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Degradation by sunlight of dissolved fluorescing substances in the upper layers of the Eastern Atlantic Ocean
Netherlands aTournalof Sea Research 13 (2): 325-329 (1979)
DEGRADATION BY S U N L I G H T O F D I S S O L V E D FLUORESCING SUBSTANCES IN THE UPPER LAYERS OF THE EASTERN ATLANTIC OCEAN by C.J.M. KRAMER
(Netherlands Institutefor Sea Research, Texel, The Netherlands) CONTENTS I. II. III. IV. V.
Introduction . . . . . Methods . . . . . . Results and Discussion Summary . . . . . . References . . . . . .
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325 326 326 328 328
I. I N T R O D U C T I O N
Natural fluorescence of sea water under an ultraviolet light source is caused by dissolved substances as humic and fulvic acids. It was first described by KALLE (1949) and has been studied by many authors since (of. review by DUURSMA, 1974). The character of the fluorescing compounds--often called "Gelbstoff" (KALLE, 1937)--is only partly known. DUURSMA (1965), following KALLE, suggested the reaction of methylglyoxal-like compounds with nitrogen compounds, forming melanin structures. It is commonly assumed that in the sea two sources contribute: the marine environment by excretion and decomposition products of plankton and the rivers by decomposition and resynthesis products (STuRRMER & HARVEY, 1974). Natural fluorescence of dissolved matter has thus been used as a tracer for water masses (OTTo, 1967; HOJERSLEV, 1971; YENTSCH, 1971; ZIMMERMAN • ROMMETS, 1974). In some cases nonconservative behaviour was observed (POSTMA, MANUELS & ROMMETS, 1976).
The distribution of these soluble fluorescing materials has been described for a number of seas, e.g. the Irminger Sea (KALLE, 1957), the Mediterranean (IvANOFF, 1962), west of Africa and South America (JERLOV, 1951), the Black Sea (KARABASHEV, 1970) and the North Sea (ZIMMERMAN & ROMMETS, 1974). In this study its distribution was measured in 6 profiles at 20°N in the North Equatorial Current as part of the NECTAR programme of our Institute in November 1978 (BAARS, ZIJLSTRA & TUSSEN, 1979).
326
c.j.M. KRAMER
Acknowledgements.--Discussions with J. C. Duinker and D. Spitzer and the assistance of J. W. Rommets are gratefully acknowledged. Thanks are due to the crew of H. M. S. Tydeman. II. METHODS
Samples were taken with Niskin bottles and 30 litres Go-Flo sampling bottles (General Oceanics Inc.), mounted on a rosette frame. The samples were filtered immediately through 0.45 ~m Sartorius membrane filters. For the determination of the fluorescence a Turner Fluorometer was equipped with a General Purpose lamp and 365 nm and 460 nm filters for excitation and emission; a cylindrical glass cuvette was used. Measurements were carried out at least in duplicate. There was no effect of filtration with respect to the measurements. The results were expressed in mF1 units, according to KALLE (1963). Correction for absorption ( D u u R S M A & ROMMETS , 196 l) was unnecessary because of the very low values found. III. RESULTS
AND
DISCUSSION
The observations were limited to the upper 300 m of the water column. Values in the surface layer were about 0.3 mFl; higher values were measured in the upwelling zone near the African coast (station 2, Fig. 1) 3(2z'3o'w)
Station 2 (18~10' W)
0
O4 08
12
Depth 0 - J ~ = ~ - - t - - ~ - = -
,°m
2ot I0
30t ?o
-~
/ \
I
'°
100
150
200
250
300
/ ]
O~t 08
\
4(27°W) 12
\
6(37°w)
7(41=4o'w)
o o4 o,~ ,2
\
/x
\
5(3~2o'w>
o4 q8 ,,z
!
l
\
\l
t!
\.
o ~
\
!
o8 ,i2
!
Fig. 1. Natural fluorescence (mFl) measurements at different depths at 6 stations in the eastern tropical Atlantic at 20 ° N a n d indicated latitudes.
