Open AccessOceanic iron supply mechanisms which support the spring diatom bloom in the Oyashio region, western subarctic Pacific
Author(s) -
Nishioka Jun,
Ono Tsuneo,
Saito Hiroaki,
Sakaoka Keiichiro,
Yoshimura Takeshi
Publication year - 2011
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jc006321
Subject(s) - subarctic climate , mixed layer , surface water , oceanography , bloom , thermocline , phytoplankton , transect , environmental science , mesoscale meteorology , chlorophyll a , diatom , deep chlorophyll maximum , spring bloom , surface layer , geology , nutrient , photic zone , layer (electronics) , chemistry , biology , ecology , biochemistry , organic chemistry , environmental engineering
Multiyear (2003–2008) time series observations along the A line provided information on the temporal variability of the dissolved iron (diss‐Fe) concentration in the Oyashio region of the western subarctic Pacific, and the data indicated that there was an annual cycle in the concentration of surface diss‐Fe occurring every year. Diss‐Fe was supplied into the surface water in this region every winter and supports the spring phytoplankton bloom after development of the thermocline. The diss‐Fe concentration was drawn down during the phytoplankton bloom period and was depleted in summer in some water masses. Then diss‐Fe increased from autumn to winter with the increasing depth of the surface mixed layer. The high diss‐Fe concentrations in the surface layer in winter were controlled by mesoscale oceanic intrinsic processes, such as vertical winter mixing and horizontal Fe‐rich intermediate water transport. Difference in magnitude of the winter mixing processes among different water masses caused the heterogeneous distribution of diss‐Fe concentration in the surface layer. Moreover, the vertical section profiles along a cross‐Oyashio transect showed the occurrence of Fe‐rich intermediate water, and upward transport of materials from the intermediate water to the surface layer via tidal and winter mixing processes are important mechanisms to explain the high winter surface diss‐Fe concentrations. Additionally, the substantially higher diss‐Fe/NO 3 ratio in the winter surface layer in this studied area other than the high‐nutrient low‐chlorophyll region indicates that the winter surface water in the Oyashio and the Oyashio‐Kuroshio transition zone has a high potential to stimulate phytoplankton growth.