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Modelling the biogenic transport of atmospheric particles in surface and deep marine waters
198 MODELLING THE BIOGENIC TRANSPORT OF ATMOSPHERIC PARTICLES IN SURFACE AND DEEP MARINE WATERS
EL NINO AND LITTLE ICE ACE EFFECTS ON !'FU[IILINC IN THE EASTERN TROPICAL PACIFIC
D. RUIZ-PINO. C. E. LAMBERT, C. JEANDEL and P. BUAT-MENARD. (Laboratoire de Physique et Chimie Marines, CEROV, BP 8, F-06230, Villefranche sur Met, France).
G.T. SHEN R.B. DUNBAR M.W. COLGAN
There is some evidence that most of the yearly atmospheric flux of trace elements to the Mediterranean basin is delivered during sporadic events such as Saharan dust storms. To help assessing the geochemical impact of such events we have developped a non-steady state, one-dimensional model of the transport of insoluble atmospheric particles in the water column. This model has 3 forcing variables: i) the atmospheric source function which is of a gaussian type, based on time-series data obtained at coastal stations in the Ligurian Sea (Capo Cavallo, Corsica and Cap Ferrat). ii) The removal rate of atmospheric particles from the euphoric zone which is assumed to be a first-order process controlled by zooplankton grazing activity, iii) An average eddy diffusion coefficient between surface and deep waters for the whole western Mediterranean basin. The value adopted was 1.5x1012 m3/yr when the upper water column is stratified, as in spring and summer. In winter, because of convective mixing this coefficient was assumed to be equal to 40x1012m3/yr. Model runs over a year period show satisfactory agreement with experimental data. It appears that following a Saharan dust storm event, particulate concentrations of terrigenous material will be enhanced significantly only in surface waters and for a few weeks. Temporal changes in the terrigenous particulale flux out of the euphoric zone are affected by the intensity and duration of the dust storm, with a response time sometimes as short as a week. The temporal pattern of this flux lroughout the water column is however primarily related to changes in primary productivity during spring and summer, whereas during winter, convective mixing can also be a dominant factor. In the future, this model will be extended to the fraction of the atmospheric input which dissolves in seawater.
HYDROTHERMAL MANGANESE A N D METHANE PLUMES IN THE NORTH FIJI BASIN P N. SEDWICK, T. GAMO, and G. M. McMURTRY (Department of Oceanography, University of Hawaii, Honolulu, Hawaii, U.S A 96822) During the 1987 North Fiji Basin (NFB) Expedition of the R/V Moans Wav~, seven hydrocasta were taken at locations of suspected seafloor hydrothermal activity between 13.2 " S and 171 " S along the NFE spreading center. Stations were selected using SEAMARC lI acoustic imaging and seismic reflection techniques. Water samples were subsequently analyzed for dissolved methane and total dissovable manganese (TDM). Anomalous deep water concentrations of these two species indicate recent seafloor hydrothermal circulation in this area. Dissolved methane w ~ determined at sea by g ~ chromatography with flame ionization detection following cryogenic trapping. TDM was determined by flameless graphite furnace atomic absorption spectrophotometry after preconcentration by coprecipitation with gallium hydroxide. The vertical concentration profiles of dissolved methane and TDM both exhibit discrete deep-water m ~ i m a centered at depths of 2-2.5 km and 3-3.5 km Anomalous methane concentrations of more than three times background and TDM concentrations of nearly ten times background were observed. These data suggest at least two hydrothermal plume sources along this portion of the NFB spreading center. Our methane and TDM profiles are mimilar to those obtained by Auzende et el. (1987), whose data suggest additional hydrothermal activity at around g km depth near our study area and at approximately 2.8 km depth to the 8outh of our hydrocast stations. An unusual feature in our data is the presence of a strong TDM anomaly in the absence of any methane anomaly. This possibly represent8 distal plume water from a zone of intense hydrothermal activity at 188 " S on the NFB spreading center indentifiedby Craigand Poreda(1987),assumingrelatively rapidin sltuconsumptionof deep-oceanmethane.
