Category: Publications-summaries

Mogen, S. C., Lovenduski, N. S., Dallmann, A. R., Gregor, L., Sutton, A. J., Bograd, S. J., Quiros, N. C., Di Lorenzo, E., Hazen, E. L., Jacox, M. G., Buil, M. P., & Yeager, S. (2022). Ocean Biogeochemical Signatures of the North Pacific Blob. Geophysical Research Letters, 49(9), e2021GL096938. https://doi.org/10.1029/2021GL096938

 

Summary

The global ocean is experiencing major changes due to human-made carbon emissions and climate change, leading to a warming ocean with increasing acidity and declining oxygen. On top of these long-term changes in the ocean are short-term extreme events, such as marine heatwaves. These extreme events quickly change the ocean state and can stress marine ecosystems in multiple ways. The Northeast Pacific marine heat wave (2013–2016) was one such marine heatwave. Here we focus on the early portion of this marine heatwave, called the “Blob”. While the ocean temperature changes during the event are well understood, the effects on ocean biogeochemistry have not been fully examined. In this study, a simulation of the Blob was performed to examine short-term changes in oxygen and acidity. The authors find that the warming signal leads to a decline in the effects of ocean acidification, mainly due to changes in the movement of carbon, and lowers the amount of oxygen, due primarily to temperature-driven effects. These results suggest that some effects of climate change may be exacerbated (warming) or mitigated (ocean acidification) by marine heatwaves.

Desmet, F., Gruber, N., Köhn, E. E., Münnich, M., & Vogt, M. (2022). Tracking the Space-Time Evolution of Ocean Acidification Extremes in the California Current System and Northeast Pacific. Journal of Geophysical Research: Oceans, 127(5), e2021JC018159. https://doi.org/10.1029/2021JC018159

 

Summary

The emission of carbon dioxide by human activities causes ocean acidification (OA), that is, the decrease of the pH and saturation level of seawater with respect to the carbonate mineral aragonite. Episodic events of unusually low pH and aragonite saturation levels punctuate these long-term declines, potentially intensifying stress on marine plankton. Particularly prone to extremes is the California current system off the U.S. West Coast due to its naturally low pH-aragonite waters and its strong variability. The authors identified and characterized extreme events associated with OA in this region, and their drivers. They find extremes to have a broad range of volumes, durations, and strengths, with a quarter of them carrying corrosive conditions for shelled organisms, that is, aragonite saturation levels below 1. The largest and longest-lived events are associated with cyclonic eddies (whirls of approximately 50–100 km in diameter) that trap upwelled low pH-aragonite waters near the coast. Although representing only 3% of the events, they cause most of the total excess of acidity induced by all identified extremes. The vertical extent and duration of extremes with corrosive mean conditions are expected to impact calcifying organisms, such as pteropods.

Frémont, P., Gehlen, M., Vrac, M., Leconte, J., Delmont, T. O., Wincker, P., Iudicone, D., & Jaillon, O. (2022). Restructuring of plankton genomic biogeography in the surface ocean under climate change. Nature Climate Change, 12(4), 393–401. https://doi.org/10.1038/s41558-022-01314-8

 

Summary

The impact of climate change on diversity, functioning and biogeography of marine plankton remains a major unresolved issue. In this study, environmental niches are evidenced for plankton communities at the genomic scale for six size fractions from viruses to meso-zooplankton. The spatial extrapolation of these niches portrays ocean partitionings south of 60° N into climato-genomic provinces characterized by signature genomes. By 2090, under the high emission scenario (RCP8.5), provinces are reorganized over half of the ocean area considered, and almost all provinces are displaced poleward. Particularly, tropical provinces expand at the expense of temperate ones. Sea surface temperature is identified as the main driver of changes (50%), followed by phosphate (11%) and salinity (10%). Compositional shifts among key planktonic groups suggest impacts on the nitrogen and carbon cycles. Provinces are linked to estimates of carbon export fluxes which are projected to decrease, on average, by 4% in response to biogeographical restructuring.

 

Policy relevant message

By 2090, under the high emission scenario (RCP8.5), provinces are reorganized over half of the ocean area considered, and almost all provinces are displaced poleward. Particularly, tropical provinces expand at the expense of temperate ones. Sea surface temperature is identified as the main driver of changes (50%), followed by phosphate (11%) and salinity (10%). Compositional shifts among key planktonic groups suggest impacts on the nitrogen and carbon cycles. Provinces are linked to estimates of carbon export fluxes which are projected to decrease, on average, by 4% in response to biogeographical restructuring.

