CHAPTER 6 



OBTAINING BOTTOM SEDIMENT SAMPLES 



6-1 GENERAL REMARKS.— Marine sedi- 

 mentation embracss that phase of oceanography 

 which is related to the deposition, composition, 

 and classification of organic and inorganic 

 material found on the ocean floor. Various 

 sampling devices are utilized to obtain bottom 

 sediments from a particular locality under 

 investigation. Once obtained, samples are 

 packed and shipped to a sedimentation labora- 

 tory to be analyzed and classified. 



6-2 Analysis. — Analysis of marine sedi- 

 ments generally includes the determination of 

 size, shape, and percentage of component parti- 

 cles; identification of minerals and ratio of light 

 to heavy minerals ; wet density ; pH ; and calcium 

 carbonate content. Biological and ecological 

 studies emphasize the animal population as well 

 as the environmental factors determined by 

 temperature, depth, type of sediment, and geo- 

 graphic location. 



6-3 Classification. — Classification of bot- 

 tom sediments is based on composition. Hence, 

 one may have samples composed of terrigenous 

 material, subaerial or submarine volcanic ma- 

 terial, organic matter, inorganic material, and 

 extraterrestrial matter. Size of the component 

 materials may range in extremes and is used as 

 a further, more detailed classification criteria. 

 Bottom samples composed of volcanic materials 

 for example, may range in size from very fine 

 ash to pebble and cobbles. Very often bottom 

 samples contain an aggregation of sizes so that 

 a combination of volcanic ash and other ma- 

 terial of pebble size is possible. 



6-4 Charts. — Bottom sediment charts are 

 prepared from thousands of reported classifi- 

 cations and collected samples. These charts 

 illustrate the nature of the sea bottom in coastal 

 and oceanic areas. 



6-5 Collecting Samples. — Collecting marine 

 sediments involves the use of a variety of bot- 

 tom samplers which fall into three basic cate- 

 gories: Coring tubes, snappers, and dredges. 

 Selection and use of the proper instrument is a 

 function of the nature of the investigation, the 

 character of the bottom, the depth of the water. 



and the availability of the proper wire, winch, 

 boom, crane, or A-frame required for the 

 operation. 



6-6 GENERAL PROCEDURES FOR COR- 

 ING OPERATIONS.— Coring activities aboard 

 Navy survey ships are guided by procedures in- 

 tended to facilitate operations, insiu-e a maxi- 

 mum degree of efficiency, and allow for a proper 

 distribution of working time. Survey instruc- 

 tions provide for a coring program as part of the 

 oceanographic survey and take into account 

 the nature of the investigation, type of corer 

 to be used, location of the desired cores, time 

 allowed for coring, and disposition of the core 

 samples (fig. 6-1). 



Upon reaching the station area, prior to lower- 

 ing any coring gear over the side, determine the 

 sonic depth of the ship's position and note these 

 on oceanographic log sheet M. This log sheet 

 is described in chapter 14. Duration of a coring 

 operation is largely dependent on the depth of 

 the bottom and the speed at which the wire is 

 payed out. Deep-sea cores taken with a 

 Phleger corer and an oceanographic winch of the 

 type used aboard Navy survey ships, take about 

 1 to 2 hours. Those made with a Ewing piston 

 corer and a deep-sea anchoring winch may take 

 3 to 5 hours to complete. It must be noted 

 that these are average times; each coring oper- 

 ation will differ. 



6-7 HOW TO DETERMINE THE 

 AMOUNT OF WIRE TO PAY OUT FROM 

 THE WIRE ANGLE.— Frequently during bot- 

 tom sampling operations, high wire angles occur 

 as a result of the ship's drift. It is necessary to 

 know how much wire to pay out so that the 

 instrument will reach the bottom without lay- 

 ing an excessive amount of wire. When wire is 

 layed on the bottom, it usually kinks so badly 

 that the kinked portion has to be cut off before 

 the wire can be used again. By using the cosine 

 of the surface wire angle and the sonic or 

 charted depth of the area, the approximate 

 amount of wire needed can be estimated. 

 Figure 6-2 illustrates the problem. This 

 method of estimating the amount of wire to 



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