Hydrography and distribution of chaetognaths over the continental shelf off North Carolina 93 



found bottom living fauna, algae and plankton in Onslow Bay having in general 

 tropical affinities. However, they noted in their winter and spring collections, in 

 addition to the usual populations, a few individuals from a small number of species 

 with northern affinities. 



Our recent collections provide material for a better understanding of the hydro- 

 graphic influence on the distribution of the chaetognaths in the area than has been 

 available heretofore and indicate how the hydrographic barrier at Cape Hatteras is 

 occasionally breached, thus permitting the temporary establishment of the anomalous 

 communities noted by Williams, Pearse and Sutcliffe. 



ACKNOWLEDGEMENT 

 While the many outstanding investigations of Henry B. Bigelow do not strictly 

 pertain to the area under discussion, the authors are especially grateful for his studies 

 of the waters of the Gulf of Maine and the continental shelf from Cape Cod to 

 Chesapeake Bay. His efforts have been a constant influence as we have attempted to 

 extend the knowledge of shelf waters slightly beyond the area he so carefully and 

 completely considered. 



THE DATA 



The data comprise a series of hydrographic sections together with plankton col- 

 lections made in May and June 1953 (Caryn Cruise 64) and January 1954 (Atlantis 

 Cruise 196) (Fig. 1). 



At each station serial temperature-salinity depth determinations were made to the 

 bottom or to nearly 500 metres, whichever was less. At most stations quantitative 

 oblique plankton tows, using Plankton Samplers (Clarke and Bumpus, 1950) fitted 

 with #2 silk nets, were made from near the bottom or 100 metres. When feasible 

 two Plankton Sampler tows were made dividing the water column in two. The chaetog- 

 naths were picked out of the plankton samples and identified (Tables I and II, Fig. 12). 

 These plankton data are more nearly quantitative and extend closer to the shore than 

 those of Pierce (1953). 



HYDROGRAPHY 



Bumpus (1955) has shown that, south of Cape Hatteras, a southerly flowing coastal 

 current, such as is common north of Cape Hatteras, is a transient afi"air. Such a 

 current, when present, is restricted to a very narrow portion of the continental shelf. 

 The dynamic pressure gradient resulting from the combined effect of the runolf and 

 the cross-shelf thermal gradient together with the prevailing wind and the frictional 

 drag of the Florida Current provide for a northeasterly drift over a broad pari o\' the 

 Carolina continental shelf. 



In addition to the water of the Florida Current there arc two types of water in this 

 region which we have named Virginian Coastal water and Carolinian Coastal water.* 

 There are also mixtures of each of these with the Florida Current water. Virginian 

 refers to the shelf water from Cape Cod to Cape Hatteras. Carolinian refers \o the 



* We have used here two names apparently new to oceanography inasmuch as we have been unable 

 to find names concisely describing the separate continental shelf regions north and south of Cape 

 Hatteras. Because the terms Virginian and Carolinian are used to describe the faunal subprovinces 

 of the continental shelf, we shall introduce these terms to identify the water types on the shelf. 



