Distribution of Dissolved Organic Carbon in the Continental Margin off Northern Taiwan

Jia-Jang Hung,Po-Ling Lin

doi:10.3319/tao.1995.6.1.13(keep-mass)

Abstract

Analytical precision of dissolved organic carbon (DOC) in seawater using the high-temperature catalytic method (HTCO) and distributions of DOC in the continental margin off northern Taiwan were investigated. The DOC concentration of Kuroshio water off northeastern Taiwan varied from 122-136μM C at the surface to 65-74μM C at the bottom. The concentration decreased sharply downward in the upper 200m of the water column and then decreased slightly toward the bottom. The pattern showed neither seasonal variation nor a significant difference from that observed in the water off southeastern Taiwan. The concentration of DOC was found to be inversely correlated with apparent oxygen utilization (AOU) in the Kuroshio water. The slope, however, was smaller than that predicted from the Redfield stoichiometry, indicating that only a small fraction (＜25%) of AOU was derived from the oxidation of DOC. Distributions of DOC were found to vary, both temporally and spatially in the continental shelf and slope waters. Although the distributions were relatively patchy in the inner and middle shelves, they were influenced apparently by the upwelled Kuroshio subsurface water in the outer shelf and slope regions. DOC may have been diluted in the intensive upwelling regime but enhanced on the margin of the up- welling center. Terrestrial DOC was largely confined to areas close to the continent. DOC was higher in near bottom waters, indicating that it diffused from sediments and/or was released from resuspended sediments. Thus, DOC varied non-conservatively across the continental margin through various blogeochemical processes. The horizontal gradient of surface DOC decreasing from the southern East China Sea (ECS) to the N. Pacific may reflect a similar trend of surface biological productivity and suggest the potential export of DOC out of the ECS continental margin as well.

Highlights

The study of the distribution of dissolved organic carbon (DOC) in marginal seas is highly desirable because it may act as an important sink of atmospheric carbon dioxide and play an important role in detennining the carbon flux from continental margins to open oceans (Toggweiler, 1 989; Sharp, 199 1 ; IGBP, 1 992)
During the Seattle DOC comparison workshop, instrument blanks, especially for the high-temperature catalytic method (HTCO) method, was ascertained to be the source of disagreement in the data reported by different groups of analysts
It was generally agreed that a careful assessment of the blank should be made prior to DOC measurements and further interpretations

Summary

INTRODUCTION

The study of the distribution of DOC in marginal seas is highly desirable because it may act as an important sink of atmospheric carbon dioxide and play an important role in detennining the carbon flux from continental margins to open oceans (Toggweiler, 1 989; Sharp, 199 1 ; IGBP, 1 992). The scarcity is further impeded by the reality of ''missing DOC'' proposed by Sugimura and Suzuki ( 1 988). Sharp ( 1 993) initiated an interlaboratory comparison .of DOC measurements and provided participants with samples that had been measured by his own group, so that each individual analyzer had an opportunity to see how well the blank water and reference samples were measured. In taldng this opportunity, the authors were able to re-evaluate the instrument blank and compare the results with the previous data (Hung and Chang, 1 992).

MATERIALS AND MET HODS

Intercalibration

DOC in Kuroshio Water

Spatial and TeQtporal Distributions of DOC in Shelf and Slope Waters

' Acknowledgments