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A U-Th depth profile for the western pacific
197 A U-T'n DEI~fll PROFILE FOR THE ~
PACIFIC
TRACE METALS IN THE WESTERN INDIAN OCEAN
TYPIIOON LEE i ,aND J . H . CHEN z (llnst. of Earth Sol., Academia Sinioa, Taipei; 2Div. Geol. & Planet. Sei., Caitech, Pasadena,CA}.
N.H. MORLEY, P.J. STATHAM and J.D. BURTON (Department of Oceanography, University of Southampton, Southampton S09 5NH, UK)
We report results for a U,Th depth profile from the western Pacific using newly improved mass spectrometric techniques. Five water samples ~ere collected on June 23, 1987 from a station (23' ZI.7'N,IZI~54.8'W, 4500m) ~:50~a E of Taiwan at depths O, 160, 5 0 0 , 1200, 2800m by RV Ocean Researcher I. The 101samples were acidified and spiked with Th-229 and U-236+233 tracers but not filtered. Th and U were separated {see Ill} with yields of 85 and 95% and blanks, 2.8 and 3.2 pg, for U and Th respectively. At this station 1 c.oncentration is uniform with depth (mean=3.3(I -0.03ng/g, salinity normalized to 3.5%). Further, z34U/23%i ratios are also uniform and the mean, I6.28+0.06)x10 -s is 148/.. higher than the eqtnlibrium ratio. These values are similar to those obtained previously f o r the E . P a e i t ' i c a n d Atlantic C*ueans b y C h e n e t a l . [ l l except that [ [ ] ma> be 2% h i g h e r . Th con~-entratlons lsurfaee to bottom: 8 5 , 3 0 , 4 0 , 110 a n d 1 3 0 p g / k g ) a r e c l e a r l y st, ratlt'ied. Salinities ar~ determined hy a I:TD c a s t j u s t F~f'ore our sampling. Five distinct water ra~sses c'an be identified by their salinities: i) surt'aep mixed layer; 21"tr0pical w a t o r ( 3 0 - 1 5 O m ) ; 3 l t h o r m o c[Jne 1150-350m>; t) N.Paeific Intermediate Water (350-950m); a n d 5) D e e p & B o t t o m ~ a t e r l N ~ P D W I . Th i n Las-er~ 3 a n d 4 a r e a f m - t o r o f Z - 3 l o w e r t h a n i n layers 1 and 5. Further, [ T h I may i n c r e a s e in l a s e r 5 towards b o t t o m . T h i s gradient is similar' t o , h u t much s m a l l e r than, that obsemod f o r NPDW a t 3 0 - 3 5 ' N b y N n z a k i & H n r i h e [ 2 i , who a t t r i h t d e it tn vertioal diffusinn t'rnm a b e t t o m g o u r ( ~ e . T h e 2~°]'h/Z32Th o f N~PDW ( : . O , O O O 1 0 t 3 ) is on the lo~c ~ J d ~ r~I l h e a v e r a g o v a l u e f o r t h e d e e p water. Th~e ana i5 so~ ~.ere performod at Lunar ic ~s:.-ium ~hore t]l~ lirst author was a visiting prnfessor. l~t'~.[l]
A preliminary account is given of the findings from measurements made on vertical profiles along a section through the western basins of the Indian Ocean between 7-27°S in August 1986. Vertical profiles of trace metals were investigated at seven stations. Metals (Mn, Ni, Cu, Cd and Zn) in preserved samples were analysed ashore using graphite furnace atomic absorption spectrometry after a chelation/solvent extraction procedure. Clean handling methods were employed at all stages. Concentrations of cadmium in deeper waters are intermediate between those reported for the central North Atlantic and central North Pacific, as expected from the general circulation of the deep waters. The results for nickel show a residual concentration of about 2 nmol i-' above the nutricline, a value which is similar to the surface water concentrations observed in the North Pacific and North Atlantic Oceans. The deep water concentrations of 6.5-8 nmol 1--' are intermediate between those for the other basins. Concentrations of copper in surface waters were generally in the range 0.7-0.8 nmol i~' , somewhat higher than those found in the North Pacific Central Gvre but significantly lower than lhose in North Atlantic central waters. Enhanced concentrations of manganese occurred in surface waters as has been found for other ocean regions. Deep water concentrations averaged <0.2 nmol l-'.
GEOCHEMISTRY ~ PROVEN~XCE OF NORTH ATLAX~IC ABYSSAL PLAIN SEDIMENTS T. PEA~CE and I . JA~VIS. (School o f Geological Sciences, Kingston Polytechnic, Penrhyn Road, Kingston upon Thames, Surrey KTI 2EE, UK).
