>The National Oceanographic Data Center (NODC) has recently updated its Ocean Heat Content (OHC) data for the depths of 0-700 meters. This dataset was released with the Levitus et al (2009) Paper. The update included data for the first quarter of 2010. There were no changes to earlier data.
Figures 1 and 2 are time-series graphs of the OHC data from January 1955 to March 2010 for the global oceans (Figure 1) and for the tropical Pacific (Figure 2). The 2009/10 El Niño did not have a major impact on the tropical Pacific OHC.
Also illustrated are the OHC data broken down into hemispheres and into individual ocean basins, Figures 6 through 14. There weren’t any major rises or falls.
Before presenting those graphs, a few notes.
DISPARITY OF NORTH ATLANTIC OCEAN BASIN TREND
In the last update, OHC Linear Trends and Recent Update of NODC OHC (0-700 Meters) Data, the linear trends of the individual ocean basins from 1955 to 2009 were presented. I noted that since 1955 the linear trend of the North Atlantic OHC (0.205 GJ/meter^2/decade) was approximately 3 to 4 times higher than the linear trends of most of the other ocean basins.
Figure 3 illustrates the linear trends of the ocean basins since 1975. The data have been smoothed with a 13-month running-average filter. The year 1975 was chosen since it is about that time that the Atlantic Multidecadal Oscillation began its rise. 1975 is also approximately one year before the Pacific Climate Shift, which changed the frequency and magnitude of ENSO events. Since 1975, the North Atlantic OHC trend (0.323 GJ/meter^2/decade) was significantly higher than the linear trends of other ocean basins. The North Atlantic linear trend is approximately 1.75 times higher than the Arctic Ocean trend, but keep in mind that much of the Arctic Ocean is directly impacted by the North Atlantic. In fact, based on the coordinates used for those two datasets, they share data between 65N-75N and 78W-10E. At the other end of the spectrum, the North Atlantic OHC trend is almost 5 times the Indian Ocean OHC trend since 1975.
NORTH ATLANTIC ALSO RESPONSIBLE FOR MUCH OF THE DROP IN GLOBAL OHC
Referring back to Figure 1, Global OHC has been declining since about 2005. It is quite obvious looking at the OHC data for the individual ocean basins, Figure 4, that the drops in the North Atlantic OHC and in the adjoining Arctic and South Atlantic datasets (that are directly influence by the North Atlantic) are the cause of the global decline. And as shown in Figure 3, those datasets have the highest trends since 1975.
I’ll repeat a section from the past NODC OHC update. IF the multi-decade variations in North Atlantic OHC are similar in timing to the AMO, and IF the AMO did peak in 2005, and IF (lots of big IFs) the decline in North Atlantic OHC persists for another two plus decades, will global OHC continue to remain flat (or decline) for that long, too? Many of the other ocean basins are showing recent flattening or declines, so the North Atlantic is not alone. Regardless, a long-term decline in North Atlantic OHC (if one were to occur) would definitely not help long-term projections of a monotonous rise in OHC. And since the only variables that appear to cause significant rises in the other ocean basins are multiyear La Nina events and shifts in sea level pressure, a continued drop in North Atlantic OHC would have to be counteracted by one of those other factors.
There are significant differences between the North Atlantic OHC trends and those of the other basins, for the long-term periods when OHC is rising and for the recent short-term decline in OHC. These differences should call attention to the fact that factors other than anthropogenic greenhouse gases dominated the rise in Global Ocean Heat Content since 1955.
The following are links to earlier posts that illustrate and discuss how natural variables (including ENSO events and changes in sea level pressure as represented by the North Atlantic Oscillation and North Pacific Index) are responsible for most of the rise in OHC since 1955:
ENSO Dominates NODC Ocean Heat Content (0-700 Meters) Data,
North Atlantic Ocean Heat Content (0-700 Meters) Is Governed By Natural Variables,
North Pacific Ocean Heat Content Shift In The Late 1980s
COVERAGE OF SUBSURFACE TEMPERATURE READINGS
Like Sea and Land Surface Temperature datasets, subsurface ocean temperature data used in OHC data are incomplete in early years. How incomplete? Harrison and Carson (2007) in “Is the World Ocean Warming? Upper-Ocean Temperature Trends: 1950–2000” presented the number of temperature readings at various depths, from 100 meters to 2000 meters, contained in the World Ocean Database (2001). This is the database used by Levitus et al for their OHC data. Link to Harrison and Carson (2007):
Figure 5 is Harrison and Carson’s Figure 1. I’ve added the depths in red to simplify viewing. The numbers of temperature readings are shown by the color scale at right, with the light blue and “warmer” colors representing readings of 100 to 150 and more. The vast majority of the data, where there are readings, are in the darker cells, which show fewer readings. Those are the areas with 10 to 100 readings. Note that the numbers of readings are not annual or decadal. They are the total number of readings for the period of 1950 to 2000.
Note: Harrison and Carson (2007) provides an interesting perspective on subsurface temperature data and trends at different depths. It is worth reading.
HEMISPHERIC AND INDIVIDUAL BASIN OHC UPDATE THROUGH DECEMBER 2009
For those who enjoy information overload, the following are time-series graphs of OHC data (0-700 meters) for the hemispheres and the individual ocean basins, without commentary.
Figure 6 – Northern Hemisphere OHC
Figure 7 – Southern Hemisphere OHC
Figure 8 – North Atlantic OHC
Figure 9 – South Atlantic OHC
Figure 10 – North Pacific
Figure 11 – South Pacific
Figure 12 – Indian Ocean
Figure 13 – Arctic Ocean
Figure 14 – Southern Ocean
NODC OHC data is available through the KNMI Climate Explorer website. Many thanks to Dr. Geert Jan van Oldenborgh: