C1-C3 Hydrocarbons and Chlorophyll a Concentrations in the

Jun 1, 1975 - The objective was to determine if a correlation existed between the C1-C3 hydrocarbons and chlorophyll a in open ocean environments...
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14 C - C Hydrocarbons and Chlorophyll a 1

3

Concentrations in the Equatorial Pacific

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Ocean R O B E R T A . L A M O N T A G N E , W A L T E R D . S M I T H , and JOHN W. SWINNERTON U.S. Naval Research Laboratory, Washington, D . C. 20375

C - C hydrocarbons and chlorophyll a analyses were performed on approximately 400 near-surface water samples ( = 2 m below the surface) during a one and half month cruise to the Equatorial Pacific Ocean. The hydrocarbons were determined by a flame ionization gas chromatograph. Chlorophyll a was determinedfluorometrically.The objective was to determine if a correlation existed between the C - C hydrocarbons and chlorophyll a in open ocean environments. A slight correlation was found between chlorophyll a and ethylene and propylene (R = 0.56). No correlation was found between chlorophyll a and methane, ethane, or propane. 1

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' " p h e relationship between the biological community and dissolved gases **• has been of interest for many years. M u c h work has been done on oxygen production and carbon dioxide utilization. Some recent work has centered around gas production b y various kelp communities ( I ) and siphonophores ( 2 ) . However, very little work has been published eluci­ dating the relationship between organisms, primarily one-celled orga­ nisms, and dissolved light hydrocarbons ( C 1 - C 4 ) . Wilson et al. (3), showed the production of carbon monoxide, ethylene, and propylene with laboratory experiments using dissolved organic carbon produced b y phytoplankton and with an ultradiatom Chaetoceros galvestonensis. D u r ­ ing a six-month field study of a nearshore environment off Key Biscayne, F l a . , unpublished data b y Swinnerton et al. (4) showed correlations between chlorophyll a and carbon monoxide and between light hydro­ carbon gas production and chlorophyll a. Zsolnay ( 5 ) reported a corre163 Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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METHODS IN OCEANOGRAPHY

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lation between chlorophyll a and non-aromatic hydrocarbons for an area off West Africa. During a recent cruise to the equatorial Pacific, chloro­ phyll a and C 1 - C 3 dissolved hydrocarbons were measured to establish whether a correlation existed between dissolved light hydrocarbons and chlorophyll a i n the open ocean. Water samples, taken every 3 h r whenever possible, were obtained from a submersible pump which was mounted approximately 2 m below the surface of the water on the bow of the ship. The method of Swinnerton and Linnenbom (6) was used on all samples for C1-C3 hydrocarbon analysis. Chlorophyll a measurements were made following the method for the fluorometric determination of chlorophylls ( 7 ) . Results Figure 1 shows the cruise track from Ecuador to Panama via H a w a i i and Tahiti onboard the U S N S Hayes i n M a r c h and A p r i l 1974. Also shown is a portion of a cruise taken i n November and December 1972, onboard the U S C G C Glacier, which intersects the 1974 cruise track. 1

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Figure 1. Cruise track of USNS Hayes, (Δ), denoting noon position. USCGC Glacier cruise track, (•). Figure 2 shows the ethylene ( C H ) concentrations i n the surface waters between H a w a i i and Tahiti (Table I I ) . Excluding the values obtained just outside H a w a i i (3/21/74) and Tahiti (3/29/74), a broad general increase is apparent with a maximum average value of « 4.0 X 10" ml/1 and a low average value of « 2.4 X 10" ml/1. Plotted over 2

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Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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14.

LAMONTAGNE E T AL.

2I°N I29°W 1

Cf-Cs Hydrocarbons and Chlorophyll a

I5°N I34°W 1

I0°N I36°W 1

5°N I39°W 1

0° 5°S IO°S I 4 2 ° W I44°W I46°W 1 1 1

I5°S I49°W 1—

10 d

8

11/18

Figure 3.

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11/19

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11/20

11/21

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L 11/22 11/23 1972

11/24

11/25

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11/26

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11/27

Surface water ethylene concentrations, (X), of USCGC Glacier cruise between 20°Ν and 20°S

Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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ANALYTICAL METHODS IN OCEANOGRAPHY

Table I.

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Date 2/28 3/1 3/2 3/3 3/4 3/5 3/6 3/7 3/8 3/9 3/10 3/11 3/12 3/13 3/14 3/15 3/16

CHS (ml/l) 12.22 4.81 4.94 5.32 5.44 4.71 4.40 4.36 4.45 4.33 4.45 4.30 4.12 4.09 4.11 4.11 4.03

± 9.78 db 0.22 zb 0.43 zb 0.12 zb 0.21 zb 0.10 zb 0.11 zb 0.27 zb 0.19 zb 0.19 zb 0.09 zb 0.08 zb 0.17 zb 0.16 ± 0.12 zb 0.13

C H,

(ml/l)

0.51 0.51 0.45 0.54 0.53 0.44 0.34 0.30 0.34 0.32 0.19 0.24 0.24 0.18 0.23 0.23 0.21

=b 0.09 zb 0.18

2

C

zb 0.07 zb 0.02 zb 0.12 =b 0.07 ± 0.08 zb 0.08 ± 0.19 zb 0.03 ± 0.07 =b 0.08 db 0.04 zb 0.07 =b 0.04 =b 0.05

CJHs (ml/l) 11.15 8.26 8.02 10.07 10.79 8.21 4.92 4.45 4.28 3.35 2.65 2.15 1.82 1.65 1.88 1.71 1.77

=b 1.90 zb 0.75 db 1.32 =b 1.75 =b 1.59 =b 0.89 =b 0.64 =b 1.39 =b 0.07 =b 0.22 zb 0.22 zb 0.19 =b 0.12 =b 0.18 =b 0.17 =b 0.15

Leg I—

CzH

(ml/l)

c

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0.52 0.43 0.31 0.63 0.39 0.30 0.22 0.20 0.24 0.17 0.14 0.10 0.07 0.04 0.05 0.06 0.04

± 0.19 zb 0.20 zb 0.32 zb 0.04 zb 0.09 zb 0.05 zb 0.04 zb 0.07 zb 0.08 zb 0.03 zb 0.02 zb 0.03 zb 0.01 zb 0.01 zb 0.02 zb 0.01

Daily averages with one σ standard deviation. Values obtained from « 2 m below the surface of the water. In most cases the average is of six or seven values. a

these data are the daily average chlorophyll a concentrations. The chloro­ p h y l l a curve exhibits the same general shape as the ethylene curve. Figure 3 shows the ethylene concentrations reported by Lamontagne et al. (7) for the cruise i n 1972 which intersects the 1974 cruise track. A t that time, an average maximum value for ethylene of « 5.3 X 10 m l / l , and an average l o w value of « 2.6 X 10~ m l / l was found. This broad 1972 maximum and the 1974 maximum fit the geographic location of the South Equatorial current relatively well. N o chlorophyll a data were obtained i n 1972. Tables I, II, and III list the daily averages for Legs I, II, and III with one σ standard deviation for the surface water concentrations of methane r6

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Table II. Date

CH

3/21 3/22 3/23 3/24 3/25 3/26 3/27 3/28 3/29

3.93 3.90 3.92 3.89 4.12 4.02 3.88 3.85 3.81

b

A

(ml/l)

C H,

(ml/l)

C H,

(ml/l)

zb 0.51 zb 0.18 zb 0.12 zb 0.10 zb 0.09 ± 0.14 zb 0.12 zb 0.12 zb 0.17

0.19 0.14 0.13 0.17 0.26 0.24 0.21 0.19 0.14

zb 0.18 zb 0.03 zb 0.03 zb 0.05 zb 0.05 zb 0.04 zb 0.05 zb 0.05 =b 0.05

6.87 2.41 2.64 2.34 2.50 3.88 3.32 3.19 4.22

=b 3.81 zb 0.22 zb 0.21 zb 0.11 zb 0.22 =b 0.30 zb 0.16 =b 0.68 zb 0.87

2

C

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C

CH

Leg II— c

(ml/l)

