Multi-decadal variations in the oceanic CO2 uptake and biogeochemical parameters over the northern and southern high latitudes

Abstract

The Community Earth System Model with the biogeochemistry module (CESM1-BGC) was used with the historical and RCP8.5 scenario to examine the spatial and temporal variability in the oceanic CO2 flux and biogeochemical parameters for the years 1850–2100. The 10-year periods of 1850–1860, 2010–2020, and 2090–2100 were used to represent the oceanic conditions in the past (historical), present, and future climate, respectively. The model simulations showed interesting differences between CO2 flux and biogeochemical parameters in the northern (NH) and southern (SH) high latitude oceanic regions. The sea surface temperature increases monotonically during 1960–2100 in both the hemispheres. The enhanced CO2 concentrations in the air lead to an increase in CO2 flux into the SH high-latitudes resulting into increasing oceanic acidification. However, over the NH high latitudes, the increase in CO2 flux ceased by the year 2050 and decreased during 2080–2100. This decrease in the CO2 flux of Arctic waters could be associated with the freshwater addition due to ice-melt that reduces the mixed layer depth in northern high latitudes and decreases CO2 uptake in future climate. The biological productivity (Chl concentrations) in the NH high latitudes found to decrease rapidly (2.5 mg m−3 lower than present) during 2000–2100. The time-series analysis of biogeochemical parameters at three regions in each hemisphere reveals marked differences over different oceanic regions within the same hemisphere in addition to the inter-hemispheric differences. The changes in large-scale overturning circulation and enhanced stratification leads to a reduction in nutrient supply to surface waters from deeper layers and decreases Chl concentration in the NH region. The mixing caused by Antarctic circumpolar current plays crucial role in maintaining Chl concentrations in the southern ocean. The multi-decadal spatiotemporal variability in physical and biogeochemical parameters are discussed in terms of their inter-dependence, oceanic processes, air-sea exchange in the warming climate.