Stable isotope profiles of bivalve shells: seasonal temperature variations, latitudinal temperature gradients and biological carbon cycling along the east coast of Korea

Abstract

The stable oxygen (delta(18)O) and carbon (delta(13)C) isotopes of the living bivalve shells collected from four localities (Keojin, Jumunjin, Pohang and Kampo) in the shallow waters along the east coast of Korea (Sea of Japan) were measured at close intervals along the maximum growth line of bivalve shells to obtain the isotope profiles. High-resolution delta(18)O profiles exhibit distinct and annual cycles from which the seasonal temperature variations of each locality can be compared. The amplitude of delta(18)O profiles as well as delta(18)O(max) and delta(18)O(min) values demonstrates that each bivalve clearly represents the seasonal temperature variations at the collection site and the latitudinal temperature gradients can be deduced. The delta(13)C profiles show less distinct cyclicity, in contrast to the delta(18)O profiles, which may reflect the stability of available carbon isotope in the water column throughout the collection sites. The small range of variation of the delta(13)C values is likely to be attributed to the shallow water depth above the thermocline where the seasonal change of carbon isotope may not be well recorded. The insignificant level of seasonal blooming of primary production is likely to result in the steady biological cycling of carbon isotope associated with consistent delta(13)C values. However, the northward decrease of mean delta(13)C values may imply either the gradual increase in light carbon (C-12) due to the organic matter oxidation or the different level of primary production activity on the carbon isotope. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.