Climate variability in the North Atlantic Ocean: wind-induced changes in heat content, sea level and overturning.

Lead Research Organisation: University of Liverpool
Department Name: Earth, Ocean and Ecological Sciences

Abstract

The climate system is widely accepted as warming. Much of the extra heat provided to the climate system is estimated to have been taken up by the oceans. However, this warming of the oceans is not happening uniformly. For the North Atlantic, the most well observed basin, there has been warming in the tropics and mid latitudes, but cooling at high latitudes over the last 50 years. These changes in heat content are associated with changes in atmospheric forcing from winds and surface heat fluxes. As well as the oceans changing their temperature, there are salinity changes with a general freshening at high latitudes and increase in salinity at low latitudes, perhaps associated with a strengthening in the atmospheric water cycle. The strong gyre-scale contrast in these ocean properties suggest that the wind forcing and gyre dynamics are playing an important role. The small residual density changes over the basin are reflected in changes in the dynamical signals for overturning and sea level. The ocean overturning response to these water-mass changes appears to be surprising: based on our historical analyses, there is a slightly weakening over the subtropical gyre and slightly strengthening over the subpolar gyre during the last 50 years. These overturning changes might reflect the effect of the wind forcing, where gyre-scale property changes feedback onto changes in the overturning. The effect of the winds also directly affects sea level and the interpretation of the tide gauge record: there are large-scale correlations between the interannual variations in air pressure over the central part of the ocean basins and eastern boundary sea level. In our study, we plan to test hypotheses as to how the climate variability in the North Atlantic is controlled. Our aim is (i) to extend our analyses and assimilation of the historical data; (ii) conduct model experiments designed to reveal the effect of changing winds on the gyre contrasts in temperature and salinity, on how heat content and overturning are related, and on the relationship with sea level; and (iii) assess how tide gauge records for sea level are affected by gyre dynamics and overturning in order to interpret changes in the long historical records of sea level rise in the North Atlantic.

Publications

10 25 50

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Barton A (2014) The impact of fine-scale turbulence on phytoplankton community structure Phytoplankton and turbulence in Limnology and Oceanography: Fluids and Environments

 
Description Identified how there are gyre-scale contrasts in ocean heat content driven by latitudinal changes in meridional overturning, which are excited by atmospheric forcing.

The heat content changes are associated with sea level variations.
Exploitation Route There have been follow up NERC grants to explain why this reversing heat content pattern often forms in the North Atlantic. For example, the international Overturning in the Subpolar North Atlantic Programme (OSNAP) has drawn upon this work, involving a total of £30M of international investment from the US, UK, Germany, Canada, the Netherlands and China.
Sectors Education,Environment

URL https://www.youtube.com/channel/UCWApV_3EUlgw4aEzfk76n0Q
 
Description NERC Discovery Science
Amount £3,750,000 (GBP)
Funding ID NE/K010972/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 09/2013 
End 08/2018