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

Published 06 July 2020: Kwiatkowski, L., O. Torres, L. Bopp, O. Aumont, M. Chamberlain, J.R. Christian, J.P. Dunne, M. Gehlen, T. Ilyina, J.G. John, A. Lenton, H. Li, N.S. Lovenduski, J.C. Orr, J. Palmieri, Y. Santana-Falcón, J. Schwinger, R. Séférian, C.A. Stock, A. Tagliabue, Y. Takano, J. Tjiputra, K. Toyama, H. Tsujino, M. Watanabe, A. Yamamoto, A. Yool, and T. Ziehn: Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections, Biogeosciences, 17, 3439–3470, 2020. https://doi.org/10.5194/bg-17-3439-2020

Summary

We assess 21st century projections of marine biogeochemistry in the CMIP6 Earth system models. 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.

Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2

Published 15 June 2020: MacDougall, A.H., T.L. Frölicher, C.D. Jones, J. Rogelj, H.D. Matthews, K. Zickfeld, V.K. Arora, N.J. Barrett, V. Brovkin, F.A. Burger, M. Eby, A.V. Eliseev, T. Hajima, P.B. Holden, A. Jeltsch-Thömmes, C. Koven, N. Mengis, L. Menviel, M. Michou, I.I. Mokhov, A. Oka, J. Schwinger, R. Séférian, G. Shaffer, A. Sokolov, K. Tachiiri, J. Tjiputra, A. Wiltshire, and Tilo Ziehn: Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2, Biogeosciences, 17, 2987–3016, 2020. https://doi.org/10.5194/bg-17-2987-2020

Summary

The Zero Emissions Commitment (ZEC) is the change in global temperature expected to occur following the complete cessation of CO2 emissions. The authors of this study used 18 climate models to assess the value of ZEC. Through their experiments they found that ZEC 50 years after emissions cease is between −0.36 to +0.29 °C. The most likely value of ZEC was assessed to be close to zero. However, substantial continued warming for decades or centuries following cessation of CO2 emission cannot be ruled out.

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

Published 08 June 2020: Franke, A., T. Blenckner, C.M. Duarte, K. Ott, L.E. Fleming, A. Antia, T.B.H. Reusch, C. Bertram, J. Hein, U. Kronfeld-Goharani, J. Dierking, A. Kuhn, C. Sato, E. van Doorn, M. Wall, M. Schartau, R. Karez, L. Crowder, D. Keller, A. Engel, U. Hentschel, and E. Prigge: Operationalizing Ocean Health: Toward Integrated Research on Ocean Health and Recovery to Achieve Ocean Sustainability, One Earth, 2, 557–65, 2020. 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 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

Published 11 May 2020: Terhaar, J., T. Tanhua, T. Stöven, J. C. Orr, and L. Bopp: Evaluation of Data‐Based Estimates of Anthropogenic Carbon in the Arctic Ocean, Journal of Geophysical Research: Oceans, 125, e2020JC016124, 2020. 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 author 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.

Can we project changes in fish abundance and distribution in response to climate?

Published 07 May 2020: Fernandes, J.A., L. Rutterford, S.D. Simpson, M. Butenschön, T.L. Frölicher, A. Yool, W.W.L. Cheung, A. Grant: Can we project changes in fish abundance and distribution in response to climate? Glob Change Biol. , vol 2020:00, 1–15, 2020. https://doi.org/10.1111/gcb.15081

Summary

Large scale and long-term changes in fish abundance and distribution in response to climate change have been simulated using both statistical and process-based models. However, national and regional fisheries management requires also shorter-term projections on smaller spatial scales, and these need to be validated against fisheries data. A 26-year time series of fish surveys with high spatial resolution in the North East Atlantic provides a unique opportunity to assess the ability of models to correctly simulate the changes in fish distribution and abundance that occurred in response to climate variability and change. In this study, a model forced by physical-biogeochemical output from eight ocean models was used to simulate changes in fish abundance and distribution at scales down to a spatial resolution of 0.5°. When comparing the model simulation with the available fish survey, authors concluded that predictions based on different biogeochemical models are often more similar to each other than they are to the survey data, except for some pelagic species. Additionally, the authors stressed that model results can be used to guide fisheries management at larger spatial scales, but more caution is needed at smaller scales.

Information content of absorption spectra and implications for ocean color inversion

Published on 27 April 2020: Cael, B.B., A. Chase, E. Boss: Information content of absorption spectra and implications for ocean color inversion, Applied Optics, 59, 13, 3971-3984, 2020. https://doi.org/10.1364/AO.389189

Summary

The increasing use of hyperspectral optical data in oceanography, both in situ and via remote sensing, holds the potential to significantly advance characterization of marine ecology and biogeochemistry because, in principle, it can provide much more detailed inferences of ecosystem properties via inversion. This study focuses on complementary approaches to quantify the degrees of freedom in hyperspectral measurements in the case of in situ particulate absorption measurements, though these approaches can also be used on other such data, e.g., ocean colour remote sensing.

