Ocean productivity: A personal perspective since the first Liege Colloquium

- The biological oceanography research agenda has evolved over the last 40 years with technology and international scope.
- Respiration, both autotrophic and heterotrophic, is key to understanding ocean productivity.
- The depth of the euphotic zone can now be determined on the basis of biology.
- The dissolved component of primary production, DPP, remains unresolved.
- Knowing the euphotic zone depth and DPP can help resolve the issue of the metabolic balance in the ocean.

I briefly review the changing dominant research agenda in ocean productivity over the time since the first Liege Colloquium, 44 years ago, and coincidentally, about when I started in oceanography. I then consider two lingering issues, the depth of the ocean's productive layer and the dynamics of dissolved organic carbon. These two topics are united through respiration, the former concerning autotrophic respiration, and the latter heterotrophic respiration.