  Liquid water oceans are at the center of our search for life on exoplanets
because water is a strict requirement for life as we know it. However, oceans
are dynamic habitats---and some oceans may be better hosts for life than
others. In Earth's ocean, circulation transports essential nutrients such as
phosphate and is a first-order control on the distribution and productivity of
life. Of particular importance is upward flow from the dark depths of the ocean
in response to wind-driven divergence in surface layers. This `upwelling'
returns essential nutrients that tend to accumulate at depth via sinking of
organic particulates back to the sunlit regions where photosynthetic life
thrives. Ocean dynamics are likely to impose constraints on the activity and
atmospheric expression of photosynthetic life in exo-oceans as well, but we
lack an understanding of how ocean dynamics may differ on other planets. We
address this issue by exploring the sensitivity of ocean dynamics to a suite of
planetary parameters using ROCKE-3D, a fully coupled ocean-atmosphere GCM. Our
results suggest that planets that rotate slower and have higher surface
pressure than Earth may be the most attractive targets for remote life
detection because upwelling is enhanced under these conditions, resulting in
greater nutrient supply to the surface biosphere. Seasonal deepening of the
mixed layer on high obliquity planets may also enhance nutrient replenishment
from depth into the surface mixed layer. Efficient nutrient recycling favors
greater biological activity, more biosignature production, and thus more
detectable life. More generally, our results demonstrate the importance of
considering oceanographic phenomena for exoplanet life detection and motivate
future interdisciplinary contributions to the emerging field of
exo-oceanography.
