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Lake Tanganyika Geochemical and Hydrographic Study: 1973 Expedition

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Lake Tanganyika Geochemical and Hydrographic Study: 1973 Expedition UC San Diego SIO Reference Title Lake Tanganyika Geochemical and Hydrographic Study: 1973 Expedition Permalink https://escholarship.org/uc/item/4ct114wz Author Craig, Harmon Publication Date 1974-12-01 eScholarship.org Powered by the California Digital Library University of California Scripps Institution of Oceanography University of California, San Diego La Jolla, California 92037 LAKE TANGANYIKA GEOCHEMICAL AND HYDROGRAPHIC STUDY: 1973 EXPEDITION Compiled by: H. Craig December 19 74 SIO Reference Series 75-5 TABLE OF- CONTENTS SECTTON I. [NTI<OI)UC'I' LON SECTION 11. STATION POSITIONS, SAEZI'LING I.OCATIONS, STATION 1 CAST LISTS, BT DATA SFCTION 111. HYDROGRAPHIC DATA, MEASUREMENTS AT SIO 111-1. Hydrographic Data: T, c1 111-2. Total C02 and C13/~12Ratios 111-3. Radiunl-226 111-4. Lead-210 111-5. Hel.ium and He 3 /He4 Ratios 111-6. Deuterium and Oxygen-18 111-7. References, Section 111 SECTION IV. LAW CKEMISTRY: EZEASIIREMENTS AT MLT IV-1. Major Ions IV-2. Nutrients IV-3. Barium SECTION V. UNIVERSITY OF MIAMI CONTRIBUTIONS V-1. Tritium Measurements V-2. Equation oE State STA'SLON I'OSITIONS, LAKE SURFACE IJKSl$I< SAMPLES RIVER SAMPLE LOCATIONS STATION 1: Complete Cast List STATION 1: Bottle Depths by Cast STATION 1: Depths Sampled and Corresponding Dot tle Numbers 16 Bc\TltYTI1ERMOGRAP1I MEASUREMENTS 18 MY1)ROGMPI-IIC DATA: STATION 1 STATIONS 2, 3 STATIONS 4, 5 CMLORZDIS DATA: STATIONS A, B, C; RIVERS TOTAL C02 AND 6C13: STATION 1 STATIONS 2 - 5 RADIUM-226 PROFILES: STATIOV 1 LEAD-210 PROFI1,E : STATION 1 I-IELIUM 3 AND 4 PROFILES DEUTERIUM, OXYGEN-18: STATION 1 STATIONS 2, 3 STATIONS 4, 5 STATIONS A, B, C; RIVER SAMPLES D, 018, CHLORIDE; TIME SERIES: STATION 5 RUZIZI RIVER MAJOR ION DATA: STATION 1 67 RIVER SAMPLES 68 NUTRIENT DATA: STATION 1 7 1 STATIONS 2 - 5 7 2 RIVER SMLES 7 3 SILICATE: RUZIZI RIVER, STATION 5, TIME SERIES 74 BARIUM: STATION 1 75 TRITIUM DATA: LAKE SURFACE AND STATION 1 RIVER ShElPLES sii T,oci~Cion oE Stations, 1,nlte surface s;~n~ples, ant1 Kiver samples. 8 'l'cmp~raturc ilnd cliloride profiles at Station 1 ("Kigoma Stntion"). Pig. 3; Te~~~pctiltureprofS:les at Station I, 100-5001n, together with the BT record. Fig. 4. I'rofiles of total. inorganic carbon (CC02), 6~~3,and titrotion alkalinity (Arr) at Stntion 1. PI&. 5. Total C02 vs. 6~"at Station I. Pig. 6. Rn-226 and Pb-210 profiles at Stntion I. Fig. 7. lie" and lle3/11e" ratlo anomaly profil.cs at Station 1. klc3 vs. II~"concentration plot: Station 1. 1)euter:Lum and oxygen-18 prof il.es : Stations 1 and 5. Deuteriun~vs. oxygen-18: Lake Tonganyika and Rivers. Major ion profiles at Station I.. Nutrient and alkalinity profiles, Station I. Tritium profile nt Station 1. I. INTRODUCTION llhis report describes the work carried out on Lake Tangonyilta during n ooperative expedition in February, 1973. The propost11 for sncll an expedition ,as initiated by correspondence between tl. Craig of the Scripps Institution g Oceanography, University of California, G. W. Coulter of the Burundi Fishery .esearch Project, and C. tl. Clay, FAO, Rome, Permission to carry out research ,,, ,,, Lake'~angan~ikawith the Burundi Fishery Project (FAO) was ltindly granted , the Directeur des Eaux et Porets, Burundi, and permission to work with pro- ect staff and facilities was given by the Coordinator of Lake Projects, FAO, :one. This study of Lake Tanganyika originated in the desire to apply the geo- :hemica1 methods and techniques recently developed for oceanographic research :o the problems encountered in trying to understand the circulation and chemistry tf a large and deep lake. In this respect, Lake Tanganyika is OF outstanding ;cieutiEic interest to the international community of oceanographers, limno- -ogists, and hydrologists. In many .ways Lake Tanganyilta resembles the oceans, 'specially in the 1.ong "residence time" of deep water relative to replacement ty mixing with surface water. This time is estimated to be of the order of 2000 rears in both Lake Tanganyika and in the oceans. In the ocean, the mixing is :apid enough, and the rate of consumption of oxygen in the deep water is slow =llough, so that most deep ocean water maintains a significant concentration of lissolved oxygen and supports life. However, in certain areas such as the Zropical waters of the Eastern Pacific and in some of the deep trenches, the 'Xygen is entirely consumed and the waters resemble the deep water of Lake ranganyika which is anoxic and does not support life. In both cases the decorn- 'Qsition of sinking organic matter takes place under anaerobic conditions and ;I vcry spcci.i~lchen~istry dcvelogs which cl~arnctcrizcsthe production of 1111tri- cnt c?letnr?nts in so:l.t~bLeform in the clc!c.p w:lter. Siticc it :is tlic opwell.ing of thesc ilr~trientel.ements which supports tlie pi:otluctiv:Lty of the surface waters, it is vitally is~porta~itto underst;rnd the clicniicol prclccsfics l.11 tlie dk?c.p water wl~icl~protluce the nt~tricuts,and tl~cphysicill processes wlr:Lch bring the 11utrl.