Description: Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence—although each with important uncertainties—lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments.

Description: Surface delta(15)N(PON) increased 3.92 +/- 0.48 over the course of 20 days following additions of iron (Fe) to an eddy in close proximity to the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. The change in delta(15)N(PON) was associated with an increase in the 〉20 mu m size fraction, leading to a maximal difference of 6.23 between the 〉20 mu m and 〈20 mu m size fractions. Surface delta(13)C(POC) increased 1.18 +/- 0.31 over the same period. After a decrease in particulate organic matter in the surface layer, a second phytoplankton community developed that accumulated less biomass, had a slower growth rate and was characterized by an offset of 1.56 in delta(13)C(POC) relative to the first community. During growth of the second community, surface delta(13)C(POC) further increased 0.83 +/- 0.13. Here we speculate on ways that carboxylation, nitrogen assimilation, substrate pool enrichment and community composition may have contributed to the gradual increase in delta(13)C(POC) associated with phytoplankton biomass accumulation, as well as the systematic offset in delta(13)C(POC) between the two phytoplankton communities.

Description: Quantitative distributions of major functional PFTs of the world ocean improve the understanding of the role of marine phytoplankton in the global marine ecosystem and biogeochemical cycles. Chl-a fluorescence gives insight on the health of phytoplankton and is related to phytoplankton biomass. In this study, global ocean color satellite products of different dominant phytoplankton functional types' (PFTs') biomass and chlorophyll fluorescence retrieved from hyperspectral satellite data using Differential Optical Absorption Spectroscopy applied to phytoplankton (PhytoDOAS) are presented (see also Bracher et al. 2009, Sadeghi et al. 2012a). Data are compared to ocean color products from multispectral sensors and application of the hyperspectral data set in studying phytoplankton dynamics are presented (Sadeghi et al. 2012b, Ying et al. 2012). Although current hyperspectral sensors have poor spatial resolution (〉30kmx30km), they are useful for the verification and improvement of the high spatially resolved multi-spectral ocean color products. Future applications of PhytoDOAS retrieval to other hyperspectral sensors and its synergistic use with information gained from multispectral ocean color sensors are proposed.

Description: Quantitative distribution of major functional phytoplankton types (PFTs) of the world ocean improves the understanding of the role of marine phytoplankton in the global marine ecosystem and biogeochemical cycles. Because phytoplankton pigments absorb light for photosynthesis, satellite sensors detecting the ocean color can monitor phytoplankton on the global scale with reasonable spatial and temporal resolution. The analysis of hyper-spectral satellite data with PhytoDOAS, a method of Differential Optical Absorption Spectroscopy (DOAS) currently specialized for SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) on ENVISAT (details in Bracher et al. 2009, Sadegi et al. 2011), enables to extract the optical signature of marker pigments specific for certain PFTs. With including the calculation of the light penetration depth derived from the retrieval of inelastic scattering, the biomass (chl-a) of the PFTs is calculated and data from 2002-2011 have been processed. The lecture will give insight on the retrieval method and show the global maps of PFT distribution of four different dominant PFTs (diatoms, cyanobacteria, coccolithophores, dinoflagellates). In addition, results of evaluating the PHYTODOAS PFT products with in-situ data obtained from collocated pigment water samples analyzed via HPLC, with other satellite and model PFT products will be shown. The use of these global PFT satellite data sets for studying PFT bloom dynamics in specific oceanic regions or for evaluating an ecosystem model will be presented. References: Bracher A., Vountas M., Dinter T., Burrows J.P., Rottgers R., Peeken I. (2009) Quantitative observation of cyanobacteria and diatoms from space using PhytoDOAS on SCIAMACHY data. Biogeosciences 6: 751-764 Sadeghi A., Dinter T., Vountas M., Taylor B., Peeken I., Bracher A. Improvements to PhytoDOAS method for identification of major phytoplankton groups using high spectrally resolved satellite data. Ocean Sciences (submitted)

