16:30–16:45 | ABSTRACT 1289
TIMING IN PRODUCTION AND GRAZING IN THE SUBARCTIC NORTH PACIFIC AND ATLANTIC OCEANS REVEALED BY DIEL VARIATIONS IN PHYTOPLANKTON BIOMASS AND SIZE STRUCTURE
Time series of phytoplankton cell concentration and other biomass measures can show evidence of daily synchronized cell division, enabling computation of specific growth rates. Synchronized biomass loss can result from biological processes including grazing and viral lysis. Resolving growth, division, and biological loss rates is complicated: cell division doubles cell concentration with no biomass change, while cell growth can double biomass with no change in cell concentration. Here, we quantify daily specific growth and loss rates using continuous inline observations from optical sensors and an Imaging Flow CytoBot deployed in the subpolar North Pacific and North Atlantic Oceans as part of the NASA-sponsored EXPORTS program. Optical and microscopy-based estimates of phytoplankton biomass and size structure were strongly correlated and revealed diel variations. Daily biomass minima were observed at dawn concurrent with an optical particle size proxy indicating a shift toward relatively small cells; daily biomass maxima were observed at dusk concurrent with an optical particle size proxy indicating a shift toward relatively larger cells. The diel signals were particularly strong in the nanoplankton-sized cells in both oceans and specifically in the nanoplankton-sized dinoflagellates in the Pacific. In both oceans daytime specific growth rates approached 0.5 d–1, nearly a doubling per day, and were matched by nighttime grazing losses with little long-term biomass changes. The similarity in cycles and structure between the two very different ocean regimes is remarkable and suggests that differences in ecosystem structure and export would be driven by larger microplankton.
Collin Roesler, Bowdoin College, [email protected], https://orcid.org/0000-0003-3839-2241
Heidi M. Sosik, Wood Hole Oceanographic Institution, [email protected]
E. Taylor Crockford, Wood Hole Oceanographic Institution, [email protected]
Susan L. Drapeau, Bowdoin College, [email protected]
Emily E. Peacock, Wood Hole Oceanographic Institution, [email protected]
