Knowledge Bank

The ocean regulates CO2 concentrations in the atmosphere through physical, biological and carbonate pumps. The biological pump sequesters CO2 in the form of organic carbon (organic carbon export) while the carbonate pump sequesters the CO2 in the form of inorganic carbon in marine sediments. In this study, carbonate content and barite accumulation rate (BAR) were used as carbon export proxies to reconstruct ocean conditions at Shatsky Rise in the Pacific Ocean over a ~70 kyr time interval during the Maastrichtian at ~67 million years ago (Ma). Since carbonate accumulation in deep sea sediments can be affected by temperature, pH, depth and productivity of phytoplankton, BAR was used to eliminate the possibility of low primary productivity and constrain interpretations of the carbonate proxy. Barite is a refractory mineral with high preservation rate (~30%) in deep sea sediments that are not sulfate reducing. Marine barite forms in the water column when the organic matter degrades. Eight consecutive samples (67.776 Ma to 67.704 Ma) from Ocean Drilling Program (ODP) Expedition 198 Site 1210B were processed through a sequential leaching method to obtain barite residue. BAR is the highest (5.0 mg/cm2.kyr) starting from 232.78 mbsf until 232.83 mbsf (10kyr) suggesting carbon export and primary production during this interval is the highest. The BAR results show negative correlation to the color reflectance used to estimate carbonate content in the core. The drop in carbonate content might be caused by decreasing bottom water temperature and more corrosive water dissolving carbonate resulting in the short term shoaling of the carbonate compensation depth (CCD). Based on previous work, the bottom water temperature and chemistry was changing due to variations in ocean circulation at this time.