Author: Marina

Jeltsch-Thömmes, A., Stocker, T. F., & Joos, F. (2020). Hysteresis of the Earth system under positive and negative CO2 emissions. Environmental Research Letters, 15(12), 124026. https://doi.org/10.1088/1748-9326/abc4af

Summary:

Carbon dioxide removal (CDR) from the atmosphere is part of all emission scenarios of the IPCC that limit global warming to below 1.5 °C. In this study, hysteresis characteristics were investigated in 4 x pre-industrial atmospheric CO₂ concentration scenarios with exponentially increasing and decreasing CO₂ using the Bern3D-LPX Earth system model. Hysteresis is quantified as the difference in a variable between the up and down pathway at identical cumulative carbon emissions. Due to hysteresis, sustained negative emissions are required to return to and keep a CO₂ and warming target. The results suggest, that not emitting carbon in the first place is preferable over carbon dioxide removal, even if technologies would exist to efficiently remove CO₂ from the atmosphere and store it away safely.

Policy relevant message:

Not emitting carbon in the first place is preferable over carbon dioxide removal, even if technologies would exist to efficiently remove CO₂ from the atmosphere and store it away safely.

Fontela, M., Pérez, F. F., Mercier, H., & Lherminier, P. (2020). North Atlantic Western Boundary Currents Are Intense Dissolved Organic Carbon Streams. In Frontiers in Marine Science (Vol. 7, p. 1050). https://www.frontiersin.org/article/10.3389/fmars.2020.593757

Summary:

In the North Atlantic, there are two main western boundary currents related to the Atlantic Meridional Overturning Circulation (AMOC): the Gulf Stream flowing northward and the Deep Western Boundary Current (DWBC) flowing southward. The authors of this study analysed the data from the OVIDE section (GO-SHIP A25 Portugal-Greenland 40–60°N) that crosses the DWBC and the northward extension of the Gulf Stream, the North Atlantic Current. This study shows that North Atlantic western boundary currents play a key role in the transport of dissolved organic matter, specifically dissolved organic carbon (DOC). Revisited transports and budgets of DOC with new available data identify the eastern Subpolar North Atlantic (eSPNA) as an important source of locally produced organic matter for the North Atlantic and a key region in the supply of bioavailable DOC to the deep ocean. The East Greenland Current, and its upstream source the East Reykjanes Ridge Current on the eastern flank of the mid-Atlantic ridge, are export pathways of bioavailable DOC toward subtropical latitudes. The fast overturning and subsequent remineralization of DOC produced in the autotrophic eSPNA explains up to 38% of the total oxygen consumption in the deep North Atlantic between the OVIDE section and 24°N. Carbon budgets that do not take into account this organic remineralization process overestimates the natural uptake of carbon dioxide (CO₂) from the atmosphere by one third. The inclusion of DOC transports in regional carbon budgets reconciles the estimates of CO₂ uptake in the North Atlantic between model and observations.

Padin, X. A., Velo, A., & Pérez, F. F. (2020). ARIOS: a database for ocean acidification assessment in the Iberian upwelling system (1976–2018). Earth System Science Data, 12(4), 2647–2663. https://doi.org/10.5194/essd-12-2647-2020

Summary:

The ARIOS (Acidification in the Rias and the Iberian Continental Shelf) database holds biogeochemical information from 3357 oceanographic stations, giving 17 653 discrete samples. This unique collection is a starting point for evaluating ocean acidification in the Iberian upwelling system, characterized by intense biogeochemical interactions as an observation-based analysis, or for use as inputs in a coupled physical–biogeochemical model to disentangle these interactions at the ecosystem level.

