A cylindrical vessel of cross-sectional area $A$ holds two immiscible liquids: density $\rho_1$ filling a depth $h_1$ on top, and density $\rho_2 > \rho_1$ filling a depth $h_2$ on the bottom. A small solid block of mass $m$ and density $\rho_3$, with $\rho_1 < \rho_3 < \rho_2$, is gently lowered into the vessel and comes to rest floating stably at the interface, with part of its volume in each liquid. By how much does the gauge pressure at the bottom of the vessel increase compared to before the block was added?