As autonomous instruments are becoming typical tools to explore the ocean’s chlorophyll variability, scientists are adopting common-practice methods to cross-calibrate and validate different chlorophyll concentration estimates. Roesler and Barnard’s Line Height Absorption (LHA) method developed in year 2013 is a popular method often used to estimate chlorophyll concentrations from high frequency absorption measurements. The slope of the relationship between absorption and chlorophyll concentration is known as the chlorophyll-specific absorption line height (a_LH*). The a_LH* varies with phytoplankton community composition and pigment packaging, and while the importance of regional tuning is accounted for, the effect of seasonality on a_LH* is not. The following evaluates the impact of temporal or seasonal variability on the LHA. The study was carried out in the Northern Gulf of Alaska (NGA), which is intensely seasonal. It was found that the a_LH* for the NGA ranged between 0.0108 and 0.0136, with the highest values occurring in summer and the lowest in spring. This translates into a non-negligible 26% variability in chlorophyll estimates. The size fractionated chlorophyll data strongly suggests that a shift in the phytoplankton size is a major driver of the a_LH* variability between spring and summer. Given these results, we encourage others to consider the seasonality factor when using the LHA method to obtain chlorophyll estimates from absorption measurements.

Primary Presenter: Benjamin Lowin, Skidaway Institute of Oceanography (ben.lowin@gmail.com)

Authors:

Benjamin Lowin, Sidaway Institute of Oceanography  (ben.lowin@uga.edu)

Suzanne Strom, Western Washington University  (stroms@wwu.edu)

Will Burt, Planetary Technologies, Halifax Canada  (willburt86@gmail.com)

Sara Rviero-Calle, Skidaway Institute of Oceanography  (rivero@uga.edu)