Olson Elise M. B.

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Elise M. B.

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  • Article
    The depth-distribution of nitrogen fixation by Trichodesmium spp. colonies in the tropical–subtropical North Atlantic
    (Elsevier, 2015-07-02) Olson, Elise M. B. ; McGillicuddy, Dennis J. ; Dyhrman, Sonya T. ; Waterbury, John B. ; Davis, Cabell S. ; Solow, Andrew R.
    Nitrogen fixation is an important yet still incompletely constrained component of the marine nitrogen cycle, particularly in the subsurface. A Video Plankton Recorder (VPR) survey in the subtropical North Atlantic found higher than expected Trichodesmium colony abundances at depth, leading to the hypothesis that deep nitrogen fixation in the North Atlantic may have been previously underestimated. Here, Trichodesmium colony abundances and modeled nitrogen fixation from VPR transects completed on two cruises in the tropical and subtropical North Atlantic in fall 2010 and spring 2011 were used to evaluate that hypothesis. A bio-optical model was developed based on carbon-normalized nitrogen fixation rates measured on those cruises. Estimates of colony abundance and nitrogen fixation were similar in magnitude and vertical and geographical distribution to conventional estimates in a recently compiled climatology. Thus, in the mean, VPR-based estimates of volume-specific nitrogen fixation rates at depth in the tropical North Atlantic were not inconsistent with estimates derived from conventional sampling methods. Based on this analysis, if Trichodesmium nitrogen fixation by colonies is underestimated, it is unlikely that it is due to underestimation of deep abundances by conventional sampling methods.
  • Article
    Mesoscale eddies and Trichodesmium spp. distributions in the southwestern North Atlantic
    (John Wiley & Sons, 2015-06-08) Olson, Elise M. B. ; McGillicuddy, Dennis J. ; Flierl, Glenn R. ; Davis, Cabell S. ; Dyhrman, Sonya T. ; Waterbury, John B.
    Correlations of Trichodesmium colony abundance with the eddy field emerged in two segments of Video Plankton Recorder observations made in the southwestern North Atlantic during fall 2010 and spring 2011. In fall 2010, local maxima in abundance were observed in cyclones. We hypothesized surface Ekman transport convergence as a mechanism for trapping buoyant colonies in cyclones. Idealized models supported the potential of this process to influence the distribution of buoyant colonies over time scales of several months. In spring 2011, the highest vertically integrated colony abundances were observed in anticyclones. These peaks in abundance correlated with anomalously fresh water, suggesting riverine input as a driver of the relationship. These contrasting results in cyclones and anticyclones highlight distinct mechanisms by which mesoscale eddies can influence the abundance and distribution of Trichodesmium populations of the southwestern North Atlantic.