UTILIZATION OF GEOCHEMICAL TRACERS IN A MODEL FOR THE TRANSPORT AND CARBON EXCHANGES IN THE INDIAN OCEAN. N.METZL , B. MOORE and A. POISSON (Laboratoire de Physique et Chimie Marines, Univ. P. et M. Curie, T.24-25, 4, place Jussieu 75230 PARIS, France) To quantifing the internal and external exchanges, dynamical (advection, mixing) and biochemical which participate to the carbon cycle in the oceans, we use simultaneous information on salinity, temperature, oxygen and phosphates (1400 stations), in a multi-box model formulation of the Indian Ocean. The model is resolved by inverse methodology. With respect to the steady-state, in order to minimize the utilization of variable parameters (e.g., surface data, water exchanges, gas exchanges, planktonic bloom...), the topology is limited to a temporal non-pertubated zone (below density 26.45). The Indian Ocean is decomposed in 12 regions divided by main hydrological fronts and ridges. The vertical discretization is isopycnal (5 layers). The advection unknowns are constrained by geostrophy. First results will be presented.
The Madeira Abyssal Plain lies 700kin ~ s t of Madeira and the Canary Islands, approximately half-way between the NW A f r i c a n Continental Shelf and the M i d - A t l a n t i c Ridge. Late Quaternary sediments from the abyssal p l a i n c o n s i s t of a l t e r n a t i o n s o f m e t r e - t h i c k d i s t a l t u r b i d i t e s and centimetre t o d e c i m e t r e - t h i c k pelagic c l a y s , marls and oozes. Detailed geochemical analyses o f two r e p r e s e n t a t i v e piston cores from the NE and W c e n t r a l p a r t s o f the area, have demonstrated t h a t three separate groups o f t u r b i d i t e can be d i f f e r e n t i a t e d : ( i ) Organic-rich t u r b i d i t e s are characterised by containing 0.3-2% organic carbon, and probably o r i g i n a t e d from the ic~er c o n t i n e n t a l slope o f NW A f r i c a north o f 20=N, although one t u r b i d i t e may have been derived from south o f t h i s l a t i t u d e . (2) "Volcanic' t u r b i d i t e s contain high T i contents, and were sourced predominantly from the Canaries and Madeira to the east. (3) Calcareous turbidites contain more than 75% CaCO~, and ~ere derived from the Great Meteor-Cruiser Seamount Chain, west of the Madeira Abyssal Plain. New geochemical data on a larger number of cores distributed across the area indicate that significant lateral geochemical variation occurs within individual turbidites. Geographical trends have been correlated with tur0idite iso[lach m a ~ , allowing a petter understanding of sediment sources and transport pathways within the reqlon.
PACIFIC
TRACE METALS IN THE WESTERN INDIAN OCEAN
TYPIIOON LEE i ,aND J . H . CHEN z (llnst. of Earth Sol., Academia Sinioa, Taipei; 2Div. Geol. & Planet. Sei., Caitech, Pasadena,CA}.
N.H. MORLEY, P.J. STATHAM and J.D. BURTON (Department of Oceanography, University of Southampton, Southampton S09 5NH, UK)
We report results for a U,Th depth profile from the western Pacific using newly improved mass spectrometric techniques. Five water samples ~ere collected on June 23, 1987 from a station (23' ZI.7'N,IZI~54.8'W, 4500m) ~:50~a E of Taiwan at depths O, 160, 5 0 0 , 1200, 2800m by RV Ocean Researcher I. The 101samples were acidified and spiked with Th-229 and U-236+233 tracers but not filtered. Th and U were separated {see Ill} with yields of 85 and 95% and blanks, 2.8 and 3.2 pg, for U and Th respectively. At this station 1 c.oncentration is uniform with depth (mean=3.3(I -0.03ng/g, salinity normalized to 3.5%). Further, z34U/23%i ratios are also uniform and the mean, I6.28+0.06)x10 -s is 148/.. higher than the eqtnlibrium ratio. These values are similar to those obtained previously f o r the E . P a e i t ' i c a n d Atlantic C*ueans b y C h e n e t a l . [ l l except that [ [ ] ma> be 2% h i g h e r . Th con~-entratlons lsurfaee to bottom: 8 5 , 3 0 , 4 0 , 110 a n d 1 3 0 p g / k g ) a r e c l e a r l y st, ratlt'ied. Salinities ar~ determined hy a I:TD c a s t j u s t F~f'ore our sampling. Five distinct water ra~sses c'an be identified by their salinities: i) surt'aep mixed layer; 21"tr0pical w a t o r ( 3 0 - 1 5 O m ) ; 3 l t h o r m o c[Jne 1150-350m>; t) N.Paeific Intermediate Water (350-950m); a n d 5) D e e p & B o t t o m ~ a t e r l N ~ P D W I . Th i n Las-er~ 3 a n d 4 a r e a f m - t o r o f Z - 3 l o w e r t h a n i n layers 1 and 5. Further, [ T h I may i n c r e a s e in l a s e r 5 towards b o t t o m . T h i s gradient is similar' t o , h u t much s m a l l e r than, that obsemod f o r NPDW a t 3 0 - 3 5 ' N b y N n z a k i & H n r i h e [ 2 i , who a t t r i h t d e it tn vertioal diffusinn t'rnm a b e t t o m g o u r ( ~ e . T h e 2~°]'h/Z32Th o f N~PDW ( : . O , O O O 1 0 t 3 ) is on the lo~c ~ J d ~ r~I l h e a v e r a g o v a l u e f o r t h e d e e p water. Th~e ana i5 so~ ~.ere performod at Lunar ic ~s:.-ium ~hore t]l~ lirst author was a visiting prnfessor. l~t'~.[l]
