scholarly journals Model constraints on the anthropogenic carbon budget of the Arctic Ocean

2018 ◽  
Author(s):  
Jens Terhaar ◽  
James C. Orr ◽  
Marion Gehlen ◽  
Christian Ethé ◽  
Laurent Bopp
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
The Arctic ◽  
Global Ocean ◽  
Cmip5 Models ◽  
Lateral Transport ◽  
Coarse Resolution ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon

Abstract. The Arctic Ocean is projected to experience not only amplified climate change but also amplified ocean acidification. Modeling future acidification depends on our ability to simulate baseline conditions and changes over the industrial era. Such centennial-scale changes require a global model to account for exchange between the Arctic and surrounding regions. Yet the coarse resolution of typical global models may poorly resolve that exchange as well as critical features of Arctic Ocean circulation. Here we assess how simulations of Arctic Ocean storage of anthropogenic carbon (Cant), the main driver of open- ocean acidification, differ when moving from coarse to eddy admitting resolution in a global ocean circulation-biogeochemistry model (NEMO-PISCES). The Arctic's regional storage of Cant is enhanced as model resolution increases. While the coarse- resolution model configuration ORCA2 (2°) stores 2.0 Pg C in the Arctic Ocean between 1765 and 2005, the eddy-admitting versions ORCA05 and ORCA025 (1/2° and 1/4°) store 2.4 and 2.6 Pg C. That result from ORCA025 falls within the uncertainty range from a previous data-based Cant storage estimate (2.5 to 3.3 Pg C). Yet those limits may each need to be reduced by about 10 % because data-based Cant concentrations in deep waters remain at ∼ 6 μmol kg−1, while they should be almost negligible by analogy to the near-zero observed CFC-12 concentrations from which they are calculated. Across the three resolutions, there was roughly three times as much anthropogenic carbon that entered the Arctic Ocean through lateral transport than via the flux of CO2 across the air-sea interface. Wider comparison to nine earth system models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) reveals much larger diversity of stored anthropogenic carbon and lateral transport. Only the CMIP5 models with higher lateral transport obtain Cant inventories that are close to the data-based estimates. Increasing resolution also enhances acidification, e.g., with greater shoaling of the Arctic's average depth of the aragonite saturation horizon during 1960–2012, from 50 m in ORCA2 to 210 m in ORCA025. To assess the potential to further refine modeled estimates of the Arctic Ocean's Cant storage and acidification, sensitivity tests that adjust model parameters are needed given that century-scale global ocean biogeochemical simulations still cannot be run routinely at high resolution.

scholarly journals Model constraints on the anthropogenic carbon budget of the Arctic Ocean

2019 ◽  
Vol 16 (11) ◽  
pp. 2343-2367 ◽  
Author(s):  
Jens Terhaar ◽  
James C. Orr ◽  
Marion Gehlen ◽  
Christian Ethé ◽  
Laurent Bopp
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
Lower Limit ◽  
Ocean Circulation ◽  
The Arctic ◽  
Model Resolution ◽  
Lateral Transport ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon ◽  
The Difference

