Persistent iron-limited water masses in the California Current Ecosystem

The California Current Ecosystem (CCE) is characterized by vertical and lateral gradients in inorganic nutrients and primary production, whereby vigorous stirring of the surface ocean transports phytoplankton-rich coastal waters offshore. During the spring and summer, diatom blooms are strongly limited by the availability of the micronutrient iron (Fe), leading to decoupling of silicate (Si) and nitrate (N) concentrations in upwelled waters. We leveraged at 25-year timeseries of coastal upwelling and offshore transport to understand how periodicity and anomalous extremes in regional climate impact the degree of Fe-limitation experienced in the CCE LTER domain through measurements of the geochemical proxy, Si_ex. Upwelling followed by retention is believed to be the primary physical mechanism favoring diatom blooms, and here we show a recent dramatic increase in the retention of Fe-limited water masses in the nearshore since 2014. These results could indicate that carbon export associated with Fe-limited diatom blooms is enhanced closer to shore and on continental shelves under recent upwelling conditions. Finally, the timeseries shows persistence of Fe-limitation in the CCE.

Presentation Preference: Oral

Primary Presenter: Kiefer Forsch, University of Southern California (forsch@usc.edu)

Authors:

Kiefer Forsch, University of Southern California  (forsch@usc.edu)

Pierre Chabert, Brown University  (pierre_chabert@brown.edu)

Katherine Barbeau, Scripps Institution of Oceanography, UC San Diego  (kbarbeau@ucsd.edu)