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The Effect of Typhoon on POC Flux

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The Effect of Typhoon on POC Flux Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Biogeosciences Discuss., 7, 3521–3550, 2010 Biogeosciences www.biogeosciences-discuss.net/7/3521/2010/ Discussions BGD doi:10.5194/bgd-7-3521-2010 7, 3521–3550, 2010 © Author(s) 2010. CC Attribution 3.0 License. The effect of typhoon This discussion paper is/has been under review for the journal Biogeosciences (BG). on POC flux Please refer to the corresponding final paper in BG if available. C.-C. Hung et al. The effect of typhoon on particulate Title Page Abstract Introduction organic carbon flux in the southern East Conclusions References China Sea Tables Figures C.-C. Hung1, G.-C. Gong1, W.-C. Chou1, C.-C. Chung1,2, M.-A. Lee3, Y. Chang3, J I H.-Y. Chen4, S.-J. Huang4, Y. Yang5, W.-R. Yang5, W.-C. Chung1, S.-L. Li1, and 6 E. Laws J I 1Institute of Marine Environmental Chemistry and Ecology, National Taiwan Ocean University Back Close Keelung, 20224, Taiwan 2Center for Marine Bioscience and Biotechnology, National Taiwan Ocean University Keelung, Full Screen / Esc 20224, Taiwan 3 Department of Environmental Biology and Fisheries Science, National Taiwan Ocean Printer-friendly Version University, 20224, Taiwan 4Department of Marine Environmental Informatics, National Taiwan Ocean University, Interactive Discussion Keelung, 20224, Taiwan 5Taiwan Ocean Research Institute, National Applied Research Laboratories, Taipei, Taiwan 3521 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | BGD 6 Department of Environmental Sciences, School of the Coast and Environment, Louisiana 7, 3521–3550, 2010 State University, Baton Rouge, LA 70803, USA Received: 16 April 2010 – Accepted: 7 May 2010 – Published: 19 May 2010 The effect of typhoon on POC flux Correspondence to: C.-C. Hung ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. C.-C. Hung et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 3522 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD Severe tropical storms play an important role in triggering phytoplankton blooms, but the extent to which such storms influence carbon flux from the euphotic zone is unclear. 7, 3521–3550, 2010 In 2008, typhoon Fengwong provided a unique opportunity to study the in situ biolog- 5 ical responses including phytoplankton blooms and particulate organic carbon fluxes The effect of typhoon associated with a severe storm in the southern East China Sea (SECS). After pas- on POC flux sage of the typhoon, the sea surface temperature (SST) in the SECS was markedly cooler (∼25 to 26 ◦C) than before typhoon passage (∼28 to 29 ◦C). The POC flux 5 C.-C. Hung et al. days after passage of the typhoon was 265 ± 14 mg-C m−2 d−1, which was ∼1.7-fold −2 −1 10 that (140–180 mg-C m d ) recorded during a period (June–August, 2007) when no typhoons occurred. A somewhat smaller but nevertheless significant increase in POC Title Page −2 −1 flux (224–265 mg-C m d ) was detected following typhoon Sinlaku which occurred Abstract Introduction approximately 1 month after typhoon Fengwong, indicating that typhoon events can in- crease biogenic carbon flux efficiency in the SECS. Remarkably, phytoplankton uptake Conclusions References 15 accounted for only about 5% of the nitrate injected into the euphotic zone by typhoon Tables Figures Fengwong and it is likely that phytoplankton population growth was presumably con- strained by a combination of light limitation and grazing pressure. Modeled estimates of new/export production were remarkably consistent with the average of new and ex- J I port production following typhoon Fengwong. The same model suggested that during J I 20 non-typhoon conditions approximately half of the export of organic carbon occurs via convective mixing of dissolved organic carbon, a conclusion consistent with earlier Back Close work at comparable latitudes in the open ocean. Full Screen / Esc 1 Introduction Printer-friendly Version Recent research has shown that typhoons (severe tropical storms also referred to as Interactive Discussion 25 tropical cyclones or hurricanes) can cause marked cooling of the sea surface, enhance nutrient pumping and result in phytoplankton blooms along storm paths of the typhoon 3523 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and in adjacent areas (Babin, et al., 2004; Bates, et al., 1998; Chang, et al., 1996, 2008; Lin, et al., 2003; Shang, et al., 2008; Walker, et al., 2005; Zheng and Tang, BGD 2007). Previous studies of typhoon induced phytoplankton blooms have been based 7, 3521–3550, 2010 largely on satellite remote sensing data, but it can often be difficult to obtain clear ocean 5 color images during or shortly after the typhoon passages because of extensive cloud cover. Sea-based measurements of pre- and post-typhoon phytoplankton biomass The effect of typhoon and biological activity are also limited because of the dangers inherent in field work on POC flux associated with typhoon events. Consequently, in situ field observations on the effects of typhoons on biological processes are rare (Chang, et al., 1996; Chen, et al., 2003; C.