Lidar calibrated satellite sensed CDOM in the Southern Ocean

Luca Fiorani, Roberta Fantoni, Antonio Palucci
ENEA, Frascati, 00044, Italy
fiorani@frascati.enea.it

Luigi Lazzara, Ilaria, Nardello
University of Florence, Florence, 50125, Italy

Igor G. Okladnikov
SCERT, Tomsk, 634055, Russia

ABSTRACT

The plausibility of a process that links oceanic dymethil sulfide (DMS) with climate has been discussed years ago by Carlson et al. (1987). Recently, Toole and Siegel (2004) demonstrated the connection between ultraviolet radiation fluxes in the open ocean and feedbacks in the global climate system, driven by the DMS emitted by phytoplankton cells. It would desirable to have information on the global distribution and dynamics of DMS but, unfortunately, the present ocean colour satellite radiometers do not provide surface layer DMS concentrations. DMS concentration, however, is significantly correlated with the absorption coefficient for chromophoric dissolved organic matter (CDOM) (Toole et al. 2002), and some algorithms have been suggested for the calculation of the CDOM absorption coefficient from ocean colour data products (Aiken et al. 1995, Hoge et al. 1999, Barbini et al. 2002, Siegel et al. 2002, Johannessen et al. 2003). Nevertheless, the debate on the satellite retrieval of CDOM is still open: e.g. a standard CDOM algorithm is not available for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), even if the SeaWiFS Project Office recognized its usefulness (McClain et al. 2004).

In this framework, we present a lidar calibrated CDOM algorithm for satellite products. It is based on the data collected by the ENEA Lidar Fluorosensor (ELF) onboard the research vessel Italica during the 18^th Italian Antarctic Oceanographic Campaign, carried out from 5 January to 5 March 2003 in the Ross Sea, with particular emphasis on coastal zones and polynya areas. ELF is based on laser-induced fluorescence (LIF) and continuously provides concentrations of CDOM and phytoplankton pigments all along the ship's track. The approach of this study is similar to that followed for a lidar calibrated chlorophyll-a algorithm (Barbini et al. 2003), but requires the retrieval of the CDOM absorption coefficient from fluorescence measurements (Hoge et al. 1995).

Although the results are preliminary, they provide valuable information on distribution and dynamics of CDOM in the Southern Ocean, one of the less studied but more interesting zones of our planet from the biological point of view because of a series of circumpolar fronts that result in the definition of different oceanographic provinces, where the development of endemic phytoplankton is favoured (Boyd 2002). The CDOM data are useful both for understanding the DMS distribution and dynamics, and the biogeochemical factors affecting primary productivity (PP). Finally, the information gathered on DMS and PP will improve our comprehension of the world climate.

Last Update: 2005-03-15