Oseana, Volume XXII, Nomor 2, 1997 : 35-41 ISSN 0216-1877 ... - Lipi

sumber:www.oseanografi.lipi.go.idOseana, Volume XXII, Nomor 2, 1997 : 35-41 ISSN 0216-1877BIOGENIC CALCIUM CARBONATE AND SILICIATE IN THE MARINEENVIRONMENT AND THE PROCESSES DETERMININGTHE NATURE OF EACH DISTRIBUTIONByDwi Eny Djoko Setyono 1)ABSTRACTKALSIUM KARBONAT DAN SILIKAT DI LINGKUNGAN LAUTDAN PROSES DISTRIBUSI ALAMIAHNYA. Air laut kaya dengan kandunganbeberapa unsur kimia termasuk kalsium karbonat dan silikat. Kedua elementtersebut sangat penting dalam proses penyusunan cangkang dan bagian-bagiankeras (tulang, sirip, sisik) pada biota laut. Distribusi kalsium karbonat dan silikatbervariasi menurut kedalaman dan geografi, yaitu dipengaruhi oleh tingkatkejenuhan (saturation), suhu dan tekanan air lautINTRODUCTIONSeawater has abundance of manychemicals elements. The concentration ofevery element varies between places. However,according to the rule of "The Principleof Constant Composition or Proportion"(open University, 1989), the ratios betweenthe amount of major ions in open oceans areconstant. The ionic composition of openocean water is the same from place to placeand from depth to depth because of thethorough mixing over geologic times.A margin of continent and an oceanbasin floor receive a continuous supply ofparticles from many sources. These particleshave their origin in living organisms, land,atmosphere and the sea its self. Since theionic concentration of the oceans is nearlyconstant with time, the input an ion is equalto the rate of loss into sediment, The particleswill form a sediment when the losses ofparticles do not effect the ionic concentrationbalance in the water.It is known that biogenous sedimentsare sediments derived from living organisms,include shell and coral fragments as well asthe hard skeletal part of single-celled plantsand animals that live in the surface waters.Pelagic biogenic sediments are composedmostly of the remains of calcareus (carbonate)and sileceous (silicate) planktonic organisms,principally cocolitophores, foraminifera,pteropods, diatoms and radiolarian(BROECKER & PENG, 1982; DUXBURY& DUXBURY 1991).35Oseana, Volume XXII no. 2, 1997

sumber:www.oseanografi.lipi.go.idcarbonate accumulation or sediment(DUXBURY & DUXBURY, 1991). Minutesingle-celled plants, coccolithophores, coveredwith calcareous plate called coccoliths alsoplay a role in the formation of these bottomdeposits. The distribution of carbonate sedimentis directly controlled by environmentalparameters, favorable for the growth of calcitecarbonate organisms. Carbonate sedimentsgenerally were deposited near the site of theirorigin (MOORE, 1989). The map of calciumcarbonate distributions in surfaces sediments ofthe world ocean is presented in Figure 1.Biogenic SilicateThe siliceous elements remain in organismsare resistant to dissolution and dobreakdown slowly, even though the entirewater colomn through which they fall isunder saturation. These elements are found at alldepths because of their slow dissolution rates ateither warm or cold temperatures. So, biogenicsilliceous distributes in all of oceans around theworld. The distribution of biogenic silicate insurface sediments of the world ocean ispresented in Figure 2.38Oseana, Volume XXII no. 2, 1997

sumber:www.oseanografi.lipi.go.idBROECKER & PENG (1982) andOpen University (1989) mentioned that thesource of silicate was most commonly opalinebiogenic debris, such as radiolarians,silicate-flagellates, diatoms,and sponge spicules.The test and frustules of these marineorganisms were accumulated in great quantitiesover extensive area of the sea floor,especially around the polar region or around theAntartic (for siliceous diatoms) and around theequatorial belt of high biological productivity inthe Pacific (for siliceous radiolarian anddiatoms). They also accumulated in other areaswhere the water was cold, and nutrient rich waterupwell, such as offshore Southerm Californiaand Peru (the Pacific) and north Africa (theAtlantic).DUXBURY & DUXBURY (1991)mentioned that siliceous oozes (mud) haveone principal source in the temperature latitudes,i.e., single-celled plants called diatoms.Diatoms are distinguished by box-like shellof silicate. Diatoms are microscopic, onecelled algae belonging to the plant divisionChrysophyta and the class Bacillariophyceae.Diatoms constituted an important food supplyin the ocean environment (GROVES & HUNT,1980).Diatom reproduces rapidly in the coldwater because of availability of the sunlight atthe ocean's surface, the abundance of thenutrients, and the suitable temperature. Asan example it happens around the Antarcticduring the summer. At that season, nutrientswere abundant and solar energy that wasneeded for photosynthesis process was available.The nutrients were transported by thedeep current called North Atlantic underwater current. It flew from the north hemisphereto the south hemisphere up to theAntarctic sea. The water current was a watermass that had rich nutrients that were neededby diatoms for their growth. When diatomsdeath, their shell sink to the ocean floor(GROVES & HUNT, 1980). HEATH (1977)noted that silicate rich sediments were depositedbeneath a biologically productive surfaceregion where nutrient-rich deep water upwell39Oseana, Volume XXII no. 2, 1997

