Distribution and photoreactivity of chromophoric dissolved organic matter in the Antarctic Peninsula (Southern Ocean)
Résumé
Chromophoric dissolved organic matter (CDOM) plays a key role regulating light attenuation in the ocean. This optically reactive pool of organic matter is driven by several physical and biological processes such as photobleaching, photohumification, and biogeneration, that act as primary sinks and sources of CDOM. In this study. we described the geographical and vertical distribution of CDOM in the Antarctic Peninsula area (Southern Ocean), and assessed its potential driving factors, with special emphasis on CDOM photo reactivity. CDOM values were between the detection limit and 2.17 m(-1) at 325 nm and between the detection limit and 0.76 m(-1) at 443 nm (average a(325) = 0.36 +/- 0.02 m(-1), average a(443) = 0-11 +/- 0.01 m(-1)). with the highest values inside Deception Island in 2004, and the lowest in the Eastern Bransfield Strait. In Bellingshausen Sea, CDOM was higher below the mixed layer suggesting a significant role of photobleaching. By contrast in the Weddell Sea maximum values were found within the mixed layer. In the Weddell Sea, a positive correlation between CDOM and both chlorophyll a and bacterial production and a negative correlation with salinity suggest a biological source of CDOM likely associated to ice melting. Salinity was also negatively related to the spectral slopes from 275 to 295 nm, considered a good proxy for DOM molecular weight. The experimental results demonstrate the photoreactive nature of CDOM, with half lives from 2.1 to 5.1 days due to photobleaching in the upper layer and duplication times from 4.9 to 15.7 days due to photohumification, that highlight the highly dynamic nature of CDOM in this area