Schwinger, J., Asaadi, A., Goris, N., & Lee, H. (2022). Possibility for strong northern hemisphere high-latitude cooling under negative emissions. Nature Communications, 13(1), 1095. https://doi.org/10.1038/s41467-022-28573-5

Summary

It is well established that a collapse or strong reduction of the Atlantic meridional overturning circulation (AMOC) would substantially cool the northern high latitudes. In this study the authors show that there is a possibility that such cooling could be amplified under deliberate CO₂ removal and result in a temporary undershoot of a targeted temperature level. This behaviour was found in Earth system models that show a strong AMOC decline in response to anthropogenic forcing. Idealised simulations of CO₂ removal with one of these models indicate that the timing of negative emissions relative to AMOC decline and recovery is key in setting the strength of the temporary cooling. This study shows that the pronounced temperature-fluctuations at high northern latitudes found in these simulations would entail considerable consequences for sea-ice and permafrost extent as well as for high latitude ecosystems.

Policy relevant message:

Cooling of the northern hemisphere as a result of a collapse or strong reduction of the Atlantic meridional overturning circulation (AMOC) can be amplified by Carbon dioxide removal (CDR) techniques. Therefore, not emitting CO₂ into the atmosphere is a preferable action over post emission CO₂ removal.

Norberg, J., Blenckner, T., Cornell, S. E., Petchey, O. L., & Hillebrand, H. (2022). Failures to disagree are essential for environmental science to effectively influence policy development. Ecology Letters, 00, 1–19. https://doi.org/10.1111/ele.13984

Summary

While environmental science, and ecology in particular, is working to provide better understanding to base sustainable decisions on, the way scientific understanding is developed can at times be detrimental to this cause. Locked-in debates are often unnecessarily polarised and can compromise any common goals of the opposing camps. The present paper is inspired by a resolved debate from an unrelated field of psychology where Nobel laureate David Kahneman and Garry Klein turned what seemed to be a locked-in debate into a constructive process for their fields. The present paper is also motivated by previous discourses regarding the role of thresholds in natural systems for management and governance, but its scope of analysis targets the scientific process within complex social-ecological systems in general. The authors of this paper identified four features of environmental science that appear to predispose for locked-in debates: (1) The strongly context-dependent behaviour of ecological systems. (2) The dominant role of single hypothesis testing. (3) High prominence is given to theory demonstration compared to an investigation. (4) The effect of urgent demands to inform and steer policy. This fertile ground is further cultivated by human psychological aspects as well as the structure of funding and publication systems.

Völker, C., & Ye, Y. (2022). Feedbacks Between Ocean Productivity and Organic Iron Complexation in Reaction to Changes in Ocean Iron Supply. Frontiers in Marine Science, 9. https://doi.org/10.3389/fmars.2022.777334

Summary

Low concentrations of iron, an important micronutrient for photosynthetic organisms, limit growth in large parts of the ocean. The solubility and availability of iron are to a large degree determined by organic iron-binding molecules, so-called ligands. While ligands come from a variety of sources, many of them are produced in autotrophic (nutrition produced by organisms themselves) or heterotrophic (nutrition gained externally) production in the ocean, leading to the possibility of feedbacks between marine primary production and iron availability. The diversity of ligands, reaching from siderophores, small molecules involved in bacterial iron uptake, to breakdown products and long-lived macromolecules like humic substances, means that feedbacks could be both negative and positive or there may even be no feedback at all. The authors of this study investigate first, how the cycling of this ligand pool can be described simplistically in a model such that it reproduces the observed global distribution of dissolved iron and phosphorus as closely as possible. They show that the inclusion of a ligand similar to refractory dissolved organic carbon leads to an improved agreement with observations in our model. The inclusion of a second, shorter-lived siderophore-like ligand does not strongly affect this agreement. In a second step, the authors study how feedbacks affect how iron distribution and oceanic productivity react to changes in external supply of iron. To be consistent with present-day iron distribution, the dominant feedback is positive, increasing the sensitivity of global biological productivity and hence carbon cycling to changes in iron supply. The strength of the feedback increases with increasing ligand life-time. The negative feedback associated with siderophore-like ligands has the potential to mitigate the positive feedback, especially at the surface and for global export production, but more research on the production and decay of siderophores is needed for a better quantification. Ocean biogeochemical models that assume a constant ligand concentration and hence neglect possible feedbacks may therefore underestimate the reaction of the global carbon cycle to the strong increase in dust deposition under future or glacial climate conditions.

