Author: Dagmara Rusiecka

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.

Ziegler, M., Anton, A., Klein, S. G., Rädecker, N., Geraldi, N. R., Schmidt-Roach, S., Saderne, V., Mumby, P. J., Cziesielski, M. J., Martin, C., Frölicher, T. L., Pandolfi, J. M., Suggett, D. J., Aranda, M., Duarte, C. M., & Voolstra, C. R. (2021). Integrating environmental variability to broaden the research on coral responses to future ocean conditions. Global Change Biology, 27(21), 5532–5546. https://doi.org/10.1111/gcb.15840

Summary

Our understanding of the response of reef-building corals to changes in their physical environment is largely based on laboratory experiments, analysis of long-term field data, and model projections. Experimental data provide unique insights into how organisms respond to variation of environmental drivers. However, an assessment of how well experimental conditions cover the breadth of environmental conditions and variability where corals live successfully is missing. In this study the authors compiled and analysed a globally distributed dataset of local seasonal and daily cycle variability of key environmental drivers (temperature (ocean warming), pCO₂ (ocean acidification), and O₂ ocean deoxygenation)) critical for the growth and livelihood of reef-building corals. The authors compared the variability of environmental conditions set in coral experimental studies to current and projected conditions in their natural habitats. The scientists found that annual temperature profiles projected for the end of the 21st century were characterized by distributional shifts in temperatures with warmer winters and longer warm periods in the summer, not just peak temperatures. Furthermore, short-term hourly fluctuations of temperature and pCO₂ may regularly expose corals to conditions beyond the projected average increases for the end of the 21st century. Coral reef sites varied in the degree of coupling between temperature, pCO₂, and dissolved O₂, which warrants site-specific, differentiated experimental approaches depending on the local hydrography and influence of biological processes on the carbonate system and O₂ availability. This study highlights that a large portion of the natural environmental variability at short and long timescales is underexplored in experimental designs, which may provide a path to extend our understanding on the response of corals to global 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.

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).

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.

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.

Carracedo, L. I., Mercier, H., McDonagh, E., Rosón, G., Sanders, R., Moore, C. M., Torres-Valdés, S., Brown, P., Lherminier, P., & Pérez, F. F. (2021). Counteracting Contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: Enhanced Imbalance in 2010. Global Biogeochemical Cycles, 35(6), e2020GB006898. https://doi.org/10.1029/2020GB006898

Summary

The North Atlantic Ocean is a major reservoir which absorbs atmospheric carbon dioxide (CO₂) due in part to the extensive plankton (microscopic marine algae) blooms which form there supported by nutrients supplied by ocean circulation. Hence, changes in ocean circulation and/or stratification (separation of the water column into layers with different densities caused by differences in temperature or salinity or both) may influence biological production and carbon export into the deep ocean. In this study, the inorganic nutrient budgets for 2004 and 2010 are evaluated in the North Atlantic based on observations from the transatlantic the Greenland-Portugal section. The water column nutrient budgets were split into upper and lower limbs. The authors found that in 2010 an anomalous circulation led to an enhanced northward transport of more nutrient-rich waters by the upper limb. This anomalous circulation event favoured an enhancement of the nutrient consumption and associated biological CO₂ uptake, which represents a 50% of the mean annual sea–air CO₂ flux in the region. These results indicate that the upper limb modulates the biological carbon uptake, and the lower limb modulates nutrient inventories in the North Atlantic.

Fontela, M., Velo, A., Gilcoto, M., & Pérez, F. F. (2021). Anthropogenic CO2 and ocean acidification in Argentine Basin Water Masses over almost five decades of observations. Science of The Total Environment, 779, 146570. https://doi.org/10.1016/j.scitotenv.2021.146570

Summary:

This study evaluated chemical data from eleven hydrographic cruises conducted between 1972-2019 in the Argentine Basin, western South Atlantic Ocean. The aim was to quantify natural and human induced stressors in the carbon system. The authors reported an increase of the mean annual atmospheric carbon dioxide concentration (CO₂^atm) from 325 to 408 ppm of volume (ppm) (64%) in a 47 year time-span covered this study. This increase leads to an increase in anthropogenic carbon (C_ant) across all the water column and consequently to ocean acidification (a decrease in excess carbonate), in particular in the upper and intermediate water masses, that in the Argentine Basin region are very sensitive to changes in carbon system. The large rate of intermediate water masses acidification is a combined effect of carbon uptake, deoxygenation, and increased remineralization of organic matter. If CO₂ emissions follow the path of business-as-usual emissions (SSP 5.85), the upper water masses would become undersaturated with respect to carbonate ion concentrations at the end of the century. The undersaturation in the intermediate water masses in the region of the Argentine Basin is virtually unavoidable.

 

Policy relevant message:

The upper water masses in the Argentine Basin region will become undersaturated with respect to carbonate ion concentrations at the end of the century if CO₂ emissions follow the path of business-as-usual emissions. The undersaturation in the intermediate water masses in the region is virtually unavoidable.

García-Lafuente, J., Sammartino, S., Huertas, I. E., Flecha, S., Sánchez-Leal, R. F., Naranjo, C., Nadal, I., & Bellanco, M. J. (2021). Hotter and Weaker Mediterranean Outflow as a Response to Basin-Wide Alterations. Frontiers in Marine Science, 8, 150. https://doi.org/10.3389/fmars.2021.613444

Summary

Time series collected from 2004 to 2020 at an oceanographic station located nearby the Strait of Gibraltar to monitor the Mediterranean outflow into the North Atlantic. Data collected at this station provides insights into changes occurring in the Mediterranean basin. The water mass exchange at the Strait of Gibraltar has decreased slightly and a warming trend was recorded in the deepest layer of the outflow from 2013 onwards. This trend is an order of magnitude greater than any other reported so far in the water masses of the Mediterranean Sea. Biogeochemical (pH) data display a negative trend indicating a gradual acidification of the outflow in the monitoring station. According to data analysis of this study, Levantine Intermediate Water contribution in the outflow is progressively getting larger. This study adds to growing evidence of the impact of acidification and warming of the Mediterranean Sea basin.

Policy relevant message:

This study adds to growing evidence that the Mediterranean Sea is progressively getting warmer and more acidic and therefore more corrosive to many vital marine species.