# The Big Picture

## The World (and ocean) were not always full of Oxygen

Geological record for the Great Oxidation Event

## Historic Anoxic Events and Mass Extinctions coincide

Climate change forces threaten ocean oxygenation and PH

## This is more than just fertilizer induced dead zones

But the time scale is longer than simple climate catastrophe

## Oxygen only gets in via surface mixing and photosynthesis

Photosynthesis only happens in a big way down to about 1-200 meters

## Surface effects have an outsize influence

The surface is even more disproportionately effected by excess CO2 and heat

Mixing down to deeper strata takes thousands of years... until it *stops* circulating normally