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Sharks and Tuna in the Deep

9 November 2023
Biology, Geology

At https://sciencedaily.com/releases/2023/11/231107131931.htm … microfossils of algae have been found in rocks in western Australia. These seem to push back the beginning of life forms on the geochronological tree. It is thought they coincide with the sudden rise in oxygen in earth’s atmosphere and oceans – roughly 2.4 billion years ago.

At https://phys.org/news/2023-11-historical-volcanic-eruptions-triggered-short-term.html … very cold periods of climate are said to coincide with volcanoes – especially in the far noth. Cold decades occur in the AD540s, 1450s, and for most of the 1600s. Research by an international team based at the University of St Andrews reveal high latitude volcanic eruptions caused dramatic, but short lived, climate cooling. The necessary requirement are eruptions rich in sulfate particles that are able to reflect incoming sunlight. The origin of the said volcanoes is an unknown. However, sulfates are present in isotopes found in Greenland ice cores – and the results correlate with tree ring low growth episodes. All are known factors but now confirmed. Mike Baillie was saying much the same in the 1990s. This seems to imply any connection with other causes can be ignored, such as heavy meteoric activity, or solar minimums such as Sporer and Maunder. They aren’t mentioned but funnily enough, they do say short lived – as in two or three years of cold weather. In order to get a  whole decade that is cold does that require a succession of eruptions? or are the other factors still in play? After all, meteors and dim Suns are a feature of written documents in all those periods cited. While it is likely that some volcanoes can cause a burst of cold weather that hardly explains the Little Ice Age as a whole.

The research involved a relook at the isotopes in ice cores and it was found that sulfate content was only half of what it was previously considered. Hence, the role of sulfates would seem to be exaggerated somewhat – but is that splitting hairs. See also the full info at https://doi.org/10.1073/pnas.2221810120 … which should explain in detail what the authors have in mind.

Finally, at https://phys.org/news/2023-11-animals-dark-deep-sea.html … sharks spend a fraction of their time near the surface – but a lot of their time is spent out of sight. It seems large predatory fish such as sharks, tuna, and billfish, dive deep into the depths, 200m to 1000m below the surface, and spend most of the daylight hours there. Information derived from tagging fish was used to discover the places they visited – and the depths came as a surprise. Is there food available at that depth? It is when the Sun sets that these fish are more likely to be near the surface, feeding. Hence, sharks are around during the night time hours but not so much during the middle of the day.

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