5:15 PM - 6:45 PM
[AOS13-P08] Variability of the euphotic depth over the global ocean: extension from the Arctic study
Keywords:Euphotic depth, photosyntesis, photobreaching, thermal energy, ocean
Transport of the radiative energy from the Sun into the Earth’s oceans play three major roles on physical, chemical and biological aspects of the oceanography: (i) providing thermal energy into subsurface layers of oceans, (ii) causing photo-breaching of chemical compounds such as the chromophoric dissolved organic matter (CDOM), and (iii) fueling primary production via photosynthetic process. All three roles are ubiquitously found in the global oceans. The radiative energy into the ocean is known to be regulated by planetary motion of the Earth: the higher the solar altitude observed on the Earth’s surface is, the deeper the penetration of the solar radiation is at that observation point. This is due to a change of path length of the solar radiation penetrating from the surface to a depth of interest. On the other hand, the previous study by the Author, which was dedicated to the Arctic ocean, revealed that the optically active agents within the seawater can significantly vary the penetration depth of the photosynthetically active radiation (PAR), or the euphotic depth (zeu), too. In fact, the effects of the optically active agents on zeu outcompeted the effects of the planetary motion in some parts of the Arctic oceans, as a dominant mode of the variability of zeu over the seasonal and inter-annual scales. Here the Author extended the analysis to the global oceans to find out if there are any other oceans where the optically active agents can exhibit larger effects on zeu. The result shows that not only the Arctic but also the Southern ocean and even the equatorial ocean exhibit stronger effects from the optically-active agents. Especially, the absorption of PAR by CDOM was found a main agent for the effects in the Southern ocean while the absorption of phytoplankton in the equatorial ocean.