Water and Carbon Cycles as Linked by Space-Based Observation of Salinity

Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. The accumulation of greenhouse gases, such as, carbon dioxide (CO2) and water vapor is believed to accentuate the imbalance and lead to global warming. The quantification of ocean as the source and sink of these greenhouse gases is still not sufficient. The association of sea surface salinity in global water cycle and climate change has been traditionally studied through the examination of its tendency and advection as manifestation of ocean’s heat and water fluxes with the atmosphere and the thermal-haline circulation in the ocean. The perturbation of latent fluxes also requires an atmospheric radiation response. Besides the link of salinity to greenhouse warming through water balance, this study will focus on the effect of changing salinity on CO2 flux between the ocean and the atmosphere. We have built statistical models to estimate the partial pressure of carbon dioxide (pCO2) and ocean acidification (in terms of total alkalinity and pH) using spacebased data. PCO2 is a critical parameter to estimate CO2 flux that may mitigate greenhouse warming and may cause ocean acidification, which is detrimental to marine lives and ecology. Before we had sufficient spacebased salinity measurements coincident with in situ pCO2 measurement, we trained our statistical models to use satellite sea surface temperature and chlorophyll, with one model using salinity climatology and the other without. We found significant differences between the outputs of the two models in regions of strong hydrological forcing through river discharge and surface water flux. The pCO2 output follows the seasonal salinity advection of the Amazon outflow. The seasonal reversal of salinity advection between Bay of Bengal and Arabian Sea are followed by change of pCO2 and total alkalinity. At shorter time scales, the signatures of rain associated with intraseasonal organized convection of summer monsoon can be detected. We have observed distribution agreement of among pCO2, surface salinity, and surface water flux for variations from a few days to a few years under the Pacific Intertropical Convergence Zone; the agreement varies slightly with season and longitudes and the reason is under study.