The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities

Fontela, M., Pérez, F. F., Carracedo, L. I., Padín, X. A., Velo, A., García-Ibañez, M. I., & Lherminier, P. (2020). The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities. Scientific Reports, 10 (1), 14714. https://doi.org/10.1038/s41598-020-71793-2

Summary:

The oceanic uptake of atmospheric carbon dioxide (CO2) emitted by human activities alters the seawater carbonate system. The increase of atmospheric CO2 leads to an increase in ocean anthropogenic carbon (Cant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate undersaturation. In this study the authors examined the chemical status of the Northeast Atlantic by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). A progression to undersaturation with respect to carbonate could compromise the conservation of the habitats and ecosystem services developed by benthic marine calcifiers inhabiting the mid-layer depth range, such as the cold-water corals (CWC) communities. The authors also stressed that for each additional ppm in atmospheric pCO2 the waters surrounding CWC communities lose carbonate at a rate of − 0.17 ± 0.02 μmol kg−1 ppm−1. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ will avoid the exhaustion of excess carbonate in the Northeast Atlantic.

Policy relevant message:

Increasing amount of atmospheric CO2 causes alterations of oceanic carbon system, which leads to destructions of cold-water corals. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ is critical to avoid further alterations of carbon system in the Northeast Atlantic.

Reemergence of Anthropogenic Carbon Into the Ocean’s Mixed Layer Strongly Amplifies Transient Climate Sensitivity

Rodgers, K. B., Schlunegger, S., Slater, R. D., Ishii, M., Frölicher, T. L., Toyama, K., Plancherel, Y., Aumont, O., & Fassbender, A. J. (2020). Reemergence of Anthropogenic Carbon Into the Ocean’s Mixed Layer Strongly Amplifies Transient Climate Sensitivity. Geophysical Research Letters, 47 (18), e2020GL089275. https://doi.org/10.1029/2020GL089275

Summary:

A positive marine chemistry‐climate feedback was originally proposed by Revelle and Suess (1957, https://doi.org/10.3402/tellusa.v9i1.9075), whereby the invasion flux of anthropogenic carbon into the ocean serves to inhibit future marine CO2 uptake through reductions to the buffering capacity of surface seawater. In this paper, an ocean circulation‐carbon cycle model was used to identify an upper limit on the impact of reemergence of anthropogenic carbon into the ocean’s mixed layer on the cumulative airborne fraction of CO2 in the atmosphere. The study authors found under an RCP8.5 emissions pathway (with steady circulation) that the cumulative airborne fraction of CO2 has a sevenfold reduction by 2100 when the CO2 buffering capacity of surface seawater is maintained at preindustrial levels. The results results indicate that the effect of reemergence of anthropogenic carbon into the mixed layer on the buffering capacity of CO2 amplifies the transient climate sensitivity of the Earth system.

Tracking Improvement in Simulated Marine Biogeochemistry Between CMIP5 and CMIP6

Séférian, R., Berthet, S., Yool, A., Palmiéri, J., Bopp, L., Tagliabue, A., Kwiatkowski, L., Aumont, O., Christian, J., Dunne, J., Gehlen, M., Ilyina, T., John, J. G., Li, H., Long, M. C., Luo, J. Y., Nakano, H., Romanou, A., Schwinger, J., … Yamamoto, A. (2020). Tracking Improvement in Simulated Marine Biogeochemistry Between CMIP5 and CMIP6. Current Climate Change Reports, 6(3), 95–119. https://doi.org/10.1007/s40641-020-00160-0

Summary:

Increasing availability of ocean biogeochemical data, as well as an improved understanding of the underlying processes, allows advances in the marine biogeochemical components of the current generation of ESMs. The present study scrutinizes the extent to which marine biogeochemistry components of ESMs have progressed between the 5th and the 6th phases of the Coupled Model Intercomparison Project (CMIP).

