Abrupt shifts in 21st-century plankton communities

Cael, B. B., Dutkiewicz, S., & Henson, S. (2021). Abrupt shifts in 21st-century plankton communities. Science Advances, 7(44), eabf8593. https://doi.org/10.1126/sciadv.abf8593

Summary

Marine microbial communities are critical in sustaining ocean food webs. However, these communities will change with climate through gradual or foreseeable changes but likely have much more substantial consequences when sudden and unpredictable. Through a complex mathematical model of marine microbial ecosystem, the authors of this study found that climate change–driven shifts over the 21st century are often abrupt, large in amplitude and extent, and unpredictable using standard early warning signals. Phytoplankton (microscopic marine algae) with unique resource needs are prone to abrupt shifts. These abrupt shifts in biomass, biological productivity, and phytoplankton community structure are concentrated in Atlantic and Pacific subtropics. Abrupt changes in environmental variables such as temperature and nutrients rarely precede these ecosystem shifts, indicating that rapid community restructuring can occur in response to gradual environmental changes, particularly in nutrient supply rate ratios.

 

Marine high temperature extremes amplify the impacts of climate change on fish and fisheries

Cheung, W. W. L., Frölicher, T. L., Lam, V. W. Y., Oyinlola, M. A., Reygondeau, G., Sumaila, U. R., Tai, T. C., Teh, L. C. L., & Wabnitz, C. C. C. (2021). Marine high temperature extremes amplify the impacts of climate change on fish and fisheries. Science Advances, 7(40), eabh0895. https://doi.org/10.1126/sciadv.abh0895

Summary

Extreme temperature events have occurred in all ocean basins in the past two decades with detrimental impacts on marine biodiversity, ecosystem functions, and services. However, global impacts of temperature extremes on fish stocks, fisheries, and dependent people have not been quantified. This study, using a mathematical model, projected that, on average, when an annual high temperature extreme occurs in an exclusive economic zone, 77% of exploited fishes and invertebrates therein will decrease in biomass while maximum catch potential will drop by 6%, adding to the decadal-scale mean impacts under climate change. The net negative impacts of high temperature extremes on fish stocks are projected to cause losses in fisheries revenues and livelihoods in most maritime countries, creating shocks to fisheries social-ecological systems particularly in climate-vulnerable areas. This study highlights the need for rapid adaptation responses to extreme temperatures in addition to carbon mitigation to support sustainable ocean development.

Policy relevant message:

When an annual high temperature extreme occurs in an exclusive economic zone, 77% of exploited fishes and invertebrates therein will decrease in biomass while maximum catch potential will drop by 6%, adding to the decadal-scale mean impacts under climate change. This study highlights the need for rapid adaptation responses to extreme temperatures in addition to carbon mitigation to support sustainable ocean development.

Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth system model

Tivig, M., Keller, D. P., & Oschlies, A. (2021). Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth system model. Biogeosciences, 18(19), 5327–5350. https://doi.org/10.5194/bg-18-5327-2021

Summary

Nitrogen is one of the most important elements for life in the ocean. A major source is the riverine discharge of dissolved nitrogen. While global models often omit rivers as a nutrient source, the authors of this study included nitrogen from rivers in the Earth system computational model. They found that additional nitrogen affected marine biology not only locally but also in regions far off the coast. Depending on regional conditions, primary production was enhanced or even decreased due to internal feedbacks in the nitrogen cycle. This study highlights the importance of incorporation of riverine nitrogen input in the earth system models.

COMFORT General Assembly 2021

 

The general assembly 2021 of the H2020 project took place digitally 15-17 September with 80-90 participants from Europe, Australia, India, Japan, South Africa, US west coast and Hawaii in parallel. The plenary agenda included a suite of science highlights from all work packages, which included presentations from early career scientists, but also a region-oriented session, a poster session, a stakeholder group exchange session as well as a discussion with the international advisory board, and recommendations from our EU adviser. One of the highlights of the meeting was a fantastic presentation from Colin Jones (UK MetOffice) entitled “An overview of CMIP6: Robustness of results across the multi-model, multi-MIP ensemble“. We are pleased that the project is still on track despite the challenging situation in the ongoing crisis thanks to highly motivated scientists within the consortium. We also hope for an in-person meeting in 2022!

