Is C/N Decoupling Caused by Harmful Algal Blooms in Santa Monica Bay?

R/CONT-209
Start/End: February, 2010 to April, 2014

It is well known that nutrients in lawn and crop fertilizers, washed into the ocean by rivers, rain and runoff, can trigger some marine algal blooms. But somewhat paradoxically, blooms can also happen when nitrate levels at the ocean's surface are very low. This occurs because some algae, known as dinoflagellates, can propel themselves with whirling, tail-like structures and forage for nutrients. This project was originally funded in the hopes that scientists would be able to sample waters in Santa Monica Bay before, during and after a late-summer or early-fall dinoflagellate bloom. The field samples were, ideally, supposed to capture dinoflagellates in action during periods of low surface nutrient levels. That is, they hoped to observe a draw down in nitrate levels beneath the surface mixed layer, associated with dinoflagellate foraging, and a simultaneous draw down in surface dissolved organic carbon concentrations, associated with cell grown in sun-lit waters. In this way, researchers had hoped to explain an apparent decoupling of surface carbon and subsurface nitrate levels, as the chemical footprint of sub-surface dinoflagellate foraging. The ocean has not been cooperating, however, and in 2012 and 2013, late-summer blooms in Santa Monica Bay were dominated by another kind of algae, diatoms, which do not propel themselves up and down in the water column and are typically associated with spring upwelling events. Scientists have speculated that ocean acidification may be creating conditions that favor diatoms over dinoflagellates.

Co-principal Investigators