Black Sea dissolved organic matter dynamics: Insights from optical analyses

Abstract

To obtain qualitative information on the Black Sea's dissolved organic matter (DOM) pool, the optical properties (absorption and fluorescence) were measured in 111 samples collected across the basin. Chromophoric dissolved organic matter (CDOM) was considered at three wavelengths (254 nm, 280 nm, and 325 nm), along with the spectral slope between 275 nm and 295 nm (S275–295) and the specific ultraviolet absorbance at 254 nm (SUVA254). Using parallel factor analysis, a five‐component model identified three humic‐like components, a protein‐like component, and a polycyclic aromatic hydrocarbon‐like component. In the basin's oxic layer (upper ∼ 100 m), protein‐like CDOM was elevated, likely due to the production of this labile material, while humic‐like material was low, suggesting its removal by photo‐oxidation. In the underlying waters, the protein‐like material decreased, perhaps due to the utilization of this nitrogen‐containing DOM, while humic‐like material increased, suggesting its production at depth. In the anoxic layer (lower ∼ 2000 m), dissolved organic carbon (DOC) varied by only ∼ 10% while CDOM increased with depth by a factor of approximately two; the optical properties correlated well with the H2S‐equivalence of mineralization, referred to here as apparent carbon mineralization (ACM), while DOC did not. The strong correlation between CDOM and ACM is similar to correlations previously identified in the open ocean that compared CDOM with apparent oxygen utilization, suggesting that CDOM accumulates as a function of mineralization, independently of the oxidizing agent (i.e., oxygen or sulfate).

Sulfurization of dissolved organic matter in the anoxic water column of the Black Sea

“…S1 and S2). This lower percentage is in line with previous estimates based on optical analyses, suggesting 4 to 12% of terrigenous DOC in the central Black Sea (39). Consistently, all these complementary compositional characteristics suggest that the dissolved organics accumulating in the Black Sea are a mix of terrigenous, marine, and autochthonous material (39).…”

Consistency between Satellite Ocean Colour Products under High Coloured Dissolved Organic Matter Absorption in the Baltic Sea

“…From the dispersion of the points at higher R rs (λ) values in the blue and the resulting low S, clearly improvements in OLCI-A POLYMER are required for the Baltic Sea region. Overall the results for OLCI-A POLYMER are encouraging and imply that this AC could also be accurate in regions with similar IOPs and range in a CDOM (λ) such as the Amazon River plume (a CDOM (355) 0.3-2.5 m −1 ) [59], the Black Sea (a CDOM (325) 0.4-1.4 m −1 ) [60], Bohai, east China and Yellow Seas (a CDOM (355) 0.2-1.2 m −1 ) [61].…”

Soothsaying DOM: A Current Perspective on the Future of Oceanic Dissolved Organic Carbon

“…The deep waters of the Black Sea exhibit DOC concentrations that are 2.5-fold higher than DOC concentrations in the deep ocean (Ducklow et al, 2007;Margolin et al, 2016). It remains unclear whether the DOC accumulation is directly linked to terrestrial DOC inputs to this anoxic basin (Margolin et al, 2016) or is derived from a mixture of terrestrial, marine, and autochthonous DOC (Margolin et al, 2018). The East Japan Sea is a semi-enclosed marginal sea where DOC accumulation is attributed to decreased reactivity resulting from low bottom water temperatures (<1 • C) (Kim et al, 2015).…”