The seasonal evolution of dissolved inorganic carbon (DIC) and CO 2 air-sea fluxes in the Jiaozhou Bay was investigated by means of a data set from four cruises covering a seasonal cycle during 2003 and 2004. The results revealed that DIC had no obvious seasonal variation, with an average concentration of 2035 µmol kg-1 C in surface water. However, the sea surface partial pressure of CO 2 changed with the season. pCO 2 was 695 µatm in July and 317 µatm in February. Using the gas exchange coefficient calculated with Wanninkhof's model, it was concluded that the Jiaozhou Bay was a source of atmospheric CO 2 in spring, summer, and autumn, whereas it was a sink in winter. The Jiaozhou Bay released 2.60 × 10 11 mmol C to the atmosphere in spring, 6.18 × 10 11 mmol C in summer, and 3.01 × 10 11 mmol C in autumn, whereas it absorbed 5.32 × 10 10 mmol C from the atmosphere in winter. A total of 1.13 × 10 12 mmol C was released to the atmosphere over one year. The behaviour as a carbon source/sink obviously varied in the different regions of the Jiaozhou Bay. In February, the inner bay was a carbon sink, while the bay mouth and the outer bay were carbon sources. In June and July, the inner and outer bay were carbon sources, but the strength was different, increasing from the inner to the outer bay. In November, the inner bay was a carbon source, but the bay mouth was a carbon sink. The outer bay was a weaker CO 2 source. These changes are controlled by many factors, the most important being temperature and phytoplankton. Water temperature in particular was the main factor controlling the carbon dioxide system and the behaviour of the Jiaozhou Bay as a carbon source/sink. The Jiaozhou Bay is a carbon dioxide source when the water temperature is higher than 6.6ºC. Otherwise, it is a carbon sink. Phytoplankton is another controlling factor that may play an important role in behaviour as a carbon source or sink in regions where the source or sink nature is weaker.
SUMMARY: The vertical distributions of bulk and molecular biomarker compositions in the samples from four sediment cores of the Changjiang (Yangtze River) Estuary were determined. The changes in the bulk and molecular compositions with depth suggest that there have been recent changes in the marine autogenic and terrigenous supply. In the site at the boundary of the turbidity maximum (Site 8) and the most southern site (Site 26), the autogenic and allochthonous inputs make almost the same contribution to sedimentary organic matter. In the site close to the river mouth (Site 11), the organic matter mainly comes from the terrestrial input carried by the Changjiang water, whereas, in the most eastern site (Site 17), the organic matter consists of a mixture of recent and ancient Changjiang delta sedimentary residues. Significant downcore fluctuations were observed in the patterns of the bulk and molecular compositions, as well as in several biomarker ratios, which also indicates the different anoxic conditions at different depths of the core besides the source variation. In addition, the distributions of molecular compounds show that the organic matter is a mixture of immature and mature in the sediments of the four cores, which further indicates that the microbial activity is active in anoxic conditions, especially in the surface sediment. The vertical distributions of molecular compounds also show that the autogenic marine organic matter is more easily degraded, and that the molecular compounds evolve from unstable steric configurations to stable ones in the early diagenetic processes.Keywords: bulk parameter, molecular characterization, sediment, hydrocarbon, the Changjiang Estuary.RESUMEN: FUENTES Y PRESERVACIÓN DE MATERIA ORGÁNICA EN SEDIMENTOS RECIENTES DEL ESTUARIO DEL RÍO YANGTZE, CHINA.-Este artículo analiza la distribución vertical de la composición mayoritaria y de biomarcadores moleculares en muestras de sedimentos de cuatro testigos obtenidos en el estuario del río Yangtze. Los cambios de composición en profundidad sugieren variaciones recientes de los aportes autógenos y terrígenos. En el máximo de turbidez y en sus limites (estación 8) y en la estación más al sur (estación 26), los aportes autógenos y alóctonos tienen casi la misma contribución a la materia orgánica sedimentaria. En la estación próxima a la desembocadura (estación 11), la materia orgánica procede principalmente de los aportes terrestres del río Yangtze, mientras que en la estación situada mas al Este (estación 17), la materia orgánica consiste en una mezcla de aportes recientes del río Yangtze y de residuos sedimentarios de un antiguo delta del mismo río. Fluctuaciones significantes de la composición mayoritaria y molecular, así como de biomarcadores, fueron observadas a lo largo de los testigos, lo cual indica también condiciones de anoxia diferentes a distintas profundidades, aparte de las diferencias en la procedencia de los sedimentos. Además, la distribución de compuestos moleculares muestra que la materia orgánica es una mezcla ...
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