 

Future phytoplankton diversity in a changing climate

Henson, S. A., Cael, B. B., Allen, S. R., & Dutkiewicz, S. (2021). Future phytoplankton diversity in a changing climate. Nature Communications, 12(1), 5372. https://doi.org/10.1038/s41467-021-25699-w

Summary

The future response of marine ecosystem diversity to continued anthropogenic forcing is not well understood. Phytoplankton are a diverse set of organisms (microscopic marine algae) that form the base of the marine ecosystem. This study finds that the community structure becomes increasingly unstable in response to climate change over the 21st century. This implies a loss of ecological resilience with likely knock-on effects on the productivity and functioning of the marine environment.

Significant variability of structure and predictability of Arctic Ocean surface pathways affects basin-wide connectivity

Wilson, C., Aksenov, Y., Rynders, S., Kelly, S. J., Krumpen, T., & Coward, A. C. (2021). Significant variability of structure and predictability of Arctic Ocean surface pathways affects basin-wide connectivity. Communications Earth & Environment, 2(1), 164. https://doi.org/10.1038/s43247-021-00237-0

Summary

The Arctic Ocean is of central importance for the global climate and ecosystem. It is a region undergoing rapid climate change, with a dramatic decrease in sea ice cover over recent decades. Surface pathways connect the transport of nutrients, freshwater, carbon and contaminants with their sources and sinks. Pathways of drifting material are deformed, due to atmosphere-ocean-ice coupling. Deformation is largest at fine space- and time-scales and is associated with a loss of potential predictability, analogous to weather often becoming unpredictable. However, neither satellite observations nor climate model projections resolve fine-scale processes responsible for this. The authors of this study used a high-resolution ocean model to determine these fine scale physical processes and transport pathways and their interannual variability.

Pathways to sustaining tuna-dependent Pacific Island economies during climate change

Bell, J. D., Senina, I., Adams, T., Aumont, O., Calmettes, B., Clark, S., Dessert, M., Gehlen, M., Gorgues, T., Hampton, J., Hanich, Q., Harden-Davies, H., Hare, S. R., Holmes, G., Lehodey, P., Lengaigne, M., Mansfield, W., Menkes, C., Nicol, S., … Williams, P. (2021). Pathways to sustaining tuna-dependent Pacific Island economies during climate change. Nature Sustainability, 4(10), 900–910. https://doi.org/10.1038/s41893-021-00745-z


Summary

Climate-driven redistribution of tuna threatens to disrupt the economies of Pacific Small Island Developing States (SIDS) and sustainable management of the world’s largest tuna fishery. This study shows that by 2050, under a high greenhouse gas emissions scenario (RCP 8.5), the total biomass of three tuna species in the waters of ten Pacific SIDS could decline by an average of 13% due to a greater proportion of fish occurring in the high seas. The potential implications for Pacific Island economies in 2050 include an average decline in purse-seine catch of 20%, an average annual loss in regional tuna-fishing access fees of US$90 million and reductions in government revenue of up to 13% for individual Pacific SIDS. However, redistribution of tuna under a lower-emissions scenario (RCP 4.5) is projected to reduce the purse-seine catch from the waters of Pacific SIDS by an average of only 3%, indicating that even greater reductions in greenhouse gas emissions, in line with the Paris Agreement, would provide a pathway to sustainability for tuna-dependent Pacific Island economies. An additional pathway involves Pacific SIDS negotiating within the regional fisheries management organization to maintain the present-day benefits they receive from tuna, regardless of the effects of climate change on the distribution of the fish.


Policy relevant message:

By 2050, under a high greenhouse gas emissions scenario (RCP 8.5), the total biomass of three tuna species in the waters of ten Pacific Small Island Developing States (SIDS) could decline by an average of 13%. The potential implications for Pacific Island economies in 2050 include an average decline in purse-seine catch of 20%, an average annual loss in regional tuna-fishing access fees of US$90 million and reductions in government revenue of up to 13% for individual Pacific SIDS. Redistribution of tuna under a lower-emissions scenario (RCP 4.5) is projected to reduce the purse-seine catch from the same waters by only 3%, indicating that even greater reductions in greenhouse gas emissions, in line with the Paris Agreement, would provide a pathway to sustainability for tuna-dependent Pacific Island economies. An additional pathway involves Pacific SIDS negotiating within the regional fisheries management organization to maintain the present-day benefits they receive from tuna, regardless of the effects of climate change on the distribution of the fish.

