Glaciers and Land‐to‐Ocean Flux of Carbon

Abstract

Glaciers, ice caps, and ice sheets currently cover 12% of the Earth's land surface. The vast majority of glaciers worldwide are now in a state of retreat at unprecedented rates, with the most substantial mass loss originating from Greenland (37% of the global). The mass of ice‐locked organic matter is substantial and represents a hitherto poorly understood reservoir of organic carbon. In this article, we aim to summarize the current data on the concentrations of organic carbon across glacial systems and its origin and fate. Further, we aim to discuss the land‐to‐ocean flux of organic carbon and the effect on downstream environments. Several studies have suggested the glacial dissolved organic carbon (DOC) to have a pronounced impact on the coastal ecosystems because glacial DOC is highly bioavailable, i.e. has a high potential to feed downstream heterotrophic organisms. These studies, however, do not consider that the bioavailable carbon of coastal systems is in fact higher than in the glacial runoff. Contrary to previous studies, we, therefore, stress that glaciers are not a major source of neither DOC or bioavailable DOC and instead identify new focus areas in the field, such as the influence of the catchment area and the role of particulate organic carbon.

Understanding Regional and Seasonal Variability Is Key to Gaining a Pan-Arctic Perspective on Arctic Ocean Freshening

“…However, as with inorganic nutrients, glacial and ice sheet organic carbon concentrations are orders of magnitude lower than runoff from the large Arctic Rivers and coastal erosion (Hood et al, 2015;Paulsen et al, 2017;Hopwood et al, 2018;Wadham et al, 2019). Thus, while labile, glacial runoff contributions of allochthonous carbon are likely acting to dilute dissolved organic carbon concentrations (Paulson and Robson, 2019;Hopwood et al, 2020), and enhance particulate organic carbon in glacial fjords (Paulson and Robson, 2019). Organic carbon and nutrients from the Greenland Ice Sheet are likely to have little impact offshore; rather, their influence is likely limited to within local fjords (Hopwood et al, 2020).…”

Glacial Water: A Dynamic Microbial Medium

“…Glacial meltwater is an important source of cells and nutrients in outflow systems, carrying bioavailable Fe, DOC, N, P, Si, and rare metals, together with sediments and glacial flour [ 183 , 192 , 193 , 194 , 195 , 196 , 197 ]. How the proglacial system impacts downstream systems [ 198 , 199 , 200 , 201 ] depends on different factors, where the morphology of the proglacial system (i.e., land or maritime terminating) and its nutrient state (e.g., oligotrophic vs. eutrophic) play important roles [ 202 ].…”

“…Here, the glacial water creates a top layer of sediment-rich water which can inhibit primary productivity in the proximity of the land because of the decrease of light filtration in the system [ 214 , 215 ] ( Figure 3 A). Whereas this is often the case in the Arctic, land-terminating glaciers in the Antarctic can have positive effects because water is so oligotrophic that even the import of low nutrient concentrations can increase primary production [ 202 , 213 , 216 , 217 ].…”