. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . AMMONIUM (;ig at N/l) 100km -J Figure 58-5. Ammonium (/ig at N/l) cross section in the eastern Bering Sea along a transect extending from 56° 59 N- 177°0l'W to 61°00'N-169°00 W (Hakuho Maru KH-78-3 cruise, Hattori 1979). of ammonium roughly coincides with the depth of percent light penetration, and also with the depth at which concentrations of dissolved oxygen shift from oversaturation to undersaturation (Fig. 58-7). The maximum concentration of ammonium thus occurs near the boundar
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . AMMONIUM (;ig at N/l) 100km -J Figure 58-5. Ammonium (/ig at N/l) cross section in the eastern Bering Sea along a transect extending from 56° 59 N- 177°0l'W to 61°00'N-169°00 W (Hakuho Maru KH-78-3 cruise, Hattori 1979). of ammonium roughly coincides with the depth of percent light penetration, and also with the depth at which concentrations of dissolved oxygen shift from oversaturation to undersaturation (Fig. 58-7). The maximum concentration of ammonium thus occurs near the boundary between the euphotic and disphotic layers and near the "compensation point" with respect to primary production. The fact that ammonium concentrations below the pycnocline are relatively low suggests that this maximum comes from pelagic rather than benthic sources. Cross-shelf ammonium distributions are similar southeast of the Pribilof Islands (Fig. 58-8). A pelagic food web, therefore, appeeirs to dominate wide expanses of the southeast Bering outer-shelf domain. Excretion of ammonium by zooplankton and other animals is the most likely source of the ammonium in the outer- shelf subsurface maximum. Nutrient data collected by the PROBES program (Figs. 58-9 and 58-10) suggest that in the outer- shelf domain southeast of the Pribilof Islands ammo- nium concentrations are inversely correlated with nitrate concentrations. Ammonium concentrations are relatively low in the southern area (Fig. 58-9), where nitrate concentrations are high. Conversely, very high concentrations of ammonium are found in the northern regions, where the largest vertical gradients in nitrate decline were observed (Fig. 58-10). This inverse relationship is found over ex- tensive areas of the Bering Sea and the northern North Pacific in midsummer (Fig. 58-11). When nitrate concentrations in the surface layer of the southeast Bering Sea outer-shelf domain are high, ammonium concentrations in the
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