Elevated carbon flux in deep waters of the South China Sea

Yung-Yen Shih,Chen-Tung Arthur Chen,Chin-Chang Hung,Dewang Li,Hsueh-Han Hsieh,Hsi-Hsiang Lin

doi:10.1038/s41598-018-37726-w

Yung-Yen Shih, Chen-Tung Arthur Chen + Show 4 more

Open Access

https://doi.org/10.1038/s41598-018-37726-w

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Abstract

We measured particulate organic carbon (POC) fluxes from the euphotic zone into the twilight zone and deep waters (>1000 m) that occurred between the shelf and the basin in the South China Sea (SCS) and at the SouthEast Asia Time Series Station (SEATS) using floating sediment trap arrays. Additionally, selected sinking particles were imaged by scanning electron microscope (SEM) to reveal particle morphology and composition. Results showed large variations in POC fluxes with elevated values (32–104 mg-C m−2 d−1) below the euphotic zone and a trend towards lower values in the deep SCS. Vertical POC fluxes measured in deep waters between the shelf and the SCS basin were much higher than those estimated by Martin’s attenuation equation. These elevated POC fluxes in deep waters were attributed to lateral particle transport as opposed to enhanced settling out of the euphotic zone. SEM images of sinking particles at 150 m show abundant marine biogenic detritus, while those in deep waters contained a higher proportion of lithogenic material. A great deal of the spatial variability in POC fluxes across the twilight zone and deep waters of the SCS cannot be represented by current biogeochemical models.

Highlights

The export of particulate organic carbon (POC) transfers anthropogenic carbon dioxide into the ocean interior[1], and provides energy to the ocean food web[2,3]
The results show that both biogenic and non-biogenic particles contributed to the POC flux in deep waters
The POC flux decreases with increasing depth either through its decomposition to dissolved inorganic carbon (DIC) or its conversion to dissolved organic carbon (DOC)[1]

Summary

Introduction

The export of particulate organic carbon (POC) transfers anthropogenic carbon dioxide into the ocean interior[1], and provides energy to the ocean food web[2,3] Such carbon transport is often simplified to one-dimensional vertical process due to the dominant of sinking POC flux[4,5]. Some researchers have questioned the applicability of this flux equation because of discrepancies between observed and modeled carbon fluxes in deep waters They have suggested that the POC flux attenuation may be controlled by the magnitude of the flux, the characteristics of sinking particles and the specifics of sampling locations[7,8].

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