ABSTRACT

Although the history of carbonate dissolution has been studied for many years, few records of dissolution through an entire glacial cycle are available for the western North Atlantic (North American Basin). Using 14 cores from the Muir and Siboney Seamounts, located about 240 km northeast of Bermuda, changes in carbonate dissolution were examined over the last 125,000 years. The core depth range spans more than 3000 m, 1780 m-4980 m, insuring that major changes in dissolution will be recorded. Weight percent carbonate was plotted as a function of water depth for five stratigraphically defined levels to determine temporal changes in the sedimentary lysocline and calcite compensation depth (CCD). During the Holocene, the lysocline is located between 4050 m and 4350 m; the CCD is not pre ent even in the deepest sample (4980 m). The late glacial ( 18,000 years B.P.) lysocline may have shoaled to about 2500 m, whereas during early glacial time ( 72,000 years B.P) it deepened to about 3400 m. The mid-glacial carbonate maximum ( 60,000 years B.P; interstadial?) is marked by a deepening of the lysocline to about 3800 m. During the entire glacial episode, the CCD aappears to have remained fixed at 4650 m. The last interglacial ( 125,000 years B.P) was a time favorable to carbonate preservation; the lysocline was deeper than 4650 m, the deepest core containing sediments of this age

Increased glacial dissolution appears to result from changes in deep circulation. The establishment of the CCD during glacial time is interpreted as indicating increased Antarctic Bottom Water flow. The lysocline, on the other hand, may reflect the degree of stagnation of North Atlantic Deep Water.