The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6

Robson, J., Aksenov, Y., Bracegirdle, TJ, Dimdore-Miles, O., Griffiths, PT, Grosvenor, DP, Hodson, DLR, Keeble, J., MacIntosh, C., Megann, A., Osprey, S., Povey, AC, Schröder, D., Yang, M., Archibald, AT, Carslaw, KS, Gray, L., Jones, C., Kerridge, B.,… Wilcox, LJ (2020). The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6. Journal of Advances in Modeling Earth Systems, 12 (9), e2020MS002126. https://doi.org/10.1029/2020MS002126

Summary:

The North Atlantic climate system plays an important role in regulating Earth’s climate, and variability within the Atlantic can have important impacts on society. However, we do not understand all the linkages between different parts of the North Atlantic. Furthermore, climate simulations, which are an essential tool for improving our understanding, have shortcomings that can affect their utility. New developments in Earth System climate simulations could remedy these shortcomings. The extent to which the addition of complex Earth system developments have changed or improved the simulation of the physical climate is still unknown. In this paper, a multidisciplinary evaluation of the North Atlantic climate in simulations made with the UK’s Earth System Model, UKESM1 is presented. The simulations made with UKESM1 capture many aspects of the North Atlantic climate and that human activities have a large impact on the North Atlantic in UKESM1. Nevertheless, some shortcomings of the simulations, many of which are like those seen in physical climate simulations are highlighted. The authors stressed the importance of further development of both the physical and Earth system components to improve climate simulations in the future.

Contrasting Upper and Deep Ocean Oxygen Response to Protracted Global Warming

Frölicher, T. L., Aschwanden, M. T., Gruber, N., Jaccard, S. L., Dunne, J. P., & Paynter, D. (2020). Contrasting Upper and Deep Ocean Oxygen Response to Protracted Global Warming. Global Biogeochemical Cycles, 34 (8), e2020GB006601. https://doi.org/10.1029/2020GB006601

Summary:

It is well established that the ocean is currently losing dissolved oxygen (O2) in response to ocean warming (the solubility of O2 decreases with increasing seawater temperature resulting in less O2 available to marine life). However, the long‐term equilibrium response of O2 to a warmer climate is neither well quantified nor understood. In this study, multimillennial global warming simulations with a comprehensive Earth system model was used to show that the equilibrium response in ocean O2 differs fundamentally from the ongoing transient response. The deep ocean is better ventilated and oxygenated compared to preindustrial conditions, even though the deep ocean is substantially warmer. In contrast, O2 in most of the upper tropical ocean is substantially depleted. This study emphasizes the millennial‐scale impact of global warming on marine life, with some impacts emerging many centuries or even millennia after atmospheric CO2 has stabilized.

Policy relevant message:

The impact of global climate change on marine life not only is already clearly visible and well recorded, but the millennial‐scale impact of global warming will also emerge many centuries or even millennia after atmospheric CO2 has stabilized.

Climate change, tropical fisheries and prospects for sustainable development

Lam, V. W. Y., Allison, E. H., Bell, J. D., Blythe, J., Cheung, W. W. L., Frölicher, T. L., Gasalla, M. A., & Sumaila, U. R. (2020). Climate change, tropical fisheries and prospects for sustainable development. Nature Reviews Earth & Environment, 1(9), 440–454. https://doi.org/10.1038/s43017-020-0071-9

Summary:

Tropical fisheries substantially contribute to the well-being of societies in both the tropics and the extratropics, the latter through ‘telecoupling’ — linkages between distant human–natural systems. Tropical marine habitats and fish stocks, however, are vulnerable to the physical and biogeochemical oceanic changes associated with rising greenhouse gases. These changes to fish stocks, and subsequent impacts on fish production, have substantial implications for the UN Sustainable Development Goals. In this Review, the effects of climate change on tropical marine fisheries are synthesised, highlighting the socio-economic impacts to both tropical and extratropical nations, and discuss potential adaptation measures. Driven by ocean warming, acidification, deoxygenation and sea-level rise, the maximum catch potential of tropical fish stocks in some tropical exclusive economic zones is projected to decline by up to 40% by the 2050s under the RCP8.5 emissions scenario, relative to the 2000s. Climate-driven reductions in fisheries production and alterations in fish-species composition will subsequently increase the vulnerability of tropical countries with limited adaptive capacity. Thus, given the billions of people dependent on tropical marine fisheries in some capacity, there is a clear need to account for the effects of climate change on these resources and identify practical adaptations when building climate-resilient sustainable-development pathways.