DISSOLVED F L U O R E S C I N G SUBSTANCES
327
and in the very top layer of the remote station 7, probably as result of the high algal concentration in the surface water. In profiles of most stations, in depleted ocean water, a distinct increase at a depth of approximately 100 m is observed, reaching a constant level of about 1.1 mF1. Data obtained at the same stations during the first NECTAR cruise in 1977, demonstrate that no further increase or decrease occurs below this depth up to at least 1500 m. A similar vertical distribution of natural fluorescence was observed in the Tyrrhenean Sea (IvANOFF, 1962). The correlation between fluorescence and diffusion coefficient only for depths less than 75 m in that water mass, was interpreted by assuming decomposition of phytoplankton at greater depths. The depth at which a change in fluorescence occurred, increased from east to west (Fig. 1). This fits with the distribution of the chlorophyll maximum observed by GIESr~s, KRnAY & TUSSEN (1978). Thus, the interpretation given by IVANOFF (1962) could also apply to the present data. Alternatively the observed gradient in the concentration of soluble fluorescing compounds may be explained as caused by photodegradation of this material. The existence of photodecomposition has been reported for other organic microconstituents in sea water; e.g. vitamin Bz, , thiamine and biotin (CARLUCCI,SILBERNAGEL& MCNALLY,1969), lipids (WHEELER, 1972) and chlorophyll a (GIESKES, KRAAY & TIJSSEN, % 150.
•
140130. f20. I10" I00-
• o
-:
-
90-
80, 70. 60.
,.5040. 3020. I0-
o-
b
b
,'~
~
~5 aoys
Fig. 2. Degradation of natural fluorescence in coastal sea water (Dutch Wadden Sea) during storage in sunlight (×, &), in sunlight after sterilization (I) and in darkness (0) (100% = 14 mF1).
328
c . j . M . KRAMER
1978). Natural fluorescent material in the fresh water lake IJsselmeer, Netherlands was found to be subject to breakdown (PoSTMA, MANUELS & ROUMETS, 1976) which might also be the result of the same process. It is supported by theoretical considerations of the possibility of photochemical reactions in the marine environment (ZAvmmv, 1977). In order to study w h e t h e r this process m a y actually take place, a simple experiment was performed. O f duplicate filtered coastal sea water samples (Dutch W a d d e n Sea), contained in quartz bottles, one was kept in the dark, the other exposed to sunlight. Subsamples were analysed at regular time intervals. A 60% decrease of the fluorescence was observed in the exposed bottle within 20 days, while no change occurred in the reference sample (Fig. 2). Also a sterilized sample was exposed to sunlight. Initially, after sterilization, fluorescence increased. A rapid decrease occurred after exposure to sunlight towards values nearly identical to those in non-sterilized samples (Fig. 2). Thus, intracellular constituents provide equally easily degradable compounds with similar fluorescence properties. No biological effect can account for this decrease. It is obvious from Figs 1 and 2 that the removal of natural fluorescing material is not complete, neither in the experiment nor in the surface layer of the ocean. This relates to the presence of refractory components.
IV. S U M M A R Y Natural dissolved fluorescent material was measured in the upper 300 m at stations in the eastern tropical Atlantic Ocean. Lower concentrations of the surface layer are caused by degradation by sunlight of dissolved organic substances, as was demonstrated by a laboratory experiment.
V. R E F E R E N C E S
BAARS,M. A., J. J. ZIJLSTRA~K S. B. TIJSSEN, 1979. Investigations in the euphotic zone of the tropical North Atlantic: programme and hydrography during the Nectar eruises.--Neth. J. Sea Res. 15 (1) : 40-57. CARLUCCI,A. F., S. B. SILBERNAOEL& P. M. McNALLV,1969. Influence of temperature and solar radiation on persistence of vitamin B12,thiamine and biotin in sea water.--Jnl Phycol. (U.S.) 5: 302-305. DUURSMA, E.K., 1965. The dissolved organic constituents of sea water. In: J. P. RILEY& G. SKmROW.Chemical oceanography. Acad. Press, Lond., New York: 433--475. ----, 1974. The fluorescence of dissolved organic matter in the sea. In: N.G. JERLOV• E. STEEMANNNIELSEN.Optical aspects of oceanography. Acad. Press, Lond., New York: 237-256.
