INFLUENCE OF INCREASED CARBON DIOXIDE ON PHYTOPLANKTON TRACE METAL QUOTAS IN CULTURES AND FIELD-COLLECTED NATURAL ASSEMBLAGES
Abstract
A significant consequence of future global climate change scenarios on the world's oceans is a rise in the partial pressure of CO2 (pCO2) and associated acidification. This change in carbonate chemistry is likely to affect both the (bio)availability of trace metal ‘micronutrients' to marine phytoplankton and their trace metal requirements. To assess the influence of pCO2 on phytoplankton, we examined trace metal quotas and cell physiology in both culture and field-based incubation experiments using trace metal clean techniques and air:CO2 mixtures including glacial (190 ppm), current (380 ppm), and year 2100 estimates (750 ppm). From various culture experiments with eukaryotic phytoplankton and natural assemblages in field experiments, from the subtropical Pacific (off New Zealand) and the coastal Northeastern Pacific (off southern California), we observed general declines in Fe and Zn quotas with increasing pCO2 – consistent with current trace metal-CO2 availability hypotheses. Interestingly, when co-limited by the essential vitamin B12, a diatom culture experiment showed a positive correlation in Fe, Zn, and Co quotas with pCO2. This highlights the need for experiments that test not only the influence of pCO2 on trace metal quotas, but also the effect of predicted changes in nutrient availability. The use of culture and field approaches for global change experiments both suggest that rising oceanic pCO2 may lead to shifts in phytoplankton trace metal requirements, which in combination with predicted changes in trace metal availability, could have critical impacts on future phytoplankton productivity, dominant phytoplankton taxa, and major nutrient (C, N, and P) oceanic biogeochemistry.