-C. Hung et al. 10 Shiah, et al., 2000; Zheng and Tang, 2007) and no reports of the effects of typhoon passage on ocean biogeochemistry, especially carbon export fluxes measured using Title Page floating sediment traps, have appeared. The upwelling of subsurface water on the shelf-break of the SECS has long been Abstract Introduction observed (Chen, et al., 1990; Gong, et al., 1995; Liu, et al., 1992). The wax and wane Conclusions References 15 of the outcrop of cool upwelled water were attributed to inflow of the Taiwan Strait water Gong, et al., 1995, or an influence of the strong northeast monsoon in winter (Chuang Tables Figures and Liang, 1994; Gong, et al., 1995). Recently, Wu et al. (2008) and Chang et al. (2009) reported a remarkable seasonal variability of this upwelling at depths of 100 m or more J I below the surface in summer but such upwelling was weak in winter. In addition to 20 such factors, typhoons may also enhance upwelling in the SECS following passage of J I a typhoon through an adjacent region (Chang, et al., 2008; Tsai, et al., 2008). Tsai et Back Close al. (2008) reported that a typhoon induced significant upper water column cooling off northeastern Taiwan). Chang et al. (2008) reported that upwelled water persisted in Full Screen / Esc the SECS for more than a week after a typhoon resulting in a phytoplankton bloom in 25 the shelf region. Printer-friendly Version Several studies (Bates, et al., 1998; Lin, et al., 2003; Walker, et al., 2005; Zhao, et al., 2008; Zheng and Tang, 2007) have inferred that large quantities of nutrients Interactive Discussion were carried to the ocean surface resulting in enhanced phytoplankton biomass (even phytoplankton blooms) in the open ocean and coastal waters several days after a 3524 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | typhoon event. However, the cited reports were based on study of satellite images, and the reported phytoplankton biomass (e.g. usually determined from chlorophyll ab- BGD sorption spectra) has seldom been confirmed by in situ measurements. Thus, Shang 7, 3521–3550, 2010 et al. (2008) indicated with caution that dissolved organic matter and detritus could 5 significantly affect detected chlorophyll (chl a) values near the coast of the northern South China Sea. The study area of Shang et al. (2008) was adjacent to the mouth The effect of typhoon of the Mekong River, which may discharge runoffs containing a high concentration of on POC flux chromophoric dissolved organic matter. However, no large river was located near the our study area and the satellite ocean color data are thus likely to accurately represent C.-C. Hung et al. 10 of the sea conditions, being unaffected by influx of terrestrial materials. Besides, they are supported by ship-based measurements and, therefore, are included in this study Title Page as an important source of information. Most importantly, the flux of particulate organic carbon (POC) from the Abstract Introduction euphotic zone is unknown because typhoons form in remote regions of the open Conclusions References 15 ocean and sea-based experiments are difficult to conduct due to strong winds and high waves. Typhoons Fengwong passed through the SECS on 28 July 2008, and in Tables Figures the following 4–5 days we had a unique opportunity to conduct sea-based investiga- tions in the affected area of the southern ECS. The main objective of the study was J I to conduct in-situ experiments to examine the physical and biological responses of the 20 water column to typhoon forcing. We used hydrographic data (including information on J I temperature, salinity, density, light intensity and nitrate concentration) in efforts to in- Back Close terpret possible mechanisms affecting biogeochemical responses (chl a concentration and POC flux). Full Screen / Esc 2 Materials and methods Printer-friendly Version Interactive Discussion 25 Sampling was conducted in the euphotic zone (depth of 1% surface light penetration) of the SECS, in an area approximately 70 km northeast of Taiwan (25.40◦ N, 122.45◦ E, Fig. 1), from the R/V Ocean Researcher II (OR II). Three cruises were conducted: one 3525 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | each in June and August 2007 (non-typhoon periods) and one in August 2008 (2–3 Au- gust, 2008) during the passage of typhoon Fengwong. Data on wind speed during the BGD typhoon were provided by the Central Weather Bureau of Taiwan. Water temperature 7, 3521–3550, 2010 was recorded using a SeaBird model SBE9/11 plus conductivity/temperature/depth 5 (CTD) recorder. The concentrations of nitrate (NO3) and chlorophyll a (chl a) at depths of 0, 10, 25, 50, 75, 100 and 125 m were determined according to Gong et al.
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