Justiniano-Santos, Aurora M.

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    Influence of Saharan aerosols on phytoplankton biomass in the tropical North Atlantic Ocean
    (2010-12) Justiniano-Santos, Aurora M.; Armstrong, Roy A.; College of Arts and Sciences - Sciences; Detrés, Yasmín; López, José M.; Gilbes Santaella, Fernando; Aponte, Nilda; Department of Marine Sciences; Navarro, Ana
    Atmospheric transport of aerosols from desert regions of Africa supply nutrients, such as iron, to oligotrophic oceanic waters. Phytoplanktonic organisms in surface waters use bio-available Fe, increasing their rate of photosynthesis. This work investigates the possible atmospheric Fe fertilization of oligotrophic North Atlantic and Caribbean waters. Level 3 weekly averaged images from SeaWiFS, MODIS Terra and MODIS Aqua satellite sensors were used to retrieve aerosol optical thickness (AOT) and chlorophyll concentration (Chl_a) data from Sept. 1997 through Dec. 2007. Results are presented for three areas in the Tropical North Atlantic Ocean and the Caribbean Sea, located at 17.5°N, 67.0°W, Caribbean Time Series Station (CaTS), 19°N, 57°W Western Atlantic Ocean and 20°N, 67°W Atlantic, North of Puerto Rico. A time series analysis exhibited a seasonal cycle with a summer maximum for mean AOT concentration. The strongest correlation between both parameters was observed for the Western Atlantic Ocean with a time-lag of approximately 1 month between AOT and Chl_a. Visible reflectance spectroscopy (VRS) and trace element analysis were used to assess the presence of Fe in Saharan dust. Iron content was measured in samples from desert regions in Africa, starting from their source (African soil samples), their transformation across the Atlantic Ocean (Saharan dust collected at sea) and finally in the fraction reaching remote land areas (filtered air samples collected in Puerto Rico). Iron oxide mineral content was determined using reflectance spectroscopy and first derivative analysis. Distinctive peaks of two iron-bearing minerals, hematite and goethite, in the first derivatives were observed (555 to 580 for hematite and 435 nm for goethite). In addition, Fe and Al trace element concentration was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The analysis showed evidence of the presence of Fe in all our samples. Results showed higher percent Fe in the finer particle size samples transported away from the desert. Finally, satellite and in-situ AOT and Chl_a measurements were compared for the Tropical North Atlantic Ocean during March 2004 to observe the potential of satellite measurements in estimating atmospheric and oceanographic bio-optical properties. Aerosol and Chl _a measurements were obtained onboard the NOAA Ship Ronald H. Brown during the Aerosol and Oceanographic Science Expedition (AEROSE, February 29 - March 26 2004). This data were compared with two GIOVANNI (GES DISC Interactive Online Visualization and ANalysis Infrastructure) products, AOT (MODIS Aqua) and Assimilated Total Chlorophyll. Results showed a strong linear relation (R2 = 0.86) between satellite and field AOT measurements. A strong relationship (R2 = 0.76) was also observed between shipboard and satellite Chl_a, although the satellite product tended to underestimated chlorophyll concentrations relative to the field data. Also, monthly Giovanni’s AOT and Chl_a products were compared to determine if a relationship between African dust input and Chl_a concentration can be established using Giovanni’s satellite data. A time-lag of one month between AOT and Chl_a was also observed. Since the studied period (March 2004) coincided with one of the biggest dust storms for this season we examined AOT values and the North Atlantic Oscillation (NAO) index for the Western Atlantic Ocean Station (19ºN, 57ºW) to determine if the unusual dust event encounter during March 2004 was related to the NAO. A weak linear relationship between both parameters was observed.