40 BROECKER 



Now let me mention residence times again. Residence time, or response time, 

 is obtained by dividing the amount of an element dissolved in the ocean by the 

 rate at which it is being added to the ocean. It can be thought of as replacement 

 time (Table 3). For calcium this time is about a million years; for total dissolved 

 carbon it is about a hundred thousand years; for phosphorus it is about 30 

 thousand years. Because carbonate ion is only about 7°o of the total dissolved 

 carbon in the sea, it responds 13 times more rapidly than the total dissolved 

 carbon itself. It can adjust to balance input and loss in something like seven 

 thousand years — a fraction of a glacial period. For the excess cations, alkalinity 

 adjusts on the order of a hundred thousand years. 



TABLE 3 



REPLACEMENT TIMES IN YEARS 



OF Ca, TOTAL C0 2 , P, COf, 



AND EXCESS CATIONS 



Replacement times, years 



We can look into the deep-sea sediments to see whether or not this system 

 has been going along at a constant pace or whether it has been fluctuating. The 

 major thing that has happened to our planet for the time scales in this discussion 

 is, of course, glaciation. We have had one major climatic cycle every hundred 

 thousand years. It would be interesting to see if there has been any major change 

 in ocean chemistry as a result of these great climatic changes. Because what 

 leaves the ocean has to equal what is coming in; looking at the bulk chemistry of 

 sediments does not tell much about the chemistry of the ocean. The chemistry 

 of the ocean is adapting itself to maintain throughput of this material. Thus 

 different ocean chemistries may have been necessary at different times to 

 dispense with the same input. The question then is, "What can be examined in 

 deep-sea sediments that will provide the evidence we seek?" One interesting 

 thing to look at would be the rate of calcium carbonate accumulation (Fig. 5). 

 Some parts of the ocean floor are collecting all the calcium carbonate that falls. 

 These places are flux monitors. In other places we are quite sure that much of 

 what falls is dissolving, and what we are seeing is a record that has been distorted 

 by subsequent dissolution of carbonate material. There are tests that can be 

 applied to see whether this has happened or not. If the chemistry of the ocean is 

 changing and the compensation level is going up and down, then we would 