Hauck, J., Zeising, M., Le Quéré, C., Gruber, N., Bakker, D. C. E., Bopp, L., Chau, T. T. T., Gürses, Ö., Ilyina, T., Landschützer, P., Lenton, A., Resplandy, L., Rödenbeck, C., Schwinger, J., & Séférian, R. (2020). Consistency and Challenges in the Ocean Carbon Sink Estimate for the Global Carbon Budget. In Frontiers in Marine Science (Vol. 7, p. 852). https://www.frontiersin.org/article/10.3389/fmars.2020.571720

Summary:

Based on the 2019 assessment of the Global Carbon Project, the ocean took up on average, 2.5 ± 0.6 PgC yr⁻¹ or 23 ± 5% of the total anthropogenic CO₂ emissions over the decade 2009–2018. This sink estimate is based on simulation results from global ocean biogeochemical models (GOBMs) and is compared to data-products based on observations of surface ocean pCO₂ (partial pressure of CO₂) accounting for the outgassing of river-derived CO₂. In this study, the GOBM simulations are evaluated by comparing the simulated surface ocean pCO₂ to observations. Based on this comparison, the simulations are well-suited for quantifying the global ocean carbon sink on the time-scale of the annual mean and its multi-decadal trend, as well as on the time-scale of multi-year variability, despite the large model-data mismatch on the seasonal time-scale. Biases in GOBMs comparison have a small effect on the global mean ocean sink (0.05 PgC yr⁻¹), but need to be addressed to improve the regional budgets and model-data comparison. Additionally, GOBMs and data-products point consistently to a shift from a tropical CO₂ source to a CO₂ sink in recent years. On average, the GOBMs reveal less variations in the sink than the data-based products. Despite the reasonable simulation of surface ocean pCO₂ by the GOBMs, there are discrepancies between the resulting sink estimate from GOBMs and data-products. These discrepancies are within the uncertainty of the river flux adjustment, increase over time, and largely stem from the Southern Ocean. Progress in our understanding of the global ocean carbon sink necessitates significant advancement in modeling and observing the Southern Ocean carbon sink including (i) a game-changing increase in high-quality pCO₂ observations, and (ii) a critical re-evaluation of the regional river flux adjustment.

Reygondeau, G., Cheung, W. W. L., Wabnitz, C. C. C., Lam, V. W. Y., Frölicher, T., & Maury, O. (2020). Climate Change-Induced Emergence of Novel Biogeochemical Provinces. In Frontiers in Marine Science (Vol. 7, p. 657). https://www.frontiersin.org/article/10.3389/fmars.2020.00657

Summary:

The global ocean is commonly partitioned into 4 biomes subdivided into 56 biogeochemical provinces (BGCPs). Each province corresponds to a unique regional environment that shapes biodiversity and constrains ecosystem structure and functions. Biogeochemical provinces are dynamic entities that change their spatial extent and position with climate and are expected to be perturbated in the near future by global climate change. In this study, the changes in spatial distribution of BGCPs from 1950 to 2100 using three earth system models under two representative concentration pathways (RCP 2.6: zero CO₂ emissions by 2100 and RCP 8.5: “no mitigation”) were characterised. Projection of the future distribution of BGCPs also revealed the emergence of new climate that has no analog with past and current environmental conditions. These novel environmental conditions, are named No-Analog BGCPs State (NABS), will cover areas where a substantial proportion of global marine biodiversity presently occurs and with a crucial dependence on seafood production and will expand from 2040 to 2100 at a rate of 4.3 Mkm² per decade (1.2% of the global ocean). The NABS were characterized by very warm mean annual temperatures, high salinity, low oxygen concentration and low net primary production. Most marine species will be physiologically stressed under such conditions, which could impact their survival rate. This study subsequently quantified the potential number of marine species and annual volume of fisheries catches that would experience such novel environmental conditions to roughly evaluate the impact of NABS on ecosystem services. If the global climate is not kept below 2°C warming, NABS areas can be expected to emerge, as early as 20 years from the 2010s. It would affect 19% of the total number of exploited species in 2050 and 59% in 2100 and would cover regions that are currently responsible for 8% of global marine fisheries catch in 2050 and 30% in 2100, under RCP 8.5. These numbers would change to only 15% of exploited species and 5% of total fisheries catches in NABS areas by the end of the 21st century under the RCP 2.6 scenario. Mitigating anthropogenic pressures at a level sufficient to reach the Paris agreement targets would therefore substantially reduce the risk of emergence of large NABS regions in the global ocean, and the dramatic consequences that such large-scale ecological changes would entail for tropical marine biodiversity, associated fisheries and the human communities that they support.