0.04 0.09 0.05 0.09 0.08 0.08 0.05 0.04 0.05

=b 0.02 zb 0.01 zb 0.02 zb 0.04 db 0.02 zb 0.03 zb 0.01 zb 0.01 zb 0.02

z

g

Daily average with one σ standard deviation. Values obtained from « 2 m below the surface of the water. In most cases the average is of six or seven values. α

Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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Cj-Cg Hydrocarbons and Chlorophyll a

167

Ecuador to Hawaii, 1974

e

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C f l , ' (ml/l)

6 c

Chl. a (mg/m )

2.15 db 0.56 3.11 ± 0.09

0.24 0.16

2.86 3.43 2.70 1.65 1.37 1.64 0.99 0.88 0.68 0.59 0.73 0.77 0.73 0.67

0.74 0.12 0.14 0.32 0.12 0.17 0.15 0.13 0.12 0.10 0.06 0.04 0.05 0.05

— ± 0.33 ± ± =fc ± ± ± ± ± ± ± ± ± ±

Noon Position

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0.49 0.34 0.16 0.06 0.53 0.12 0.09 0.11 0.07 0.05 0.11 0.11 0.05

± 0.08 ± 0.04

\ J

— ± 0.18 ± ± ± ± ± ± ± ± ± ± ± ± ±

0.04 0.04 0.17 0.02 0.04 0.06 0.02 0.02 0.03 0.01 0.01 0.01 0.01

Guayaquil River, Galapagos Islands Marchina Island Santa Cruz Island 0°25'N 93°46'W 2°40'N 98°24'W 4°32'N 102°32'W 6°34'N 107°41'W 8°29'N 112°30'W 10°29'N 116°50'W 12°02'N 122°00'W 13°48'N 126°56'W 15°26'N 132°00'W 16°54'N 136°48'W 18°31'N 142°41'W 19°49'N 147°59'W 20°49'N 153°41'W

10" ml/l. 10" ml/l. 6

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( C H ) , ethane ( C H ) , ethylene ( C H ) , propane ( C H ) , propylene ( C H ) , and chlorophyll a. The date and noon positions are also listed. Methane concentrations average 4.22 =t 0.15 X 10" m l / l for the entire cruise. As shown i n the tables, methane varies as one changes latitudes and hence crosses currents of varying temperature and salinity. Ethane concentrations under open ocean conditions do not vary greatly as seen in the latter portion of L e g I, where the concentration is 0.26 ± 0.08 X 10" m l / l (away from the Galapagos Islands and the Ecuadorian coast). L e g II exhibits an average concentration of 0.19 ± 0.06 X 10" m l / l . The average concentration for L e g III is 0.25 ± 0.06 X 10" m l / l with values increasing as we approach the Gulf of Panama. The agree4

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Hawaii to Tahiti, 1974° C #6 3

0.52 0.88 1.12 0.96 1.14 1.31 1.58 1.40 1.37 e

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C

(ml/l)

± ± =b =b zb =b zb =b zb

0.22 0.18 0.07 0.15 0.12 0.16 0.07 0.03 0.08

Chl. a (mg/m ) 3

0.05 0.03 0.03 0.07 0.09 0.09 0.08 0.07 0.04

± zb zb zb zb zb =b =b zb

0.01 0.01 0.00 0.03 0.02 0.02 0.02 0.01 0.01

Noon Position Pearl Harbor Area 17°19'N 157°05'W 12 28'Ν 1 5 0 W W 8°05'N 155°00'W 3°30'N 1 5 4 ° 0 5 ^ 0°32'S 1 5 3 ° 1 5 ^ 5°46'S 152°39'W l O ^ ' S 151°29'W 14°30'S 150°22'W 0

10" ml/l. 6

ΙΟ" ml/l. 8

Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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Table III.

