The strength of the ocean's "biological pump," wherein organic carbon produced by photosynthesis in surface waters is exported to sediments and sequestered from recycling, helps regulate the concentration of CO2 in the atmosphere. How has the biological pump responded to long-term changes in solar insolation? One way to estimate paleoproductivity is by measuring the organic content of marine sediments, which makes the assumption that organic carbon content is a good surrogate for productivity.
Perks et al. applied a sensitive analytical technique, combustion oxygen demand (COD), to estimate the amount of organic carbon in sediments from the western and eastern equatorial Pacific Ocean. Tropical surface water productivity in both sides of the Pacific has varied synchronously during the past 400,000 years, mainly in response to the 23,000-year precessional period of insolation, suggesting that productivity increases were caused by more vigorous equatorial upwelling driven by stronger trade winds. This pattern of basin-wide variation is difficult to reconcile with predictions of west-east asymmetry of paleoproduction. Future interpretations of paleoceanographic data sets from the equatorial Pacific may require more detailed consideration of equatorial circulation and biogeochemistry. -- HJS
Paleoceanography 17, 10.1029/2000PA000603 (2002).
