -89.530000 * Date/Time: 1993-04-26T13:10:00 * Campaign: NECOP1993 * Basis: Pelican * Method/Device: Bottle, Niskin (NIS)
NECOP1993-#A4 * Latitude: 29.130000 * Longitude: -89.750000 * Date/Time: 1993-04-25T12:15:00 * Campaign: NECOP1993 * Basis: Pelican * Method/Device: Bottle, Niskin (NIS)
NECOP1993-#A5 * Latitude: 28.950000 * Longitude: -89.570000 * Date/Time: 1993-04-26T10:40:00 * Campaign: NECOP1993 * Basis: Pelican * Method/Device: Bottle, Niskin (NIS)
Size:
27 datasets

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Datasets listed in this publication series

  1. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#A3. https://doi.org/10.1594/PANGAEA.139787
  2. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#A4. https://doi.org/10.1594/PANGAEA.139788
  3. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#A5. https://doi.org/10.1594/PANGAEA.139789
  4. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#A7. https://doi.org/10.1594/PANGAEA.139790
  5. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#A8A. https://doi.org/10.1594/PANGAEA.139791
  6. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#B4. https://doi.org/10.1594/PANGAEA.139792
  7. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#B7. https://doi.org/10.1594/PANGAEA.139793
  8. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#C3. https://doi.org/10.1594/PANGAEA.139794
  9. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#C6B. https://doi.org/10.1594/PANGAEA.139795
  10. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#C7. https://doi.org/10.1594/PANGAEA.139796
  11. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#D2. https://doi.org/10.1594/PANGAEA.139797
  12. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#D4. https://doi.org/10.1594/PANGAEA.139798
  13. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#D6. https://doi.org/10.1594/PANGAEA.139799
  14. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#E2A. https://doi.org/10.1594/PANGAEA.139800
  15. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#E4. https://doi.org/10.1594/PANGAEA.139801
  16. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#R1. https://doi.org/10.1594/PANGAEA.139802
  17. Nelson, DM; Dortch, Q (1996): Biogenic silica at niskin bottle station NECOP1993-#R3. https://doi.org/10.1594/PANGAEA.139803
  18. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#A1. https://doi.org/10.1594/PANGAEA.140517
  19. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#A3. https://doi.org/10.1594/PANGAEA.140518
  20. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#A5. https://doi.org/10.1594/PANGAEA.140519
  21. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#C3. https://doi.org/10.1594/PANGAEA.140520
  22. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#C6B. https://doi.org/10.1594/PANGAEA.140521
  23. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#C9. https://doi.org/10.1594/PANGAEA.140522
  24. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#CB6. https://doi.org/10.1594/PANGAEA.140526
  25. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#D1. https://doi.org/10.1594/PANGAEA.140523
  26. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#D2. https://doi.org/10.1594/PANGAEA.140524
  27. Nelson, DM; Dortch, Q (1996): Biogenic Silica at niskin bottle station Station#E2. https://doi.org/10.1594/PANGAEA.140525