. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . AMMONIUM (mq at N/l) / \ 0 50 km _i Figure 58-8. Ammonium (yug at N/l) cross section in outer Bristol Bay south of the Pribilof Islands (PROBES Thomas G. Thompson cruise 138 leg 3, 29-31 May 1979). discussed earlier, confirm the slow regeneration of nitrate in Bering Sea subsurface waters. The steep pycnocline hinders the vertical diffusion of water and dissolved materials and slows the sinking of particu- late matter (Fig. 58-12). The high concentrations of ammonium in the subsurface la
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . AMMONIUM (mq at N/l) / \ 0 50 km _i Figure 58-8. Ammonium (yug at N/l) cross section in outer Bristol Bay south of the Pribilof Islands (PROBES Thomas G. Thompson cruise 138 leg 3, 29-31 May 1979). discussed earlier, confirm the slow regeneration of nitrate in Bering Sea subsurface waters. The steep pycnocline hinders the vertical diffusion of water and dissolved materials and slows the sinking of particu- late matter (Fig. 58-12). The high concentrations of ammonium in the subsurface layer thus probably result from a combination of biological and hydro- graphic processes. In actuality, the ratios of nitrate plus ammonium to the corrected phosphate in the ammonium layer are near the expected 15:1. Ratios obtained on the 1978 R/V Hakuho Maru cruise ranged from :1 to :1 (average ± :1). The presence of ammonium maxima in subsurface layers appears to be a common feature of highly productive boreal seas dominated by pelagic food webs. In the mid-shelf domain, no such maximum con- centration of ammonium is found in the subsurface layer. Instead, very high concentrations of ammo- nium exist near the bottom (Fig. 58-5 and 58-8), sug- gesting a benthic source of ammonium. There appears to be no relation between this near-bottom maximum and the subsurface maximum in the outer- shelf domain. The mid-shelf front between the mid-shelf and outer-shelf domains extends to the bottom and effectively prevents the dispersion of mid-shelf ammonium offshore. The different patterns of ammonium distributions in the mid- and outer-shelf domains of the southeast Bering Sea appear to result from zonal differences in food webs. A complex combination of biological and environmental factors influences the occurrence and productivity of organisms at all trophic levels of a food web. On the shelf of the southeastern Bering Sea, the distribution and abundance of herbi- vores
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