Biogeochemical Responses in the Southern East China Sea After Typhoons

Chin-Chang Hung,Gwo-Ching Gong

doi:10.5670/oceanog.2011.93

Abstract

To understand the biogeochemical impact of typhoons in marginal seas, 16 sea-going expeditions were conducted from 2007 to 2009, covering all four seasons and including periods following the passage of several typhoons in the southern least China (SECS). Higher surface nitrate and chlorophylil a (Chl a) concentrations were measured in winter and spring but surface nitrate (<0.1 mu M) and Chl a (0.47 +/- 0.17 mg m(-2)) concentrations were loss in summer under nontyphoon conditions. In comparison, elevated surface nitrate (0.2-2.3 mu M) and Chl a concentration (1.11 +/- 0.40 mg m(-2)) were recorded in the SECS several days after the passage of each of three typhoons in 2008. The results demonstrate that nutrient-rich water are brought to the surface after the passage of typhoons, after which phytoplankton flourish. Most importantly, elevated particulate organic carbon (POC) fluxes (552 +/- 28 mg cm(2) d(-2)) were observed after Typhoon Jangal, about a threefold increase from the monthly mean value (184 +/- 37 mg m(2) d(2)). These field investigations demonstrate that typhoons can have a profound effect on nutrient supply, phytoplankton growth, and POC: fluxes to marginal seas.

Highlights

The diatom Chaetoceros sp. is one of the dominant phytoplankton in the southern East China Sea in April and June
To understand the biogeochemical impact of typhoons in marginal seas, 16 sea-going expeditions were conducted from 2007 to 2009, covering all four seasons and including periods following the passage of several typhoons in the southern East China Sea (SECS)
Higher surface nitrate and chlorophyll a (Chl a) concentrations were measured in winter and spring, but surface nitrate (< 0.1 μM) and Chl a (0.47 ± 0.17 mg m–3) concentrations were low in summer under nontyphoon conditions

Summary

Biogeochemical Responses in the Southern East China Sea After Typhoons

To better understand the biogeochemical impacts of typhoons on marginal seas, we present hydrographic information (e.g., temperature, nitrate concentration, and Chl a) and POC flux measurements in the SECS from 2007 to 2009, covering all four seasons and including periods following the passage of several typhoons (Figure 2, Table 1). Our current understanding of the summer nutrient supply in the SECS is that it cannot support the high biological activity that Hung et al (2000) reported (PP = 1,000 mg-C m–2 d–1 in summer) or that Chen et al (2001) reported (PP = 1,010 mg-C m–2 d–1 in summer) These concentrations imply that any combination of regular nitrate upwelled under nontyphoon conditions, atmospheric deposition, and riverine input cannot account for the observed high nitrogen export flux out of the euphotic zone. Some SST and Chl a data before the typhoons were not available (na) due to cloud cover

Before After Before After Before After

JJ FSS

Findings

Jangmi na na