Earth Observations for Assessing Transport of Climatically-Active Gases in the Eastern Boundary Upwelling Systems
Garbe, Christoph¹; Garcon, Veronique²; Butz, Andre³; Illig, Serena²; Monte, Ivonne⁴; Sudre, Joel²; Paulmier, Aurelien²; Vihharev, Jevgeni⁵; Dewitte, Boris²; Dadou, Isabelle^2
1IWR, University of Heidelberg, GERMANY; ²LEGOS / CNRS, FRANCE; ³KIT, GERMANY; ⁴GEOMAR, GERMANY; ⁵IWR University of Heidelberg, GERMANY

The EBUS (Eastern Boundary Upwelling Systems) and OMZs (Oxygen Minimum Zone) contribute very significantly to the gas exchange between the ocean and the atmosphere, notably with respect to the greenhouse gases (hereafter GHG). Invasion or outgasing fluxes of radiatively-active gases at the air-sea interface result in coupled or decoupled sink and source configurations. From in-situ ocean measurements, the uncertainty of the net global ocean-atmosphere CO2 fluxes is between 20 and 30%, and could be much higher in the EBUS-OMZ. Off Peru, very few in-situ data are available presently, which justifies alternative approaches for assessing these fluxes.

GHG vertical column densities (VCD) can be extracted from satellite spectrometers. The accuracy of these VCDs needs to be very high in order to make extraction of sources feasible. To achieve this accuracy is extremely challenging, particularly above water bodies, as water strongly absorbs infra-red (IR) radiation. To increase the amount of reflected light, specular reflections (sun glint) can be used on some instruments such as GOSAT. Also, denoising techniques from image processing may be used for improving the signal-to-noise ratio (SNR).

GHG air-sea fluxes are inferred from inverse modeling applied to VCDs, using an optimal control approach at low spatial resolution. For accurately linking sources of GHGs to EBUS and OMZs, the resolution of the source regions needs to be increased. To this end, we developed a non-linear, multiscale approach to infer a higher spatial resolution mapping of the fluxes and the associated sinks and sources between the atmosphere and the ocean. Such an inference takes into account the cascading properties of physical variables across the scales in complex signals. It relies on coupled satellite data (e.g. SST and/or Ocean colour) which carries turbulence information associated to ocean dynamics. This allows us to evaluate air-sea fluxes at an unprecedented detail level, based purely on turbulence characteristics on multiple scales.

We will present a framework as described above for determining sources and sinks of GHG from satellite remote sensing with the Peru OMZ as a test bed. The approach includes resolutions enhancements from a multiscale processing method. The applicability is validated against ground truth observations and numerical model studies.