Spatial-temporal variability of phytoplankton types in the Southern Ocean
During the last years, the potential effects of climate change on the polar regions was recognized globally. These regions are considered as indicators of global warming by the observation of ice melting and represent a sink of atmospheric carbon due to photosynthesis in the phytoplankton. The Antarctic region attracts special attention since studies suggested that the Southern Ocean was a strong sink of atmospheric CO2 during the last glacial age due to increased phytoplankton production (Moore et al., 2000). Through photosynthesis CO2 is fixed in the sea surface. The incorporated carbon is then exported to the deep sea by sinking of organic particles. The fixation and sinking of atmospheric carbon are parts of a process called biological pump. The intensity of this process strongly depends on the size and composition of phytoplankton cells in addition to the structure of the trophic community. Therefore, information on phytoplankton composition is needed for a better estimate of the oceanic primary production and to assess the contribution of different phytoplankton functional types (PFT) to the oceanic carbon cycle.
In this context, the main goal of my research is to investigate the spatial-temporal variability of phytoplankton primary production in the Circumpolar Southern Ocean (CSO) looking at different PFT. The research is mainly conducted using remote sensing data. Combining remote sensing with traditional oceanographic data can be a useful tool to investigate polar oceans due to its remoteness, providing a cost effective solution for a good coverage of these regions.
The first task is to study the variability of the main PFT retrieved with the PhytoDOAS method from SCIAMACHY data (according to Bracher et al. 2009). As a validation strategy, a regional approach of the method developed by Uitz et al. (2006) for quantifying the chlorophyll-a concentration (chl-a) associated to three phytoplankton size-classes (microplankton, nanoplankton and picoplankton) is tested (Figure 1). After that, the previous results will be used to model of primary production of the PFT in the SO. Finally, changes in the PFT distribution will be analyzed in relation to the regional climate variability (e.g. sea ice) and large-scale climatic conditions.
Figure 1 – The upper panel shows the distribution of the chlorophyll-a associated with microplankton within 1.5*euphotic layer (Zeu) determined with the Uitz et al. (2006) approach. The lower panel displays the distribution of the chlorophyll-a associated with diatoms using the PhytoDOAS method (Bracher et al., 2009). Both images represent the monthly mean of chlorophyll-a concentration for January 2006.
Acknowledgments:
This work is founded by CAPES, Brazil, through a PhD studentship and by the Helmholtz Innovative Network Fund via the project PHYTOOPTICS.
References:
Bracher, A., Vountas, M., Dinter, T., Burrows, J.P., Röttgers, R., Peeken, I., 2009. Quantitative observation of cyanobacteria and diatoms from space using PhytoDOAS on SCIAMACHY data. Biogeosciences, 6, 751-764.
Moore, J. K.; Abbot, M. R.; Richman, J. G.; Nelson, D. M. The Southern Ocean at the Last Glacial Maximum: A Strong Sink for Atmospheric Carbon Dioxide. Global Biogeochemical Cycles, v. 14, p. 455-475, 2000.
Uitz, J., Claustre, H., Morel, A., Hooker, S. B., 2006. Vertical distribution of phytoplankton communities in open ocean: An assessment based on surface chlorophyll. J. Geophys. Res. 111: C08005, doi:10.1029/2005JC003207.
