Terrestrial and marine perspectives on modeling organic matter degradation pathways

Abstract

Organic matter (OM) plays a major role in both terrestrial and oceanic biogeochemical cycles. The amount of carbon stored in these systems is far greater than that of carbon dioxide (CO2 ) in the atmosphere, and annual fluxes of CO2 from these pools to the atmosphere exceed those from fossil fuel combustion. Understanding the processes that determine the fate of detrital material is important for predicting the effects that climate change will have on feedbacks to the global carbon cycle. However, Earth System Models (ESMs) typically utilize very simple formulations of processes affecting the mineralization and storage of detrital OM. Recent changes in our view of the nature of this material and the factors controlling its transformation have yet to find their way into models. In this review, we highlight the current understanding of the role and cycling of detrital OM in terrestrial and marine systems and examine how this pool of material is represented in ESMs. We include a discussion of the different mineralization pathways available as organic matter moves from soils, through inland waters to coastal systems and ultimately into open ocean environments. We argue that there is strong commonality between aspects of OM transformation in both terrestrial and marine systems and that our respective scientific communities would benefit from closer collaboration.

Modeling CO2 emissions from Arctic lakes: Model development and site‐level study

“…For example, while photochemical degradation usually accounts for a minor fraction of DOC loss in the water column of lakes in other climate zones [ Bertilsson and Tranvik , ; Groeneveld et al ., ], it was found to contribute up to 95% of DOC loss in some Arctic lakes [ Cory et al ., ]. In addition to oxidizing DOC directly to inorganic forms (e.g., CO 2 ), sunlight can alter the rate of DOC degradation indirectly by producing free radicals and reactive oxygen (O 2 ) species [ Burd et al ., ] and fueling microbial degradation [ Cory et al ., ]. The increased DOC export from the permafrost region can cause carbon and nutrient enrichment in Arctic lakes [ Walter Anthony et al ., ].…”

Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition

“…Furthermore, a growing body of evidence reveals that anthropogenic N deposition can slow the microbial decay of plant detritus and increase soil C storage across a wide range of terrestrial ecosystems (Liu & Greaver, 2010;Frey et al, 2015;Maaroufi et al, 2015). However, the molecular and microbial mechanisms underlying this biogeochemical response are not well understood, and they are not a component of any coupled climate-biogeochemical model estimating ecosystem C storage (Thornton et al, 2009;Burd et al, 2016).…”

A synthesis of the arctic terrestrial and marine carbon cycles under pressure from a dwindling cryosphere

“…Besides, ESMs tend to ignore lateral flows from the terrestrial to the marine environment (Anav et al 2013; Burd et al 2016), even though it has long been known that the inclusion of riverine carbon input can have a significant impact on the ocean (Aumont et al 2001). This input may be especially significant for the Arctic Ocean due to its small size compared to the relatively large riverine inflow.…”