EGU2020-6318
https://doi.org/10.5194/egusphere-egu2020-6318
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Upper ocean heat content (OHC) changes in the tropical Pacific induced by orbital insolation and greenhouse gases (GHG)

Yue Wang1, Zhimin Jian1, Haowen Dang1, Zhongfang Liu1, Haiyan Jin1, Shuai Zhang2, Li Luo2, and Xingxing Wang1
Yue Wang et al.
  • 1Tongji University, State Key Laboratory of Marine Geology, Shanghai, China (163wangyue@163.com)
  • 2Hohai University, Nanjing, China

The ocean is the largest heat capacitor of the earth climate system and a main source of atmospheric moist static energy. Especially, upper ocean heat content changes in the tropics can be taken as the heat engine of global climate. Here we provide an orbital scale perspective on changes in OHC obtained from a transient simulation of the Community Earth System Model under orbital insolation and GHG forcings. Considering the vertical stratification of the upper ocean, we calculate OHC for the mixed layer and the upper thermocline layer according to the isotherm depths of 26℃ and 20℃ respectively. Generally, our simulated OHC are dominated by thickness changes rather than temperature changes of each layer. In details, there are three situations according to different forcings:

(1) Higher GHG induces positive mixed layer OHC anomalies inside the western Pacific warm pool but with neglected anomalies outside it. For the upper thermocline layer, there are negative OHC anomalies inside the warm pool and positive anomalies in the subtropical Pacific of two hemispheres. For the total OHC above 20℃ isotherm depth, positive anomalies mainly come from the mixed layer between 15ºS-15ºN and from the thermocline between 15º-30º. Lower obliquity induces similar spatial patterns of OHC anomalies as those of higher GHG, but total OHC anomalies are more contributed by upper thermocline anomalies.

(2) Lower precession results in positive mixed layer OHC anomalies in the core of warm pool (150ºE-150ºW, 20ºS-10ºN) and the subtropical northeastern Pacific, but with negative anomalies in other regions of the tropical Pacific. Upper thermocline layer OHC anomalies have similar patterns but with opposite signs relative to the mixed layer in regions between 15ºN-30ºS. As a combination, positive total OHC anomalies occupy large areas of 130ºE-120ºW from 30ºS to10ºN, while negative anomalies dominate the subtropical north Pacific, the western and eastern ends of the tropical Pacific.

If confirmed by paleoceanographic proxies, our simulated OHC results can be served as the first guide map of anomalous energetic storage & flows in the earth climate system under orbital forcings.

How to cite: Wang, Y., Jian, Z., Dang, H., Liu, Z., Jin, H., Zhang, S., Luo, L., and Wang, X.: Upper ocean heat content (OHC) changes in the tropical Pacific induced by orbital insolation and greenhouse gases (GHG), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6318, https://doi.org/10.5194/egusphere-egu2020-6318, 2020

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Presentation version 1 – uploaded on 14 Apr 2020
  • CC1: Comment on EGU2020-6318, Chris Brierley, 05 May 2020

    Dear Wang et al,

    I was wondering if you could clarify about the acccelerated forcing in this work. You seem to have sped up the forcing by 100x - which would imply that you've given the system 60 simulated years to reach mid-Holocene conditions. Do you expect the Pacific Subtropical overturning cell to reach equilibrium is just 60 years? If not, do you know what impact the lack of spin-up would have on your results?

    Chris 

    • AC1: Reply to CC1, Yue Wang, 05 May 2020

      Dear Chris, thanks very much your comments!

      Indeed, with 100x acceleration, we can not expect the Pacific Subtropical overturning cell to fully reach equilibrium in this transient experiment considering the varied response time of the upper ocean temperature at different water depths. But in our previous paper (Wang et al., 2019, JC), we accessed the impact of the accelaration method by analyzing results from several time slice experiments of the same CESM model under fixed orbital insolation forcing, in which the equatorial upper water temperature above 150m water depth should have reached equilibrium after 100 model years and share much similarity with those from the transient simulation. Since the isotherm depths of 26℃ and 20℃ in the Indo-Pacific warm pool regions may be much deeper and have longer response time scales, similar accessment will be conducted on them to check whether the OHC will be seriously biased by the acceleration. I hope this accessment will improve the reliability of our foundings above.

      Thanks very much again and best wishes!

       Yue Wang

      2020-05-05

      • AC2: Reply to AC1, Yue Wang, 05 May 2020

        References:

        Wang Y., Jian Z.M., Zhao P., Xu K., Dang H.W., Liu Z.F., Xiao D., Chen J.M. (2019) Precessional forced zonal triple-pole anomalies in the tropical Pacific annual cycle. Journal of Climate, 32(21), 7369-7402.