- enl- elenieots to the surface to support the f:lsl~;iod pl.ankton population. Tlte stutly of tliesc cl~cmicaliund physicnl proc:esOes wlii.ch support the protluctivi.ty in surface waters i.s a nicc?t:l~i[:-gror.111~1in whiclt ocennog~:il])lrers i~nrll:L~~~no:logLsts I share n colnnlon interest 111 :I ~~HCII~CIIilrfil CIC vitlll ~.I~~~I:~LIIICCEor rlie cxp.lo:it- i~tioiiof world's aqueous envj.ron~nent. Naturally occurring rnrlioactive isotopes sl~clias rnd:loc;utbon (carbon-1.4) radium, atld sil.lcon-32, provide c,:loclts with time-sciiles ri~ngingfro~n 500 to 5,000 years, w1if.c.h arc currently being usetl it1 oceanogriiphic stt~diesto lltensurc c.lrculat:Lon and mixl.ng rntes in the sen which are so slow that they cannot be studied by ally other tochnirlue. At the sanle tinie, man-made radioisotopes pro- tlucecl by nuclear explosions io the atmosphere., such as tritium (hydrol:cn-3), enter the water surface and nix tiownward on a time scale of the order of 20 years. Such isotopes prov:l.de infor~~~ationon the rate of dow~iwardcirculution of n~aterialJnto the depths. l?inoll.y, the lneasrlretllcnt of certain natural trace-element isotopes sucll as lead-210, whiclt is c1iemical.ly scavenged by organ- isms, provides a time scale for the rate at which particulate matter sinks from the surface to supply the nutrients to the deep water. 1\11 of these, and many other recent techniques for oceanic research, can be fruitfully applied to developing our understantling of the physical and chenl- ical regime of a deep lake such as Tanganyika. Thus our objective in this pre- liminary resoarch project on Lake Tonganyika was to obtain measurements of tlie distribution of the most important of these geochemical parameters, in order to provide a basic framework for further detailed studies based on these methods. Such studies of the pl~ysicaland chemi.ca1 processes by which nutri- ents reach the surface waters are basic to the project research on biological and fish production now being carried out by the Buruudi FA0 project. The 1973 Expedition Our work on the lake itself was done aboard the FA0 boats "Lady Alice 11" and "Banga-finnga" based in Bujumbura. The personnel included Professor and Mrs. H. Craig and I?. Dixon from Scripps Institution of Oceanography, Professor J. Ed~uoncl of the Massachusetts Institute of Technology, Dr. G. Coulter and Mr. W. Perro of the Burundi Fishery Project, and boat crew members A. Bolingo, J. Racinoni, and E. Nikomeze. Five hydrographic stations were occupied in the northern part of the lake, and 23 hydrographic casts were made during the six days at sea, during which more than 400 samples of lake water were collected. The following stations were occupied: Station 1: seven miles off Kigoma in 1350 meters of water. Station 2: off Nyanza Lac (480 meters). Station 3: off Kagongo (375meters). Station 4: off Magara (308 meters). Station 5: 10 miles west of Bujumbura (210 meters). Numerous water samples were also collected from the Ruzizi River, the Muzazi River and one of its tributaries, and from streams at Magara, Mutumba, and Kagongo. These river samples are most important for studyingthe chemical "budgets" of the major and minor elements in the lake, as they provide a mea- sure of the input of all chemical species by runoff from the surrounding level. In addition to the facilities, boats, and equipment provided by PAO, Burundi, specialized equipment was brought to Burundi from the Scripps Insti- tution of Oceanography and NIT for interim use on our mission. Transit entry of this equipment duty-free, was very kindly authorized by the Director of Customs, according to the request by the Directeur des Eaux et Forets. Sample Collection and Analysis Over 400 samples ranging in amounts from 50 ml. to 20 liters, were col- lected at the five stations. The total amount of water shipped to the U.S. for .analysis was 400 kg. Most of .the analytical work has been carried out in the laboratories of H. Craig at Scripps Institution of Oceanography and J. Edmond at MIT, but specialized analytical work has also been done at the University of Miami (tritium analyses) and at the Tata Instituto of Fundamental ~esearcb,Bombay, India (silicon-32, uranium,. thorium). At Scripps and MIT water has been analysecl for major and minor cations and anions, nutrient substances, stable and radio- active isotopes of water (deuterium and oxygen-18), dissolved gases, carbon isotope ratios, trace elements, radium, radioactive lead-210, etc, The physical separation of the participants in the field and analytical work, and the heavy involvement of several of us in a nine-month Pacific Ocean expedi- tion program during 1973-1974, have precluded the preparation of an integrated and logically-arranged presentation of the data in this report.
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