PACE observes the ocean in more than a hundred wavelengths rather than a handful. Previous ocean colour instruments measured chlorophyll and therefore total phytoplankton abundance; hyperspectral measurement allows different types of plankton to be distinguished by their pigment signatures.
That distinction matters ecologically. Diatoms, coccolithophores, cyanobacteria and dinoflagellates play very different roles in the carbon cycle and the food web, and knowing which is blooming where changes the interpretation entirely — including for harmful algal blooms that threaten fisheries and public health.
The mission also carries two polarimeters, which measure the polarisation of scattered light to characterise aerosol particle size and shape. Aerosols are the largest remaining uncertainty in climate forcing, chiefly because their effect on clouds depends on properties that conventional instruments cannot determine.
Combining ocean biology and atmospheric aerosols on one platform was deliberate: the two interact, with dust deposition fertilising ocean productivity and marine organisms emitting compounds that seed clouds.
It launched in February 2024 after surviving several budget proposals that would have cancelled it, and its early data has already been used to map plankton community composition globally for the first time.
