Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

Abstract

It is recognized that open ocean properties, especially biological ones, are chronically undersampled. During the last decade, thanks to the emergence of sea glider and profiling float technology, the density of observations has nevertheless been drastically increased, especially for the description of temperature and salinity fields. However, most of the research conducted to date using this new technology has remained restricted to 60°N-60°S (e.g., Argo program). In order to develop observational capabilities in harsh polar conditions, the use of animals as an alternative platform has been progressively tested and proved to be efficient. This new field of biologging was made possible thanks to recent progress in microelectronics, miniaturization, and satellite telemetry. While the first objective was to provide a host of new information for biologists, the idea of simultaneously gathering oceanographic parameters has naturally emerged. A synergy between biologist's efforts to understand the marine life and physical oceanographic studies became possible in the early 2000s with the development of satellite-relay biologging devices incorporating high-accuracy oceanographic sensors. These Satellite Relay Data Loggers (SRDLs) were developed at the Sea Mammal Research Unit (SMRU-UK) and provide fundamental information not only for biologists, but also for oceanographers in the form of vertical profiles of temperature and salinity using a miniaturized conductivity-temperature-depth (CTD) cell (Fedak 2004;Charrassin et al. 2008 , and Christophe Guinet AbstractAs the proxy for Chlorophyll a (Chl a) concentration, thousands of fluorescence profiles were measured by instrumented elephant seals in the Kerguelen region (Southern Ocean). For accurate retrieval of Chl a concentrations acquired by in vivo fluorometer, a two-step procedure is applied: 1) A predeployment intercalibration with accurate determination by high performance liquid chromatography (HPLC) analysis, which not only calibrates fluorescence in appropriate Chl a concentration units, but also strongly reduces variability between fluorometers, and 2) a profile-by-profile quenching correction analysis, which effectively eliminates the fluorescence quenching issue at surface around noon, and results in consistent profiles between day and night. The quenching correction is conducted through an extrapolation of the deep fluorescence value toward surface. As proved by a validation procedure in the Western Mediterranean Sea, the correction method is practical and relatively reliable when there is no credible reference, especially for deep mixed waters, as in the Southern Ocean. Even in the shallow mixed waters, the method is also effective in reducing the influence of quenching.

A new transportable floating mesocosm platform with autonomous sensors for real‐time data acquisition and transmission for studying the pelagic food web functioning

“…The continuous Chl a measurement also provides an interesting insight into physiological phytoplankton processes. For instance, the slight dip in fluorescence detected at noon (around 13:45, local time) may be due to the nonphotochemical quenching as a photoprotection mechanism under strong light (Xing et al 2012, Sackmann et al 2008Cullen and Lewis 1995). Photoprotection mechanisms only occur over very short periods when the natural incident light is at its greatest and can only be detected by continuous measurement.…”

Towards a merged satellite and in situ fluorescence ocean chlorophyll product

“…A Student test to compare re-adjusted fluorescence with HPLC ratios in the two conditions (i.e. with and without quenching correction) reveals that the positive effect of the Xing et al (2012) NPQ correction is significant (p-value < 0.01).…”

“…Although NPQ represents a serious issue for the fluorescence calibration (Cullen and Lewis, 1995), methods exist to evaluate, and if possible correct, the NPQ impact on the Chl a C to fluorescence ratio (Sackmann et al, 2008;Xing et al, 2012). The most complex approaches (i.e.…”

“…Additionally, the use of the whole 1.5 Z e layer instead of only surface records to correct fluorescence allows for a minimization of the error that would be induced by a wrong NPQ parameterization. To assess the relevance of the Xing et al (2012) NPQ correction in the present merging method, we used the 776 pairings of matchup points located in mixed layer for the three data sets tested, obtaining a median ratio of re-adjusted fluorescence to HPLC data of 0.93, if the Xing et al (2012) NPQ correction was previously applied and 0.78 if it was not. A Student test to compare re-adjusted fluorescence with HPLC ratios in the two conditions (i.e.…”

Fluorescence-Based Approach to Estimate the Chlorophyll-A Concentration of a Phytoplankton Bloom in Ardley Cove (Antarctica)

“…Bands setting at 667, 678, and 748 nm help MODIS become the only satellite to achieve the baseline nFLH approach, which estimates chlorophyll-a through fluorescence intensity from photosynthesis products [21].…”