The IOD Impacts on the Indian Ocean Carbon Cycle

Abstract

This paper examines the impacts of Indian Ocean Dipole (IOD) Mode on the upper ocean carbon cycle and its variability in the Indian Ocean with available biogeochemical observations and 60 years (1960-2019) of model outputs from a global ocean biogeochemical general circulation model. The upper ocean carbon cycle variability of the Indian Ocean is faithfully reproduced by the model when compared with available observations. The IOD leads to a substantial sea-to-air CO 2 flux variability in the southeastern tropical Indian Ocean over a broad region (70-105°E, 0-20°S), with more focus near the coast of Java-Sumatra due to the prevailing upwelling dynamics and associated westward propagating anomalies. The sea-to-air CO 2 fluxes, surface ocean partial pressure of CO 2 (pCO 2), the concentration of dissolved inorganic carbon (DIC), and ocean alkalinity (ALK) range as much as ±1.0 mole m −2 year −1 , ±20 μatm, ±35 μmole kg −1 , and ±22 μmole kg −1 within 80-105°E, 0-10°S due to IOD. The DIC and ALK are significant drivers of pCO 2 variability associated with IOD. The roles of temperature (T) and biology are found negligible. A relatively warm T and extremely high freshwater forcing make the southeastern tropical Indian Ocean carbon cycle variability submissive to DIC and ALK evolutions in contrast to the tropical eastern Pacific where changes in DIC and T dominate the pCO 2 interannual variability. For the first time, this study provides a most comprehensive and extended analysis for the region while highlighting significant differences in carbon cycle variability of the eastern tropical Indian Ocean compared to that of the other parts of the global oceans. Plain Language Summary The most popular interannual variability in the tropical Indian Ocean is known as Indian Ocean Dipole (IOD) Mode. It significantly influences Asian and Australian Monsoon systems and teleconnected to other major tropical-to-midlatitude oceans. However, the role of IOD in Indian Ocean carbon cycle variability was poorly known. Using 60 years of model simulations and available observations, we examined the relation between IOD and carbon cycle variability in the upper oceans of the southeastern tropical Indian Ocean. The results show that a positive (negative) IOD causes positive (negative) anomalies of sea-to-air CO 2 fluxes, surface ocean pCO 2 , concentrations of surface ocean dissolved inorganic carbon, and surface ocean alkalinity. The dissolved inorganic carbon and alkalinity dynamics, together with freshwater forcing, control the southeastern tropical Indian Ocean's carbon cycle variability due to IOD. The study also identifies the similarities and differences of southeastern tropical Indian Ocean compared to the eastern tropical Pacific.

Subsurface Water Property Structures Along 80°E Under the Positive Indian Ocean Dipole Mode in December 2019

“…Although the DIC decrease below the mixed layers was also observed on the isobar surfaces, relatively large increases in DIC were observed on the sea surface at approximately 10°S, which was consistent with the relationship between DIC changes and the IOD based on previous numerical simulations (Valsala et al, 2020). Horizontal advection might be more important for the simultaneous formation of positive DIC anomalies on the surface in the pIOD than vertical mixing at the bottom of the mixed layers at 80°E.…”

Impact of March North Atlantic Oscillation on Indian Ocean Dipole: role of air–sea interaction over the Western North Pacific

“…A positive IOD event brings about warm and cold sea surface temperature (SST) anomalies (SSTAs) in the tropical western and southeastern Indian Ocean, respectively, while a negative IOD event does the opposite (Saji et al 1999;Webster et al 1999). Such IOD events significantly influence variabilities in oceanic processes (Chen et al 2015(Chen et al , 2016aLiu et al 2015), the Indian Ocean carbon cycle (Valsala et al 2020), and climate over the Indian Ocean rim and remote countries by altering ocean-atmosphere circulations (Saji and Yamagata 2003;Cai et al 2014;Xu et al 2020;Zhang et al 2021). Therefore, academic research on the triggering and development mechanisms of IOD is considered worthwhile.…”

The fingerprint of Indian Ocean rain and river water in salinity and circulation

“…Thirdly, we also have no clear idea of the consequence of the RRW in Indian Ocean circulation. Fourthly, RRW was even found to manifest other biogeochemical cycles (Valsala et al, 2020). For instance, the intense freshwater forcing is found to be the fundamental reason why southeastern Indian Ocean sea-to-air CO 2 flux variations are dominated by freshwater driven concentration changes in dissolved inorganic carbon and alkalinity instead of a direct dependency of carbon fluxes to sea surface temperature as in the eastern tropical Pacific (Valsala et al, 2020).…”

“…Fourthly, RRW was even found to manifest other biogeochemical cycles (Valsala et al, 2020). For instance, the intense freshwater forcing is found to be the fundamental reason why southeastern Indian Ocean sea-to-air CO 2 flux variations are dominated by freshwater driven concentration changes in dissolved inorganic carbon and alkalinity instead of a direct dependency of carbon fluxes to sea surface temperature as in the eastern tropical Pacific (Valsala et al, 2020). Fifthly, the state-of-the-art coupled climate models are known to have RRW biases in long-term simulations, which has direct and obvious impacts on the simulated salinity (Vinayachandran and Nanjundiah, 2009).…”