Pérez-Almeida, N., González, A. G., Santana-Casiano, J. M., & González-Dávila, M. (2022). Ocean Acidification Effect on the Iron-Gallic Acid Redox Interaction in Seawater. Frontiers in Marine Science, 9. https://doi.org/10.3389/fmars.2022.837363

Summary

Ocean acidification impacts the iron (Fe) biogeochemistry both its oxidation state and complexation reactions with other substances and thus affect its bioavailability to marine organisms. This has a direct effect on the ecosystems since Fe is an essential micronutrient. Some substances such as gallic acid produced by marine microorganisms can also alter the oxidation state of Fe in seawater. The authors of this study found that gallic acid impacts iron’s redox state for longer periods and thus favours its bioavailability.

Arnone, V., González-Santana, D., González-Dávila, M., González, A. G., & Santana-Casiano, J. M. (2022). Iron and copper complexation in Macaronesian coastal waters. Marine Chemistry, 240, 104087. https://doi.org/10.1016/j.marchem.2022.104087

Summary

Iron and Copper are trace metals that are bioessential micronutrients to marine organisms. In this study the authors studied dissolved concentrations of these two metals and the strength of their complexes with other substances in the surface coastal waters of the Macaronesia region (Cape Verde, Canary Islands, and Madeira). Due to biological activity and water mixing induced by the wind around the islands, dissolved metals and ligand concentrations were greater at the coastal stations than in oceanic water. Variations were observed between the eastern and western parts of Fogo, Tenerife and Gran Canaria. On the east coasts, the increase in dissolved metals and ligand concentrations were related to wind-induced water mixing. The results of this study improve our understanding of the impact of coastal areas on the Fe and Cu biogeochemical cycles.

Qiu, C., Ciais, P., Zhu, D., Guenet, B., Chang, J., Chaudhary, N., Kleinen, T., Li, X., Müller, J., Xi, Y., Zhang, W., Ballantyne, A., Brewer, S. C., Brovkin, V., Charman, D. J., Gustafson, A., Gallego-Sala, A. V, Gasser, T., Holden, J., … Westermann, S. (2022). A strong mitigation scenario maintains climate neutrality of northern peatlands. One Earth, 5(1), 86–97. https://doi.org/10.1016/j.oneear.2021.12.008

Summary

Intact peatlands remove carbon dioxide (CO₂) from the atmosphere through photosynthesis and store the carbon in soils in waterlogged conditions, while emitting methane (CH₄) to the atmosphere. The net climate impact of peatlands depends on the relative magnitude of these two greenhouse gases. In this study the authors assessed the future CO₂ and CH₄ balance of northern peatlands using five large-scale, process-based peatland models. Their results suggest that under climate policies and action, northern peatlands are likely be climate neutral because the climate-warming effect of peatland CH₄ emissions is offset by the cooling effect of peatland CO₂ sinks. However, if action on climate change is not taken, northern peatlands could accelerate global warming because CH₄ emissions are projected to increase substantially, and northern peatlands may turn from CO₂ sinks to sources driven by strong warming and drying.

Policy relevant message:

If action on climate change is not taken, northern peatlands could accelerate global warming because CH₄ emissions are projected to increase substantially, and northern peatlands may turn from CO₂ sinks to sources driven by strong warming and drying.

Bourgeois, T., Goris, N., Schwinger, J., & Tjiputra, J. F. (2022). Stratification constrains future heat and carbon uptake in the Southern Ocean between 30°S and 55°S. Nature Communications, 13(1), 340. https://doi.org/10.1038/s41467-022-27979-5

Summary
The Southern Ocean between 30°S and 55°S is a major sink of excess heat and anthropogenic carbon, but model projections of these sinks remain highly uncertain. Reducing such uncertainties is required to effectively guide the development of climate mitigation policies for meeting the ambitious climate targets of the Paris Agreement. This study shows that the large spread in the projections of future excess heat uptake efficiency and cumulative anthropogenic carbon uptake in this region are strongly linked to the models’ contemporary stratification. This relationship is robust across two generations of Earth system models and is used to reduce the uncertainty of future estimates of the cumulative anthropogenic carbon uptake by up to 53% and the excess heat uptake efficiency by 28%. These results highlight that, for this region, an improved representation of stratification in Earth system models is key to constrain future carbon budgets and climate change projections.