DISSOLVED F L U O R E S C I N G SUBSTANCES
329
DUURSMa, E . K . & J. W. ROMMETS, 1961. Interprdtation mathdmatique de la fluorescence des eaux douces, saum~tres et marines.--Neth. J. Sea Res. 1 (3) : 391-405. GmSKRS, W. W. C., G. W. KRAAY & S. B. TUssEN, 1978. Chlorophylls and their degradation products in the deep pigment maximum layer of the tropical North Atlantic.--Neth. J. Sea Res. 12 (2): 195-204. HOJERSLEV, N . K . , 1971. Tyndall and fluorescence measurements in Danish and Norwegian waters related to dynamical features. Kobenhavns Universitet Rep. Inst. Fys. Oceanogr. 16: 1-99. IVANOFF,A., 1962. Au sujet de la fluorescence des eaux de mer.--C, r. hebd. S6anc. Acad. Sci., Paris 254: 4190-4192. JgRLOV, N. G., 1951. Optical studies of ocean water. Rep. Swedish Deep Sea Exped. I I I : 1-154. KALLE, K., 1937. N/ihrstoff-Untersuchungen als hydrographisches Hilfsmittel zur Unterscheidung von Wasserk6rpern.~Annln Hydrogr. Berl. 65" 1-18. , 1949. Fluoreszenz und Gelbstoff im Botnischen und Finnischen Meerbusen.-Dt. Hydrogr. Z. 2: 117-124. , 1957. Chemische Untersuchungen in der Irminger See in Juni 1955.--Ber. dt. wiss. Kommn Meeresforsch. 14: 313-328. , 1963. l~ber das Verhalten und die Herkunft der himmelblauen Fluoreszenz.-Dt. hydrogr. Z. 16: 153-166. KARABASnEV, G.S., 1970. (A method of studying the photoluminescence of seawater.)--Oceanology, Acad. Sci. USSR 10:703-707 (Eng. transl.). OTTO, L., 1967. Investigations on optical properties and water masses of the southern North Sea.--Neth. J. Sea Res. 3 (4): 532-552. POSTmX, H., M. W. MANUALS& J. W. ROMMETS, 1976. Breakdown and production of fluorescent substances in Dutch waters.--Neth. J. Sea Res. 10 (4): 499-516. STUERMER, D . H . & G. R. HARVRY, 1974. Humic substances from s e a w a t e r . Nature, Lond. 250: 480~81. WHEF.LER,J. R., 1972. Some effects of solar levels of ultraviolet radiation on lipids in artificial seawater.--J, geophys. Res. 77: 5302-5306. Y~NTSCH, C.S., 1971. Remote sensing in marine biology and fishery resources. Proc. Symp., Texas A & M Univ. College Station: 75-97. ZAFmXOU, O. C., 1977. Marine organic photochemistry previewed.--Mar. Chem. 5: 497-522. ZXM~mR~, J. T. F. & J. W. ROMMETS, 1974. Natural fluorescence as a tracer in the Dutch Wadden Sea and the adjacent North Sea.--Neth. J. Sea Res. 8 (2-3) : 117-125.
DEGRADATION BY S U N L I G H T O F D I S S O L V E D FLUORESCING SUBSTANCES IN THE UPPER LAYERS OF THE EASTERN ATLANTIC OCEAN by C.J.M. KRAMER
(Netherlands Institutefor Sea Research, Texel, The Netherlands) CONTENTS I. II. III. IV. V.
Introduction . . . . . Methods . . . . . . Results and Discussion Summary . . . . . . References . . . . . .
. . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .
325 326 326 328 328
I. I N T R O D U C T I O N
Natural fluorescence of sea water under an ultraviolet light source is caused by dissolved substances as humic and fulvic acids. It was first described by KALLE (1949) and has been studied by many authors since (of. review by DUURSMA, 1974). The character of the fluorescing compounds--often called "Gelbstoff" (KALLE, 1937)--is only partly known. DUURSMA (1965), following KALLE, suggested the reaction of methylglyoxal-like compounds with nitrogen compounds, forming melanin structures. It is commonly assumed that in the sea two sources contribute: the marine environment by excretion and decomposition products of plankton and the rivers by decomposition and resynthesis products (STuRRMER & HARVEY, 1974). Natural fluorescence of dissolved matter has thus been used as a tracer for water masses (OTTo, 1967; HOJERSLEV, 1971; YENTSCH, 1971; ZIMMERMAN • ROMMETS, 1974). In some cases nonconservative behaviour was observed (POSTMA, MANUELS & ROMMETS, 1976).
The distribution of these soluble fluorescing materials has been described for a number of seas, e.g. the Irminger Sea (KALLE, 1957), the Mediterranean (IvANOFF, 1962), west of Africa and South America (JERLOV, 1951), the Black Sea (KARABASHEV, 1970) and the North Sea (ZIMMERMAN & ROMMETS, 1974). In this study its distribution was measured in 6 profiles at 20°N in the North Equatorial Current as part of the NECTAR programme of our Institute in November 1978 (BAARS, ZIJLSTRA & TUSSEN, 1979).
