Mid-2000s North Atlantic shift: Heat budget and circulation changes.

Area of Science:

• Oceanography
• Climate Science
• Earth System Science

Background:

• The North Atlantic Ocean previously showed the greatest warming.
• Since the mid-2000s, during a global warming hiatus, heat transfer within the North Atlantic shifted to deeper levels.
• Atmospheric heat capture dominance moved to the Indo-Pacific basin.

Purpose of the Study:

• To investigate the role of modal water transformation in the eastern North Atlantic (ENA) during the global warming hiatus.
• To explain the contrasting ocean warming behavior between the North Atlantic and Indo-Pacific basins.

Main Methods:

• Analysis of oceanographic data to identify changes in modal water properties.
• Investigation of ocean mixing and heat transfer processes.
• Examination of dynamic height gradients and regional flow patterns.

Main Results:

• A significant transformation of ENA modal waters occurred in 2005, making them saltier, warmer, and denser.
• This transformation facilitated the transfer of upper ocean heat and salt to deeper layers.
• The denser waters altered regional flow, enhancing the northward advection of saltier southern waters.
• Excess salinity promoted further heat injection via deep convection.

Conclusions:

• Transformation of ENA modal waters was crucial for the observed shift in ocean heat content.
• This process explains the reduced upper ocean warming in the North Atlantic and the increased heat capture in the Indo-Pacific during the hiatus period.