. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering STATION DATE • 2066 140579 ? 2075 150579 1 1 1 1 Mg chl a/m 1006 1459 20 30 40 50 ng chl a/I 10 Figure 56-6. Wind-mixing effects on the nitrate and ciilorophiyU profiles on PROBES Leg II, 1979 R/V Thomas G. Thompson. total phytoplankton numbers at some middle shelf domain stations during late June 1978. Evidence from nitrogen-15 kinetic uptake experiments sug- gests that regenerated nitrogen (ammonium and urea) is the primary nitrogen source for stage-Ill phyto-
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering STATION DATE • 2066 140579 ? 2075 150579 1 1 1 1 Mg chl a/m 1006 1459 20 30 40 50 ng chl a/I 10 Figure 56-6. Wind-mixing effects on the nitrate and ciilorophiyU profiles on PROBES Leg II, 1979 R/V Thomas G. Thompson. total phytoplankton numbers at some middle shelf domain stations during late June 1978. Evidence from nitrogen-15 kinetic uptake experiments sug- gests that regenerated nitrogen (ammonium and urea) is the primary nitrogen source for stage-Ill phyto- plankton species (Goering and Iverson, unpublished). Apparently Rhizosolenia alata is capable of excelling other phytoplankton species in taking up silicic acid from very low ambient silicic acid concentrations and of growing with only weakly silicified frustules. Controversy exists over which ecological factors are most important in determining the course of phy- toplankton succession. Major arguments usually center around the roles that ambient concentration of nutrients, light regimes, and grazing play in the suc- cessional changes observed in nature. In the shelf domains of the southeast Bering Sea the patterns of phytoplankton growth, biomass, and species composi- tion appear to be very directly influenced by the dis- 80 E 100 f 120 Q. Q 140 160 180 200. I ill I I I I I l_ SILICATE Oig-at/l) PROBES 79 LEG 3 13-15 JUNE _l I I I I 1 L. Figure 56-7. Cross-shelf silicate distribution Leg III, PROBES, 13-15 June 1979 R/V Thomas G. Thompson (from Whitledge and Reeburg 1979). tribution and abundance of oceanic and shelf herbi- vores (Cooney and Geist 1978, Alexander and Cooney 1979, Iverson et al. 1979b). Oceanic grazers do not invade water shoreward of the middle front (Fig. 56-2). They are confined to the outer shelf domain because of the hydrographic conditions which do not allow the extensive exchange of oceanic water with mid-shelf water. The oceanic group is composed of e
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