SURFACE-WATER ACIDIFICATION AND EXTINCTION AT THE CRETACEOUS-TERTIARYBOUNDARY

If published estimates of SO2 volatilization and NO(x) generation by t he Cretaceous-Tertiary (K-T) impact were atmospherically converted to sulfuric and nitric acid, globally dispersed, and rapidly rained out, the resulting acid concentrations would bracket a critical threshold i n surface-ocean chemistry. Rapid and globally uniform deposition of ma sses corresponding to the lowest estimates would have had no major eff ect on sea-surface chemistry. However, similar deposition of masses co rresponding to the highest estimates would have provided enough acid t o destroy the carbonate-buffering capacity of the upper 100 m of the w orld ocean and catastrophically reduce surface-ocean pH. Despite the p ossible effect of the highest estimated acid yields, scenarios that re ly on acid rain as the primary explanation of global K-T extinctions a re not readily compatible with K-T records of terrestrial and marine s urvival or culturing studies of modern marine plankton. The possibilit y that acid rain was a primary cause of K-T extinctions can be tested further by analysis of geographic variation in extinction intensity, b ecause such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than approximately 6 x 10(16) mol of H2SO4 or 1.2 x 10(17) mol of HNO3.