JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Oral

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG52] [JJ] Biogeochemical linkages between the ocean and the atmosphere during phytoplankton blooms

Thu. May 25, 2017 9:00 AM - 10:30 AM 304 (International Conference Hall 3F)

convener:Jun Nishioka(Hokkaido University, Institute of low temperature sciences), Koji Suzuki(Hokkaido University), Yuzo Miyazaki(Institute of Low Temperature Science, Hokkaido University), Hiroshi Tanimoto(National Institute for Environmental Studies), Chairperson:Jun Nishioka(Hokkaido University, Institute of low temperature sciences), Chairperson:koji Suzuki(Faculty of Environmental Earth Science, Hokkaido University)

10:15 AM - 10:30 AM

[ACG52-06] Effect of optical properties variability on retrieval of chlorophyll a from ocean color data in Oyashio and coastal Oyashio waters in early spring

*Toru Hirawake1, Hisatomo Waga2, Takuro Kaneko2, Koji Suzuki3, Youhei Yamashita3, Jun Nishioka4 (1.Faculty of Fisheries Sciences, Hokkaido University, 2.Graduate school of Fisheries Sciences, Hokkaido Univeristy, 3.Faculty of Environmental Earth Science, Hokkaido University, 4.Institute of Low Temperature Science, Hokkaido University)

Keywords:optical property, ocean color remote sensing, Oyashio

Massive phytoplankton bloom occurs in Oyahsio and coastal Oyashio waters off Kushiro during spring. Ocean color images also illustrates the spring bloom as high chlorophyll a (chl.a) concentration. While a validation result showed the estimated chl.a concentrations in these waters are within a range of +/-35% of in situ values, effects of Tokachi river plume on chl.a estimation were anticipated. However, little is known about optical properties in this region. We measured remote sensing reflectance (Rrs), absorption coefficient, backscattering coefficient (bbp) and chl.a of the waters during the cruise of R/V Hakuho-maru in March 2015 and investigated the effects of the optical properties on chl.a estimation from satellite data.
In the coastal stations of study area where was highly turbid for a few days due to passing of a low pressure during 10–13 March, absorption coefficient of non-algal particles (ad) accounted for >60% of that of particulate matters (ap) and bbp was also higher than those in offshore stations. These optical properties induced high Rrs and resulted in overestimation of chl.a concentration by 2-3 folds when the standard ocean color chl.a algorithm was applied to the Rrs. On March 20, however, ratio of ad and bbp decreased and estimated chl.a concentration using the algorithm coincided with in situ data.
Phytoplankton absorption coefficient at 443 nm (aph(443)) and bbp(555) were linearly correlated with chl.a concentration and ad(443), respectively. Estimated values of chl.a concentration and aCDOM(443) applying these relationship to satellite ocean color data indicated that relatively higher ocean color chl.a in offshore region had interferences by non-algal particles and CDOM advected from coastal region. In this study region, satellite chl.a images should be carefully used and retrieval of chl.a from aph is better than using standard band-ratio algorithm because spatio-temporal variability in optical properties are dynamic and complicated not only in coastal region but also in offshore.