Improved correction for non-photochemical quenching of in situ chlorophyll fluorescence based on a synchronous irradiance profile
|Author(s)||Xing Xiaogang1, Briggs Nathan2, Boss Emmanuel3, Claustre Herve4|
|Affiliation(s)||1 : State Ocean Adm, State Key Lab Satellite Ocean Environm Dynam SOED, Inst Oceanog 2, Hangzhou 310012, Zhejiang, Peoples R China.
2 : Univ Southampton, Natl Oceanog Ctr Southampton, Southampton SO14 3ZH, Hants, England.
3 : Univ Maine, Sch Marine Sci, 706 Aubert Hall, Orono, ME 04469 USA.
4 : Sorbonne Univ, CNRS, LOV, F-06230 Villefranche Sur Mer, France.
|Source||Optics Express (1094-4087) (Optical Soc Amer), 2018-09 , Vol. 26 , N. 19 , P. 24734-24751|
|WOS© Times Cited||30|
In situ chlorophyll fluorometers have been used to quantify the distribution of chlorophyll concentration in natural waters for decades. However, chlorophyll fluorescence is depressed during daylight hours due to non-photochemical quenching (NPQ). Corrections attempted to date have provided improvement but still remain unsatisfactory, often over-estimating the expected value. In this study. we examine the relationship between NPQ and instantaneous Photosynthetically Active Radiation (iPAR) using field data from BGC-Argo floats equipped with Chlorophyll-alpha fluorometers and radiometers. This analysis leads to an improved NPQ correction that incorporates both iPAR and mixed layer depth (MLD) and is validated against data collected at sunrise or sunset. The optimal NPQ light threshold is found to be iPAR = 15 mu mol quanta m(-2) S-1, and the proposed methods based on such a light threshold correct the NPQ effect more accurately than others, except in "shallow-mixing" waters (NPQ light threshold depth deeper than MLD). For these waters, an empirical-relationship-based method is proposed for improvement of NPQ correction using an iPAR profile. It is therefore recommended that, for optimal NPQ corrections, profiling floats measuring chlorophyll fluorescence in daytime be equipped with iPAR radiometers.