Catipovic Luka

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Last Name
Catipovic
First Name
Luka
ORCID
0000-0001-9211-4985

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  • Article
    Optical insight into riverine influences on dissolved and particulate organic carbon in a coastal arctic lagoon system
    (American Geophysical Union, 2023-04-04) Catipovic, Luka ; Longnecker, Krista ; Okkonen, Stephen R. ; Koestner, Daniel ; Laney, Samuel R.
    Arctic coastal margins receive organic material input from rivers, melted sea ice, and coastal erosion, phenomena that are all undergoing changes related to global climate. The optical properties of coastal Arctic waters contain information on this organic material, and we examined three optical properties of seawater (absorption, backscatter, and fluorescence) for their relationships to variability in dissolved and particulate organic carbon (DOC and POC) in Stefansson Sound, Alaska, a coastal Arctic embayment. During open water periods in 2018 and 2019, DOC was inversely correlated with salinity (r2 = 0.97) and positively correlated with dissolved organic matter fluorescence (fDOM; r2 = 0.67). DOC showed strong correlation with the nonparticulate absorption coefficient at 440 nm (ag(440)) only in 2018 (r2 = 0.95). The vertical structure of fDOM in Stefansson Sound aligned with density profiles more strongly in 2018 than in 2019, and higher levels of fDOM, ag(440), and backscatter seen near the bottom in 2019 suggest wind‐driven mixing and/or bottom resuspension events. In both years, DOC correlated strongly with the spectral slope of the absorption coefficient between 412 and 550 nm (r2 = 0.70), and POC was well correlated with spectral backscattering at 470, 532, and 660 nm (r2 = 0.90, 0.71, and 0.59). These interannual differences in the spatial and vertical distributions of DOC and POC, and their respective correlations with optical proxies, likely reflect regional climatological factors such as precipitation over the adjacent watersheds, wind patterns, and residual sea ice in late summer.
  • Thesis
    Interactions between rivers and coastal margins in the Alaskan Arctic
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2024-02) Catipovic, Luka ; Laney, Samuel R.
    Arctic coastal margins serve as the interface between Arctic terrestrial and oceanic carbon reservoirs. Characterized by extreme seasonality and annual variability, Alaskan Arctic coastal margins only receive riverine input of terrestrial organic material from late spring through late summer. This work examines the delivery, transformation, and distribution of organic material within Stefansson Sound, an Alaskan river-fed estuary, at the beginning and end of this period. We found that during the spring freshet, the landfast icescape over Stefansson Sound is composed of five ice and water features that are optically unique in terms of their surface reflectance spectra. One of these features is representative of freshwater flooding on ice which was found to persist in Stefansson Sound until late July. This floodwater is characterized by decreased reflectance in the blue portion of the visible light spectrum which indicates strong absorption by organic material contained within the freshet waters. Alaskan Arctic rivers drain watersheds composed of mixed proportions of tundra and mountains. During the freshet, organic material leached from the thawed soil surface horizons in the tundra is more available for microbial consumption over short periods than organic material originating in the mountains. This labile material is estimated to be higher molecular weight and more aromatic according to absorbance and fluorescence optical proxies. Fluorescence analysis revealed that tundra water contained more humic material and less amino acids when compared to water originating in the Brooks Range. This result challenges traditional assumptions that high molecular weight material in Arctic fluvial networks is refractory. In late summer, distributions of organic material in the surface waters of Stefansson Sound are driven by meteorological conditions such as precipitation over the watersheds and wind direction and speed in the estuary. Increased riverine discharge results in higher concentrations of organic material in the surface waters while faster wind speeds create deeper, well-mixed riverine plumes. Strong linear relationships between salinity and organic material indicate conservative mixing of freshwater in Stefansson sound, while new relationships between optical properties of water and organic material provide avenues forward for monitoring future climate driven changes regarding the biogeochemistry of this delicate ecosystem.