Factors influencing anthropogenic carbon dioxide uptake in the North Atlantic in models of the ocean carbon cycle

Abstract. In this paper, we present a database of the basic regimes of the carbon cycle in the ocean, the “ocean carbon states”, as obtained using a data mining/pattern recognition technique in observation-based as well as model data. The goal of this study is to establish a new data analysis methodology, test it and assess its utility in providing more insights into the regional and temporal variability of the marine carbon cycle. This is important as advanced data mining techniques are becoming widely used in climate and Earth sciences and in particular in studies of the global carbon cycle, where the interaction of physical and biogeochemical drivers confounds our ability to accurately describe, understand, and predict CO2 concentrations and their changes in the major planetary carbon reservoirs. In this proof-of-concept study, we focus on using well-understood data that are based on observations, as well as model results from the NASA Goddard Institute for Space Studies (GISS) climate model. Our analysis shows that ocean carbon states are associated with the subtropical–subpolar gyre during the colder months of the year and the tropics during the warmer season in the North Atlantic basin. Conversely, in the Southern Ocean, the ocean carbon states can be associated with the subtropical and Antarctic convergence zones in the warmer season and the coastal Antarctic divergence zone in the colder season. With respect to model evaluation, we find that the GISS model reproduces the cold and warm season regimes more skillfully in the North Atlantic than in the Southern Ocean and matches the observed seasonality better than the spatial distribution of the regimes. Finally, the ocean carbon states provide useful information in the model error attribution. Model air–sea CO2 flux biases in the North Atlantic stem from wind speed and salinity biases in the subpolar region and nutrient and wind speed biases in the subtropics and tropics. Nutrient biases are shown to be most important in the Southern Ocean flux bias. All data and analysis scripts are available at https://data.giss.nasa.gov/oceans/carbonstates/ (DOI: https://doi.org/10.5281/zenodo.996891).

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Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean

Biogeosciences Discussions ◽

10.5194/bgd-9-989-2012 ◽

2012 ◽

Vol 9 (1) ◽

pp. 989-1019 ◽

Cited By ~ 11

Author(s):

N. R. Bates ◽

M. H. P. Best ◽

K. Neely ◽

R. Garley ◽

A. G. Dickson ◽

...

Keyword(s):

Carbon Dioxide ◽

Atlantic Ocean ◽

Ocean Acidification ◽

North Atlantic ◽

North Atlantic Ocean ◽

The North ◽

Seawater Ph ◽

Anthropogenic Carbon ◽

The North Atlantic ◽

Anthropogenic Carbon Dioxide

Abstract. Fossil fuel use, cement manufacture and land-use changes are the primary sources of anthropogenic carbon dioxide (CO2) to the atmosphere, with the ocean absorbing 30 %. Ocean uptake and chemical equilibration of anthropogenic CO2with seawater results in a gradual reduction in seawater pH and saturation states (Ω) for calcium carbonate (CaCO3) minerals in a process termed ocean acidification. Assessing the present and future impact of ocean acidification on marine ecosystems requires detection of the multi-decadal rate of change across ocean basins and at ocean time-series sites. Here, we show the longest continuous record of ocean CO2 changes and ocean acidification in the North Atlantic subtropical gyre near Bermuda from 1983–2011. Dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) increased in surface seawater by ~40 μmol kg−1 and ~50 μatm (~20 %), respectively. Increasing Revelle factor (β) values imply that the capacity of North Atlantic surface waters to absorb CO2 has also diminished. As indicators of ocean acidification, seawater pH decreased by ~0.05 (0.0017 yr−1) and Ω values by ~7–8 %. Such data provide critically needed multi-decadal information for assessing the North Atlantic Ocean CO2sink and the pH changes that determine marine ecosystem responses to ocean acidification.

