Abstract
We investigated the spatio-temporal variability of chlorophyll-a (Chl-a) and total suspended matter (TSM) associated with spring–neap tidal cycles in the Ariake Sea, Japan. Our study relied on significantly improved, regionally-tuned datasets derived from the ocean color sensor Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua over a 16-year period (2002–2017). The results revealed that spring–neap tidal variations in Chl-a and TSM within this macrotidal embayment (the Ariake Sea) are clearly different regionally and seasonally. Generally, the spring–neap tidal variability of Chl-a in the inner part of the Ariake Sea was controlled by TSM for seasons other than summer, whereas it was controlled by river discharge for summer. On the other hand, the contribution of TSM to the variability of Chl-a was not large for two areas in the middle of Ariake Sea where TSM was not abundant. This study demonstrates that ocean color satellite observations of Chl-a and TSM in the macrotidal embayment offer strong advantages for understanding the variations during the spring–neap tidal cycle.
Highlights
The spring–neap tidal cycle is an important factor for the variability of chlorophyll-a (Chl-a) in macrotidal ecosystems [1,2,3,4]
Our study is different in that it relies on ocean color satellite data (MODIS-Aqua) to investigate the variability of Chl-a over the spring–neap tidal cycle, and we examine the tidal impacts on Chl-a for the whole Ariake Sea and focus on three regional areas; i.e., off Saga, Isahaya Bay, and off Kumamoto
As the spring–neap tidal variability of satellite Chl-a associated with total suspended sediment (TSM) has not been investigated for a broad area and with a long-term data set, we investigated the spring–neap tidal variability of Chl-a on the basis of annual and monthly climatology data and individual events of spring–neap tidal cycles using an improved Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua data set (2002-2017)
Summary
The spring–neap tidal cycle is an important factor for the variability of chlorophyll-a (Chl-a) in macrotidal ecosystems [1,2,3,4]. One example is the study by Shi et al [11], which investigated the spring–neap tidal effects on Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua-derived normalized water leaving radiance spectra (nLw(λ)), water diffuse attenuation coefficient at 490 nm (Kd(490)), and TSM in Bohai Sea, Yellow Sea, and East China Sea between 2002 and 2009 Another example is the study by Su et al [12], which investigated the relationship between variation in net phytoplankton growth and tidal resuspended events using the daily Medium Resolution Imaging Spectrometer (MERIS) data from 2003 to 2004 in the German Bight. The authors proposed that spring–neap tidal resuspension supplied nutrients and enhanced phytoplankton growth, which was different from the findings in the above-mentioned studies [3,5,6], indicating that the effect of spring–neap tidal cycle on the variability of Chl-a varies in regions with different characteristics
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