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 photoreactivity. 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 a325 = 0.36 ± 0.02 m- 1, average a443 = 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.
Bibliographical noteFunding Information:
Incident UV was measured with a PUV 2500 Biospherical Instrument meter in experiments #2, 3, 4 and 5. Incident radiation data were not available for the rest of the experiments. Thus, we obtained data on incident radiation from Palmer Station (Anvers Island) provided by the NSF UV Monitoring Network, operated by Biospherical Instruments Inc. under a contract with the US National Science Foundation's Office of Polar Programs via Raytheon Polar Services Company. Data on UV from Palmer Station was within 14%, on average, of estimates derived at the location where the experiments were conducted.
We thank the crew of R/V Las Palmas and Hespérides and Marine Technology Unit for their assistance in the field, María Calleja for DOC analyses, and Regino Martínez for chlorophyll a analyses. We also acknowledge two anonymous reviewers for their constructive comments on a previous version of this MS. This work was funded by the Spanish Ministry of Science and Technology (ICEPOS, REN2002-04165-CO3-02 to CD and DISPAR, CGL2005-00076 to IR). E. O.-R. was supported by fellowships of the Spanish Ministry of Science and Education and University of Granada .
- Dissolved organic matter
- Southern ocean
ASJC Scopus subject areas
- Environmental Chemistry
- Water Science and Technology