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Sensitivity analysis of an Ocean Carbon Cycle Model in the North Atlantic: an investigation of parameters affecting the air-sea CO<sub>2</sub> flux, primary production and export of detritus

Ocean Science Discussions ◽

10.5194/osd-7-1977-2010 ◽

2010 ◽

Vol 7 (6) ◽

pp. 1977-2012

Author(s):

V. Scott ◽

H. Kettle ◽

C. J. Merchant

Keyword(s):

Primary Production ◽

North Atlantic ◽

Co2 Flux ◽

Cycle Model ◽

Ocean Carbon Cycle ◽

Carbon Cycle Model ◽

The North ◽

The North Atlantic ◽

Ocean Carbon ◽

Hadley Centre

Abstract. The sensitivity of the biological parameters in a nutrient-phytoplankton-zooplankton-detritus (NPZD) model in the calculation of the air-sea CO2 flux, primary production and detrital export is analysed. The NPZD model is the Hadley Centre Ocean Carbon Cycle model (HadOCC) from the UK Met Office, used in the Hadley Centre Coupled Model 3 (HadCM3) and FAst Met Office and Universities Simulator (FAMOUS) GCMs. Here, HadOCC is coupled to the 1-D General Ocean Turbulence Model (GOTM) and forced with European Centre for Medium-Range Weather Forecasting meteorology to undertake a sensitivity analysis of its twenty biological parameters. Analyses are performed at three sites in the EuroSITES European Ocean Observatory Network: the Central Irminger Sea (60° N 40° W), the Porcupine Abyssal Plain (49° N 16° W) and the European Station for Time series in the Ocean Canary Islands (29° N 15° W) to assess variability in parameter sensitivities at different locations in the North Atlantic Ocean. Reasonable changes to the values of key parameters are shown to have a large effect on the calculation of the air-sea CO2 flux, primary production, and export of biological detritus to the deep ocean. Changes in the values of key parameters have a greater effect in more productive regions than in less productive areas. We perform the analysis using one-at-a-time perturbations and using a statistical emulator, and compare results. The most sensitive parameters are generic to many NPZD ocean ecosystem models. The air-sea CO2 flux is most influenced by variation in the parameters that control phytoplankton growth, detrital sinking and carbonate production by phytoplankton (the rain ratio). Primary production is most sensitive to the parameters that define the shape of the photosythesis-irradiance curve. Export production is most sensitive to the parameters that control the rate of detrital sinking and the remineralisation of detritus.

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Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean

Biogeosciences ◽

10.5194/bg-9-2509-2012 ◽

2012 ◽

Vol 9 (7) ◽

pp. 2509-2522 ◽

Cited By ~ 121

Author(s):

N. R. Bates ◽

M. H. P. Best ◽

K. Neely ◽

R. Garley ◽

A. G. Dickson ◽

...

Keyword(s):

Carbon Dioxide ◽

Atlantic Ocean ◽

Ocean Acidification ◽

North Atlantic ◽

North Atlantic Ocean ◽

The North ◽

Seawater Ph ◽

Anthropogenic Carbon ◽

The North Atlantic ◽

Anthropogenic Carbon Dioxide

Abstract. Fossil fuel use, cement manufacture and land-use changes are the primary sources of anthropogenic carbon dioxide (CO2) to the atmosphere, with the ocean absorbing approximately 30% (Sabine et al., 2004). Ocean uptake and chemical equilibration of anthropogenic CO2 with seawater results in a gradual reduction in seawater pH and saturation states (Ω) for calcium carbonate (CaCO3) minerals in a process termed ocean acidification. Assessing the present and future impact of ocean acidification on marine ecosystems requires detection of the multi-decadal rate of change across ocean basins and at ocean time-series sites. Here, we show the longest continuous record of ocean CO2 changes and ocean acidification in the North Atlantic subtropical gyre near Bermuda from 1983–2011. Dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) increased in surface seawater by ~40 μmol kg−1 and ~50 μatm (~20%), respectively. Increasing Revelle factor (β) values imply that the capacity of North Atlantic surface waters to absorb CO2 has also diminished. As indicators of ocean acidification, seawater pH decreased by ~0.05 (0.0017 yr−1) and ω values by ~7–8%. Such data provide critically needed multi-decadal information for assessing the North Atlantic Ocean CO2 sink and the pH changes that determine marine ecosystem responses to ocean acidification.

