World Ocean Thermocline Weakening and Isothermal Layer Warming
This paper identifies world thermocline weakening and provides an improved estimate of upper ocean warming through replacement of the upper layer with the fixed depth range by the isothermal layer, because the upper ocean isothermal layer (as a whole) exchanges heat with the atmosphere and the deep...
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| Format: | Article |
| Language: | English |
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MDPI AG
2020-11-01
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| Series: | Applied Sciences |
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| Online Access: | https://www.mdpi.com/2076-3417/10/22/8185 |
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| author | Peter C. Chu Chenwu Fan |
| author_facet | Peter C. Chu Chenwu Fan |
| author_sort | Peter C. Chu |
| collection | DOAJ |
| description | This paper identifies world thermocline weakening and provides an improved estimate of upper ocean warming through replacement of the upper layer with the fixed depth range by the isothermal layer, because the upper ocean isothermal layer (as a whole) exchanges heat with the atmosphere and the deep layer. Thermocline gradient, heat flux across the air–ocean interface, and horizontal heat advection determine the heat stored in the isothermal layer. Among the three processes, the effect of the thermocline gradient clearly shows up when we use the isothermal layer heat content, but it is otherwise when we use the heat content with the fixed depth ranges such as 0–300 m, 0–400 m, 0–700 m, 0–750 m, and 0–2000 m. A strong thermocline gradient exhibits the downward heat transfer from the isothermal layer (non-polar regions), makes the isothermal layer thin, and causes less heat to be stored in it. On the other hand, a weak thermocline gradient makes the isothermal layer thick, and causes more heat to be stored in it. In addition, the uncertainty in estimating upper ocean heat content and warming trends using uncertain fixed depth ranges (0–300 m, 0–400 m, 0–700 m, 0–750 m, or 0–2000 m) will be eliminated by using the isothermal layer. The isothermal layer heat content with the monthly climatology removed (i.e., relative isothermal layer heat content) is calculated for an individual observed temperature profile from three open datasets. The calculated 1,111,647 pairs of (thermocline gradient, relative isothermal layer heat content) worldwide show long-term decreasing of the thermocline gradient and increasing of isothermal layer heat content in the global as well as regional oceans. The global ocean thermocline weakening rate is (−2.11 ± 0.31) × 10<sup>−3</sup> (°C m<sup>−1</sup> yr<sup>−1</sup>) and isothermal layer warming rate is (0.142 ± 0.014) (W m<sup>−2</sup>). |
| first_indexed | 2024-03-10T14:45:20Z |
| format | Article |
| id | doaj.art-eb8036dc8e9e47b59d75ab425fcbb2ac |
| institution | Directory Open Access Journal |
| issn | 2076-3417 |
| language | English |
| last_indexed | 2024-03-10T14:45:20Z |
| publishDate | 2020-11-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Applied Sciences |
| spelling | doaj.art-eb8036dc8e9e47b59d75ab425fcbb2ac2023-11-20T21:28:48ZengMDPI AGApplied Sciences2076-34172020-11-011022818510.3390/app10228185World Ocean Thermocline Weakening and Isothermal Layer WarmingPeter C. Chu0Chenwu Fan1Naval Ocean Analysis and Prediction Laboratory, Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USANaval Ocean Analysis and Prediction Laboratory, Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USAThis paper identifies world thermocline weakening and provides an improved estimate of upper ocean warming through replacement of the upper layer with the fixed depth range by the isothermal layer, because the upper ocean isothermal layer (as a whole) exchanges heat with the atmosphere and the deep layer. Thermocline gradient, heat flux across the air–ocean interface, and horizontal heat advection determine the heat stored in the isothermal layer. Among the three processes, the effect of the thermocline gradient clearly shows up when we use the isothermal layer heat content, but it is otherwise when we use the heat content with the fixed depth ranges such as 0–300 m, 0–400 m, 0–700 m, 0–750 m, and 0–2000 m. A strong thermocline gradient exhibits the downward heat transfer from the isothermal layer (non-polar regions), makes the isothermal layer thin, and causes less heat to be stored in it. On the other hand, a weak thermocline gradient makes the isothermal layer thick, and causes more heat to be stored in it. In addition, the uncertainty in estimating upper ocean heat content and warming trends using uncertain fixed depth ranges (0–300 m, 0–400 m, 0–700 m, 0–750 m, or 0–2000 m) will be eliminated by using the isothermal layer. The isothermal layer heat content with the monthly climatology removed (i.e., relative isothermal layer heat content) is calculated for an individual observed temperature profile from three open datasets. The calculated 1,111,647 pairs of (thermocline gradient, relative isothermal layer heat content) worldwide show long-term decreasing of the thermocline gradient and increasing of isothermal layer heat content in the global as well as regional oceans. The global ocean thermocline weakening rate is (−2.11 ± 0.31) × 10<sup>−3</sup> (°C m<sup>−1</sup> yr<sup>−1</sup>) and isothermal layer warming rate is (0.142 ± 0.014) (W m<sup>−2</sup>).https://www.mdpi.com/2076-3417/10/22/8185isothermal layerthermoclineisothermal layer heat contentisothermal layer warmingthermocline gradientthermocline weakening |
| spellingShingle | Peter C. Chu Chenwu Fan World Ocean Thermocline Weakening and Isothermal Layer Warming Applied Sciences isothermal layer thermocline isothermal layer heat content isothermal layer warming thermocline gradient thermocline weakening |
| title | World Ocean Thermocline Weakening and Isothermal Layer Warming |
| title_full | World Ocean Thermocline Weakening and Isothermal Layer Warming |
| title_fullStr | World Ocean Thermocline Weakening and Isothermal Layer Warming |
| title_full_unstemmed | World Ocean Thermocline Weakening and Isothermal Layer Warming |
| title_short | World Ocean Thermocline Weakening and Isothermal Layer Warming |
| title_sort | world ocean thermocline weakening and isothermal layer warming |
| topic | isothermal layer thermocline isothermal layer heat content isothermal layer warming thermocline gradient thermocline weakening |
| url | https://www.mdpi.com/2076-3417/10/22/8185 |
| work_keys_str_mv | AT petercchu worldoceanthermoclineweakeningandisothermallayerwarming AT chenwufan worldoceanthermoclineweakeningandisothermallayerwarming |