Time of Emergence and Large Ensemble Intercomparison for Ocean Biogeochemical Trends

Schlunegger, S., Rodgers, KB, Sarmiento, JL, Ilyina, T., Dunne, JP, Takano, Y., Christian, JR, Long, MC, Frölicher, TL, Slater, R., & Lehner, F. (2020). Time of Emergence and Large Ensemble Intercomparison for Ocean Biogeochemical Trends. Global Biogeochemical Cycles, 34 (8), e2019GB006453. https://doi.org/10.1029/2019GB006453

Summary:

Man‐made climate change is causing physical, chemical, and biological changes in the ocean. In this study the Earth system models (climate models with an interactive carbon cycle) were used to estimate when these man‐made changes will be significantly larger than, and therefore distinguishable from, natural fluctuations in the climate and oceans. The models investigated in this study agreed that changes in sea surface temperature and the strength of the ocean carbon sink should already or will soon be detectable in the current observational record. Changes in the upper ocean biological cycling of carbon, photosynthetic activity, and salinity, however, are less certain and will take many more decades of monitoring in order for man‐made changes to potentially become visible. The authors examined sources of uncertainty inherent to projecting the ocean’s future over the coming decades and found that uncertainty in the ocean’s natural variability can be as important as uncertainty across different climate models and uncertainty in how much carbon humans will emit.

Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projection

Kwiatkowski, L., Torres, O., Bopp, L., Aumont, O., Chamberlain, M., Christian, JR, Dunne, JP, Gehlen, M., Ilyina, T., John, JG, Lenton, A ., Li, H., Lovenduski, NS, Orr, JC, Palmieri, J., Santana-Falcón, Y., Schwinger, J., Séférian, R., Stock, CA,… Ziehn, T. (2020). Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections. Biogeosciences, 17 (13), 3439–3470. https://doi.org/10.5194/bg-17-3439-2020

Summary:

In this study, 21st century projections of marine biogeochemistry in the CMIP6 Earth system models were assessed. These models represent the most up-to-date understanding of climate change. The models generally project greater surface ocean warming, acidification, subsurface deoxygenation, and euphotic nitrate reductions but lesser primary production declines than the previous generation of models. This has major implications for the impact of anthropogenic climate change on marine ecosystems.

Operationalizing Ocean Health: Toward Integrated Research on Ocean Health and Recovery to Achieve Ocean Sustainability

Franke, A., Blenckner, T., Duarte, C. M., Ott, K., Fleming, L. E., Antia, A., Reusch, T. B. H., Bertram, C., Hein, J., Kronfeld-Goharani, U., Dierking, J., Kuhn, A., Sato, C., van Doorn, E., Wall, M., Schartau, M., Karez, R., Crowder, L., Keller, D., … Prigge, E. (2020). Operationalizing Ocean Health: Toward Integrated Research on Ocean Health and Recovery to Achieve Ocean Sustainability. One Earth, 2(6), 557–565. https://doi.org/10.1016/j.oneear.2020.05.013

Summary:

Protecting the ocean has become a major goal of international policy as human activities increasingly endanger the integrity of the ocean ecosystem, often summarized as “ocean health.” By and large, efforts to protect the ocean have failed because, among other things, (1) the underlying socio-ecological pathways have not been properly considered, and (2) the concept of ocean health has been ill defined. Collectively, this paper prevents an adequate societal response as to how ocean ecosystems and their vital functions for human societies can be protected and restored. The authors reviewed the confusion surrounding the term “ocean health” and suggested an operational ocean-health framework in line with the concept of strong sustainability. Given the accelerating degeneration of marine ecosystems, the restoration of regional ocean health will be of increasing importance. The advocated transdisciplinary and multi-actor framework presented in this study, can help to advance the implementation of more active measures to restore ocean health and safeguard human health and well-being.

Evaluation of Data-Based Estimates of Anthropogenic Carbon in the Arctic Ocean

Terhaar, J., Tanhua, T., Stöven, T., Orr, J. C., & Bopp, L. (2020). Evaluation of Data-Based Estimates of Anthropogenic Carbon in the Arctic Ocean. Journal of Geophysical Research: Oceans, 125(6), e2020JC016124. https://doi.org/https://doi.org/10.1029/2020JC016124

Summary:

The Arctic Ocean is particularly vulnerable to ocean acidification, a process that is mainly driven by the uptake of anthropogenic carbon (Cant) from the atmosphere. Although Cant concentrations cannot be measured directly in the ocean, they have been estimated using data‐based methods and as a result, the total amount of Cant in the Arctic Ocean in 2005 was 8% higher and was estimated to be 3.3 ± 0.3 Pg C. In this study the authors estimated that all Arctic waters, from surface to depth, would become corrosive to aragonite by the middle of the next century even if atmospheric CO2 could be stabilized at 540 ppm.

Policy relevant message:

All Arctic waters, from surface to depth, will become corrosive to essential chemical carbonic species by the middle of the next century even if atmospheric CO2 could be stabilized at 540 ppm (>416 ppm as of February 20211).

1 https://www.esrl.noaa.gov/gmd/ccgg/trends/