Bottom Water Acidification and Warming on the Western Eurasian Arctic Shelves: Dynamical Downscaling Projections

Abstract

The impacts of oceanic CO2 uptake and global warming on the surface ocean environment have received substantial attention, but few studies have focused on shelf bottom water, despite its importance as habitat for benthic organisms and demersal fisheries such as cod. We used a downscaling ocean biogeochemical model to project bottom water acidification and warming on the western Eurasian Arctic shelves. A model hindcast produced 14–18 year acidification trends that were largely consistent with observational estimates at stations in the Iceland and Irminger Seas. Projections under SRES A1B scenario revealed a rapid and spatially variable decline in bottom pH by 0.10–0.20 units over 50 years (2.5%–97.5% quantiles) at depths 50–500 m on the Norwegian, Barents, Kara, and East Greenland shelves. Bottom water undersaturation with respect to aragonite occurred over the entire Kara shelf by 2040 and over most of the Barents and East Greenland shelves by 2070. Shelf acidification was predominantly driven by the accumulation of anthropogenic CO2, and was concurrent with warming of 0.1–2.7°C over 50 years. These combined perturbations will act as significant multistressors on the Barents and Kara shelves. Future studies should aim to improve the resolution of shelf bottom processes in models, and should consider the Kara Sea and Russian shelves as possible bellwethers of shelf acidification.

Modeled Effect of Coastal Biogeochemical Processes, Climate Variability, and Ocean Acidification on Aragonite Saturation State in the Bering Sea

“…Furthermore, observed and modeled spatial variability suggests that this timeframe may vary by up to several decades between different shelf regions. Future work will utilize ESM output to dynamically downscale OA projections using the Bering10K model (Hermann et al, 2016;Wallhead et al, 2017). This method will reduce the uncertainty of these critical threshold years and provide information on their spatial variance throughout the Bering Sea.…”

Arctic Sensitivity? Suitable Habitat for Benthic Taxa Is Surprisingly Robust to Climate Change

“…Saturation state describes the seawater concentrations of carbonate and calcium ions relative to the equilibrium concentrations for that mineral; conditions near or below saturation ( = 1) are generally considered unfavorable for production or maintenance of normal calcification. SINMOD was first run to produce a hindcast simulation , and then to produce a projection under the SRES (Special Report on Emissions Scenarios) scenario A1B (see Slagstad et al, 2015;Wallhead et al, 2017, for more details). SRES A1B is a mid-range business-as-usual scenario assuming a "balanced" use of fossil vs. non-fossil energy sources (Nakicenovic et al, 2000) that results in end-of-century global responses that are comparable to the more recent RCP6.0 scenario and and the projection period (2090-2099), respectively; figures on the far right show the differences.…”

“…substantially more conservative than the SRES A2 or RCP8.5 scenarios (Collins et al, 2013). SINMOD bottom-water output was corrected using bias estimates, calculated as a function of spatial position (temperature) or of model bathymetry ( (ar)) using a compilation of in situ observations and matched model output (see Wallhead et al, 2017). Water depth over the SINMOD grid was estimated by interpolating high-resolution bathymetry products (the 500 m resolution IBCAOv3, Jakobsson et al, 2012, where available, otherwise the 2 min ETOPOv2, National Geophysical Data Center, 2006).…”

The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

“…It is also demonstrated well how extremal increase of atmospheric CO 2 , comparable to that is already observed in the Ob' Inlet estuarine area (Makkaveev et al 2015a(Makkaveev et al , 2015b, pull up aragonite saturation horizon from the deep ocean to the shelf depths (Cao et al 2014a) and what are the consequences for the ecosystem. Modeling examinations of the CS parameters in the bottom layer have revealed negative trends in pH and aragonite saturation for the entire Kara Sea shelf by 2040 (Wallhead et al 2017).…”