[A-OS13] Exploring Variability and Changes in Ocean Biogeochemical Cycles

[AOS13-01] Modeling marine biogeochemical processes fluctuated by tropical Atlantic climate variability

★Invited Papers

*Shunya Koseki¹, Jerry Tjiputra², Flippa Fransner¹, Lander Crespo¹, Noel Keenlyside¹, David Rivas³, Rubén Vázquez⁴, William Cabos⁴, Claudia Gutiérrez⁴, Dmitry Sein⁵, Marie-Lou Bachèlery⁶, Elodie Martinez⁷, Etienne Pauthenet⁷, Patrice Brehmer⁷ (1.Geophysical Institute, University of Bergen, 2.NORCE Norwegian Research Center, 3.Departamento de Oceanografía Biológica, CICESE, 4.Departamento de de Física y Matemáticas, Universidad de Alcalá, 5.Alfred Wegener Institute for Polar and Marine Research, 6.CMCC Foundation – Euro-Mediterranean Center on Climate Change, 7.IRD, CNRS, University Brest, Ifremer)

Keywords:Tropical Atlantic, Climate variability, Carbon flux, Chlorophyll-a

Tropical Atlantic Ocean is one of the oceanic regions where inter-annual to multi-decadal variability is dominant. Nevertheless, there are less studies carried out to investigate how marine biogeochemical processes respond to such climate variability compared to the tropical Pacific. One of the reasons can be because state-of-the-art Earth system models (e.g., CMIP-class ESMs) still have difficulty to reproduce the climate state of the tropical Atlantic (e.g., sea surface temperature bias in the upwelling regions).

This study investigates impacts of climate variability in the tropical Atlantic (Atlantic Niño and Dakar Niño) on carbon cycle and marine ecosystem with several types of ESMs and observational data. The observation and a Norwegian ESM simulation showed that sea-air CO2 flux has a di-pole structured anomaly, negative in the west and positive in the east, corresponding to the Atlantic Niños (warm event). A carbon dynamics analysis revealed that the negative anomaly of CO2 flux is attributed to the freshwater flux associated with precipitation anomaly. More discussion on the mechanism of CO2 flux anomaly will be given in the presentation. In addition, we will discuss some results of chlorophyll-a response to the Dakar Niño, which is warm event along the western African coast, based on various methods and data (satellite, ocean reanalysis, storm-resolving ESM and deep learning).