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How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now, let alone during the pr

How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now, let alone during the previous interglacial periods [2] which were markedly warmer than the Holocene (i.e. the current interglacial period)? If there was a marked reduction in ocean life due to reduced oxygen levels that should be visible in fossil records. If there was no such reduction then why would there be one now? Increased CO₂ has led to a markedly "greener" planet [3] - the increase was enough to cover the US twice in vegetation by 2016. Those plants produce oxygen during photosynthesis (6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂) which is released to the environment (air or water) during daylight hours leading to a higher oxygen concentration. I suspect this balance between higher atmospheric CO₂ which leads to an increase in vegetation which then leads to an increase in oxygen production is what kept ocean life from succumbing due to oxygen deprivation during those periods when the average temperature was much higher than it is now. If this happened then, why would it not happen now? [1] https://en.wikipedia.org/wiki/Holocene_climatic_optimum https://en.wikipedia.org/wiki/Holocene_climatic_optimum [2] https://en.wikipedia.org/wiki/Quaternary_glaciation#/media/File:Vostok_Petit_data.svg https://en.wikipedia.org/wiki/Quaternary_glaciation#/media/F... [3] https://www.nature.com/articles/nclimate3004 https://www.nature.com/articles/nclimate3004

thulle 3y ago
> How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now From your wikipedia link: ---8<--- A study in 2020 estimated that the average global temperature during the warmest 200 year period of the HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD. The HCO consisted of increases of up to 4 °C near the North Pole (in one study, winter warming of 3 to 9 °C and summer of 2 to 6 °C in northern central Siberia).[8] Northwestern Europe experienced warming, but there was cooling in Southern Europe.[9] The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. ---8<--- So, the effect then was localized to the waters where there's more oxygen anyway, and having temperature going in different directions in different parts of Europe and at a much slower rate than current changes, would make it easier for the fish to migrate? Unclear how water temperatures behaved at different depths though.
- the_third_wave 3y ago
  The same is true for the current warming where the largest increases are seen in the northern winters so that does not affect the comparison. Instead of picking on one section in a Wikipedia article it would be interesting to know what exactly is different "this time" compared to earlier warmer periods, both the climatic optimum as well as e.g. the Viking and Roman warm periods, let alone those during earlier interglacials. Just stating "now it is different" is not very convincing.
  - defrost 3y ago
    In Scandinavian regions, at the very least, the Viking warm periods were not as warm as today; fresh evidence suggests that they were less warm than many have stated: Tree rings reveal that it has not been this warm in the past 1,200 years AUGUST 3, 2023: https://phys.org/news/2023-08-tree-reveal-years.html https://phys.org/news/2023-08-tree-reveal-years.html Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate https://www.nature.com/articles/s41586-023-06176-4 https://www.nature.com/articles/s41586-023-06176-4
kuhewa 3y ago
> How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now It was not 1.5—4 °C warmer. Mean air temperatures around the peak of the HCO were less than 1 °C elevated relative to preindustrial temperatures and were below last decade's mean air temperature. And those aren't ocean temperatures. Regionally, surface waters around the great barrier Reef was ~1 °C elevated relative to modern day. Anyway, the answer to your question is the rate of change since was much slower than recent temperature /pH changes. Populations, even sessile ones like corals can more successfully redistribute and move toward the poles to find optimal thermal conditions with a slower rate of change. And we are also putting the ocean under a few other confounding stresses like overfishing, eutrophication, acidification, coastal development and habitat loss, etc, which is novel territory relative to previous climactic shifts. Also I'll note what might be a blip in the geological record in terms of fossil richness could still have profound consequences for species on which we depend on for economic livelihood and food security, e.g. say you have a well managed fishery harvested at close to maximum sustainable yield. If conditions change such that the environment rapidly shifts to support only 80% of the original carrying capacity due to growing OMZs, the fishery now needs to be managed such that it will support a lot less jobs and produces less food (or, mgmt doesn't adapt and the stock gets severely overharvested, and then the job and production loss necessarily follow). > I suspect this balance between higher atmospheric CO₂ which leads to an increase in vegetation which then leads to an increase in oxygen production is what kept ocean life from succumbing due to oxygen deprivation. The article mentions why this suspicion is wrong. In fact, proliferation of the main oxygen producing taxa in the ocean is one of the primary mechanisms that exacerbates oxygen minimum zones. Phytoplankton blooms, then dies, sinks, and get eaten by microbes that consume oxygen.
ClumsyPilot 3y ago
99% of the time when people ask "how did ancient people manage to live without doctors", or whatever, you will find out that they didnt manage at all. Life did not manage sudden changes of climate, there yave been 6 mass extinctions. 99% of spieces that have ever existed are now exticlnct and we are on an express to join them
amateurCoder5 3y ago
The climatic optimum you refer to was cooler than today. From the wiki you reference: A study in 2020 estimated that the average global temperature during the warmest 200 year period of the HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD, immediately before the Industrial Revolution, and 0.3 °C cooler than the average for 2011-2019.