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Date

CHS (ml/l)

C Hs° (ml/l) 2

CJIS

(ml/l)

Leg I l l -

CH Z

C

S

(ml/l)

4/3 3.75 d= 0.03 0.13 ± 0.02 3.25 ± 0.56 0.06 ± 0.03 4/4 3.76 =h 0.15 0.14 ± 0.04 3.27 =fc 0.22 0.06 ± 0.03 4/5 3.85 =b 0.07 0.12 ± 0.03 3.06 db 0.22 0.05 ± 0.01 4/6 3.84 ± 0.10 0.14 ± 0.03 2.78 =fc 0.25 0.05 =fc 0.02 4/7 3.80 ± 0.06 0.20 ± 0.09 2.69 ± 0.43 0.10 ± 0.06 4/8 3.70 ± 0.05 0.16 ± 0.03 2.73 =fc 0.21 0.06 ± 0.02 4/9 3.79 ± 0.04 0.20 ± 0.06 2.06 zfc 0.64 0.07 =fc 0.03 4/10 4.05 =fc 0.21 0.22 db 0.05 3.91 =b 0.56 0.09 ± 0.05 4/11 4.04 db 0.22 0.23 ± 0.06 4.09 zb 0.39 0.09 =b 0.02 4/12 4.23 zb 0.10 0.24 ± 0.08 5.29 zb 0.75 0.13 =b 0.04 4/13 4.42 zb 0.08 0.37 zb 0.06 7.18 zb 0.44 0.23 =b 0.07 4/14 4.65 zb 0.17 0.43 zb 0.05 7.77 =b 0.33 0.23 zb 0.03 4/15 4.64 =b 0.08 0.46 zb 0.10 9.67 =b 1.43 0.26 =1= 0.07 4/16 4.57 zb 0.16 0.45 zb 0.04 6.91 zb 1.19 0.18 ± 0.08 4/17 4.47 ± 0.13 0.33 ± 0.08 6.70 zb 1.55 0.15 =fc 0.03 Daily averages with one σ standard deviation. Values obtained from « 2 m below the surface of the water. In most cases the average is of six or seven values. β

ment between Legs I and III i n the vicinity of the Galapagos Islands ( M a r c h 4, 5 and A p r i l 14, 15) is good; 0.49 ± 0.06 X 10~ m l / l and 0.44 ± 0.07 X 10~ m l / l , respectively. 6

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Ethylene values can vary b y almost an order of magnitude as shown in Table I. Concentrations as high as 10.79 ± 1.90 X 10" m l / l to a low of 1.71 ± : 0.17 X 10" m l / l can be found for open ocean conditions. L e g II has been discussed i n relation to Figure 2. L e g III exhibits fluctuations between 2.06 ± 0.64 X 10" m l / l and 9.67 ± 1.43 X 10" m l / l . A n over­ all average value has not been calculated for ethylene primarily because of these wide variations. Average values of 9.50 ± 1.64 X 10" m l / l and 8.72 ± 0.88 X 10" m l / l , respectively, were found for the area where Legs I and III intersect. 6

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Propane obtained on L e g I has its greatest value of 0.63 ± 0.32 X 10" m l / l i n the Galapagos Islands and one of its lowest of 0.04 ± 0.01 X 10~ m l / l near the Hawaiian Islands. L e g II has an average concentration of 0.06 ± 0.02 X 10' m l / l which represents a clean open ocean environ­ ment. Concentrations for L e g III vary from 0.06 ± 0.03 X 10" m l / l near Tahiti to 0.26 ± 0.07 X 10" m l / l i n the vicinity of the Galapagos Islands. Comparison of the values between Legs I and III i n the area of the Galapagos Islands reveals concentrations of 0.35 ± 0.06 X 10" m l / l and 0.25 db 0.05 X 10" m l / l , respectively. e

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Propylene has the same general characteristics found for the other hydrocarbons. L e g I concentrations vary from 3.43 ± 0.49 X 10" m l / l near the Galapagos Islands to 0.59 ± 0.07 X 10" m l / l for an area located « 1500 miles southeast of Hawaii. L e g II exhibits what appears to be a 6

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Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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LAMONTAGNE E T AL.

T a h i t i to Panama, 1974 CzH °

(ml/l)

1.25 ± 1.51 ± 1.49 ± 1.38 ± 1.39 ± 1.12 ± 1.35 ± 1.61 ± 1.61 ± 1.83 ± 2.30 ± 2.24 ± 3.16 ± 1.96 ± 2.06 ± » 10-« ml/l. ' 10-· ml/l.

