Climatology of surface chlorophyll a, autumn-winter and spring blooms in the southwest Pacific Ocean

• Published in: Journal of geophysical research. Oceans 2013-02, Vol.118 (2), p.1003-1018
• Main Authors: Chiswell, Stephen M., Bradford-Grieve, Janet, Hadfield, Mark G., Kennan, Sean C.
• Format: Article
• Language: English
• Subjects: Algae; Annual cycles; Autumn; Blooms; Chlorophyll; Chlorophylls; Climatology; Geophysics; Latitude; Oceans; Pacific Ocean; Spatial coherence; Spring; Springs; Stresses; Summer; Surface chlorophyll; Thermocline; Wind; Winter
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/jgrc.20088

Ocean color data from the 13 year Sea‐viewing Wide Field‐of‐view Sensor mission are used to examine the distribution of surface chlorophyll a in the southwest Pacific Ocean. The mean surface chlorophyll field is similar to that found by previous workers, with elevated levels in the Subtropical Front and around the subantarctic islands that have an associated shelf. The annual cycle in surface chlorophyll shows a ubiquitous summer bloom in subantarctic water, with autumn, winter, and spring blooms variously in subtropical water and across the Subtropical Front. The autumn blooms progress equatorward with time at the same rate as wind stress. This supports the idea that the autumn bloom develops in response to increased wind stress, with a likely mechanism for the bloom being mixing to the surface of the deep chlorophyll maximum, and/or increased production due to entrainment of nutrients. The spring bloom progresses poleward with time. It starts after the mixed layer reaches its deepest, and its timing appears to be linked to the reduction in wind stress in spring. Under the assumption that all tracers are well mixed to the seasonal thermocline in autumn and winter, we conclude that vertically integrated chlorophyll increases at all latitudes in subtropical water during autumn and winter. Unfortunately, carbon‐to‐chlorophyll ratios are not known well enough to determine whether the same is true for vertically integrated carbon biomass. Individual spring blooms show significant spatial structure and are different from year to year. This leads to low spatial coherence for the temporal variability in surface chlorophyll. Key Points SAW = summer bloom, STW = spring, autumn winter blooms with different mechanisms Vertically‐integrated chl increases in winter at all latitudes Increased annual production may occur in years with deeper mixed layers