Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models

Frölicher, Thomas L.; Sarmiento, Jorge L.; Paynter, David; Dunne, John; Krasting, John P.; Winton, Michael

doi:10.1175/jcli-d-14-00117.1

Cited by 540 publications

(512 citation statements)

References 95 publications

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“…Meanwhile, less than half of the heat stored on the equatorward flank of the ACC (40-50 • S) is derived from local surface heat uptake; the rest is due to convergence of heat by the ocean. These patterns are broadly consistent with previous modeling studies 26,27 and the observations ( Fig. 1).…”

supporting

confidence: 93%

Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

et al. 2016

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The Southern Ocean has shown little warming south of the Antarctic Circumpolar Current (ACC) over recent decades, and Antarctic sea-ice cover has been modestly expanding 1 . Along the northern flank of the ACC, however, the upper ocean has been warming rapidly 2, 3 . Using observations and general circulation model simulations, we show that these patterns -of delayed warming south of the ACC and enhanced warming to the north -are fundamentally shaped by the Southern Ocean's meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas induced heat uptake is largely balanced by anomalous northward heat transport; and heat is preferentially stored along the northern flank of the ACC, where surface waters are subducted.Further, we find that these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in atmospheric and oceanic circulations play a secondary role. These findings suggest that the Southern Ocean responds to greenhouse gas forcing on the timescale over which the deep ocean waters that are upwelled 1

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confidence: 93%

Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

et al. 2016

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“…Here, regions critical for biological production and carbon uptake are associated with mode and intermediate water formation locations (Sarmiento et al, 2004;Sallée et al, 2012). Despite the fact that the simulated net uptake rates of atmospheric CO 2 in the SO are mostly overestimated compared to the values derived from observations (as shown in this study), Frölicher et al (2015) show that the CMIP5 models underestimate the anthropogenic-carbon storage in the Southern Ocean. This indicates either a shortcoming in the simulated large-scale overturning circulation or too strong a sink of non-anthropogenic carbon simulated here.…”

Section: Discussionmentioning

confidence: 44%

The Southern Ocean as a constraint to reduce uncertainty in future ocean carbon sinks

Kessler

Tjiputra

2016

Earth Syst. Dynam.

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Abstract. Earth system model (ESM) simulations exhibit large biases compares to observation-based estimates of the present ocean CO 2 sink. The inter-model spread in projections increases nearly 2-fold by the end of the 21st century and therefore contributes significantly to the uncertainty of future climate projections. In this study, the Southern Ocean (SO) is shown to be one of the hot-spot regions for future uptake of anthropogenic CO 2 , characterized by both the solubility pump and biologically mediated carbon drawdown in the spring and summer. We show, by analyzing a suite of fully interactive ESMs simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) over the 21st century under the high-CO 2 Representative Concentration Pathway (RCP) 8.5 scenario, that the SO is the only region where the atmospheric CO 2 uptake rate continues to increase toward the end of the 21st century. Furthermore, our study discovers a strong inter-model link between the contemporary CO 2 uptake in the Southern Ocean and the projected global cumulated uptake over the 21st century. This strong correlation suggests that models with low (high) carbon uptake rate in the contemporary SO tend to simulate low (high) uptake rate in the future. Nevertheless, our analysis also shows that none of the models fully capture the observed biophysical mechanisms governing the CO 2 fluxes in the SO. The inter-model spread for the contemporary CO 2 uptake in the Southern Ocean is attributed to the variations in the simulated seasonal cycle of surface pCO 2 . Two groups of model behavior have been identified. The first one simulates anomalously strong SO carbon uptake, generally due to both too strong a net primary production and too low a surface pCO 2 in December-January. The second group simulates an opposite CO 2 flux seasonal phase, which is driven mainly by the bias in the sea surface temperature variability. We show that these biases are persistent throughout the 21st century, which highlights the urgent need for a sustained and comprehensive biogeochemical monitoring system in the Southern Ocean to better constrain key processes represented in current model systems.

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“…A large spread across all models was found (nearly 6 fold) and the spatial distribution of soil carbon, especially in the northern latitudes was found to be poor in comparison to HWSD and NCSCD, which means that most ESMs were poorly representing grid-scale soil carbon. Frölicher et al (2015) showed that CMIP5 models appeared to capture the observed pattern of anthropogenic carbon storage in the ocean, particularly in the Southern Ocean. However, overall they underestimate the magnitude of the observed oceanic global anthropogenic carbon storage since the pre-industrial.…”

Section: T Ziehn Et Al: Access-esm1 Historical Simulationsmentioning

confidence: 99%

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

et al. 2017

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Abstract. Over the last decade many climate models have evolved into Earth system models (ESMs), which are able to simulate both physical and biogeochemical processes through the inclusion of additional components such as the carbon cycle. The Australian Community Climate and Earth System Simulator (ACCESS) has been recently extended to include land and ocean carbon cycle components in its ACCESS-ESM1 version. A detailed description of ACCESS-ESM1 components including results from pre-industrial simulations is provided in Part 1. Here, we focus on the evaluation of ACCESS-ESM1 over the historical period in terms of its capability to reproduce climate and carbon-related variables. Comparisons are performed with observations, if available, but also with other ESMs to highlight common weaknesses. We find that climate variables controlling the exchange of carbon are well reproduced. However, the aerosol forcing in ACCESS-ESM1 is somewhat larger than in other models, which leads to an overly strong cooling response in the land from about 1960 onwards. The land carbon cycle is evaluated for two scenarios: running with a prescribed leaf area index (LAI) and running with a prognostic LAI. We overestimate the seasonal mean (1.7 vs. 1.4) and peak amplitude (2.0 vs. 1.8) of the prognostic LAI at the global scale, which is common amongst CMIP5 ESMs. However, the prognostic LAI is our preferred choice, because it allows for the vegetation feedback through the coupling between LAI and the leaf carbon pool. Our globally integrated land-atmosphere flux over the historical period is 98 PgC for prescribed LAI and 137 PgC for prognostic LAI, which is in line with estimates of land use emissions (ACCESS-ESM1 does not include land use change).The integrated ocean-atmosphere flux is 83 PgC, which is in agreement with a recent estimate of 82 PgC from the Global Carbon Project for the period 1959-2005. The seasonal cycle of simulated atmospheric CO 2 is close to the observed seasonal cycle (up to 1 ppm difference for the station at Mace Head and up to 2 ppm for the station at Mauna Loa), but shows a larger amplitude (up to 6 ppm) in the high northern latitudes. Overall, ACCESS-ESM1 performs well over the historical period, making it a useful tool to explore the change in land and oceanic carbon uptake in the future.

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Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models

Cited by 540 publications

References 95 publications

Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

The Southern Ocean as a constraint to reduce uncertainty in future ocean carbon sinks

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

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