Estimate chlorophyll a and POC concentrations in the Southern Ocean

Nils Haëntjens, University of Maine, Orono, ME, United States, Emmanuel Boss, University of Maine, School of Marine Science, Orono, ME, United States and Lynne D Talley, University of California San Diego, La Jolla, CA, United States
Abstract:
The Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM) is deploying hundreds of profiling floats with (NASA-funded) bio-optical sensors in the Southern Ocean. The optical sensor measure chlorophyll fluorescence (Ex/Em 470/685nm) and the backscattering coefficient at 700nm, which are routinely as proxies for chlorophyll a (chl-a) and particulate organic carbon (POC) concentrations.

To assess the quality of the chl-a and POC derived from the float’s measurements we compare them with chl-a and POC samples collected near the times the floats were deployed. Through the life of a float, we also compare its measurements to estimates of chl-a and the backscattering coefficient derived from remotely sensed ocean color. In addition, on most cruises where floats are deployed, a ‘golden’ sensor is deployed on the CTD rosette for cross-calibration between floats.

 For fluorescence measurements done when there is significant irradiance in the upper ocean we correct for non-photochemical quenching of fluorescence with an average of Xing et al. (2012) and Sackmann et al.’s (2008) methods.

To date we have found the backscattering measurement to be consistent with previous studies while chl-a estimated with fluorescence is significantly over estimated when using the manufacturer calibration (factor of ~7 relative to HPLC, ~3.5 relative to local ocean color algorithms).

We hope that our work will provide for an unprecedented, quality-controlled, dataset of chl-a and POC for the Southern Ocean to be used in biogeochemical studies.

Back to: Physical and Biogeochemical Processes in the Southern Ocean: Observations, State Estimation, and Modeling III