Seasonal Changes in Dissolved Organic Matter Composition in a Patagonian Fjord Affected by Glacier Melt Inputs

Abstract

Biogeochemical processes in fjords are likely affected by changes in surrounding glacier cover but very little is known about how meltwater directly influences dissolved organic matter (DOM) in fjords. Moreover, the data available are restricted to a handful of northern hemisphere sites. Here we analyze seasonal and spatial variation in dissolved organic carbon (DOC) concentration and DOM composition (spectrofluorescence, ultrahigh resolution mass spectrometry) in Baker-Martinez Fjord, Chilean Patagonia (48°S), to infer the impacts of rapid regional deglaciation on fjord DOM. We show that surface layer DOC concentrations do not vary significantly between seasons, but DOM composition is sensitive to differences in riverine inputs. In summer, higher protein-like fluorescence reflects increased glacial meltwater inputs, whilst molecular level data show weaker influence from marine DOM due to more intense stratification. We postulate that the shifting seasonal balance of riverine and marine waters affects the supply of biolabile peptides and organic nitrogen cycling in the surface layer. Trends in DOM composition with increasing salinity are consistent with patterns in estuaries (i.e. preferential removal of aromatic compounds and increasing relative contribution of unsaturated and heteroatom-rich DOM from marine sources). Preliminary estimates also suggest that at least 10% of the annual organic carbon stock in this fjord is supplied by the four largest, glacially fed rivers and that these inputs are dominated by dissolved (84%) over particulate organic carbon. Riverine DOC may therefore be an important carbon subsidy to bacterial communities in the inner fjord. The overall findings highlight the biogeochemical sensitivity of a Patagonian fjord to changes in glacier melt input, which likely has relevance for other glaciated fjords in a warming climate.

Meltwater Discharge From Marine‐Terminating Glaciers Drives Biogeochemical Conditions in a Greenlandic Fjord

“…The result indicated that FDOM H in glacial meltwater may be an important determinant of the dFe concentration in Areas A and C. The BIX values suggest that FDOM H in Inglefield Bredning is freshly produced DOM. Although a high contribution of microbially derived DOM in glacial meltwaters has been reported in elsewhere (e.g., Kellerman et al, 2020;Marshall et al, 2021;Pain et al, 2020), its contribution in our studied fjord is unclear. The absence of a significant correlation between dFe and FDOM H in the plume water of Area B (Figure 4a) was probably due to the high concentration of suspended sediment (Figure 5l) and removal of FDOM H by adsorption onto sediment particles.…”

Estimation of Dissolved Organic Carbon in River Flows and Identification of the Relationships Between Peat Humic Fractions and Physicochemical Qualities

“…However, DOC losses are strongly related to microbial activity only when the soil's ability to stabilize soluble carbon is low (Silveira, 2005). Due to its varying molecular weight and polarity, DOC is of considerable practical interest as it could serve as a sensitive indicator of changes in the soil ecosystem (Marshall et al, 2021), especially with its ability to complex different types of pollutants (Reyes and Crisosto, 2016). The low DOC exports out of peat systems contribute to maintaining low carbon exchanges with the external environment.…”

“…In addition, carbon losses occur in the dissolved form by leaching due to biodegradation and photochemistry/photooxidation (Reyes and Crisosto, 2016). Carbon losses, often with CO2 emission, can shift the carbon balance of peatlands from the sink to the source (Marshall et al 2021).…”