0.12 0.19 0.09 0.13 0.18 0.16 0.28 0.17 0.33 0.28 0.17 0.11 0.50 0.32 0.58

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6

C -C t

s

Hydrocarbons and Chlorophyll a

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e

Noon Position

Chl. a (mg/m ) 3

0.03 0.04 0.05 0.05 0.06 0.06 0.06 0.07 0.08 0.10 0.12 0.11 0.09 0.10 0.10

Outside T a h i t i 15°21'S 145°12'W 14°21'S 140°10'W 12°52'S 135°'47W 11°35'S 131°04'W 10°15'S 126°46'W 8°32'S 121°39'W 6°43'S 116°18'W 5°08'S 112°32'W 3°44'S 108°43'W 1°55'S 104°14'W 0°08'S 99°21'W 1°37'N 95°21'W 3°25'N 90°30'W 4°49'N 86°25'W

± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.01 ± 0.01 zh 0.01 ± 0.02 ± 0.01 ± 0.04 ± 0.02 ± 0.02 ± 0.02

shallow and broad but significant peak. A h i g h concentration of 1.58 ± 0.07 X lQr m l / l is contrasted w i t h a low value of 0.52 ± 0.22 Χ 10" m l / l outside H a w a i i and an intermediate value of 1.37 ± 0.08 Χ 10" m l / l just outside of Tahiti. Values on L e g III increase steadily from 1.25 ± 0.12 X 10" m l / l found outside of Tahiti to 3.16 ± 0.50 X 10" m l / l near the Galapagos Islands. Comparison of the values between Legs I and III near the Galapagos Islands (see above for dates) reveals good agreement of 3.06 ± 0.41 X 10-* m l / l and 2.70 ± 0.31 Χ 10" m l / l , respectively. The highest chlorophyll a values obtained during the entire cruise was i n the area of the Galapagos Islands (0.74 ± 0 . 1 8 m g / m ) . Values on L e g I decreased to 0.04 ± 0.01 m g / m near the Hawaiian Islands. L e g II exhibits a maximum of 0.09 ± 0.02 m g / m relative to the average low value of 0.04 ± 0.01 m g / m found near H a w a i i and Tahiti. Chloro­ phyll a concentrations increased from 0.03 ± 0.01 m g / m to 0.12 ± 0.01 m g / m as we progressed from Tahiti to the Galapagos Islands. Once again, comparison of values between Legs I and III, where they intersect, shows general agreement; 0.13 ± 0.04 m g / m and 0.10 ± 0.03 m g / m , respectively. 6

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Discussion Methane data show that this gas i n the surface water is i n near equilibrium with that i n the air. Methane variations do occur i n bays, coastal, and anoxic areas, but under open ocean conditions methane con­ centrations rarely if ever undergo large fluctuations. Methane shows no correlation with chlorophyll a or with any of the other light hydrocarbons measured.

Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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ANALYTICAL METHODS IN OCEANOGRAPHY

