374 



[chap. 17 



measurements (Ryther and Yentsch, 1957) and hence are not comparable to 

 values obtained by the 14 C technique, but they clearly show the relation 

 between depth and the timing of the spring flowering. A rough estimate of the 

 annual production of the shallow coastal stations, based on the 14 C data (Fig. 7), 

 is 165 g carbon/m 2 as compared to 120 g carbon/m 2 for the deep stations off 

 the edge of the shelf. Thus it would appear that annual production varies only 

 slightly between coastal and offshore environments, at least in temperate 

 regions, but that the timing of the annual cycle is decidedly related to water 

 depth. 



However, in addition to the effect of depth on the amount of light available 

 to the phytoplankton, the productivity of shallow coastal and inshore waters is 

 influenced by nutrients and suspended material of terrigenous and sedimentary 

 origin, and by the circulatory patterns common to many embayments and 

 estuaries. Redfield et at. (Chapter 2) have described the situation in positive estu- 

 aries, where surface outflow, sub-surface inflow and the sinking of particulate 



0.7 



Fig. 13. Primary production in the Great Belt off Denmark, 1955. (After Steemann 

 Nielsen, 1958.) 



organic matter combine to provide a nutrient trap. By this mechanism, the 

 fertility of estuaries may build up to levels far exceeding those of the 

 contiguous ocean waters. 



The seasonal cycle of production in shallow temperate regions charac- 

 teristically differs from that of offshore waters of the same latitude. Rather 

 than a bimodal cycle with a summer minimum, high production normally 

 persists for the entire summer in shallow waters. This has been observed in 

 Long Island Sound (Riley, 1956a), in Danish coastal waters (Steemann Nielsen, 

 1951, 1958; see also Fig. 13) and by the present author in numerous embay- 

 ments of the Woods Hole region. Persistence of a summer thermocline is rare 

 in these environments, and nutrients available from the bottom and from land 

 drainage apparently support production throughout the summer months. 