P.W. GLYNN
Lamont-Doherty G e o l o g i c a l nb~. Palisades, NY 10964 Department of Geology, Rice It. Houston, TX 7725[ Earth Sci. Board, II. Ca[if,~rnia Santa Cruz, CA 95064 Rosenstiel School of Marine and Atmos. Sci., U. Miami, FL 3314q
Variations in the cadmium/nutrient content and hence, upwelling source of eastern Equatorial Pacific surface waters are recorded in annually-banded corals at the Galapagos Islands. These variations can be used to reconstruct an E1 Nino chronology with seasonal resolution. Annual time series Cd/Ca analyses of a 350-yr old colony of P.clavus (ca. 1600-1954) reveal strong decadal variability throughout 1600-1850, followed by a relatively quiescent period marked by low Cd levels. Individual ENSO events are most easily identified over the period 1850-present. Prior to 1850, pulses of enhanced Cd of I to 6-times 20th century levels occur througbout the record. Maximum values imply that 150-400 yrs bp, surface dissolved Cd and PO~ levels reached 250 pM and 1.6 uM, rspeetively, as compared with typical modern concs, of 40 pM and 0.5 aM. These Cd enhancements are indicative of intensified upwelling and constitute important evidence of an oceanic role in the Little Ice Age. Further, vigorous upwelling events can be correlated with particularl X cold intervals in South America recorded by 6180 measurements in the Quelccaya Ice Cap (Thompson et al., 1986). Thus, an apparent coupling exists between cold temperatures in the Peruvian Andes and stronger Pacific equatorial trade winds. The results imply that the evolution, frequency, and effects of E1 Nino during the Little Ice Age might well have been different from those of the present.
MODELING THE SEASONAL CYCLE OF DISSOLVED 02 I N T H E U P P E R O C E A N A T O . W . S P. F.THOMAS t V.GARCON, J-F M/NSTER. ( G r o u p e de Recherche e n Gl~odesie Spaliale, T o u l o u s e , France) S e a s o n a l cycle o f d i s s o l v e d o x y g e n at O c e a n W e a t h e r Station P in the G u l f o f A l a s k a reveals a 4 - 6 % oversaturatiun o f o x y g e n in the u p p e r o c e a n d u r i n g the s u m m e r s o f the years 1969-1972. T h r e e m a i n p r o c e s s e s regulate the variations o f diss o l v e d 0 2 concentrations in the surface waters: g a s e x c h a n g e at the air-sea interface, vertical m i x i n g and b i o l o g i c a l activity o f m a r i n e o r g a n i s m s . W e u s e a vertical i n t e g r a l m i x e d layer m o d e l ( G a s p a r . 1985) to study the t e m p o r a l evolution o f m o n t h l y averaged d i s s o l v e d 0 2 content o f surface waters, and to assess the relative i m p o r t a n c e o f the various COntributing m e c h a n i s m s d u r i n g these years. P r o d u c t i o n and c o n s u m p t i o n due to b i o l o g i c a l activity are taken into account as an input function o f the model. R e s u l t s s h o w that a large part o f the signal o f dissolved O in surface waters can be r e p r o d u c e d b y the p h y s i c a l mode~ w h i t h o u t biological activity. H o w e v e r , to accurately simulate the t e m p o r a l evolution o f o v e r s a t u r a t i o n in the surface water, b i o l o g i c a l production is required. V a r i o u s s h a p e s ( o v e r depth and time) o f p r o d u c t i o n - c o n s u m p t i o n f u n c t i o n have b e e n tested for year 1970. T h e function w h i c h g i v e s the best fit to the 0 2 data in year 1970 is f o u n d (1) to b e c o n s t a n t throughout2the year, (2) with a total annual p r o d u c t i o n rate o f 5 tool O y ~ n / y r , and (3) to exhibit a c o n s t a n t p r o d u c t i o n i n the 0-5 m layer and a l o g a r i t h m i c decrease in c o n s u m p t i o n b e t w e e n 5 0 m and 300 m . A strong interarmual variability is s h o w n . T h e relative influence o f v a r i o u s p a r a m e t e r s o n the three p r o c e s s e s s u p p l y i n g 0 2 to the surface w a t e r s is investigated. T o t a l annual production P and m a x i m a l d e p t h o f production z s e e m to be the m o s t influent. W e c o n c l u d e that a goo~ k n o w l e d g e o f these p a r a m e t e r s is n e e d e d to restitute the diss o l v e d 0 2 content o f surface waters. W e also s h o w that m i x i n g processes, even at short t i m e scale, have to be well described to give a realistic temporal e v o l u t i o n o f d i s s o l v e d 0 2 in the water column.