Abstract. The Arctic Ocean is projected to experience not only amplified climate change but also amplified ocean acidification. Modeling future acidification depends on our ability to simulate baseline conditions and changes over the industrial era. Such centennial-scale changes require a global model to account for exchange between the Arctic and surrounding regions. Yet the coarse resolution of typical global models may poorly resolve that exchange as well as critical features of Arctic Ocean circulation. Here we assess how simulations of Arctic Ocean storage of anthropogenic carbon (Cant), the main driver of open-ocean acidification, differ when moving from coarse to eddy-admitting resolution in a global ocean-circulation–biogeochemistry model (Nucleus for European Modeling of the Ocean, NEMO; Pelagic Interactions Scheme for Carbon and Ecosystem Studies, PISCES). The Arctic's regional storage of Cant is enhanced as model resolution increases. While the coarse-resolution model configuration ORCA2 (2∘) stores 2.0 Pg C in the Arctic Ocean between 1765 and 2005, the eddy-admitting versions ORCA05 and ORCA025 (1∕2∘ and 1∕4∘) store 2.4 and 2.6 Pg C. The difference in inventory between model resolutions that is accounted for is only from their divergence after 1958, when ORCA2 and ORCA025 were initialized with output from the intermediate-resolution configuration (ORCA05). The difference would have been larger had all model resolutions been initialized in 1765 as was ORCA05. The ORCA025 Arctic Cant storage estimate of 2.6 Pg C should be considered a lower limit because that model generally underestimates observed CFC-12 concentrations. It reinforces the lower limit from a previous data-based approach (2.5 to 3.3 Pg C). Independent of model resolution, there was roughly 3 times as much Cant that entered the Arctic Ocean through lateral transport than via the flux of CO2 across the air–sea interface. Wider comparison to nine earth system models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) reveals much larger diversity of stored Cant and lateral transport. Only the CMIP5 models with higher lateral transport obtain Cant inventories that are close to the data-based estimates. Increasing resolution also enhances acidification, e.g., with greater shoaling of the Arctic's average depth of the aragonite saturation horizon during 1960–2012, from 50 m in ORCA2 to 210 m in ORCA025. Even higher model resolution would likely further improve such estimates, but its prohibitive costs also call for other more practical avenues for improvement, e.g., through model nesting, addition of coastal processes, and refinement of subgrid-scale parameterizations.

scholarly journals Arctic Ocean acidification over the 21st century co-driven by anthropogenic carbon increases and freshening in the CMIP6 model ensemble

2021 ◽  
Vol 18 (6) ◽  
pp. 2221-2240
Author(s):  
Jens Terhaar ◽  
Olivier Torres ◽  
Timothée Bourgeois ◽  
Lester Kwiatkowski
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
21St Century ◽  
Sea Surface ◽  
Total Alkalinity ◽  
The Arctic ◽  
Cmip5 Models ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon ◽  
Projected Changes

Abstract. The uptake of anthropogenic carbon (Cant) by the ocean leads to ocean acidification, causing the reduction of pH and the saturation states of aragonite (Ωarag) and calcite (Ωcalc). The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states and due to ongoing freshening and the concurrent reduction in total alkalinity in this region. Here, we analyse ocean acidification in the Arctic Ocean over the 21st century across 14 Earth system models (ESMs) from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of Cant into the Arctic Ocean interior, with simulated historical increases in Cant in improved agreement with observational products. Moreover, in CMIP6 the inter-model uncertainty of projected changes over the 21st century in Arctic Ocean Ωarag and Ωcalc averaged over the upper 1000 m is reduced by 44–64 %. The strong reduction in projection uncertainties of Ωarag and Ωcalc can be attributed to compensation between Cant uptake and total alkalinity reduction in the latest models. Specifically, ESMs with a large increase in Arctic Ocean Cant over the 21st century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in Cant simulate a relatively strong freshening and concurrent total alkalinity reduction. Although both mechanisms contribute to Arctic Ocean acidification over the 21st century, the increase in Cant remains the dominant driver. Even under the low-emissions Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6), basin-wide averaged Ωarag undersaturation in the upper 1000 m occurs before the end of the century. While under the high-emissions pathway SSP5-8.5, the Arctic Ocean mesopelagic is projected to even become undersaturated with respect to calcite. An emergent constraint identified in CMIP5 which relates present-day maximum sea surface densities in the Arctic Ocean to the projected end-of-century Arctic Ocean Cant inventory is found to generally hold in CMIP6. However, a coincident constraint on Arctic declines in Ωarag and Ωcalc is not apparent in the new generation of models. This is due to both the reduction in Ωarag and Ωcalc projection uncertainty and the weaker direct relationship between projected changes in Arctic Ocean Cant and changes in Ωarag and Ωcalc.

scholarly journals Arctic Ocean acidification over the 21st century co-driven by anthropogenic carbon increases and freshening in the CMIP6 model ensemble

2021 ◽  
Author(s):  
Jens Terhaar ◽  
Olivier Torres ◽  
Timothée Bourgeois ◽  
Lester Kwiatkowski
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
Coupled Model ◽  
Sea Surface ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon ◽  
Projected Changes ◽  
Emergent Constraint ◽  
New Generation

