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Biogeochemistry in oligotrophic ocean gyres
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Quantum yield of photosynthesis in oligotrophic gyres and its application to estimate primary production from remote sensing
Tuesday 8th @ 1530-1550, Multifunction Hall
Zhongping Lee* , School of the Environment, University of Massachusetts, Boston, MA, USA
Maria Laura Zoffoli, Mer Molecules, Facultes des Sciences et Techniques, University de Nantes, Nantes, France
John Marra, Department of Earth and Environmental Sciences, Brooklyn College (CUNY), Brooklyn, NY, USA
Presenter Email: zpli2015@xmu.edu.cn |
| Quantum yield of photosynthesis (Phi) expresses the efficiency of phytoplankton for Carbon fixation given certain amount of absorbed light. This parameter is key to obtain reliable estimates of primary production in oceans based on remote sensing products (PPsat). Several works have shown that Phi changes temporally, vertically and horizontally in the water column, where the primary factor ruling its variability is light intensity. In this work, we estimated Phi utilizing long time-series of in situ data in the North Subtropical Oligotrophic Gyres, at HOT and BATS stations (Pacific and Atlantic oceans, respectively). Then, Phi m (the maximum quantum yield) and K Phi (light intensity at half Phi m) were calculated from Phi. Median annual of in situ Phi m was found as 0.020 and 0.063 mol C mol photons-1 at HOT and BATS, respectively, with higher values in winter. K Phi values were 7.6 and 10.8 mol photons m-2 d-1 for HOT and BATS, respectively. Temporal variability in K Phi showed the highest values in summer. We further proposed dynamical parameterizations for both regions using independent environmental factors as proxies: temperature for Phi m and light intensity for K Phi. Such parameterizations were finally included in PPsat models based in phytoplankton absorption (PPsat-aphy-based) and a comparison was made with the conventional VGPM model, the widest used PPsat model based in chlorophyll concentration (PPsat-chl-based). Our findings showed that the PPsat-aphy-based model coupled with dynamical parameterization improves PP estimates. While PPsat-chl-based underestimated PP with differences of 62.8% at HOT and 37.8% at BATS, PPsat-aphy-based showed a similar magnitude with in situ PP and differences of 7.7% at HOT and 26% at BATS. PPsat-aphy-based was also able to better reproduce the seasonal cycle of PP in both areas. These results further advocate the use of phytoplankton absorption and quantum yield for the estimation of basin scale primary production via ocean color remote sensing. |
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