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.

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.

Contrasting drivers and trends of ocean acidification in the subarctic Atlantic

Pérez, F. F., Olafsson, J., Ólafsdóttir, S. R., Fontela, M., & Takahashi, T. (2021). Contrasting drivers and trends of ocean acidification in the subarctic Atlantic. Scientific Reports, 11(1), 13991. https://doi.org/10.1038/s41598-021-93324-3

Summary

The processes of warming and acidification in the subarctic zone of the North Atlantic are unequivocal in the time-series measurements of the Iceland (IS-TS, 1985–2003) and Irminger Sea (IRM-TS, 1983–2013) stations. Both stations show high rates of acidification with different rates of warming, salinification (water becoming more saline) and stratification (separation of the water column into layers with different densities caused by differences in temperature or salinity or both) linked to regional water circulation. Furthermore, warming contributes to the increase in acidification at the IRM-TS.

A committed fourfold increase in ocean oxygen loss

Oschlies, A. (2021). A committed fourfold increase in ocean oxygen loss. Nature Communications, 12(1), 2307. https://doi.org/10.1038/s41467-021-22584-4

Summary:

Less than a quarter of ocean deoxygenation that will ultimately be caused by historical CO2 emissions is already realized, according to millennial-scale model simulations that assume zero CO2 emissions from year 2021 onwards. About 80% of the committed oxygen loss occurs below 2000 m depth, where a more sluggish overturning circulation will increase water residence times and accumulation of respiratory oxygen demand. According to the model results, the deep ocean will thereby lose more than 10% of its pre-industrial oxygen content even if CO2 emissions and thus global warming were stopped today. In the surface layer, however, the ongoing deoxygenation will largely stop once CO2 emissions are stopped. Accounting for the joint effects of committed oxygen loss and ocean warming, metabolic viability representative for marine animals declines by up to 25% over large regions of the deep ocean, posing an unavoidable escalation of anthropogenic pressure on deep-ocean ecosystems.

Policy relevant message:

In the surface layer, the ongoing deoxygenation will largely stop once CO2 emissions are stopped. The deep ocean, however, will lose more than 10% of its pre-industrial oxygen content even if CO2 emissions and thus global warming were stopped today, posing an unavoidable escalation of anthropogenic pressure on deep-ocean ecosystems.