<p>The uptake of anthropogenic carbon (C<sub>ant</sub>) by the ocean leads to ocean acidification, causing the reduction of pH and the calcium carbonate saturation states of aragonite (Ω<sub>arag</sub>) and calcite (Ω<sub>calc</sub>). The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states and due to ongoing freshening and the concurrent reduction in alkalinity in this region. Here, we present projections of  C<sub>ant</sub> and ocean acidification in the Arctic Ocean over the 21<sup>st</sup> century across Earth System Models (ESMs) from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), the inter-model uncertainty of projected end-of-century Arctic Ocean Ω<sub>arag/calc</sub> is reduced by 44–64 %. The strong reduction in projection uncertainties of Ω<sub>arag/calc</sub> can be attributed to compensation between C<sub>ant</sub> uptake and alkalinity reduction in the latest models. Specifically, ESMs with a large increase in Arctic Ocean C<sub>ant</sub> over the 21<sup>st</sup> century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in C<sub>ant</sub> simulate a relatively strong freshening and concurrent alkalinity reduction. Although both mechanisms contribute to Arctic Ocean acidification over the 21<sup>st</sup> century, the increase in C<sub>ant</sub> remains the dominant driver. Even under the low-emissions shared socioeconomic pathway SSP1-2.6, basin-wide averaged aragonite undersaturation occurs before the end of the century. While under the high-emissions pathway SSP5-8.5, the Arctic Ocean mesopelagic is projected to even become undersaturated with respect to calcite. An emergent constraint, identified in CMIP5, which relates present-day maximum sea surface densities in the Arctic Ocean to the projected end-of-century Arctic Ocean C<sub>ant</sub> inventory, is found to generally hold in CMIP6. However, a coincident constraint on Arctic declines in Ω<sub>arag/calc</sub> is not apparent in the new generation of models. This is due to both the reduction in Ω<sub>arag/calc</sub> projection uncertainty and the weaker direct relationship between projected changes in Arctic Ocean C<sub>ant</sub> and Ω<sub>arag/calc</sub>. In CMIP6, models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of C<sub>ant</sub> into the Arctic Ocean interior, with simulated historical increases in C<sub>ant</sub> in improved agreement with observational products.</p>

scholarly journals Arctic Ocean acidification over the 21<sup>st</sup> century co-driven by anthropogenic carbon increases and freshening in the CMIP6 model ensemble

2020 ◽  
Author(s):  
Jens Terhaar ◽  
Olivier Torres ◽  
Timothée Bourgeois ◽  
Lester Kwiatkowski
Keyword(s):  
Ocean Acidification ◽  
Arctic Ocean ◽  
21St Century ◽  
Coupled Model ◽  
Sea Surface ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Anthropogenic Carbon ◽  
Projected Changes ◽  
Emergent Constraint

Abstract. The uptake of anthropogenic carbon (Cant) by the ocean leads to ocean acidification, causing the reduction of pH and the calcium carbonate saturation states of aragonite (Ωarag) and calcite (Ωcalc). The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states and due to ongoing freshening and the concurrent reduction in alkalinity in this region. Here, we analyse ocean acidification in the Arctic Ocean over the 21st century across 14 Earth System Models (ESMs) from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), the inter-model uncertainty of projected end-of-century Arctic Ocean Ωarag/calc is reduced by 44–64 %. The strong reduction in projection uncertainties of Ωarag/calc can be attributed to compensation between Cant uptake and alkalinity reduction in the latest models. Specifically, ESMs with a large increase in Arctic Ocean Cant over the 21st century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in Cant simulate a relatively strong freshening and concurrent alkalinity reduction. Although both mechanisms contribute to Arctic Ocean acidification over the 21st century, the increase in Cant remains the dominant driver. Even under the low-emissions shared socioeconomic pathway SSP1-2.6, basin-wide averaged arag undersaturation occurs before the end of the century. While under the high-emissions pathway SSP5-8.5, the Arctic Ocean mesopelagic is projected to even become undersaturated with respect to calcite. An emergent constraint, identified in CMIP5, which relates present-day maximum sea surface densities in the Arctic Ocean to the projected end-of-century Arctic Ocean Cant inventory, is found to generally hold in CMIP6. However, a coincident constraint on Arctic declines in Ωarag/calc is not apparent in the new generation of models. This is due to both the reduction in Ωarag/calc projection uncertainty and the weaker direct relationship between projected changes in Arctic Ocean Cant and arag/calc. In CMIP6, models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of Cant into the Arctic Ocean interior, with simulated historical increases in Cant in improved agreement with observational products.