sumber:www.oseanografi.lipi.go.idto the photic zone, rather than in areas wherethe nutrients (silicate) entered the sea.In the tropical areas the siliceoussediments are not produced by diatoms becausethe water at these latitudes is too warm.Here the principle source is a single-celledamoeba like animal (the radiolarian). Radiolarianis the name for a subclass of protozoanclass Actinopodea. These minute protozoansare noted for the striking forms ofsiliceous skeletons (GROVES & HUNT,1980). Radiolarian produces a siliceous outershell that is often covered with long spine.MOORE (1989) mentioned that incontrast to calcium carbonate distribution,silicate was generally formed outside thebassin of deposition. Physical processes controltheir distribution, and the water currenttransported them into places of accumulation.Therefore silicates are found worldwide andare abundance at all depths. This facts showedthat siliceous deposits were distributed mostlyin areas that had a high biological fertility,especially the ocean margin and the equatorialdivergence (KENNET, 1982).CONCLUSIONThe extent of biogenic calcium carbonateand silicate in the sea depend on thedegree of saturation of the water, the rain rateof the ements, and the rain rate of dilutingmaterials (water and other elements).The solubility of biogenic calciumcarbonate is influenced by water pressure andtemperature. It increases with the water pressuredue to increasing the depth, but itdecreases when water temperature increases.However, seawater is under saturated concerningsilicates at all depth.The geographical separation of biogeniccalcium carbonate and silicate sedimentsare related to the preservation potentialof the planktonic organisms and the chemistryof seawater column. Biogenic sedimentsare most abundant where productivity in thesurface water is high. Therefore the extent ofbiogenic calcium carbonate and silicate sedimentscan be applied to predict the productivityof the ocean (at the past and present).ACKNOWLEDGMENTSI would like thank to Dr. Barrie Peake(Department of Chemistry, University ofOtago, New Zealand) for suggesting the topicand evaluating the paper.REFERENCESBROECKER, W.S. and T.H. PENG 1982.Traces in the Sea. The Lamont-DohertyGeological Observatory, ColumbiaUniversity, New York : 690 pp.DUXBURY, A. C. and A. B. DUXBURY1991. An Introduction to the World'sOceans. Third Edition. Wm C. BrownPublisher, USA : 446 pp.GROVES, D. G. and L. M. HUNT, 1980.Ocean World Encyclopedia. McGraw-Hill Book Company, New York : 443 pp.HEALTH, G.R. 1977. Dissolved silicate anddeep sea sediments. Benchmark Papersin Geology / 40. Dowden,Hutchinson & Ross, Inc. pp : 325-341.HUNTER, K. A. 1992. Acid-Base Chemistryin Marine Systems. Lecture Notes, OtagoUniversity, New Zealand : 160 pp.KENNET, J. 1982. Marine Geology. Prentice-Hall Inc., Englewood Cliffs, N. J. :813 pp.MOORE, c. h. 1989. Carbonate diagenesisand porosity. Elsevier, Amsterdam :338 pp.40Oseana, Volume XXII no. 2, 1997

sumber:www.oseanografi.lipi.go.idOpen University 1989. Ocean Chemistry and ROOS, D.A. 1977. Intruduction to Oceanog-Deep-Sea Sediment (BEARMAN, g. raphy. Prentice-Hall, Inc London : 438Ed.) Pergamon Press, Oxford : 134 pp.pp.41Oseana, Volume XXII no. 2, 1997