Ocean Primary Production from Space

Dr. ZhongPing Lee
Xiamen University, China,
Email: zhongping.lee@umb.edu

Increasing carbon dioxide (CO₂) and other greenhouse gas (GHG) emissions are causing significant changes to our planet’s climate with cascading impacts on both natural and human systems. During 2008–2017, global anthropogenic carbon emissions increased every decade from an average of 3.1 Gt C/yr in the 1960s to 9.4 Gt C/yr today. The consequent increase in extreme events caused by the build-up of CO₂ and other GHGs in our planet’s atmosphere, have prompted national, state, local governments, and international agencies, to accelerate plans and policies to reduce GHG emissions drastically and attain net neutral carbon emissions by 2100.

The oceans are huge sink for anthropogenic CO₂, and an important means by which CO₂ is stored in the oceans is via marine phytoplankton photosynthesis. Although a significant fraction of this newly produced organic carbon is remineralized as it sinks, the portion of organic matter that survives grazing and bacterial metabolism and is exported to the ocean floor, becomes a long term sink for anthropogenic CO₂. In the absence of primary production and carbon export to the ocean floor, atmospheric CO₂ would have been ~200 ppm higher than at present, raising average global temperatures by ~2 °C.

Despite the ocean’s critical role in balancing carbon between the ocean and atmosphere, the economic significance of the ecosystem service provided by phytoplankton photosynthesis is poorly represented in carbon policy and management narratives. While stocks and flows of carbon in the ocean have been identified and described in broad terms, there is large uncertainty in current estimates of primary production (PP). This has led to a great deal of uncertainty in future projections of atmospheric CO₂. The 2019 IPCC report indicates that the oceans capacity to sequester atmospheric CO₂ and the strength of the biological pump will diminish due to density stratification of the upper ocean, but this projection is also fraught with uncertainties. None of the IPCC projections address accuracy of current estimates of global PP, and there is no effort to understand and assess the scientific value of reducing their uncertainties, or to understand the socio-economic costs associated with a potential reduction in the global ocean’s carbon sequestration service.