Ethane concentrations exhibit the same type of relative constancy as methane. The only variable and high concentrations (relative to open ocean values) of « 0.50 X 10~ m l / l are found near the Galapagos Islands and Ecuador. There is good agreement between the average concentra­ tion found in 1972 (0.20 X 10" m l / l . ) and 1974 ( 0.28 X 10' m l / l . ) . Propane is quite similar to ethane i n distribution. The highest and most interesting concentrations are also found near the Galapagos Islands and Ecuador. As with ethane, relative agreement is found between the average concentration obtained in 1972 and that found in 1974: 0.30 X 10~ m l / l and 0.20 X 10" m l / l , respectively. There is a broad but significant increase for ethylene between « 5° Ν and 10° S which corresponds to the position of the South Equatorial Current ( S . E . C . ) . The data reported by Lamontagne et al. (7, Figure 3) shows this maximum for ethylene i n the same area. A similar but smaller maximum was found for propylene i n 1972, and this is also the case for the 1974 cruise. It is likely that these broad gentle increases for ethylene and propylene result from the S.E.C. sweeping biologically rich upwelled water away from the South American coast. Chlorophyll a data follow the general pattern set forth by ethylene and support this speculation. In regard to the work of Wilson et al. (3) where the only hydro­ carbons produced were ethylene and propylene and that of Swinnerton et al. (4), we thought that an analysis of correlation between the un­ saturated hydrocarbons and chlorophyll a for the entire cruise track would be beneficial. A correlation coefficient, R, of 0.56 was obtained using ethylene and propylene against chlorophyll a. A correlation coeffi­ cient of 0.59 was obtained between ethylene only and chlorophyll a. This latter correlation was done because the ethylene values are much greater than the propylene and also because ethylene was the prominent hydro­ carbon gas produced in the work by Wilson et al. (3). Zsolnay published correlation coefficients for hydrocarbons and chlorophyll a of 0.67 (5) and 0.50 (8) for an upwelling area northwest of Africa and for a transect from Nova Scotia to Bermuda, respectively. The chlorophyll a concentrations obtained off the coast of Africa i n the upwelling region are an order of magnitude greater than ours while those reported for the area between Nova Scotia and Bermuda (0.02-0.81 m g / m ) are within the same range we obtained for the 1974 cruise. Zsolnay analyzed for nonvolatile hydrocarbons; thus the comparison between his correlation coefficient and ours concerns two different sets of hydrocarbons. In spite of this, the comparison is useful because the values reported by each of us may represent about the maximum corre­ lation coefficient, with R = 1 being the optimum correlation, considering the number of variables encountered. The variability of the size and type of biomass involved, the growth phase of the organisms (i.e., log phase 6

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Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

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14.

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Cf-C

s

Hydrocarbons and Chlorophyll a

171

of growth, senescence), season, prevailing current (circulation patterns), and availability of sunlight i n the possible photochemical breakdown of organic matter present a l l contribute to the observed hydrocarbon con­ centration. A n interesting aspect of all this is the fact that comparing a l l of the hydrocarbons taken on the present cruise to chlorophyll a gives a correlation coefficient of 0.50. This indicates that a correlation w i t h chlorophyll a may not be applicable under open ocean conditions. A t the present time, w e are conducting laboratory experiments to help elucidate whether the major production of these light hydrocarbon gases occurs by the decay of organic matter (dead biomass, etc.), photo­ chemical reactions of very labile organic material excreted b y organisms, or direct synthesis b y the living biomass. This information would be beneficial i n assessing whether the light hydrocarbon concentrations are a product of the immediate time and area or whether they are the result of a long-term sequence of events i n that given area and/or elsewhere. A possible area of future work on the correlation between dissolved fight hydrocarbons and biomass is the vicinity of the Galapagos Islands. The large and variable concentrations found i n that area coupled with the transporting mechanisms there would be ideal for studying production and transport away from source areas. Acknowledgment The authors would like to thank J. Haluska and W . Anderson from O l d Dominion University, Norfolk, V a . for their collection and analysis of the chlorophyll a data. Mechanical assistance from F . Kiselak and G . Bugg from N . R . L . was greatly appreciated.

Literature Cited

1. Loewus, M. W., Delwicke, C. C., PlantPhysiol.(1963) 38, 371. 2. Pickwell, G. V., Barham, E. G., Wilton, J. W., Science (1964) 140, 860. 3. Wilson, D. J., Swinnerton, J. W., Lamontagne, R. Α., Science (1970) 168, 1577. 4. Swinnerton, J. W., Bunt, J. S., Lamontagne, R. Α., unpublished data, 1972. 5. Zsolnay, Α., Deep-Sea Res. (1973) 20, 923. 6. Swinnerton, J. W., Linnenbom, V. J., J. Gas Chromatogr. (1967) 5, 510. 7. Strickland, J. D. H., Parsons, T. R., "A Practical Handbook of Seawater Analysis," Fisheries Research Board of Canada, 1972. 8. Lamontagne, R. Α., Swinnerton, J. W., Linnenbom, V. J., Tellus (1974) 26, 71. 9. Zsolnay, Α., "Hydrocarbon Content and Chlorophyll Correlation in the Waters Between Nova Scotia and the Gulf Stream." Proceedings on Marine Pollution Monitoring—Symposium and Workshop, Gaithersburg, Maryland, 1974. RECEIVED February 25, 1975 Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.