326
c.j.M. KRAMER
Acknowledgements.--Discussions with J. C. Duinker and D. Spitzer and the assistance of J. W. Rommets are gratefully acknowledged. Thanks are due to the crew of H. M. S. Tydeman. II. METHODS
Samples were taken with Niskin bottles and 30 litres Go-Flo sampling bottles (General Oceanics Inc.), mounted on a rosette frame. The samples were filtered immediately through 0.45 ~m Sartorius membrane filters. For the determination of the fluorescence a Turner Fluorometer was equipped with a General Purpose lamp and 365 nm and 460 nm filters for excitation and emission; a cylindrical glass cuvette was used. Measurements were carried out at least in duplicate. There was no effect of filtration with respect to the measurements. The results were expressed in mF1 units, according to KALLE (1963). Correction for absorption ( D u u R S M A & ROMMETS , 196 l) was unnecessary because of the very low values found. III. RESULTS
AND
DISCUSSION
The observations were limited to the upper 300 m of the water column. Values in the surface layer were about 0.3 mFl; higher values were measured in the upwelling zone near the African coast (station 2, Fig. 1) 3(2z'3o'w)
Station 2 (18~10' W)
0
O4 08
12
Depth 0 - J ~ = ~ - - t - - ~ - = -
,°m
2ot I0
30t ?o
-~
/ \
I
'°
100
150
200
250
300
/ ]
O~t 08
\
4(27°W) 12
\
6(37°w)
7(41=4o'w)
o o4 o,~ ,2
\
/x
\
5(3~2o'w>
o4 q8 ,,z
!
l
\
\l
t!
\.
o ~
\
!
o8 ,i2
!
Fig. 1. Natural fluorescence (mFl) measurements at different depths at 6 stations in the eastern tropical Atlantic at 20 ° N a n d indicated latitudes.
DISSOLVED F L U O R E S C I N G SUBSTANCES
327
and in the very top layer of the remote station 7, probably as result of the high algal concentration in the surface water. In profiles of most stations, in depleted ocean water, a distinct increase at a depth of approximately 100 m is observed, reaching a constant level of about 1.1 mF1. Data obtained at the same stations during the first NECTAR cruise in 1977, demonstrate that no further increase or decrease occurs below this depth up to at least 1500 m. A similar vertical distribution of natural fluorescence was observed in the Tyrrhenean Sea (IvANOFF, 1962). The correlation between fluorescence and diffusion coefficient only for depths less than 75 m in that water mass, was interpreted by assuming decomposition of phytoplankton at greater depths. The depth at which a change in fluorescence occurred, increased from east to west (Fig. 1). This fits with the distribution of the chlorophyll maximum observed by GIESr~s, KRnAY & TUSSEN (1978). Thus, the interpretation given by IVANOFF (1962) could also apply to the present data. Alternatively the observed gradient in the concentration of soluble fluorescing compounds may be explained as caused by photodegradation of this material. The existence of photodecomposition has been reported for other organic microconstituents in sea water; e.g. vitamin Bz, , thiamine and biotin (CARLUCCI,SILBERNAGEL& MCNALLY,1969), lipids (WHEELER, 1972) and chlorophyll a (GIESKES, KRAAY & TIJSSEN, % 150.
•
140130. f20. I10" I00-
• o
-:
-
90-
80, 70. 60.
,.5040. 3020. I0-
o-
b
b
,'~
~
~5 aoys
Fig. 2. Degradation of natural fluorescence in coastal sea water (Dutch Wadden Sea) during storage in sunlight (×, &), in sunlight after sterilization (I) and in darkness (0) (100% = 14 mF1).
328
c . j . M . KRAMER
1978). Natural fluorescent material in the fresh water lake IJsselmeer, Netherlands was found to be subject to breakdown (PoSTMA, MANUELS & ROUMETS, 1976) which might also be the result of the same process. It is supported by theoretical considerations of the possibility of photochemical reactions in the marine environment (ZAvmmv, 1977). In order to study w h e t h e r this process m a y actually take place, a simple experiment was performed. O f duplicate filtered coastal sea water samples (Dutch W a d d e n Sea), contained in quartz bottles, one was kept in the dark, the other exposed to sunlight. Subsamples were analysed at regular time intervals. A 60% decrease of the fluorescence was observed in the exposed bottle within 20 days, while no change occurred in the reference sample (Fig. 2). Also a sterilized sample was exposed to sunlight. Initially, after sterilization, fluorescence increased. A rapid decrease occurred after exposure to sunlight towards values nearly identical to those in non-sterilized samples (Fig. 2). Thus, intracellular constituents provide equally easily degradable compounds with similar fluorescence properties. No biological effect can account for this decrease. It is obvious from Figs 1 and 2 that the removal of natural fluorescing material is not complete, neither in the experiment nor in the surface layer of the ocean. This relates to the presence of refractory components.
