Kranz Sven A.
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PreprintGross and net production during the spring bloom along the Western Antarctic Peninsula( 2014-10) Goldman, Johanna A. L. ; Kranz, Sven A. ; Young, Jodi N. ; Tortell, Philippe D. ; Stanley, Rachel H. R. ; Bender, Michael L. ; Morel, Francois M. M.This study explores some of the physiological mechanisms responsible for high productivity near the shelf in the Western Antarctic Peninsula despite a short growing season and cold temperature. We measured gross and net primary production at Palmer Station during the summer 2012/2013 via three different techniques: 1) incubation with H218O; 2) incubation with 14CO2; and 3) in situ measurements of O2/Ar and triple oxygen isotope. Additional laboratory experiments were performed with the psychrophilic diatom Fragilariopsis cylindrus. During the spring bloom, which accounted for more than half of the seasonal gross production at Palmer Station, the ratio of net to gross production reached a maximum greater than ~60%, among the highest ever reported. The use of multiple-techniques showed that these high ratios resulted from low heterotrophic respiration and very low daylight autotrophic respiration. Laboratory experiments revealed a similar ratio of net to gross O2 production in F.cylindrus and provided the first experimental evidence for an important level of cyclic electron flow (CEF) in this organism. The low ratio of community respiration to gross primary production observed during the bloom at Palmer Station may be characteristic of high latitude coastal ecosystems and partially supported by a very active CEF in psychrophilic phytoplankton.
ArticleMetabolic balance of coastal Antarctic waters revealed by autonomous pCO2 and ΔO2/Ar measurements(John Wiley & Sons, 2014-10-03) Tortell, Philippe D. ; Asher, Elizabeth C. ; Ducklow, Hugh W. ; Goldman, Johanna A. L. ; Dacey, John W. H. ; Grzymski, Joseph J. ; Young, Jodi N. ; Kranz, Sven A. ; Bernard, Kim S. ; Morel, Francois M. M.We use autonomous gas measurements to examine the metabolic balance (photosynthesis minus respiration) of coastal Antarctic waters during the spring/summer growth season. Our observations capture the development of a massive phytoplankton bloom and reveal striking variability in pCO2 and biological oxygen saturation (ΔO2/Ar) resulting from large shifts in community metabolism on time scales ranging from hours to weeks. Diel oscillations in surface gases are used to derive a high-resolution time series of net community production (NCP) that is consistent with 14C-based primary productivity estimates and with the observed seasonal evolution of phytoplankton biomass. A combination of physical mixing, grazing, and light availability appears to drive variability in coastal Antarctic NCP, leading to strong shifts between net autotrophy and heterotrophy on various time scales. Our approach provides insight into the metabolic responses of polar ocean ecosystems to environmental forcing and could be employed to autonomously detect climate-dependent changes in marine primary productivity.