Marine heatwaves exacerbate climate change impacts for fisheries in the northeast Pacific

Published on 21 April 2020: Cheung, W.W.L., and T.L. Frölicher: Marine heatwaves exacerbate climate change impacts for fisheries in the northeast Pacific, Scientific Reports, 10, 6678, 10 pages, 2020. https://doi.org/10.1038/s41598-020-63650-z

Summary

Marine heatwaves (MHWs) have occurred in all ocean basins with severe negative impacts on coastal and ocean ecosystems. The northeast Pacific 2013–2015 MHW received major societal concerns. Yet, the knowledge about how MHWs impact fish stocks is limited. The authors of this study combined various model outputs to simulate responses of major northeast Pacific fish stocks to MHWs and showed that MHWs cause biomass decrease and shifts in biogeography of fish stocks with projected a doubling of impact levels by 2050 amongst the most important fisheries species over previous assessments. The authors stress the additional challenges from MHWs for fisheries and their management under climate change.

Is deoxygenation detectable before warming in the thermocline?

Published on 07 April 2020: Hameau, A., T.L. Frölicher, J. Mignot, and F. Joos: Is deoxygenation detectable before warming in the thermocline? Biogeosciences, 17, 1877–1895, 2020. https://doi.org/10.5194/bg-17-1877-2020

Summary

Anthropogenic greenhouse gas emissions cause ocean warming and oxygen depletion, with adverse impacts on marine organisms and ecosystems. Warming is one of the main indicators of anthropogenic climate change, but thermocline1, changes in oxygen and other biogeochemical tracers may be a result of natural variability prior to warming. In about a third (35±11 %) of the global thermocline deoxygenation emerges prior to warming. In these regions, both reduced ventilation and reduced solubility add to the oxygen decline. In addition, reduced ventilation slows the propagation of anthropogenic warming from the surface into the ocean interior, further contributing to the delayed emergence of warming compared to deoxygenation. This study underlines the importance of an ocean biogeochemical observing system and that the detection of anthropogenic impacts becomes more likely when using multi-tracer observations.

1Thermocline: a sudden temperature change in water column, distinct from temperature of a layer above and below.

Global vulnerability of marine mammals to global warming

Published on 03 March 2020: Albouy, C., V. Delattre, G. Donati, T.L. Frölicher, S. Albouy-Boyer, M. Rufino, L. Pellissier, D. Mouillot, and Fabien Leprieur: Global vulnerability of marine mammals to global warming, Scientific Reports, 10:548, 12 pages, 2020. https://doi.org/10.1038/s41598-019-57280-3

Summary

Although extinctions due to climate change are still uncommon, they might surpass those caused by habitat loss or overexploitation over the next few decades. Among marine megafauna, mammals fulfil key and irreplaceable ecological roles in the ocean, and the collapse of their populations may therefore have irreversible consequences for ecosystem functioning and services. Using a model approach, this study assessed the vulnerability of all marine mammals to global warming under high and low greenhouse gas emission scenarios for the middle and the end of the 21st century. Furthermore, the North Pacific Ocean, the Greenland Sea and the Barents Sea host the species that are most vulnerable to global warming. The authors of this study stressed the importance of these regions in future conservation plans, where there are long histories of overexploitation and there are high levels of current threats to marine mammals. Beyond species loss, the potential extinctions of the marine mammals that were most vulnerable to global warming might induce a disproportionate loss of functional diversity, which may have profound impacts on the future functioning of marine ecosystems worldwide.

They Came From the Pacific: How Changing Arctic Currents Could Contribute to an Ecological Regime Shift in the Atlantic Ocean

Published 05 February 2020: Kelly, S.J., E. Popova , Y. Aksenov, R. Marsh , and A. Yool: They Came From the Pacific: How Changing Arctic Currents Could Contribute to an Ecological Regime Shift in the Atlantic Ocean, Ocean. Earth’s Future, 8, e2019EF001394, 2020. https://doi.org/10.1029/2019EF001394

Summary

With a warming Arctic Ocean, it has been suggested that the ocean currents that connect the Pacific to the Atlantic may change. This could have potential biological consequences, including bringing Pacific species of plankton to the Atlantic. We investigate how the pathways bringing Pacific water to the Atlantic have changed, identify a pathway that takes less time that other routes to bring waters from Pacific to the Atlantic (but that is only occasionally available), and note that even the shortest timescales are over 2 years.