Introduction
The Arctic Ocean is home to a unique ecosystem that supports extraordinary wildlife. With climate change, the Arctic is undergoing unprecedented changes, such as amplified warming, reduction of sea ice, and permafrost thaw. These changes affect the Arctic Ocean ecosystem and fisheries via changes in net primary production (NPP) or ocean acidification (OA). NPP by phytoplankton is the base of this ecosystem and changes in NPP will be felt through the entire food chain. In addition, the Arctic Ocean ecosystem is threatened by ongoing and intensifying OA, to which the Arctic Ocean is especially vulnerable due to its naturally low temperatures and calcium carbonate saturation states.
In this rapidly changing Arctic Ocean, reliable projections of the Arctic Ocean NPP and OA are thus essential for effective and proactive stewardship of the Arctic Ocean ecosystem and the fisheries it supports. The main tools for these projections are global Earth System Models (ESMs). Unfortunately, these ESMs struggle to represent present-day Arctic Ocean NPP and OA despite continuous model development and increased model resolution. Consequently, projections of Arctic Ocean NPP and OA remain also highly uncertain. The large inter-model differences mainly occur because ocean biogeochemical models embedded in ESMs are developed to represent the open ocean and often do not include or greatly simplify local-scale processes that are important and observed in the Arctic Ocean such as carbon and nutrients fluxes from rivers, coastal and subsea erosion, lability and remineralization of (terrestrial) dissolved and particulate organic matter in the water column, and remineralization and burial in coastal sediments.
Methods
The ”Arctic Ocean biogeochemical and ecosystem modeling” group uses GFDL-ESM2M, a fully-coupled ESM from Princeton (USA), to provide much needed more reliable projections of Arctic Ocean NPP and OA. To achieve this overall objective, we will create new temporally and spatially resolved forcing files for Arctic carbon, alkalinity, and nutrient fluxes from rivers and coastal erosion using the most recent observations of riverine fluxes from the Arctic Great River Observatory and of coastal and subsea erosion. These modern forcing files will be extrapolated in time over the historical period since 1850 and over the 21st century under different warming scenarios. In addition, we will improve the representation of organic matter remineralization and benthic processes in the ocean biogeochemical component of GFDL-ESM2M by using a large number of observations, a data-assimilation approach for tuning the representation of biogeochemical dynamics in the water column and by coupling a sediment model to GFDL-ESM2M and tuning it to the Arctic Ocean. Based on these improvements in GFDL-ESM2M, we will provide an assessment of the past, present, and future of the Arctic Ocean NPP and OA.
Impact
At a time when more high-quality observations in the remote and hostile Arctic environment are available and the high-resolution earth system modeling becomes computationally feasible, our work will bridge the gap between the Arctic Ocean observations and Earth system modeling and represent the special Arctic biogeochemical conditions in ESMs. Using a fully-coupled ESM and most recent observations, we will provide much needed more reliable projections of Arctic Ocean NPP and OA under global warming that can guide policy makers in taking preventive and effective action to conserve a unique and changing ecosystem and its fisheries.
Projects
Stressors of the Arctic Ocean Ecosystem over the 21st Century (ArcticEco) (https://data.snf.ch/grants/grant/209044)
