From the INSTITUTE OF ATMOSPHERIC PHYSICS, CHINESE ACADEMY OF SCIENCES
The global ocean has become more stratified and stable over the past few decades with global warming. This has major consequences for life in the ocean by reducing nutrients and oxygen, and it greatly affects climate.
CREDIT Jiang Zhu
A new study, by a group of international researchers from China and U.S., published in Nature Climate Change found that the global ocean has become more layered and resistant to vertical mixing as warming from the surface creates increasing stratification.
Sea water generally forms stratified layers with lighter waters near the surface and denser waters at greater depth, i.e. warmer fresher waters atop colder more saline ones. This stable stratified configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Therefore, the stratification is a central element of Earth’s climate system, and understanding its changes with global warming has great scientific, societal and ecological consequences.
As human-caused greenhouse warming has fundamentally altered oceanic temperature and salinity fields, impacts to stratification are expected but the details have been difficult to discern until now. The main basis for estimating the stratification change is the sparse distribution of ocean observations both horizontally and vertically. Previous quantification of stratification change has been limited to a simple index and has neglected the spatial complexity of ocean density change.
The new study overcomes the key limitations and provides an estimate on ocean stratification for the upper 2000m and also its spatial structures. This study used a carefully evaluated ocean temperature and salinity data (IAP products) which overcomes previous systematic biases associated with sampling. The study also adopted an improved metric of stratification (related to the density gradient over depth), and then provide a true estimate of ocean stratification and its changes.
The new data shows that ocean has become more stratified by 5.3% since 1960 for the upper 2000m. An even stronger ocean stratification increase, as much as 18%, has been observed for the upper 150m.
This observed long-term increasing trend of stratification is mainly caused by stronger ocean warming for upper layers versus the deep oceans (~97%), but salinity changes play an important role locally. This stratification increase reveals a robust human-driven change in the ocean due the long-term temperature and salinity change structures. Therefore, the observed ocean stratification increase is another irrefutable piece of evidence of human-driven global warming.
In the tropics, there is a very strong stratification increase at upper 200m. This indicates a significant change in tropical thermocline depth that is important to the El Nino phenomenon. In the middle and high latitudes, significant increases of ocean stratification appear below 500m, implying an impact on deep ocean stability by climate change.
The increase of ocean stratification feedbacks to climate change. With increased stratification, heat from climate warming cannot penetrate into the deep ocean as readily, which helps to raise the surface temperature. It also reduces the capability of ocean carbon storage, exacerbating the global warming. It prevents the vertical exchanges of nutrients and oxygen, and impacts the food supply of the whole marine ecosystems.
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The paper: https://www.nature.com/articles/s41558-020-00918-2
Abstract
Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down to depths of 2,000 m using the squared buoyancy frequency N2 and newly available ocean temperature/salinity observations. We find that stratification globally has increased by a substantial 5.3% [5.0%, 5.8%] in recent decades (1960–2018) (the confidence interval is 5–95%); a rate of 0.90% per decade. Most of the increase (~71%) occurred in the upper 200 m of the ocean and resulted largely (>90%) from temperature changes, although salinity changes play an important role locally.
Perhaps this is what is causing the warming, a stratification and less vertical turning with the very cold bottom ocean that is 90% of the volume of the ocean. Causing an Atlantification and a Pacification of the Arctic Ocean as the warm waters reach into the northern realms, warming the northern climes and decreasing ice. Then they cycle keeps going and we go into a cooler period sometime in the future.
We are altering the ocean in a couple of major ways. 1. Dissolved silica run-off. This alters the phytoplankton blooms as diatoms, which bloom first in the spring, bloom for longer. This reduces the time for DMS production, meaning less stratocumulus cloud, more warming and stratification.
2. Light oil* and surfactant spills form smooths with a one molecule layer reducing wave action Less turbulence, more stratification, less mixing with fewer nutrients in the upper light layer, less DMS.
It would be worth looking at phytoplankton surfactant production — if there’s more of that for some reason then this, too will lead to stratification.
*Hence the ‘blip’.
JF
Mann and Trenberth? Dear, oh dear.
There are some 300 million square kilometers of sea – oceans etc.
How many samples?
So – how far apart?
Auto
Just askin’, you know.
It only takes one but its a very special one we call him the yamal trench :-).
“Therefore, the observed ocean stratification increase is another irrefutable piece of evidence of human-driven global warming.”
Really-irrefutable? Nothing else could cause these stratification observations? Not natural warming? Not observational error? Not misinterpretation of data? Not lack of sufficient data? So this study is the missing link. No other research has yet produced proof that warming of earth’s oceans is caused by humans but this one does? I am not convinced. I don’t think there is proof that humans have caused an appreciable increase in CO2 or that increased CO2 has caused any warming so I can’t possibly see how this estimate of changes in stratification cna be considered “irrefutable evidence of human-driven global warming”.
And so these “scientists” are basing their conclusions on a few years of data, the merest blink of an eye in the time frame of the earth as usual.
The starting hypothesis and immediate question for them is the same as for the rest of the AGW doomsters. “What caused previous climate changes?” “How has the earth reacted in the past during the many, many previous climactic changes that occurred without the excuse of mankind even being there?”
It seems to me that until they answer these most basic questions the “paper” they are writing on is useful as toilet paper and not much else.
That’s not the effect of rising CO2 forcing, it’s the result of weaker indirect solar forcing driving a warm AMO and increased El Nino conditions, which then reduce low cloud cover. The stratification should be reduced with the next cold AMO phase and increased La Nina.