EL NINO AND LITTLE ICE ACE EFFECTS ON !'FU[IILINC IN THE EASTERN TROPICAL PACIFIC
D. RUIZ-PINO. C. E. LAMBERT, C. JEANDEL and P. BUAT-MENARD. (Laboratoire de Physique et Chimie Marines, CEROV, BP 8, F-06230, Villefranche sur Met, France).
G.T. SHEN R.B. DUNBAR M.W. COLGAN
There is some evidence that most of the yearly atmospheric flux of trace elements to the Mediterranean basin is delivered during sporadic events such as Saharan dust storms. To help assessing the geochemical impact of such events we have developped a non-steady state, one-dimensional model of the transport of insoluble atmospheric particles in the water column. This model has 3 forcing variables: i) the atmospheric source function which is of a gaussian type, based on time-series data obtained at coastal stations in the Ligurian Sea (Capo Cavallo, Corsica and Cap Ferrat). ii) The removal rate of atmospheric particles from the euphoric zone which is assumed to be a first-order process controlled by zooplankton grazing activity, iii) An average eddy diffusion coefficient between surface and deep waters for the whole western Mediterranean basin. The value adopted was 1.5x1012 m3/yr when the upper water column is stratified, as in spring and summer. In winter, because of convective mixing this coefficient was assumed to be equal to 40x1012m3/yr. Model runs over a year period show satisfactory agreement with experimental data. It appears that following a Saharan dust storm event, particulate concentrations of terrigenous material will be enhanced significantly only in surface waters and for a few weeks. Temporal changes in the terrigenous particulale flux out of the euphoric zone are affected by the intensity and duration of the dust storm, with a response time sometimes as short as a week. The temporal pattern of this flux lroughout the water column is however primarily related to changes in primary productivity during spring and summer, whereas during winter, convective mixing can also be a dominant factor. In the future, this model will be extended to the fraction of the atmospheric input which dissolves in seawater.
HYDROTHERMAL MANGANESE A N D METHANE PLUMES IN THE NORTH FIJI BASIN P N. SEDWICK, T. GAMO, and G. M. McMURTRY (Department of Oceanography, University of Hawaii, Honolulu, Hawaii, U.S A 96822) During the 1987 North Fiji Basin (NFB) Expedition of the R/V Moans Wav~, seven hydrocasta were taken at locations of suspected seafloor hydrothermal activity between 13.2 " S and 171 " S along the NFE spreading center. Stations were selected using SEAMARC lI acoustic imaging and seismic reflection techniques. Water samples were subsequently analyzed for dissolved methane and total dissovable manganese (TDM). Anomalous deep water concentrations of these two species indicate recent seafloor hydrothermal circulation in this area. Dissolved methane w ~ determined at sea by g ~ chromatography with flame ionization detection following cryogenic trapping. TDM was determined by flameless graphite furnace atomic absorption spectrophotometry after preconcentration by coprecipitation with gallium hydroxide. The vertical concentration profiles of dissolved methane and TDM both exhibit discrete deep-water m ~ i m a centered at depths of 2-2.5 km and 3-3.5 km Anomalous methane concentrations of more than three times background and TDM concentrations of nearly ten times background were observed. These data suggest at least two hydrothermal plume sources along this portion of the NFB spreading center. Our methane and TDM profiles are mimilar to those obtained by Auzende et el. (1987), whose data suggest additional hydrothermal activity at around g km depth near our study area and at approximately 2.8 km depth to the 8outh of our hydrocast stations. An unusual feature in our data is the presence of a strong TDM anomaly in the absence of any methane anomaly. This possibly represent8 distal plume water from a zone of intense hydrothermal activity at 188 " S on the NFB spreading center indentifiedby Craigand Poreda(1987),assumingrelatively rapidin sltuconsumptionof deep-oceanmethane.