Description: The relationship between phytoplankton assemblages and the associated optical properties of the water body is important for the further development of algorithms for large-scale remote sensing of phytoplankton biomass and the identification of phytoplankton functional types (PFTs), which are often representative for different biogeochemical export scenarios. Optical in-situ measurements aid in the identification of phytoplankton groups with differing pigment compositions and are widely used to validate remote sensing data. In this study we present results from an interdisciplinary cruise aboard the RV Polarstern along a north-to-south transect in the eastern Atlantic Ocean in November 2008. Phytoplankton community composition was identified using a broad set of in-situ measurements. Water samples from the surface and the depth of maximum chlorophyll concentration were analyzed by high performance liquid chromatography (HPLC), flow cytometry, spectrophotometry and microscopy. Simultaneously, the above- and underwater light field was measured by a set of high spectral resolution (hyperspectral) radiometers. An unsupervised cluster algorithm applied to the measured parameters allowed us to define bio-optical provinces, which we compared to ecological provinces proposed elsewhere in the literature. As could be expected, picophytoplankton was responsible for most of the variability of PFTs in the eastern Atlantic Ocean. Our bio-optical clusters agreed well with established provinces and thus can be used to classify areas of similar biogeography. This method has the potential to become an automated approach where satellite data could be used to identify shifting boundaries of established ecological provinces or to track exceptions from the rule to improve our understanding of the biogeochemical cycles in the ocean.

Description: The PhytoDOAS algorithm by Bracher et al. (2009), modified by and Sadeghi et al. (2011), enables the concurrent retrieval of global chl-a of phytoplankton groups (diatoms, cyanobacteria, coccolithophores, dinoflagellates) from hyperspectral satellite data, such as measured by SCIAMACHY onboard ENVISAT. For applying the Differential Optical Absorption Spectroscopy (DOAS) fit from 430-530nm the following absorbers are considered in the analysis: atmosphere: O3, O4, NO2, H2Og, Glyoxal, Ring; ocean: inelastic scattering, water, PFTs; The non-differentisl absorption and scattering is approximated with low order polynomial. The global data set of the four phytoplankton groups is avaiable on a monthly resolution for July 2002 until today.

Description: Quantitative distributions of major functional PFTs of the world ocean improve the understanding of the role of marine phytoplankton in the global marine ecosystem and biogeochemical cycles. Chl-a fluorescence gives insight on the health of phytoplankton and is related to phytoplankton biomass. In this study, global ocean color satellite products of different dominant phytoplankton functional types' (PFTs') biomass and chlorophyll fluorescence retrieved from hyperspectral satellite data using Differential Optical Absorption Spectroscopy (DOAS) are presented. Global biomass distributions from 2002 -2010 of different dominant PFTs (diatoms, cyanobacteria, coccolithophores, dinoflagellates) are derived with PhytoDOAS, the currently specialized method of DOAS for deriving chl-a of PFTs from satellite data of SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) on ENVISAT (details in Bracher et al. BG 2009, Sadeghi et al. OSD 2011). Results of the global maps of PFT distribution are validated with global PFT data derived from using Hirata et al. (2011) approach of parameterizing satellite chl-a from Globcolour with collocated HPLC pigment data. In addition, SCIAMACHY monthly mean data of coccolithophore biomass in three selected oceanic regions were compared to related satellite products, including the total surface phytoplankton, i.e., total chlorophyll-a (from GlobColour merged data) and the particulate inorganic carbon (from MODIS-Aqua). The DOAS method was also adapted to detect successfully globally the filling-in of Fraunhofer Lines caused by chlorophyll fluorescence in the backscattered SCIAMACHY spectra and compared to data of fluorescence-line-height from MODIS and MERIS. The results suggest that DOAS is a valid method for retrieving PFTs and chlorophyll fluorescence from hyper-spectral measurements. Overall, DOAS products are much less dependent on a priori information than common multi-spectal ocean colour products which result from empirical and semi-analytical methods. In addition, the DOAS technique has the advantage to overcome problems with an accurate atmospheric correction encountered for the traditional multi-spectral ocean color products because only the differential signals of both atmospheric and oceanic absorbers are fitted while all other (broad-band) absorption and scattering processes are successfully approximated with an low order polynomial. Although current hyperspectral sensors have poor spatial resolution (〉30kmx30km), they are useful for the verification and improvement of the high spatially resolved multi-spectral ocean color products. Future applications of PhytoDOAS retrieval to other hyperspectral sensors and its synergistic use with information gained from multispectral ocean color sensors are proposed.