A compilation of surface inherent optical properties and phytoplankton pigment concentrations from the Atlantic Meridional Transect

Abstract. In situ measurements of particulate inherent optical properties (IOPs) – absorption (a_p(λ)), scattering (b_p(λ)), and beam attenuation (c_p(λ)) – are crucial for development of optical algorithms that retrieve biogeochemical quantities such as Chlorophyll a, particulate organic carbon (POC) and total suspended matter (TSM). Here we present a compilation of particulate absorption-attenuation spectrophotometric data measured underway on nine Atlantic Meridional Transect (AMT) cruises between 50° north to 50° south from 2009–2019. The compilation includes co-incident high performance liquid chromatography (HPLC) phytoplankton pigment concentrations, which are used to calibrate transects of Total Chlorophyll a (Tot_Chl_a) concentrations derived from the a_p(λ) line-height method. The IOP data are processed using a consistent methodology, and include propagated uncertainties for each IOP variable, uncertainty quantification for the Tot_Chl_a concentrations based on HPLC match-ups, application of consistent set of quality-control filters, and standardisation of output data fields and formats. The total IOP dataset consists of ~310,000 measurements at a 1 minute binning (~270,000 hyper-spectral) and > 700 co-incident HPLC pigment surface samples (~600 of which are coincident with hyper-spectral IOPs). We present geographic variation in the IOPs, HPLC phytoplankton pigments, and the a_p-derived Tot_Chl_a concentrations, which are shown to have uncertainties between 8–20 %. Additionally, to stimulate further investigation of accessory pigment extraction from a_p(λ), we quantify pigment correlation matrices and identify spectral characteristics of end-member a_p(λ) spectra where accessory pigment groupings are present in higher concentrations relative to Tot_Chl_a. All data are made publicly available in SeaBASS and NetCDF formats via the following links: https://seabass.gsfc.nasa.gov/archive/PML/AMT, and https://doi.org/10.5281/zenodo.12527954.