scholarly journals The Arctic Ocean Circulation as simulated in a very high-resolution global ocean model (OCCAM)

2001 ◽  
Vol 33 ◽  
pp. 567-576 ◽  
Author(s):  
Ye. Aksenov ◽  
A.C. Coward
Keyword(s):  
High Resolution ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
Cox Model ◽  
Ocean Model ◽  
The Arctic ◽  
Global Ocean ◽  
Small Scale ◽  
The Arctic Ocean ◽  
Arctic Ocean Circulation

AbstractTo investigate the Arctic Ocean Circulation, results from a high-resolution fully global ocean model have been analyzed. The results come from two runs of the Ocean Circulation and Climate Advanced Modelling project (OCCAM) model, developed and run by the Southampton Oceanography Centre, at 1/4° × 1/4° and 1/8° × 1/8° resolution. The model is based on the Bryan-Semtner-Cox model and has 36 vertical levels. Enhancements include a free surface, an improved advection scheme and an improved treatment of the surface fresh-water flux. The model is forced with a monthly European Centre for Medium-range Weather Forecasts wind-stress climatology. It reproduces many of the fine-scale features found in the Arctic Ocean. The analysis concentrates on several of the key features, including the highly energetic eddy system in the western part of the Beaufort Sea, East Greenland West and Spitsbergen Currents and the detailed structure of the marginal currents along the Siberian and Canadian coasts. Much of the paper is focused on the water transport through the Bering and Fram Straits and through the Canadian Archipelago. Comparisons of the model net fluxes through the straits against observations are presented. The analyses of the results demonstrate the ability of the fine-resolution model to simulate features such as small-scale eddies and jets, which have some agreement with the limited observations available.

scholarly journals Arctic Ocean Water Mass Transformation in S–T Coordinates

2015 ◽  
Vol 45 (4) ◽  
pp. 1025-1050 ◽  
Author(s):  
Per Pemberton ◽  
Johan Nilsson ◽  
Magnus Hieronymus ◽  
H. E. Markus Meier
Keyword(s):  
Arctic Ocean ◽  
Ocean Circulation ◽  
Water Mass ◽  
Circulation Model ◽  
The Arctic ◽  
Global Ocean ◽  
Freshwater Flux ◽  
The Arctic Ocean ◽  
Water Mass Transformation ◽  
Water Mass Transformations

AbstractIn this paper, water mass transformations in the Arctic Ocean are studied using a recently developed salinity–temperature (S–T) framework. The framework allows the water mass transformations to be succinctly quantified by computing the surface and internal diffusive fluxes in S–T coordinates. This study shows how the method can be applied to a specific oceanic region, in this case the Arctic Ocean, by including the advective exchange of water masses across the boundaries of the region. Based on a simulation with a global ocean circulation model, the authors examine the importance of various parameterized mixing processes and surface fluxes for the transformation of water across isohaline and isothermal surfaces in the Arctic Ocean. The model-based results reveal a broadly realistic Arctic Ocean where the inflowing Atlantic and Pacific waters are primarily cooled and freshened before exiting back to the North Atlantic. In the model, the water mass transformation in the T direction is primarily accomplished by the surface heat flux. However, the surface freshwater flux plays a minor role in the transformation of water toward lower salinities, which is mainly driven by a downgradient mixing of salt in the interior ocean. Near the freezing line, the seasonal melt and growth of sea ice influences the transformation pattern.

