Optical insight into riverine influences on dissolved and particulate organic carbon in a coastal Arctic lagoon system

Abstract

Optical properties of seawater can provide valuable insight into distributions of dissolved organic carbon (DOC) and particulate organic carbon (POC), provided that their interrelationships are well understood. We examined relationships between DOC and POC, and absorption, backscatter, and fluorescence in a river-fed lagoon system in the coastal Alaskan Arctic during late summer of 2018 and 2019. Over both years analytically measured DOC levels were inversely correlated with salinity (r2 = 0.97) and DOC was positively correlated with dissolved organic material fluorescence (fDOM; r2 = 0.67). However, DOC showed strong correlation with the absorption coefficient at 440 nm (ag(440)) only in 2018 (r2 = 0.95 versus r2 = 0.00056 in 2019). Vertical structure of fDOM in our study area corresponded with density profiles more strongly in 2018 than in 2019, but higher levels of fDOM, ag(440), and backscatter near the bottom in 2019 suggest prior wind-driven mixing or bottom resuspension events. In 2018 and 2019, the spectral slope of the absorption coefficient between 412 and 550 nm was strongly correlated with DOC concentration (r2 = 0.70), and spectral backscattering coefficients were well correlated with POC concentration (r2 = 0.90, 0.71, and 0.59 for 470, 532, and 660 nm respectively). These interannual patterns in the distribution of DOC and POC and their respective relationships with optical proxies likely reflect regional climatological factors such as precipitation over the adjacent watersheds, wind patterns, and residual sea ice in late summer. Hosted fileessoar.10512826.1.docx available at https://authorea.com/users/563933/articles/610991optical-insight-into-riverine-influences-on-dissolved-and-particulate-organic-carbon-ina-coastal-arctic-lagoon-system Optical insight into riverine influences on dissolved and particulate organic carbon in a coastal Arctic lagoon system