nium fluxes and the flux of organic carbon (Figure 9.11) is apparent at any given site, a single relationship does not fit for all oceanic sites. Figure 9.12 demonstrates more than a factor of 100 range in Corg/Al values for settling particles in the oceans. Sites near continental sources have Corg/Al values that are less than one; in contrast, the ratio for Equatorial Pacific particles is approximately 100. These variations indicate that Corg and Al fluxes define a common carrier rather than a direct functional relationship. Zooplankton filtering or other aggregation processes may be responsible for the relationship, however, the available aluminosilicate debris is strongly dependent on location.

The strong correlation between the fluxes of particulate organic carbon and aluminum at any given site suggests an alternative means for computing the degree of preservation at the various sites. If the flux of aluminum to the bottom is conservative and the Corg/Al of the raining material remains constant over the time interval integrated by sediment burial rate data, the following relationship is valid:

% Corg preserved = ((Corg/Al)sediments/(Corg/Al)rain) x 100

Similar relationships can be written for any of the labile components of the particulate rain.

This approach overcomes problems that result from errors in the mass accumulation rate or trap efficiency. It is functionally equivalent to computing a correction factor for the rain rates that would make the rain rates of Al the same as the burial rate in sediments. Figure 9.13 demonstrates the change in the labile/Al ratio with depth for two sites and compares the ratio with that observed in the sediments. In Table 9.5 we have compiled the degree of preservation of Corg, CaCO3, and opal computed by this ratio-to-Al approach. In general, this means of computing the degree of preservation agrees very well with the preservation of biogenic component computed by comparison of the rain rate and the burial fluxes (Figure 9.14).

For the Hatteras Abyssal Plain site (HAP) the ratio and the flux method do not agree. The rain rate/burial rate comparison indicates 24 and 90 percent preservation of organic carbon and CaCO3 respectively (Table 9.3). In contrast, the preservation computed by the ratio-to-Al method is 4 percent for organic carbon and 11 percent for CaCO3 (Table 9.5). Since the burial and rain rates of refractory element at HAP do not agree, we suspect the ratio method provides more accurate estimates of preservation at this site.

At HAP the burial flux of Al, Fe, and Ti exceeds the rain rate of these elements by nearly an order of magnitude

FIGURE 9.12 Organic carbon flux versus Al flux. (a) Atlantic sites; (b) Equatorial Pacific; (c) California Current. Only the uppermost samples at each site were used for this comparison and the trap depths range from 500 to 1500 m.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement