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Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years.

Yang H, Zhao Y, Liu Z, Li Q, He F, Zhang Q - Sci Rep (2015)

Bottom Line: A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate.The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years.This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Climate and Ocean-Atmosphere Studies (LaCOAS) and Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.

ABSTRACT
The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

No MeSH data available.


Related in: MedlinePlus

Box model simulations in response to FWF over the past 22 kyr.(a) The black curve is mass transport change (Sv); red and grey, the FWF (0.1 Sv), similar to those in Fig. 2a but with reduced amplitude. (b) Salinity changes (psu) in surface extratropical box (red) and surface tropical box (blue); the black curve is the change in meridional sea surface salinity (SSS) gradient. (c) Same as (b) except for temperature changes (°C). (d) Changes in total MHT (black), AHT (red) and OHT (blue) in PW. (e) BJC rate. The black line is the analytical value (−1.5) based on Eq. (18) (see Methods), and blue asterisks indicate the transient BJC rate from the coupled box model.
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f4: Box model simulations in response to FWF over the past 22 kyr.(a) The black curve is mass transport change (Sv); red and grey, the FWF (0.1 Sv), similar to those in Fig. 2a but with reduced amplitude. (b) Salinity changes (psu) in surface extratropical box (red) and surface tropical box (blue); the black curve is the change in meridional sea surface salinity (SSS) gradient. (c) Same as (b) except for temperature changes (°C). (d) Changes in total MHT (black), AHT (red) and OHT (blue) in PW. (e) BJC rate. The black line is the analytical value (−1.5) based on Eq. (18) (see Methods), and blue asterisks indicate the transient BJC rate from the coupled box model.

Mentions: Conceptually, the climate evolution over the past 22 kyr is reasonably reproduced by the box model (Fig. 4). Forced by freshwater flux (FWF) in the extratropics (Methods), the variation of the northward mass transport in the box model (which mimics the AMOC in the real world) (Fig. 4a) is in a good agreement with the AMOC in the CCSM3 (Fig. 2a), except for a weaker magnitude. The H1, BA and YD events are all well simulated in the box model, in responses to the enhanced FWF during 19–15 ka, the suddenly weakened FWF around 14.5 ka and the re-enhanced FWF around 12.8 ka, respectively (Fig. 4a). The ocean component of the box model was generally freshening due to the FWF input until 12 ka, and then reversed the freshening trend toward the present climate due to the FWF reduction (Fig. 4b). The poleward sea surface salinity (SSS) gradient (Fig. 4b) followed closely the variation of FWF, intensifying during 22–19 ka and weakening gradually since 12 ka. The ocean component of the box model became colder until 12 ka and then warmed up gradually toward the present temperature (Fig. 4c), which, however, mainly occurred in the extratropical ocean (red curve in Fig. 4c), while the tropical SST hardly changed (blue curve in Fig. 4c). The change in poleward SST gradient was in phase with that in poleward SSS gradient; both of them were out of phase with mass transport (Fig. 4a). One can see that the salinity change (Fig. 4b) dominated the mass transport change (Fig. 4a), which in turn altered the ocean temperature (Fig. 4c).


Heat Transport Compensation in Atmosphere and Ocean over the Past 22,000 Years.

Yang H, Zhao Y, Liu Z, Li Q, He F, Zhang Q - Sci Rep (2015)

Box model simulations in response to FWF over the past 22 kyr.(a) The black curve is mass transport change (Sv); red and grey, the FWF (0.1 Sv), similar to those in Fig. 2a but with reduced amplitude. (b) Salinity changes (psu) in surface extratropical box (red) and surface tropical box (blue); the black curve is the change in meridional sea surface salinity (SSS) gradient. (c) Same as (b) except for temperature changes (°C). (d) Changes in total MHT (black), AHT (red) and OHT (blue) in PW. (e) BJC rate. The black line is the analytical value (−1.5) based on Eq. (18) (see Methods), and blue asterisks indicate the transient BJC rate from the coupled box model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645171&req=5

f4: Box model simulations in response to FWF over the past 22 kyr.(a) The black curve is mass transport change (Sv); red and grey, the FWF (0.1 Sv), similar to those in Fig. 2a but with reduced amplitude. (b) Salinity changes (psu) in surface extratropical box (red) and surface tropical box (blue); the black curve is the change in meridional sea surface salinity (SSS) gradient. (c) Same as (b) except for temperature changes (°C). (d) Changes in total MHT (black), AHT (red) and OHT (blue) in PW. (e) BJC rate. The black line is the analytical value (−1.5) based on Eq. (18) (see Methods), and blue asterisks indicate the transient BJC rate from the coupled box model.
Mentions: Conceptually, the climate evolution over the past 22 kyr is reasonably reproduced by the box model (Fig. 4). Forced by freshwater flux (FWF) in the extratropics (Methods), the variation of the northward mass transport in the box model (which mimics the AMOC in the real world) (Fig. 4a) is in a good agreement with the AMOC in the CCSM3 (Fig. 2a), except for a weaker magnitude. The H1, BA and YD events are all well simulated in the box model, in responses to the enhanced FWF during 19–15 ka, the suddenly weakened FWF around 14.5 ka and the re-enhanced FWF around 12.8 ka, respectively (Fig. 4a). The ocean component of the box model was generally freshening due to the FWF input until 12 ka, and then reversed the freshening trend toward the present climate due to the FWF reduction (Fig. 4b). The poleward sea surface salinity (SSS) gradient (Fig. 4b) followed closely the variation of FWF, intensifying during 22–19 ka and weakening gradually since 12 ka. The ocean component of the box model became colder until 12 ka and then warmed up gradually toward the present temperature (Fig. 4c), which, however, mainly occurred in the extratropical ocean (red curve in Fig. 4c), while the tropical SST hardly changed (blue curve in Fig. 4c). The change in poleward SST gradient was in phase with that in poleward SSS gradient; both of them were out of phase with mass transport (Fig. 4a). One can see that the salinity change (Fig. 4b) dominated the mass transport change (Fig. 4a), which in turn altered the ocean temperature (Fig. 4c).

Bottom Line: A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate.The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years.This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Climate and Ocean-Atmosphere Studies (LaCOAS) and Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.

ABSTRACT
The Earth's climate has experienced dramatic changes over the past 22,000 years; however, the total meridional heat transport (MHT) of the climate system remains stable. A 22,000-year-long simulation using an ocean-atmosphere coupled model shows that the changes in atmosphere and ocean MHT are significant but tend to be out of phase in most regions, mitigating the total MHT change, which helps to maintain the stability of the Earth's overall climate. A simple conceptual model is used to understand the compensation mechanism. The simple model can reproduce qualitatively the evolution and compensation features of the MHT over the past 22,000 years. We find that the global energy conservation requires the compensation changes in the atmosphere and ocean heat transports. The degree of compensation is mainly determined by the local climate feedback between surface temperature and net radiation flux at the top of the atmosphere. This study suggests that an internal mechanism may exist in the climate system, which might have played a role in constraining the global climate change over the past 22,000 years.

No MeSH data available.


Related in: MedlinePlus