Labrador Slope Water connects the subarctic with the Gulf Stream

New, A. L., Smeed, D. A., Czaja, A., Blaker, A. T., Mecking, J. V, Mathews, J. P., & Sanchez-Franks, A. (2021). Labrador Slope Water connects the subarctic with the Gulf Stream. Environmental Research Letters, 16(8), 84019. https://doi.org/10.1088/1748-9326/ac1293

Summary

Labrador Slope Water (LSLW) is a relatively fresh and cool water mass north of the Gulf Stream in the North Atlantic. Due to changes in wind stress in the subpolar region these waters are brought into close proximity with the Gulf Stream. Therefore, the Labrador Slope Water offers a new mechanism for decadal variability in the Atlantic climate system, through connecting the subarctic with the Gulf Stream and the Atlantic Meridional Overturning Circulation (AMOC).

Constraining Global Marine Iron Sources and Ligand-Mediated Scavenging Fluxes With GEOTRACES Dissolved Iron Measurements in an Ocean Biogeochemical Model

Somes, C. J., Dale, A. W., Wallmann, K., Scholz, F., Yao, W., Oschlies, A., Muglia, J., Schmittner, A., & Achterberg, E. P. (2021). Constraining Global Marine Iron Sources and Ligand-Mediated Scavenging Fluxes With GEOTRACES Dissolved Iron Measurements in an Ocean Biogeochemical Model. Global Biogeochemical Cycles, 35(8), e2021GB006948. https://doi.org/10.1029/2021GB006948

Summary

Iron is a key, bio essential micronutrient controlling phytoplankton growth in vast regions of the global ocean. Despite its importance, uncertainties remain high regarding external iron source fluxes and internal marine cycling on a global scale, including removal (scavenging) rates and mechanisms. Iron concentrations in the ocean are affected not only by the source fluxes but also by the presence of ligands, compounds that maintain iron in a dissolved form (more bioavailable) and counteract removal mechanisms (transferring dissolved iron to particulate, less bioavailable form). In this study, the authors used a global dissolved iron (Fe) data set, including GEOTRACES measurements, to constrain source and scavenging fluxes in the marine iron component of a global ocean biogeochemical numerical model. The variable ligand parameterization improved the global model-data misfit the most, suggesting that bacteria are an important source of ligands to the ocean. Further parameterization of atmospheric deposition and release of iron from sediments further improved the model most notably in the surface ocean. High scavenging rates were then required to maintain the iron inventory. The model simulates a tight spatial coupling between source inputs and scavenging rates, which may be too strong due to underrepresented ligands near source inputs, contributing to large uncertainties when constraining individual fluxes with dissolved iron concentrations. Model biases remain high and are discussed to help improve global marine iron cycle models.

The Sensitivity of the Marine Carbonate System to Regional Ocean Alkalinity Enhancement

Burt, D. J., Fröb, F., & Ilyina, T. (2021). The Sensitivity of the Marine Carbonate System to Regional Ocean Alkalinity Enhancement. Frontiers in Climate, 3, 68. https://doi.org/10.3389/fclim.2021.624075

Summary

Ocean Alkalinity Enhancement (OAE) simultaneously counteracts atmospheric concentrations of CO2 and ocean acidification; however, no previous studies have investigated the response of the marine carbonate system response to alkalinity enhancement on regional scales. This is a first modelling study focusing on regional implementations of OAE that can sequester more atmospheric CO2 than a global implementation. The authors revealed that regional alkalinity enhancement has the capacity to exceed carbon uptake by global OAE. Additionally, while the marine carbonate system becomes less sensitive to alkalinity enhancement in all modelled experiments globally, regional responses to enhanced alkalinity vary depending upon the background concentrations of dissolved inorganic carbon and total alkalinity. Furthermore, the Subpolar North Atlantic displays a previously unexpected alkalinity sensitivity increase in response to high total alkalinity concentrations.