Open AccessMain controlling factors of coral skeletal carbon isotopic composition and skeletal extension rate: High‐resolution study at Hainan Island, South China Sea
Author(s) -
Shimamura Michiyo,
Irino Tomohisa,
Oba Tadamichi,
Xu Guoqiang,
Lu Bingquan,
Wang Luejiang,
Toyoda Kazuhiro
Publication year - 2008
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2007gc001789
Subject(s) - coral , water column , oceanography , coral bleaching , seawater , environmental science , δ13c , geology , east asian monsoon , atmospheric sciences , monsoon , stable isotope ratio , physics , quantum mechanics
To understand the main controlling factors of coral skeletal carbon isotope ratio ( δ 13 Cc), we undertook high‐temporal‐resolution (∼1.5 d) measurements of δ 13 Cc for Porites lutea collected from the east coast of Hainan Island, China. The results were compared with factors that have previously been proposed to control coral δ 13 Cc: skeletal extension rate, carbon isotope composition of dissolved inorganic carbon in seawater ( δ 13 Cw), and light availability to the coral colony. Hainan Island is characterized by strong summer and winter monsoons that result in distinctive seasonal variations in environmental and coral growth conditions. Compared with other tropical/subtropical areas, this climate is advantageous in evaluating the effects of different environmental factors on δ 13 Cc. We found that δ 13 Cc varied in phase with solar radiation. Increased total suspended matter (TSM) in the water column was found to reduce δ 13 Cc. These data suggest that light availability, the interplay between solar intensity and attenuation of light by TSM in the water column, is the main controlling factor of δ 13 Cc in the studied coral. In addition, slower skeletal extension was found during periods of lower solar radiation and high turbidity than other periods of similar temperature conditions, suggesting that both factors influence skeletal growth. Seasonal variations in δ 13 Cw were not only too narrow in range to explain the observed δ 13 Cc, but also showed an opposite trend to that of δ 13 Cc. We also failed to detect δ 13 Cc variations due to the kinetic isotope effect (i.e., the discrimination of heavier isotopes during CO 2 hydration and hydroxylation and the resulting simultaneous negative shifts of δ 13 Cc and δ 18 Oc from equilibrium values), despite large variations in the measured skeletal extension rate. This outcome probably reflects the high skeletal extension rates of the studied coral (average, 15 mm/a; minimum, 4 mm/a).