Update And Changes To NODC Ocean Heat Content Data

As noted in the post October 2010 Update to NODC Ocean Heat Content Data, the National Oceanographic Data Center has updated itsOCEAN HEAT CONTENT (OHC) data. This is the dataset based on the Levitus et al (2009) paper “Global ocean heat content(1955-2008) in light of recent instrumentation problems”, Geophysical Research Letters. Refer to Manuscript. 

The update to the OHC data also included major changes, which have reduced the long-term rise in OHC. Refer to the gif animation, Figure 1, that shows the global OHC data from their June 2010 update (through March 2010) and from the most recent update and change (though June 2010). The revisions are considerable in many ocean basins. As described in their explanation of ocean heat content (OHC) data changes, the changes result from “data additions and data quality control,” from a switch in base climatology, and from revised Expendable Bathythermograph (XBT) bias calculations. (Refer to the NOAA FAQ webpage What is an XBT?) Immediately following Figure 1 is a link to a graph that shows the difference between the two global datasets, with the June 2010 update subtracted from the September 2010 update.

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Figure 1 – Global

Link to Graph of the Difference:

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Table 1 shows the OHC linear trends (in Gigajoules/Square Meter per Decade) for the global and hemispheric data and for the individual ocean basin subsets. Also shown are the differences (the data from the September 2010 update MINUS the data from the June 2010 update) and the percent change (difference divided by June 2010 update). Note: the June 2010 update included data through March 2010 and the September update/change included data through June 2010, but Table 1 only compares linear trends for the datasets through March 2010. As shown in Table 1, the linear trend for the Northern Hemisphere OHC data only dropped approximately 2%, while the Southern Hemisphere linear trend dropped about 16%. There was a minor increase in North Pacific trend (4%), while there were considerable drops in the linear trends of the South Atlantic (23%), South Pacific (17%) and the Southern Ocean (32%).

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Table 1

Figure 2 is the gif animation that shows the Southern Ocean OHC data (South of 60S) before and after the September 2010 changes. Prior to the mid-2000s and the introduction of ARGO buoys, the original data (through March 2010) simply appeared to be the climatology with some data added occasionally when it was available. The updated data seems to emphasize that appearance.

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Figure 2 – Southern Ocean

Link to Graph of the Difference:

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And there is good reason for that appearance. Like Sea Surface Temperature datasets based on buoys and ship sensors, there is very little Southern Hemisphere data, at all depths, prior to the ARGO buoys era. Figures 3 through 6 show the 3-month data distribution maps for January through March of 1955, 1975, 1995 and 2005, at depths of zero meters (surface), 250 meters, 500 meters and 700 meters. South of 60S there was little data even in 2005. The maps are available through the NODC Temperature data distribution figures webpage.

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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THE IMPACT OF CHANGES ON PAST POSTS ABOUT NATURAL OHC VARIATIONS

The recent changes to the OHC data have not had noticeable effects on the timing of the major variations in data that should be attributable to natural variations. For example: The tropical Pacific OHC data still drops during major El Niño events and partially rebounds during most of the La Niña events that follow, Figure 7. The major upward shifts occur during significant La Niña events, which is the recharge/overcharge mode for the tropical Pacific OHC. This, and the similar impact on other ocean basins, was discussed in the post ENSO Dominates NODC Ocean Heat Content (0-700 Meters) Data.

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Figure 7

With the changes to the data, the OHC of the North Pacific north of 20N still drops from the late 1950s to the late 1980s, Figure 8, and then suddenly rises. This increase coincides with a shift in North Pacific sea level pressure. This was discussed in the post North Pacific Ocean Heat Content Shift In The Late 1980s.

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Figure 8

The update/changes caused the OHC for most of the other basins to drop more than the North Atlantic OHC. Refer again to Table 1. This makes the contribution of the North Atlantic OHC to global OHC even greater. And much of the disproportionate rise in North Atlantic OHC is caused by Atlantic Meridional Overturning Circulation (AMOC), sea level pressure, and ENSO, as discussed in North Atlantic Ocean Heat Content (0-700 Meters) Is Governed By Natural Variables. One cell of the gif animation in Figure 9 compares global and North Atlantic OHC. The increase in North Atlantic OHC dwarfs the global rise. The second cell in Figure 9 compares the North Atlantic OHC to the global data with the North Atlantic removed. It assumes the surface area of the North Atlantic is 15% of the global ocean surface area. Note the decrease in the global trends. With the North Atlantic, the global linear trend is 0.72 GJ/square meter per decade and without the North Atlantic, the “global” data linear trend drops to 0.043 GJ/square meter per decade. Also note how sharply the North Atlantic OHC has dropped since 2005. The North Atlantic is a major contributor to the flattening of global data in recent years.

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Figure 9

GIF ANIMATIONS — BEFORE AND AFTER CHANGES

Figures 10 through 18 are gif animations that compare the NODC OHC data for the hemispheres and ocean basin subsets before and after the recent changes. I’ve also provided links to graphs of the differences, with the June 2010 data subtracted from the September 2010 data. They are provided without commentary.

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Figure 10 – Tropical Pacific

Link to Graph of the Difference:

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Figure 11 – Northern Hemisphere

Link to Graph of the Difference:

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Figure 12 – Southern Hemisphere

Link to Graph of the Difference:

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Figure 13 – North Atlantic

Link to Graph of the Difference:

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Figure 14 – South Atlantic

Link to Graph of the Difference:

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Figure 15 – Indian Ocean

Link to Graph of the Difference:

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Figure 16 – North Pacific

Link to Graph of the Difference:

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Figure 17 – South Pacific

Link to Graph of the Difference:

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Figure 18 – Arctic Ocean

Link to Graph of the Difference:

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SOURCE

The NODC OHC data is available through the KNMI Climate Explorer:

http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere

(Thanks to Dr Geert Jan van Oldenborgh of KNMI for creating and maintaining Climate Explorer.)