[A-OS14] Continental Oceanic Mutual Interaction - Planetary Scale Material Circulationn

[AOS14-09] The linkage between photosynthetic CO₂ assimilation rates in monsoon Asia and hydroclimate anomalies

*Roma Varghese¹, Swadhin k. Behera², Mukunda Dev Behera¹ (1.Centre for Ocean, River, Atmosphere and Land Sciences, Indian Institute of Technology Kharagpur, India, 2.Applications Laboratory, Japan Agency for Marine-Earth Science and Technology, Japan)

Keywords:Terrestrial vegetation CO2 uptake, Gross primary production, Monsoon Asia, Solar-induced chlorophyll fluorescence, Hydroclimate variability, Ocean-vegetation interactions

Monsoon Asia (MA) is a part of the Asian continent with seasonally reversing wind patterns. MA is the hub of highly productive ecosystems in Asia and thus serves as a potential terrestrial sink of atmospheric CO₂. In MA, vegetation gross primary productivity (GPP) or the rate of total carbon captured by plants via photosynthesis is controlled mainly by climate change and human-induced disturbances. At the same time, vegetation activity in MA has been highly susceptible to extreme climate events as the region interacts consistently with the ocean-atmosphere processes in the tropical belts through the transport and distribution of heat, moisture, and momentum. Thus variabilities associated with vegetation carbon uptake in MA appear to resonate strongly with hydroclimate fluctuations. The majority of MA is inhabited by developing nations with a rapidly growing population and a predominantly agricultural-based economy. Hence, there is a need to identify how the vegetation GPP in MA responds to hydroclimate anomalies to understand the possible global change implications on the terrestrial carbon cycle. Moreover, it also aids in the detection of vegetation growth anomalies forced by environmental stress conditions in MA. Our study comprehensively examines the recent variability of terrestrial GPP in MA and its relationship with hydroclimate anomalies. We used the remote sensing-based GOSIF GPP product to track the interannual variability of terrestrial vegetation productivity in MA. GOSIF GPP was developed by exploiting the universal linear relationships between OCO-2 based solar-induced chlorophyll fluorescence (SIF) measurements and GPP in a variety of terrestrial biomes across the globe. SIF acts as a better proxy of actual photosynthesis and offers a more realistic representation of anomalies in the vegetation carbon fixation rates. Based on the recent 20 year climatology (2001-2020), annual GPP over MA varies from 0 to 4691.3 g C m⁻² year⁻¹ with an average value of 1130.38 g C m⁻² year⁻¹. The coefficient of variance goes up to 100 g C m⁻² year⁻¹ with a domain average of 14.64 g C m⁻² year⁻¹. Large GPP variability (~ > 20 g C m⁻² year⁻¹) was predominantly observed in the northwestern parts of the Indian subcontinent and northcentral portions of eastern Asia, specifically in the Mongolian plateau. These regions are the water-limited ecosystems of MA that experiences arid and semi-arid climates. Except for the Himalayan belt, water stress acts as the primary controlling factor for GPP anomalies across the Indian subcontinent, Mongolian plateau, and northern parts of Southeast Asia. Rainfall and soil moisture (root zone) anomalies demonstrated statistically significant positive correlations with GPP variability over MA. Negative correlations observed between surface air temperature and GPP anomalies in India, Pakistan and entire Southeast Asia. In Japan and subtropical-tropical monsoonal China, air temperature anomalies have a positive impact on GPP variability. Therefore, changes in heat and moisture fluxes play a critical role in determining the GPP variability in MA. Moreover, during positive GPP anomalies in MA, negative sea surface temperature (SST) anomalies were observed in the eastern equatorial Pacific. This indicates the notable contribution of oceanic SST variability in the functioning of terrestrial ecosystems in MA. Overall, in monsoon Asia, the GPP variability of the Indian subcontinent is critically vulnerable to hydroclimate anomalies. Therefore, the terrestrial ecosystem services of the countries such as India, Pakistan, and Afghanistan dominantly face severe implications of climate variability in the era of global change.