Heat and the Ocean
The ocean can absorb large amounts of heat without causing a large increase in ocean temperatures. Most of the ocean’s heating comes from sunlight, but clouds, water vapor, and greenhouse gases also emit heat that enters the ocean. This heat absorbed eventually returns to the atmosphere, but if the ocean absorbs heat at a faster rate than it releases it, its heat content increases. This allows for relatively constant temperatures in the deep ocean, but it also means that small changes in temperature can be detrimental to deep-sea organisms and functions.
What We Know So Far
- The ocean is storing ~91% of excess heat energy trapped in Earth’s climate from greenhouse gases
- A study in late 2020 found that deep-sea temperatures fluctuate more than we used to think, and there is a trend of rising temperatures
- Temperatures are rising significantly in the deep ocean; the sites examined in the study all showed a warming trend of 0.02 to 0.04 degrees Celsius per decade between 2009 and 2019, where temperature changes are usually measured in thousandths of a degree
- The increase in temperature was only statistically significant at depths over 4,500 meters
- Warming at upper bathyal depths (200-2000 m) can cause more methance release from deep continental margins
- “Excess atmospheric CO2 absorption and the oxidation of organic matter in the water column are causing acidification of intermediate-depth waters globally”
- Warmer surface temperatures causes increased thermal stratification
- This is observed to have the greatest impact in depths of 200-700 m
- Increased stratification reduces deep-water ventilation and nutrient supply to surface waters from the deep ocean
- oxygen minimum zones are expanding
Challenges
The main challenge of studying the deep ocean is that it is difficult to conduct research and obtain measurements of it. As a consequence, there is little data and information about the deep ocean from the past.
Points of Investigation
- What drives rising temperatures in the deep ocean?
- How to study hydrographic and biodiversity changes in the deep ocean, given that there is little data about it?
- How does oxygen reduction affect deep-seafloor ecosystems?
- How does oxygen stress affect thermal and pH/CO2 tolerances and calcification rates in deep waters?
Sources:
https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content
https://research.noaa.gov/research-the-deep-sea-is-slowly-warming/
https://www.science.org/doi/10.1126/science.aad0126
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