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64 OCEANOGRAPHY IN THE NEXT DECADE 



sensors give a two-dimensional record of ocean currents to several 

 hundred meters. Acoustic techniques are also used to track sub- 

 surface floats and transmit information between ships and sen- 

 sors at depth. Yet, sound is an underemployed tool in oceanogra- 

 phy. Significant advances should be made during the next decade 

 in physical, biological, and geological oceanography as a result of 

 thoughtful application of acoustic principles and techniques for 

 direct probing and information transfer. Because of its inherent 

 global nature, the acoustic monitoring of ocean climate is a strong 

 candidate for a global ocean observing system. 



The air-sea interface provides a variety of challenges and op- 

 portunities to the oceanographer using acoustic techniques. The 

 formation and subsequent collapse of bubbles are important sources 

 of sound whose monitoring could provide an estimate of wave 

 breaking intensity from which gas transfer rates could be inferred. 

 Such measurements give important insight into poorly understood 

 sea surface physics. The passive measurement of rainfall-generated 

 sound is a way to measure precipitation in the open ocean. Direct 

 measurement of precipitation is difficult to obtain and generally 

 inaccurate. Better measurements of precipitation over the ocean are 

 important because of its effect on the global heat and water budgets. 



Some of the oceanographic applications of underwater sound 

 are simple. Others will require improvements in our understand- 

 ing of the physics of sound propagation in the sea and improved 

 signal processing techniques and instrumentation. 



DIRECTIONS FOR MARINE GEOCHEMISTRY 



Summary 



Studies of chemicals dissolved in seawater, adsorbed on sus- 

 pended particles, incorporated in living or nonliving organic ma- 

 terial, and buried in seafloor sediments have yielded much infor- 

 mation about Earth processes and past conditions. Environmental 

 conditions are imprinted on particles that fall to the seafloor and 

 are buried over time. With adequate understanding about pro- 

 cesses that affect chemical concentrations and forms after deposi- 

 tion, sediments recovered by seafloor drilling can illuminate Earth's 

 environmental history for millions of years into the past. In addi- 

 tion, modern ocean processes can be studied by measuring the 

 concentrations of trace elements and compounds in seawater. For 

 example, measurement of trace element distributions is a major 

 tool used by physical oceanographers to study ocean circulation. 



