Advertisements

Previously unknown source of carbon found in groundwater melt flow in Alaskan permafrost.

“The Arctic is heating up twice as much as the rest of the planet. With that comes permafrost thawing and the birth of aquifers, it is likely that groundwater transport in the Arctic will be more and more important in the future.” M. Bayani Cardenas, Jackson School of Geosciences

Another previously unknown significant change of deterioration in the permafrost has been discovered in the high arctic coastal region located at the Beaufort sea of Alaska.

The University of Texas presser recently summarized the new study in the scientific journal Nature Communications.

AUSTIN, Texas — A previously unknown significant source of carbon just discovered in the Arctic has scientists marveling at a once overlooked contributor to local coastal ecosystems – and concerned about what it may mean in an era of climate change.

In a Nature Communications paper released today, aquatic chemists and hydrologists from The University of Texas at Austin’s Marine Science Institute and Jackson School of Geosciences, U.S. Fish and Wildlife Service and Florida State University present evidence of significant, undetected concentrations and fluxes of dissolved organic matter entering Arctic coastal waters, with the source being groundwater flow atop of frozen permafrost. This water moves from land to sea unseen, but researchers now believe it carries significant concentrations of carbon and other nutrients to Arctic coastal food webs.

Groundwater is known globally to be important for delivering carbon and other nutrients to oceans, but in the Arctic, where much water remains trapped in frozen earth, its role has been less clear. Scientists were surprised to learn that groundwater may be contributing an amount of dissolved organic matter to the Alaskan Beaufort Sea that is almost on a par with what comes from neighboring rivers during the summer.

The research published today describes sampling the concentration and age of dissolved carbon, as well as nitrogen, in groundwater flowing beneath the land’s surface in the Arctic during the summer. The team found that as shallow groundwater flows beneath the surface at sites in northern Alaska, it picks up new, young organic carbon and nitrogen as expected. However, they also discovered that as groundwater flows toward the ocean, it mixes with layers of deeper soils and thawing permafrost, picking up and transporting century-to-millennia old organic carbon and nitrogen.

This old carbon being transported by groundwater is thought to be minimally decomposed, never having seen the light of day before it meets the ocean.

“Groundwater inputs are unique because this material is a direct shot to the ocean without seeing or being photodegraded by light,” McClelland said. “Sunlight on the water can decompose organic carbon as it travels downstream in rivers. Organic matter delivered to the coastal ocean in groundwater is not subject to this process, and thus may be valuable as a food source to bacteria and higher organisms that live in Arctic coastal waters.”

The researchers concluded that the supply of leachable organic carbon from groundwater amounts to as much as 70% of the dissolved organic matter flux from rivers to the Alaska Beaufort Sea during the summer.

From the study Introduction.

Groundwater is the largest active reservoir in the global hydrologic cycle and its movement from land to sea represents a major source of freshwater and nutrients for coastal ecological and biogeochemical processes1. However, there is little information on direct groundwater nutrient inputs to the coastal ocean in the Arctic2. This is partly because of a perception that in northern high-latitude coastal regions permafrost constrains water to flow paths on the land surface. Supra-permafrost groundwater (SPGW) does, however, flow through seasonally thawed active layer soils during the summer and early fall3,4. Therefore SPGW has the potential to deliver appreciable quantities of terrestrially-derived nutrients to Arctic coastal waters. SPGW is the principal form of terrestrial groundwater entering nearshore coastal waters in the Arctic since sub-permafrost groundwater flow is firmly separated from the surface by several hundred meters of permafrost5,6.

In the Arctic, SPGW flow and nutrient transport from soils are tightly coupled because soil water interactions are largely confined to the shallow (typically <1 m), but laterally extensive and highly permeable active layer7,8. Soils in northern high-latitude permafrost landscapes contain large amounts of organic matter with a high capacity to release dissolved organic matter (DOM) to aquatic systems9. Terrestrial DOM production and export is highest during the spring (May to June) when the thawed portion of the active layer is shallow and snowmelt-driven water flow is confined to near surface organic-rich soils and overlying plant litter layers10,11,12. DOM production and export is lower during the summer (July to October) when active layer thaw exposes deeper soil horizons and groundwater recharged from rainfall and melting ground ice saturates higher proportions of mineral soils13,14. Recent studies reveal that SPGW processes govern the summer transfer of DOM to streams and therefore influence riverine export to the coastal ocean8,15,16,17.