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Multi-decadal uptake of carbon dioxide into subtropical mode water of the North Atlantic Ocean

Biogeosciences Discussions ◽

10.5194/bgd-8-12451-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 12451-12476 ◽

Cited By ~ 4

Author(s):

N. R. Bates

Keyword(s):

Carbon Dioxide ◽

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Dissolved Inorganic Carbon ◽

Mode Water ◽

Subtropical Mode Water ◽

The North ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract. Natural climate variability impacts the multi-decadal uptake of anthropogenic carbon dioxide (Cant) into the North Atlantic Ocean subpolar and subtropical gyres. Previous studies have shown that there is significant uptake of CO2 into the subtropical mode water (STMW) that forms south of the Gulf Stream in winter and constitutes the dominant upper-ocean water mass in the subtropical gyre of the North Atlantic Ocean. Observations at the Bermuda Atlantic Time-series Study (BATS) site near Bermuda show an increase in dissolved inorganic carbon (DIC) of +1.51 ± 0.08 μmol kg−1 yr−1 between 1988 and 2011. It is estimated that the sink of CO2 into STMW was 0.985 ± 0.018 Pg C (Pg = 1015 g C) between 1988 and 2011 (~70 % of which is due to uptake of Cant). However, the STMW sink of CO2 was strongly coupled to the North Atlantic Oscillation (NAO) with large uptake of CO2 into STMW during the 1990s (NAO positive phase). In contrast, uptake of CO2 into STMW was much reduced in the 2000s during the NAO neutral/negative phase. Thus, NAO induced variability of the STMW CO2 sink is important when evaluating multi-decadal changes in North Atlantic Ocean CO2 sinks.

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Dynamical and biogeochemical control on the decadal variability of ocean carbon fluxes

Earth System Dynamics Discussions ◽

10.5194/esdd-3-1347-2012 ◽

2012 ◽

Vol 3 (2) ◽

pp. 1347-1389

Author(s):

R. Séférian ◽

L. Bopp ◽

D. Swingedouw ◽

J. Servonnat

Keyword(s):

North Atlantic ◽

North Pacific ◽

Carbon Flux ◽

Carbon Fluxes ◽

Modes Of Variability ◽

The North ◽

The North Atlantic ◽

Ocean Carbon ◽

The North Pacific ◽

Regional Variance

Abstract. Several recent observation-based studies suggest that ocean anthropogenic carbon uptake has slowed down due to the impact of anthropogenic forced climate change. However, it remains unclear if detected changes over the recent time period can really be attributed to anthropogenic climate change or to natural climate variability (internal plus naturally forced variability). One large uncertainty arises from the lack of knowledge on ocean carbon flux natural variability at the decadal time scales. To gain more insights into decadal time scales, we have examined the internal variability of ocean carbon fluxes in a 1000-yr long preindustrial simulation performed with the Earth System Model IPSL-CM5A-LR. Our analysis shows that ocean carbon fluxes exhibit low-frequency oscillations that emerge from their year-to-year variability in the North Atlantic, the North Pacific, and the Southern Ocean. In our model, a 20-yr mode of variability in the North Atlantic air-sea carbon flux is driven by sea surface temperature variability and accounts for ~40% of the interannual regional variance. The North Pacific and the Southern Ocean carbon fluxes are also characterized by decadal to multi-decadal modes of variability (10 to 50 yr) that account for 30–40% of the interannual regional variance. But these modes are driven by the vertical supply of dissolved inorganic carbon through the variability of Ekman-induced upwelling and deep-mixing events. Differences in drivers of regional modes of variability stem from the coupling between ocean dynamics variability and the ocean carbon distribution, which is set by large-scale secular ocean circulation.

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