Abstract
We analyzed a variety of satellite-based ocean color products derived using MODIS-Aqua to investigate the most accurate empirical and semi-analytical algorithms for representing in-situ chromophoric dissolved organic matter (CDOM) across a large latitudinal transect in the Bering, Chukchi, and western Beaufort Seas of the Pacific Arctic region. In particular, we compared the performance of empirical (CDOM index) and several semi-analytical algorithms (quasi-analytical algorithm (QAA), Carder, Garver-Siegel-Maritorena (GSM), and GSM-A) with field measurements of CDOM absorption (aCDOM) at 412 nanometers (nm) and 443 nm. These algorithms were compared with in-situ CDOM measurements collected on cruises during July 2011, 2013, 2014, 2015, 2016, and 2017. Our findings show that the QAA a443 and GSM-A a443 algorithms are the most accurate and robust representation of in-situ conditions, and that the GSM-A a443 algorithm is the most accurate algorithm when considering all statistical metrics utilized here. Our further assessments indicate that geographic variables (distance to coast, latitude, and sampling transects) did not obviously relate to algorithm accuracy. In general, none of the algorithms investigated showed a statistically significant agreement with field measurements beyond an approximately ± 60 h offset, likely owing to the highly variable environmental conditions found across the Pacific Arctic region. As such, we suggest that satellite observations of CDOM in these Arctic regions should not be used to represent in-situ conditions beyond a ± 60 h timeframe.
Highlights
Chromophoric dissolved organic matter (CDOM) represents the optical fraction of dissolved organic matter in natural waters, and its production impacts the heating and propagation of light in the water column [1]
We analyzed how the number of hours increasing from 0 to ±60 could affect the relationship between in-situ CDOM a443 and GSM-A a443, but we found no clear relationships (Figure 5A)
When we arrived at the 6 algorithms/time steps that were statistically significant based on the first-cut of R values, we analyzed the actual data in the scatterplots for further assessment, including the R, mean deviation (MD), mean absolute deviation (MAD), and slope (Figure 3)
Summary
Chromophoric dissolved organic matter (CDOM) represents the optical fraction of dissolved organic matter in natural waters, and its production impacts the heating and propagation of light in the water column [1]. Variability in CDOM distribution may have major effects on primary production and carbon cycling in the Arctic Ocean, in the Bering, Chukchi, and western Beaufort Seas of the Pacific Arctic region. CDOM will further shift in coastal areas as anthropogenic eutrophication occurs owing to changes in continental runoff, atmospheric nutrient deposition, and ocean warming [2,3]. Another major factor influencing CDOM production and distribution is sea-ice extent. All of these dynamics create complexities in CDOM production, distribution, and measurements across this region
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