P.W. GLYNN
Lamont-Doherty G e o l o g i c a l nb~. Palisades, NY 10964 Department of Geology, Rice It. Houston, TX 7725[ Earth Sci. Board, II. Ca[if,~rnia Santa Cruz, CA 95064 Rosenstiel School of Marine and Atmos. Sci., U. Miami, FL 3314q
Variations in the cadmium/nutrient content and hence, upwelling source of eastern Equatorial Pacific surface waters are recorded in annually-banded corals at the Galapagos Islands. These variations can be used to reconstruct an E1 Nino chronology with seasonal resolution. Annual time series Cd/Ca analyses of a 350-yr old colony of P.clavus (ca. 1600-1954) reveal strong decadal variability throughout 1600-1850, followed by a relatively quiescent period marked by low Cd levels. Individual ENSO events are most easily identified over the period 1850-present. Prior to 1850, pulses of enhanced Cd of I to 6-times 20th century levels occur througbout the record. Maximum values imply that 150-400 yrs bp, surface dissolved Cd and PO~ levels reached 250 pM and 1.6 uM, rspeetively, as compared with typical modern concs, of 40 pM and 0.5 aM. These Cd enhancements are indicative of intensified upwelling and constitute important evidence of an oceanic role in the Little Ice Age. Further, vigorous upwelling events can be correlated with particularl X cold intervals in South America recorded by 6180 measurements in the Quelccaya Ice Cap (Thompson et al., 1986). Thus, an apparent coupling exists between cold temperatures in the Peruvian Andes and stronger Pacific equatorial trade winds. The results imply that the evolution, frequency, and effects of E1 Nino during the Little Ice Age might well have been different from those of the present.
MODELING THE SEASONAL CYCLE OF DISSOLVED 02 I N T H E U P P E R O C E A N A T O . W . S P. F.THOMAS t V.GARCON, J-F M/NSTER. ( G r o u p e de Recherche e n Gl~odesie Spaliale, T o u l o u s e , France) S e a s o n a l cycle o f d i s s o l v e d o x y g e n at O c e a n W e a t h e r Station P in the G u l f o f A l a s k a reveals a 4 - 6 % oversaturatiun o f o x y g e n in the u p p e r o c e a n d u r i n g the s u m m e r s o f the years 1969-1972. T h r e e m a i n p r o c e s s e s regulate the variations o f diss o l v e d 0 2 concentrations in the surface waters: g a s e x c h a n g e at the air-sea interface, vertical m i x i n g and b i o l o g i c a l activity o f m a r i n e o r g a n i s m s . W e u s e a vertical i n t e g r a l m i x e d layer m o d e l ( G a s p a r . 1985) to study the t e m p o r a l evolution o f m o n t h l y averaged d i s s o l v e d 0 2 content o f surface waters, and to assess the relative i m p o r t a n c e o f the various COntributing m e c h a n i s m s d u r i n g these years. P r o d u c t i o n and c o n s u m p t i o n due to b i o l o g i c a l activity are taken into account as an input function o f the model. R e s u l t s s h o w that a large part o f the signal o f dissolved O in surface waters can be r e p r o d u c e d b y the p h y s i c a l mode~ w h i t h o u t biological activity. H o w e v e r , to accurately simulate the t e m p o r a l evolution o f o v e r s a t u r a t i o n in the surface water, b i o l o g i c a l production is required. V a r i o u s s h a p e s ( o v e r depth and time) o f p r o d u c t i o n - c o n s u m p t i o n f u n c t i o n have b e e n tested for year 1970. T h e function w h i c h g i v e s the best fit to the 0 2 data in year 1970 is f o u n d (1) to b e c o n s t a n t throughout2the year, (2) with a total annual p r o d u c t i o n rate o f 5 tool O y ~ n / y r , and (3) to exhibit a c o n s t a n t p r o d u c t i o n i n the 0-5 m layer and a l o g a r i t h m i c decrease in c o n s u m p t i o n b e t w e e n 5 0 m and 300 m . A strong interarmual variability is s h o w n . T h e relative influence o f v a r i o u s p a r a m e t e r s o n the three p r o c e s s e s s u p p l y i n g 0 2 to the surface w a t e r s is investigated. T o t a l annual production P and m a x i m a l d e p t h o f production z s e e m to be the m o s t influent. W e c o n c l u d e that a goo~ k n o w l e d g e o f these p a r a m e t e r s is n e e d e d to restitute the diss o l v e d 0 2 content o f surface waters. W e also s h o w that m i x i n g processes, even at short t i m e scale, have to be well described to give a realistic temporal e v o l u t i o n o f d i s s o l v e d 0 2 in the water column.