A preliminary account is given of the findings from measurements made on vertical profiles along a section through the western basins of the Indian Ocean between 7-27°S in August 1986. Vertical profiles of trace metals were investigated at seven stations. Metals (Mn, Ni, Cu, Cd and Zn) in preserved samples were analysed ashore using graphite furnace atomic absorption spectrometry after a chelation/solvent extraction procedure. Clean handling methods were employed at all stages. Concentrations of cadmium in deeper waters are intermediate between those reported for the central North Atlantic and central North Pacific, as expected from the general circulation of the deep waters. The results for nickel show a residual concentration of about 2 nmol i-' above the nutricline, a value which is similar to the surface water concentrations observed in the North Pacific and North Atlantic Oceans. The deep water concentrations of 6.5-8 nmol 1--' are intermediate between those for the other basins. Concentrations of copper in surface waters were generally in the range 0.7-0.8 nmol i~' , somewhat higher than those found in the North Pacific Central Gvre but significantly lower than lhose in North Atlantic central waters. Enhanced concentrations of manganese occurred in surface waters as has been found for other ocean regions. Deep water concentrations averaged <0.2 nmol l-'.
GEOCHEMISTRY ~ PROVEN~XCE OF NORTH ATLAX~IC ABYSSAL PLAIN SEDIMENTS T. PEA~CE and I . JA~VIS. (School o f Geological Sciences, Kingston Polytechnic, Penrhyn Road, Kingston upon Thames, Surrey KTI 2EE, UK).
UTILIZATION OF GEOCHEMICAL TRACERS IN A MODEL FOR THE TRANSPORT AND CARBON EXCHANGES IN THE INDIAN OCEAN. N.METZL , B. MOORE and A. POISSON (Laboratoire de Physique et Chimie Marines, Univ. P. et M. Curie, T.24-25, 4, place Jussieu 75230 PARIS, France) To quantifing the internal and external exchanges, dynamical (advection, mixing) and biochemical which participate to the carbon cycle in the oceans, we use simultaneous information on salinity, temperature, oxygen and phosphates (1400 stations), in a multi-box model formulation of the Indian Ocean. The model is resolved by inverse methodology. With respect to the steady-state, in order to minimize the utilization of variable parameters (e.g., surface data, water exchanges, gas exchanges, planktonic bloom...), the topology is limited to a temporal non-pertubated zone (below density 26.45). The Indian Ocean is decomposed in 12 regions divided by main hydrological fronts and ridges. The vertical discretization is isopycnal (5 layers). The advection unknowns are constrained by geostrophy. First results will be presented.
The Madeira Abyssal Plain lies 700kin ~ s t of Madeira and the Canary Islands, approximately half-way between the NW A f r i c a n Continental Shelf and the M i d - A t l a n t i c Ridge. Late Quaternary sediments from the abyssal p l a i n c o n s i s t of a l t e r n a t i o n s o f m e t r e - t h i c k d i s t a l t u r b i d i t e s and centimetre t o d e c i m e t r e - t h i c k pelagic c l a y s , marls and oozes. Detailed geochemical analyses o f two r e p r e s e n t a t i v e piston cores from the NE and W c e n t r a l p a r t s o f the area, have demonstrated t h a t three separate groups o f t u r b i d i t e can be d i f f e r e n t i a t e d : ( i ) Organic-rich t u r b i d i t e s are characterised by containing 0.3-2% organic carbon, and probably o r i g i n a t e d from the ic~er c o n t i n e n t a l slope o f NW A f r i c a north o f 20=N, although one t u r b i d i t e may have been derived from south o f t h i s l a t i t u d e . (2) "Volcanic' t u r b i d i t e s contain high T i contents, and were sourced predominantly from the Canaries and Madeira to the east. (3) Calcareous turbidites contain more than 75% CaCO~, and ~ere derived from the Great Meteor-Cruiser Seamount Chain, west of the Madeira Abyssal Plain. New geochemical data on a larger number of cores distributed across the area indicate that significant lateral geochemical variation occurs within individual turbidites. Geographical trends have been correlated with tur0idite iso[lach m a ~ , allowing a petter understanding of sediment sources and transport pathways within the reqlon.