A numerical model study on impact of vertical stratification on biological production and carbon export in the open ocean
Surface warming by solar radiation will form a subsurface thermocline in the ocean,while freshening by river runoffs,rainfall or ice melting will form a halocline in the surface.Thermocline or halocline can induce density stratification at different depths,preventing the vertical mixing of the energy and materials in the ocean.To study the impact of stratification at different depths on the ocean ecosystem,a simplified one-dimensional nutrient-phytoplankton-detritus model is used.Our results show that both surface and subsurface stratification remarkably inhibit the upward transport of nutrient,making the nutrient of the upper layer to be severely depleted.The phytoplankton biomass above the Deep Chl a Maximum(DCM)layer in both scenarios diminish and the DCM layers becomes thinner,resulting in a decrease of the biological production in the euphotic zone and carbon export to the deep ocean.Stronger stratification(weaker vertical mixing)or thicker stratification layer causes greater diminish of biological production and carbon export.Compared with the surface stratification,the subsurface stratification can further induce a deepened and smaller DCM layer and exert a larger impact on the biological production and carbon export.Our study indicates that under the influence of climate change and global warming,the intensified stratification induced by the warmer and fresher upper ocean may have significant impact on the ocean biological production and biogeochemical cycles.
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