thulle 3y ago

> How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now From your wikipedia link: ---8<--- A study in 2020 estimated that the average global temperature during the warmest 200 year period of the HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD. The HCO consisted of increases of up to 4 °C near the North Pole (in one study, winter warming of 3 to 9 °C and summer of 2 to 6 °C in northern central Siberia).[8] Northwestern Europe experienced warming, but there was cooling in Southern Europe.[9] The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. ---8<--- So, the effect then was localized to the waters where there's more oxygen anyway, and having temperature going in different directions in different parts of Europe and at a much slower rate than current changes, would make it easier for the fish to migrate? Unclear how water temperatures behaved at different depths though.

the_third_wave 3y ago
The same is true for the current warming where the largest increases are seen in the northern winters so that does not affect the comparison. Instead of picking on one section in a Wikipedia article it would be interesting to know what exactly is different "this time" compared to earlier warmer periods, both the climatic optimum as well as e.g. the Viking and Roman warm periods, let alone those during earlier interglacials. Just stating "now it is different" is not very convincing.
- defrost 3y ago
  In Scandinavian regions, at the very least, the Viking warm periods were not as warm as today; fresh evidence suggests that they were less warm than many have stated: Tree rings reveal that it has not been this warm in the past 1,200 years AUGUST 3, 2023: https://phys.org/news/2023-08-tree-reveal-years.html https://phys.org/news/2023-08-tree-reveal-years.html Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate https://www.nature.com/articles/s41586-023-06176-4 https://www.nature.com/articles/s41586-023-06176-4

kuhewa 3y ago

> How did fish manage during the climatic optimum [1] some 8500 to 5500 years ago when it was between 1.5°C and 4°C warmer than it is now It was not 1.5—4 °C warmer. Mean air temperatures around the peak of the HCO were less than 1 °C elevated relative to preindustrial temperatures and were below last decade's mean air temperature. And those aren't ocean temperatures. Regionally, surface waters around the great barrier Reef was ~1 °C elevated relative to modern day. Anyway, the answer to your question is the rate of change since was much slower than recent temperature /pH changes. Populations, even sessile ones like corals can more successfully redistribute and move toward the poles to find optimal thermal conditions with a slower rate of change. And we are also putting the ocean under a few other confounding stresses like overfishing, eutrophication, acidification, coastal development and habitat loss, etc, which is novel territory relative to previous climactic shifts. Also I'll note what might be a blip in the geological record in terms of fossil richness could still have profound consequences for species on which we depend on for economic livelihood and food security, e.g. say you have a well managed fishery harvested at close to maximum sustainable yield. If conditions change such that the environment rapidly shifts to support only 80% of the original carrying capacity due to growing OMZs, the fishery now needs to be managed such that it will support a lot less jobs and produces less food (or, mgmt doesn't adapt and the stock gets severely overharvested, and then the job and production loss necessarily follow). > I suspect this balance between higher atmospheric CO₂ which leads to an increase in vegetation which then leads to an increase in oxygen production is what kept ocean life from succumbing due to oxygen deprivation. The article mentions why this suspicion is wrong. In fact, proliferation of the main oxygen producing taxa in the ocean is one of the primary mechanisms that exacerbates oxygen minimum zones. Phytoplankton blooms, then dies, sinks, and get eaten by microbes that consume oxygen.

ClumsyPilot 3y ago

99% of the time when people ask "how did ancient people manage to live without doctors", or whatever, you will find out that they didnt manage at all. Life did not manage sudden changes of climate, there yave been 6 mass extinctions. 99% of spieces that have ever existed are now exticlnct and we are on an express to join them

amateurCoder5 3y ago

The climatic optimum you refer to was cooler than today. From the wiki you reference: A study in 2020 estimated that the average global temperature during the warmest 200 year period of the HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD, immediately before the Industrial Revolution, and 0.3 °C cooler than the average for 2011-2019.