Ocean Climate Coupling in the Tropical Pacific Ocean Over the Past 50 Years: Implications and Feedbacks
Xiujun
Wendy
Wang, University of Maryland, College Park, MD 20742 USA, wwang@essic.umd.edu
(Presenting)
Raghu
Murtugudde, University of Maryland, College Park, MD 20742, ragu@essic.umd.edu
Antonio
Busalacchi, University of Maryland, College Park, MD 20742, tonyb@essic.umd.edu
The tropical Pacific plays an important role in climate because of its significant air-sea exchanges of heat, freshwater, and carbon dioxide (CO2), and its direct linkage to climate variability: the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Here, we apply a basin-scale physical-biogeochemical model to study the responses of tropical Pacific ecosystem, biogeochemistry and carbon cycle to climate forcing over the past 50 years. Model simulations show strong ENSO impacts on the spatial and temporal variations of surface nutrient concentration, phytoplankton biomass, carbon uptake, and sea-to-air CO2 flux. There are also significant decadal variations in physics and biogeochemistry associated with the 1977 and 1997/98 PDO shifts. The 1977 regime shift caused 1°C warming and ~50% reduction in iron concentration in the Niño3.4 area. While there is a large decrease in phytoplankton growth and biomass, reduction in carbon uptake is smaller than expected, due to phytoplankton photoadaption, which increases carbon to chlorophyll ratio in the upper euphotic zone. Photoadaption also results in clearer water near the surface, allowing more solar radiation to penetrate thus enhances sub-surface production, and leading to less heating near the ocean surface. Our studies suggest that under warm climate, the tropical Pacific Ocean releases less CO2, and absorbs more heat, creating negative feedbacks to the atmosphere.
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