scholarly journals Recent Sea Ice Decline Did Not Significantly Increase the Total Liquid Freshwater Content of the Arctic Ocean

2018 ◽  
Vol 32 (1) ◽  
pp. 15-32 ◽  
Author(s):  
Qiang Wang ◽  
Claudia Wekerle ◽  
Sergey Danilov ◽  
Dmitry Sidorenko ◽  
Nikolay Koldunov ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Sea Ice ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
General Circulation ◽  
The Arctic ◽  
Sea Ice Decline ◽  
The Arctic Ocean ◽  
Eurasian Basin ◽  
The Impact

Abstract The freshwater stored in the Arctic Ocean is an important component of the global climate system. Currently the Arctic liquid freshwater content (FWC) has reached a record high since the beginning of the last century. In this study we use numerical simulations to investigate the impact of sea ice decline on the Arctic liquid FWC and its spatial distribution. The global unstructured-mesh ocean general circulation model Finite Element Sea Ice–Ocean Model (FESOM) with 4.5-km horizontal resolution in the Arctic region is applied. The simulations show that sea ice decline increases the FWC by freshening the ocean through sea ice meltwater and modifies upper ocean circulation at the same time. The two effects together significantly increase the freshwater stored in the Amerasian basin and reduce its amount in the Eurasian basin. The salinification of the upper Eurasian basin is mainly caused by the reduction in the proportion of Pacific Water and the increase in that of Atlantic Water (AW). Consequently, the sea ice decline did not significantly contribute to the observed rapid increase in the Arctic total liquid FWC. However, the changes in the Arctic freshwater spatial distribution indicate that the influence of sea ice decline on the ocean environment is remarkable. Sea ice decline increases the amount of Barents Sea branch AW in the upper Arctic Ocean, thus reducing its supply to the deeper Arctic layers. This study suggests that all the dynamical processes sensitive to sea ice decline should be taken into account when understanding and predicting Arctic changes.

scholarly journals Modelling the effect of boundary scavenging on Thorium and Protactinium profiles in the ocean

2009 ◽  
Vol 6 (4) ◽  
pp. 7853-7896 ◽  
Author(s):  
M. Roy-Barman
Keyword(s):  
Arctic Ocean ◽  
Water Column ◽  
Open Ocean ◽  
The Arctic ◽  
Transport Parameters ◽  
Lateral Transport ◽  
Transport Reaction ◽  
The Pacific ◽  
The Arctic Ocean ◽  
Boundary Scavenging

Abstract. The "boundary scavenging" box model is a cornerstone of our understanding of the particle-reactive radionuclide fluxes between the open ocean and the ocean margins. However, it does not describe the radionuclide profiles in the water column. Here, I present the transport-reaction equations for radionuclides transported vertically by reversible scavenging on settling particles and laterally by horizontal currents between the margin and the open ocean. Analytical solutions of these equations are compared with existing data. In the Pacific Ocean, the model produces "almost" linear 230Th profiles (as observed in the data) despite lateral transport. However, omitting lateral transport biased the 230Th based particle flux estimates by as much as 50%. 231Pa profiles are well reproduced in the whole water column of the Pacific Margin and from the surface down to 3000 m in the Pacific subtropical gyre. Enhanced bottom scavenging or inflow of 231Pa-poor equatorial water may account for the model-data discrepancy below 3000 m. The lithogenic 232Th is modelled using the same transport parameters as 230Th but a different source function. The main source of 232Th scavenged in the open Pacific is advection from the ocean margin, whereas a net flux of 230Th produced in the open Pacific is advected and scavenged at the margin, illustrating boundary exchange. In the Arctic Ocean, the model reproduces 230Th measured profiles that the uni-dimensional scavenging model or the scavenging-ventilation model failed to explain. Moreover, if lateral transport is ignored, the 230Th based particle settling speed may by underestimated by a factor 4 at the Arctic Ocean margin. The very low scavenging rate in the open Arctic Ocean combined with the enhanced scavenging at the margin accounts for the lack of high 231Pa/230Th ratio in arctic sediments.

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