ALBERT

Description: Radiocarbon ages on CaCO3 from deep-sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.

Description: High-resolution records of the concentration and mass accumulation rate (MAR, or flux) of biogenic sediments from core RC11-210 in the central equatorial Pacific are compared for the entire late Pleistocene. The fluxes of calcium carbonate and organic carbon correlate well. The opal flux pattern shows no direct correlation with the other two; rather, opal flux maxima correlate with slopes of (i.e. both precede and follow) the organic carbon and carbonate MAR peaks. Organic carbon and calcite therefore may both be better indicators of past productivity than opal, which is an indicator of transition at this location. We interpret the sequence low biogenic fluxes, high opal fluxes, high carbonate, carbon, and opal fluxes as representing the transition from low to high sea surface biological productivity. The phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume, the ice core CO2 record, the Pacific delta13C record, the deep nutrient (Cd/Ca) record, and the eolian grain-size record of wind intensity. We find that starting from maximum ice volume (phase angle of 0°) the phase relationships of the 100,000-year periodicity show, in the first quadrant, maximum wind intensity (30°) and maximum calcite and carbon flux (45°) occurring first, followed by maximum opal flux (75°) and then maximum deep nutrients (95°). Minimum Pacific delta13C occurs at a phase angle of 155°, the maximum CO2 in the Vostok record and minimum ice volume is at 180°. Thus, in the eccentricity climate cycle, glacial conditions lead to stronger wind-driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume.