Figure F30. Depth and temperature distribution of total bacterial populations in sediment samples from Hole 1173A. The curved dashed line represents a general regression line of bacterial numbers vs. depth in deep-sea sediments (Parkes et al., 1994), with 95% upper and lower prediction limits shown by the curved lines of longer dashes. The shaded area to the left of the figure indicates levels where bacterial populations are too low to be detected with the acridine orange direct counts technique (detection limit is ~6 × 10⁴ cells/cm³). The two horizontal lines separate bacterial groups with different temperature ranges for growth. The solid square at the base of the graph is the bacterial numbers contained in the drill fluid (surface seawater); these were 1.4 × 10⁵ cells/cm³.