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Introduction	As air breathers, we don’t think much about oxygen. It is always plentiful. The situation is different in seawater, however, and some regions of the ocean called oxygen minimum zones (OMZ) can have low levels of oxygen. Midwater oxygen minimum zones (lower oxygen concentrations at intermediate depths) exist in many regions of the world’s oceans, but are particularly prominent in the eastern tropical Pacific (ETP). Scientists have observed rising sea water temperatures (>0.5º C) over the past century (IPCC 2001). Warmer water holds less oxygen, which animals and fish in the ocean depend on to breathe. Indeed, scientists have observed decreases in oxygen concentrations (up to 12 µmoles per kg) in the Pacific (Keeling and Garcia 2002). Since global air temperatures and seawater temperatures are predicted to continue to rise, it is reasonable to expect that oxygen levels in the ocean will continue to decrease.

Introduction

As air breathers, we don’t think much about oxygen. It is always plentiful. The situation is different in seawater, however, and some regions of the ocean called oxygen minimum zones (OMZ) can have low levels of oxygen. Midwater oxygen minimum zones (lower oxygen concentrations at intermediate depths) exist in many regions of the world’s oceans, but are particularly prominent in the eastern tropical Pacific (ETP). Scientists have observed rising sea water temperatures (>0.5º C) over the past century (IPCC 2001). Warmer water holds less oxygen, which animals and fish in the ocean depend on to breathe. Indeed, scientists have observed decreases in oxygen concentrations (up to 12 µmoles per kg) in the Pacific (Keeling and Garcia 2002). Since global air temperatures and seawater temperatures are predicted to continue to rise, it is reasonable to expect that oxygen levels in the ocean will continue to decrease.