Diatoms are under threat of decline due to ocean acidification, a study shows

Diatomeoj estas sub minaco de malkresko pro oceana acidiĝo, studo montras

Global effects of slower silica dissolution under OA. a, Differences in the global vertical distribution of Si (OH)4 (zoned average for Atlantic and Pacific Ocean), including depiction of the OA-driven downward transport of Si and its capture in the deep ocean. AABW, Antarctic groundwater; AAIW, Antarctic middle water; CDW, circumpolar deep water; NADW, North Atlantic deep water; NPDW, North Pacific deep water; SAMW, sub-Antarctic water regime. b, OA impact on global diatom biomass under RCP8.5 and RCP6.0 emission scenarios. c, Spatial distribution of the difference in diatom biomass. Results show the net effect of the OA-driven slowdown of silica solution (OA), given as the difference to the standard model configuration (i.e., including effects of climate change, but excluding OA effects on Si dissolution). Panels a and c show results from year 2200 of the RCP8.5 simulation. Credit: Nature (2022). DOI: 10.1038 / s41586-022-04687-0

While calcifying organisms such as oysters and corals have difficulty forming their shells and skeletons in more acidic seawater, diatoms have been considered less sensitive to the effects of ocean acidification – a chemical change triggered by the consumption of carbon dioxide (CO).2). The world’s tiny diatoms use silicon, a compound of silicon, oxygen and hydrogen, as a building material for their shells. However, researchers at the GEOMAR Helmholtz Center for Ocean Research Kiel, the New Zealand Institute of Geological and Nuclear Sciences Limited and the University of Tasmania have now demonstrated for the first time that diatoms are under threat in a study published in Nature. For the study, researchers linked a general analysis of various data sources with the Earth system modeling. The findings provide a new assessment of the global impact of ocean acidification.

As a result of ocean acidification, the silicon shells of diatoms dissolve more slowly. This is not an advantage – it causes diatoms to sink into deeper layers of water before they chemically dissolve and are converted back into silica. As a result, this food is more efficiently exported to the deep ocean and thus becomes scarcer in the light-flooded surface layer, where new shells need to be formed. This is causing a decrease in diatoms, according to the scientists in their recent publication. Diatoms contribute 40 percent of plant biomass production in the ocean and are the basis of many marine food webs. They are also the main driver of the biological carbon pump that transports CO2 into the deep ocean for long-term conservation.

Dr. Jan Taucher, marine biologist at GEOMAR and first author of the study, says, “With a general analysis of field experiments and observational data, we wanted to know how ocean acidification affects diatoms worldwide. Our current understanding of ecology. mostly based on small-scale experiments, that is, from a particular place at a particular time.These findings can be misleading if the complexity of the Earth’s system is not taken into account.Our study uses diatoms as an example. “Because diatoms are one of the most important plankton groups in the ocean, their decline could cause a major change in the marine food web or even a change for the ocean as a carbon sink.”

Decreased diatoms due to ocean acidification

Biological oceanographer Jan Taucher is working on the mesocosm. Mesocosms are a type of large-volume, oversized test tube in the ocean with a capacity of tens of thousands of liters, in which changes in environmental conditions can be studied in a closed but otherwise natural ecosystem. Credit: Ulf Riebesell / GEOMAR

The meta-analysis examined data from five mesocosmic studies from 2010 to 2014, from different ocean regions ranging from the Arctic to subtropical waters. Mesocosms are a type of large-volume, oversized test tube in the ocean with a capacity of tens of thousands of liters, in which changes in environmental conditions can be studied in a closed but otherwise natural ecosystem. For this purpose, the water enclosed in the mesocosms has been enriched in carbon dioxide to respond to future scenarios with moderate to high increases in atmospheric CO2 levels. For the present study, the chemical composition of organic material from sediment traps was assessed as it sank through the water contained in the experimental containers during several weeks of experiments. Combined with measurements of the water column, an accurate picture of biogeochemical processes within the ecosystem has emerged.

The findings from the mesocosmic studies could be confirmed using global observational data from the open ocean. They show – according to the results of the meta-analysis – a lower dissolution of the silicon shells at a higher seawater acidity. With the resulting data, simulations were performed in an Earth system model to assess the ocean-wide consequences of the observed trends.

“By the end of this century, we expect a loss of up to ten percent of diatoms. That’s huge if you consider how important they are to life in the ocean and to the climate system,” Dr. Taucher continued. “However, it is important to think beyond 2100. Climate change will not stop abruptly, and global effects in particular need some time to become clearly visible. Depending on the amount of emissions, our model in the study predicts a loss of up to 27. percent silica in surface waters and an ocean-wide decline in diatoms of up to 26 percent by 2200 – more than a quarter of the current population. “

This finding of the study contrasts sharply with the previous state of ocean exploration, which sees calcification organisms as losers and diatoms less affected by. ocean acidification. Professor Ulf Riebesell, a marine biologist at GEOMAR and head of mesocosmic experiments, adds, “This study again highlights the complexity of the Earth’s system and the related difficulty in predicting the consequences of man-made climate change as a whole. kindly remind us once again of the incalculable risks we run if we do not oppose climate change quickly and decisively. ”

A study examines the effects of ocean acidification on phytoplankton’s energy reserves

More information:
Jan Taucher et al., Improved silica exports in the future ocean trigger global diatom decline, Nature (2022). DOI: 10.1038 / s41586-022-04687-0

Quote: Diatoms are under threat of decline due to ocean acidification, study shows (2022, May 25) taken on May 26, 2022 from https://phys.org/news/2022-05-diatoms-threat-decline-due- ocean.html

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