IV. S U M M A R Y Natural dissolved fluorescent material was measured in the upper 300 m at stations in the eastern tropical Atlantic Ocean. Lower concentrations of the surface layer are caused by degradation by sunlight of dissolved organic substances, as was demonstrated by a laboratory experiment.
V. R E F E R E N C E S
BAARS,M. A., J. J. ZIJLSTRA~K S. B. TIJSSEN, 1979. Investigations in the euphotic zone of the tropical North Atlantic: programme and hydrography during the Nectar eruises.--Neth. J. Sea Res. 15 (1) : 40-57. CARLUCCI,A. F., S. B. SILBERNAOEL& P. M. McNALLV,1969. Influence of temperature and solar radiation on persistence of vitamin B12,thiamine and biotin in sea water.--Jnl Phycol. (U.S.) 5: 302-305. DUURSMA, E.K., 1965. The dissolved organic constituents of sea water. In: J. P. RILEY& G. SKmROW.Chemical oceanography. Acad. Press, Lond., New York: 433--475. ----, 1974. The fluorescence of dissolved organic matter in the sea. In: N.G. JERLOV• E. STEEMANNNIELSEN.Optical aspects of oceanography. Acad. Press, Lond., New York: 237-256.
DISSOLVED F L U O R E S C I N G SUBSTANCES
329
DUURSMa, E . K . & J. W. ROMMETS, 1961. Interprdtation mathdmatique de la fluorescence des eaux douces, saum~tres et marines.--Neth. J. Sea Res. 1 (3) : 391-405. GmSKRS, W. W. C., G. W. KRAAY & S. B. TUssEN, 1978. Chlorophylls and their degradation products in the deep pigment maximum layer of the tropical North Atlantic.--Neth. J. Sea Res. 12 (2): 195-204. HOJERSLEV, N . K . , 1971. Tyndall and fluorescence measurements in Danish and Norwegian waters related to dynamical features. Kobenhavns Universitet Rep. Inst. Fys. Oceanogr. 16: 1-99. IVANOFF,A., 1962. Au sujet de la fluorescence des eaux de mer.--C, r. hebd. S6anc. Acad. Sci., Paris 254: 4190-4192. JgRLOV, N. G., 1951. Optical studies of ocean water. Rep. Swedish Deep Sea Exped. I I I : 1-154. KALLE, K., 1937. N/ihrstoff-Untersuchungen als hydrographisches Hilfsmittel zur Unterscheidung von Wasserk6rpern.~Annln Hydrogr. Berl. 65" 1-18. , 1949. Fluoreszenz und Gelbstoff im Botnischen und Finnischen Meerbusen.-Dt. Hydrogr. Z. 2: 117-124. , 1957. Chemische Untersuchungen in der Irminger See in Juni 1955.--Ber. dt. wiss. Kommn Meeresforsch. 14: 313-328. , 1963. l~ber das Verhalten und die Herkunft der himmelblauen Fluoreszenz.-Dt. hydrogr. Z. 16: 153-166. KARABASnEV, G.S., 1970. (A method of studying the photoluminescence of seawater.)--Oceanology, Acad. Sci. USSR 10:703-707 (Eng. transl.). OTTO, L., 1967. Investigations on optical properties and water masses of the southern North Sea.--Neth. J. Sea Res. 3 (4): 532-552. POSTmX, H., M. W. MANUALS& J. W. ROMMETS, 1976. Breakdown and production of fluorescent substances in Dutch waters.--Neth. J. Sea Res. 10 (4): 499-516. STUERMER, D . H . & G. R. HARVRY, 1974. Humic substances from s e a w a t e r . Nature, Lond. 250: 480~81. WHEF.LER,J. R., 1972. Some effects of solar levels of ultraviolet radiation on lipids in artificial seawater.--J, geophys. Res. 77: 5302-5306. Y~NTSCH, C.S., 1971. Remote sensing in marine biology and fishery resources. Proc. Symp., Texas A & M Univ. College Station: 75-97. ZAFmXOU, O. C., 1977. Marine organic photochemistry previewed.--Mar. Chem. 5: 497-522. ZXM~mR~, J. T. F. & J. W. ROMMETS, 1974. Natural fluorescence as a tracer in the Dutch Wadden Sea and the adjacent North Sea.--Neth. J. Sea Res. 8 (2-3) : 117-125.