Ocean physical and biogeochemical responses to the passage of Typhoon Meari in the East China Sea observed from Argo float and multiplatform satellites

Abstract

We elucidated ocean physical and biogeochemical responses to slow‐moving Typhoon Meari using a new method combining Argo float and satellite observations. Meari‐driven upwelling brought colder, nutrient‐rich deep water to the surface layer, causing sea surface cooling (3–6°C) and threefold enhancement of primary production (PP). Maximum surface cooling (and hence nutrient injection) and peak PP enhancement lagged Meari's passage by 1 and 3 days, respectively, implying that remarkable PP enhancement was attributed to new production (NP). This NP accounted for approximately 3.8% of annual carbon export in the East China Sea (ECS) outer shelf, suggesting that typhoon‐driven upwelling is important for biogeochemical processes in the ECS. Given the wide coverage of Argo float and satellite data, our new approach may prompt comparative studies in other basins and advance the understanding of the role of tropical cyclones in the global ocean biogeochemical cycle.

Enhancement of phytoplankton primary productivity in the southern East China Sea following episodic typhoon passage

“…A non-linear relation between PP enh and TS (Figure 2a) seemed to be the best equation to reflect a non-linear response of phytoplankton to upwelled nutrients [see Dugdale, 1985]. PP enh was not significantly correlated with MSW (Figure 2c), as has been reported in previous studies [e.g., Babin et al, 2004;Siswanto et al, 2007]. Of interest is the finding that PP enh was significantly correlated with V measured at YI (R 2 = 0.45, p < 0.01, Figure 2b).…”

“…PP enhancement (PP enh , Gg C) was computed by subtracting the pre-typhoon PP from the post-typhoon PP over the region of interest (see Section 4). Before subtraction, cloudy pixels were corrected with the simple formula of ([Tpxl/Cpxl] ICpxl), where Tpxl, Cpxl, and ICpxl are total pixels, cloud-free pixels, and integrated PP over all cloudfree pixels, respectively [see Siswanto et al, 2007].…”

“…These nLw 555 data were merged from SeaWiFS and MODIS data (see auxiliary material). On average, over the selected region, although the nLw 555 after the 16 typhoon passages (0.50 mW cm À2 mm À1 sr À1 ) was slightly higher than that before the passages (0.44 mW cm À2 mm À1 sr À1 ), these nLw 555 values were far from the levels that would indicate the presence of suspended sediment which might overestimate satellite Chl-a retrieval [see Tan et al, 2006;Siswanto et al, 2008]. Even during the highest PP enh after Hai-Tang, nLw 555 was generally <1.0 mW cm À2 mm À1 sr À1 and although this was higher than the pre-Hai-Tang nLw 555 ($0.5 mW cm À2 mm À1 sr À1 , Figures 1h and 1i) it nonetheless indicates that PP estimates were unlikely to be largely unaffected by suspended sediment.…”

“…This range was considered to represent the minimum estimate of PP enh , as we did not consider the lifetime of a phytoplankton Chl-a bloom. Considering that a Chl-a bloom can last for several days or even weeks after a typhoon's passage [e.g., Babin et al, 2004;Siswanto et al, 2007], this range of PP enh could be several times larger, suggesting that typhoon passages over the southern ECS are important phenomena supporting NP in the ECS.…”

Seasonal shifts in the contributions of the Changjiang River and the Kuroshio Current to nitrate dynamics in the continental shelf of the northern East China Sea based on a nitrate dual isotopic composition approach

“…Also, when NO 3 is taken up by phytoplankton and bacteria following a Rayleigh fractionation model in a closed system, a linear relationship is observed between the log-transformed NO 3 concentration (ln[NO 3 ]) and δ 15 N in NO 3 (Sigman et al, 1999;Teranes and Bernasconi, 2000). This provides evidence of actual uptake of NO 3 by phytoplankton and other species (e.g., denitrifying bacteria), and the extent of any deviation from linearity suggests the presence of other biological reactions in the N cycle, such as nitrogen fixation (Sigman et al, 2005) and nitrification Sugimoto et al, 2009). Because isotopic signatures provide time-and space-integrated evidence of multiple biogeochemical processes , this information should be helpful for better understanding of NO 3 dynamics on the shelf of the ECS, which have previously been explored from only snapshot surveys and water mass analysis.…”