u 



2 



ttJ 

 U 



W 

 O 



HA-1 



PH 



Fig. 4. pH-dependence of fluorescence intensity of the isolated HA samples. 



Calibration Cun-esfor the Isolated HA Samples 



The equations for the caUbration curves were determined 

 by hnear least-squares fit. They are presented below. 

 1(1 ) = (30.0 ± 0.3) X C( 1 ) + ( 16.0 ± 0.2) 

 1(2} = (44.4 ± 0.2) X C(2) + ( 16.2 ± 0.2) 

 1(3) = (45.6 ± 0.2) X C(3) + ( 16.0 ± 0.2) 

 Where / is the fluorescence intensity in relative units, C is 

 concentration of HA in ppm, and the standard deviation (SD) 

 for the method is 0.25 ppm (p = 0.05 and N = 6). 



It is clear from the given equations that both samples from 

 the Chukchi Sea show practically the same calibration curves. 

 This fact is very important. It leads to the conclusion that an HA 

 sample isolated from a local area could be used as a standard for 

 the whole basin. At least, this conclusion could be drawn for 

 moderately sized regions such as the Chukchi Sea. 



water of the Bering Strait and Chukchi Sea was 1 .25 ppm near 

 the surface and 0.85 ppm in the bottom water. In the present 

 study the concentration of HA's in the surface water of the 

 Bering Strait was 2.6 ppm and 1.8 ppm in the bottom water. 

 Taking into consideration that HA's consist of 40-50% of 

 carbon, the results from this study agree with the Loder's data 

 on DOC distribution. 



The local HA maxima (30^0 g m - or 0.6-0.8 ppm) were 

 found at Stations 26 and 27 (the Gulf of Anadyr), and Stations 

 100 and 102 (the Bering Sea Shelf). Other areas of the Bering 

 Sea and the Gulf of Anadyr that were studied were characterized 

 by an average value of HA concentration 20-22 g m - or 

 0.3-0.5 ppm. 



The distribution described here of HA was compared with 

 the distribution of nutrients, chlorophyll a, and primary 

 production in the same regions (Grebmeier, Subchapter 7.1; 

 Korsak. Subchapter 6. 1 ; Whitledge. Subchapter 3. 1 ; Zeeman, 

 Subchapter 6.2, this volume). Direct correlation between the 

 parameters was not found. However, the comparison did point 

 out that the highest HA concentration was found between the 

 two maxima in primary production at Stations 36 and 53 

 (Zeeman, Subchapter 6.2, this volume) and behind the front of 

 chlorophyll a in the Chukchi Sea (Whitledge. Subchapter 6.2; 

 Grebmeier, Subchapter 7.1, this volume). 



To explain the observed relationships between distribution 

 of primary production, chlorophyll a and HA, the following 

 factors should be taken into consideration. First, the HA pool 

 can be considered as a by-product of primary productivity. It 

 is synthesized as a result of decay of newly produced organic 

 matter and dead algal cells. However, there are great differences 

 in the half-lives of humus relative to the algal population which 

 produced it. When a phytoplankton bloom is transported 

 offshore or northward and is grazed and degraded, the synthesis 

 and accumulation of HA's goes on. This creates a lag between 

 primary production and the HA concentration. Recent studies 



Fhtorimetric Determination of Hitmic Acids in the Seawater 

 Samples 



Humic acid concentration in the seawater samples was 

 determined as described in Pershina (1987) using calibration 

 curve technique. The data are summarized in Table 2 and 

 shown in Fig. 5. 



In considering the current results, the following main 

 items could be pointed out. The highest concentration of HA's 

 (75-80gm-or 1.8-2.2 ppm) was detected in the region of the 

 Bering Strait (Stations 76, 77, and 83) and adjacent edge of the 

 Chukchi Sea (Station 74). High concentration of HA 

 (60-70 g m- or 1.6-1.7 ppm) was found in the northern edge 

 of the Bering Sea Shelf (Station 89) and in the southern part of 

 the Chukchi Sea (Station 69). Relatively high contents of 

 humic substances (30-50 g m - or 1 .0- 1 .4 ppm ) were observed 

 in practically the whole area of the Chukchi Sea except for the 

 northwestern region adjacent to the East Siberian Sea 

 (Station 45) ( 16 g m - or 0.4 ppm). 



These results from the Chukchi Sea agree with the previous 

 study on the DOC distribution in Alaskan polar, subpolar, and 

 estuarine waters (Loder. 1971; Hood & Reeburgh. 1974). In 

 this study, the average concentration of DOC in the surface 



Fig. .S. Depth-integrated distribution of humic acids (g ni -). 



234 