Policy relevant message:

The environmental changes that would occur in the global ocean along a “no mitigation” RCP 8.5 scenario would lead to a drastic reorganization of global marine biogeography, associated biodiversity and trophic networks. If the global climate is not kept below 2°C warming, these novel areas can be expected to emerge, as early as 20 years from the 2010s. It would affect 19% of the total number of exploited species in 2050 and 59% in 2100 and would cover regions that are currently responsible for 8% of global marine fisheries catch in 2050 and 30% in 2100, under RCP 8.5. These numbers would change to only 15% of exploited species and 5% of total fisheries catches in these novel areas by the end of the 21st century under the RCP 2.6 scenario (zero CO₂ emissions by 2100). Mitigating anthropogenic pressures at a level sufficient to reach the Paris agreement targets would therefore substantially reduce the risk of emergence of large NABS regions in the global ocean, and the dramatic consequences that such large-scale ecological changes would entail for tropical marine biodiversity, associated fisheries and the human communities that they support.

Burger, F. A., John, J. G., & Frölicher, T. L. (2020). Increase in ocean acidity variability and extremes under increasing atmospheric CO2. Biogeosciences, 17(18), 4633–4662. https://doi.org/10.5194/bg-17-4633-2020

Summary:

Ensemble simulations of an Earth system model reveal that ocean acidity extremes have increased in the past few decades and are projected to increase further in terms of frequency, intensity, duration, and volume extent. The increase is not only caused by the long-term ocean acidification due to the uptake of anthropogenic CO₂, but also due to changes in short-term variability. The increase in ocean acidity extremes may enhance the risk of detrimental impacts on marine organisms.

Policy relevant message:

Ocean acidity extremes have increased in the past few decades and are projected to increase further in terms of frequency, intensity, duration, and volume extent which may enhance the risk of detrimental impacts on marine organisms.

Álvarez-Salgado, X. A., Otero, J., Flecha, S., & Huertas, I. E. (2020). Seasonality of Dissolved Organic Carbon Exchange Across the Strait of Gibraltar. Geophysical Research Letters, 47(18), e2020GL089601. https://doi.org/10.1029/2020GL089601

Summary:

The Mediterranean Sea is a semi enclosed basin connected with the Atlantic Ocean through the Strait of Gibraltar. At this hot spot of ocean circulation, about 0.8 Sv (1 Sv = 106 m³ s⁻¹) of dissolved organic carbon (DOC) rich Atlantic Surface Water enters the Mediterranean Sea and the same volume of DOC poor Mediterranean Overflow Water flows oppositely to the Atlantic Ocean. Both DOC concentrations and water flows are not stationary but vary seasonally. Differences in the amplitude and timing of those seasonal cycles produce a marked bimodal variation in the net DOC flux of Atlantic water that enters the Mediterranean Sea, with minima in late June and late October and maxima in mid‐April and late August. This pattern has been observed for the first time and allowed the authors to better constrain this organic carbon flux, which represents about half of the total input of DOC in the Mediterranean Sea and supports about one third of its net organic carbon demand.

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 (C_ant) 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.

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:

In this work, the authors demonstrate that the net ocean uptake of anthropogenic carbon is strongly sensitive to perturbations in the CO₂ buffering capacity of surface ocean waters. This result is closely connected to the process of reemergence of anthropogenic carbon from the ocean interior to the surface mixed layer. In this paper, they used an ocean circulation‐carbon cycle model 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. They find 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 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.