mg C m ^ hr~* 



n«i 



Fig. 4. Three-dimensional plot of primary productivity rates estimated along 

 a transect from the Aleutian Islands to the Chukchi Sea. The major 

 peakatStation.^6reaches300mgCm 'h 'at a depth of."* I m. Selected 

 station numbers are indicated for orientation. 



(Favointe, 1974). Instantaneous shipboard measurements were 

 close to this value, although a realistic estimate of the mean flu.x 

 might be closer to 0.5-0.8 Sv (Coachman, personal 

 communication). Transport of CO, was calculated from the 

 average of surface and thermocline estimates of Z CO, and the 

 1 Sv transport. This comes to 35.3 x 10'' moles C yr ' on the 

 eastern side of the strait and 32.8 x 10'- moles C yr ' on the 

 western side. The combined east and west side transport would 

 then be 0.82 x 10'' metric tons C per year. This provides an 

 estimate of the flux of dissolved CO, but does not account for 

 particulate flux. 



The present study cannot derive a value for the total 

 particulate tlux but can estimate phytoplankton biomass and, 

 therefore, phytoplankton particulate carbon flux. During the 



Latitude 



Fig. 5. Contour plots of primary productivity, chlorophyll a, and nitrate plus 

 nitrite concentrations along a transect from the Aleutian Islands to the 

 Chukchi Sea. 



cruise we occupied transects on either side of the Diomede 

 Islands. The measured chlorophyll concentrations averaged 

 5.72 g Chi m ' on the western side and 1.1 g Chi m' on the 

 eastern side. Taking the mean chlorophyll concentration for 

 both sides and multiplying by the approximately 1 Sv transport 

 results in an estimated annual particulate phytoplankton flux. 

 Assuming a C/Chl ratio of 30, and that the chlorophyll 

 concentrations remain unchanged seasonally, then the annual 

 flux would amount to 3.2 X 1 O** metric tons C per year. This is 

 about 0.4% of the estimated dissolved carbon flux. Other 

 particulate material, either detritus or living, could contribute 

 significantly to the total particulate carbon flux. Therefore, the 

 relative magnitude of particulate versus dissolved transport 

 will need to be investigated further. 



Another aspect to consider is how much carbon is fixed by 

 primary production regionally. For example, in the region 

 north of the Bering Strait, the cruise track covered approximately 

 85,320 km-. The average rate of primary production in the 

 Chukchi was 1.6 g C m-d' (Table 2). Assuming a 60-day 

 growing season, the southern Chukchi would fix roughly 

 8.2 X 10*" metric tons of carbon. A similar calculation for the 

 Chirikov basin obtains a seasonal production of about 



221 



