Introduction To The NODC Ocean Heat Content Anomaly Data For Depths Of 0-2000 Meters
The National Oceanographic Data Center (NODC) recently posted a new Ocean Heat Content (OHC) anomaly dataset on its website. It is available on annual and quarterlybases, along with the data for its standard and documented dataset that covers depths of 0-700 meters. I looked for but was not able to find any papers (in any state of publication) that supported the new OHC data for 0-2000 meters. We’ll just have to wait and see how the NODC intends to present this dataset.
The data for the depths of 0-700 meters is, of course, documented in the paper Levitus et al (2009) “Global ocean heat content (1955-2008) in light of recent instrumentation problems”. Refer to Manuscript. It was revised in 2010 as noted in the October 18, 2010 post Update And Changes To NODC Ocean Heat Content Data. As described in the NODC’s 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.
COMPARISON OF GLOBAL OHC ANOMALIES: 0-700 METERS VERSUS 0-2000 METERS
Figure 1 compares the quarterly NODC OHC anomaly data for the depths of 0-700 meters and 0-2000 meters on a global basis. As noted on the illustration, the most obvious divergence between the two datasets occurs during the ARGO era. This is the period when ARGO floats became the dominant means of sampling of ocean temperatures and salinity at depth.
Figure 1
If we limit the comparison to the period from 1970 to 1999, Figure 2, we can see that there is basically no difference in the linear trends. There are minor differences from year to year, but the two datasets appear to be basically the same. Why?
Figure 2
There are extremely few observations prior to the year 2000 at depths greater than 1000 meters. This is illustrated in Figure 3. (Note that NOAA Climate Prediction Center Data Distributionwebpage breaks down the temperature profiles into depths of 0-250 meters, 250-500 meters, 500-1000 meters and 1000-5000 meters. Those depths don’t agree with the depths presented by the NODC for its Ocean Heat Content anomaly data.)
Figure 3
And Animation 1 shows a series of annual maps of the locations of temperature profiles from 1979 to 2005 for the depths 1000-5000 meters. As illustrated, there is also very little spatial coverage at these depths until the introduction of the ARGO floats.
Animation 1
As a reference, Figure 4 shows the number of temperature profiles for depths of 250 to 500 meters. There were between 2000 to 5000 temperature profiles per month between the late 1970s and the late 1990s at these depths before the ARGO floats were deployed. Note that the TAO/TRITON project (red curve) shows temperature profiles that were initially for the equatorial Pacific (coordinates approximately 8S-9N, 137E-95W). Those buoys were deployed for the study of El Niño and La Niña events. The locations were later expanded to include portions of the Tropical Atlantic and Indian Oceans under the PIRATA and RAMA projects. Refer to the TAO Project Global Arraywebpage. So while there are a good number of temperature profiles for the TAO project, they are limited in their location.
Figure 4
Figure 5 illustrates the difference between the two NODC Global Ocean Heat Content (OHC) datasets, where the 0-700 meter data has been subtracted from the 0-2000 meter data. Also referring back to Figure 3, the difference between the two datasets seems to increase in concert with the number of temperature samples at depths greater than 1000 meters. It appears as though the divergence of the 0-2000 meter dataset from the 0-700 meter data since around 2000 could be caused by the increased number of samples at depth and the increased spatial coverage of the ARGO floats, as shown in the animations. The impacts on short-term and long-term trends of the increased number of samples at depths greater than 700 meters and the impact of the increased area of observations should be determined. (A study such as that is well beyond my capabilities.) Maybe it will be documented in the NODC paper that accompanies the 0-2000 meter dataset.
Figure 5
Keep in mind, before the ARGO era, there were very few ocean temperature observations at any depth in the Southern Hemisphere south of about 40S. For example, Animation 2 is a gif animation of maps that illustrate the locations of temperature profiles for depths of 0-250 meters, 250-500 meters, 500-1000 meters, and 1000-5000 meters for the year 1995.
Animation 2
And Animation 3 shows the same series of temperature profile maps but for the year 2005.
Animation 3
A COUPLE OF QUESTIONS FOR READERS
Were the Expendable Bathythermograph (XBT) probes with wire lengths of 760 meters the most commonly used XBT probes before the ARGO era? Is this the reason the NODC originally limited the depth to 700 meters for the Ocean Heat Content anomaly data? Does anyone recall a paper that presents this? I had always assumed the depth of 700 meters was selected due to the number of and locations of observations, but I have never seen it stated in a paper.
LONG-TERM TRENDS PER OCEAN BASIN
When I originally prepared the graphs for this post, I could find no reason to present the long-term trends for the individual ocean basins of the 0-2000 meter data. The reason being, in some respects, the NODC OHC data for 0-2000 meters appears to me to simply be a 0-2000 meter OHC dataset spliced onto a 0-700 meter dataset. But on further thought, my failure to present the data might be thought by some as an attempt on my part to hide something. So Figure 6 (0-2000 meters) and Figure 7 (0-700 meters) are long-term trend comparisons of the Ocean Heat Content anomalies for the individual ocean basins as presented by the NODC. The most obvious similarity is that the long-term trends of the North Atlantic Ocean Heat Content are significantly higher than other ocean basins in both datasets, and in both, the North Atlantic Ocean Heat Content peaked in 2004. After that, there are significant declines. One would think this would lead researchers to examine the effects of the Atlantic Multidecadal Oscillation and Meridional Overturning Circulation on North Atlantic Ocean Heat Content observational data, yet, as far as I know, this is an area unexplored by climate scientists.
Figure 6
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Figure 7
ARGO-ERA TRENDS PER OCEAN BASIN
The ARGO-era (2003 to present) linear trends per ocean basin for the depths of 0-2000 meters and 0-700 meters are shown in Figure 8 and 9, respectively. Like the trends for the 0-700 meter data, the South Atlantic and Indian Ocean are the only basins with significantly positive linear trends for the 0-2000 meter Ocean Heat Content data. And also like the trends 0-700 meter data, the linear trends of the 0-2000 meter Ocean Heat Content anomalies in the North Atlantic and South Pacific are negative. The linear trends for those two ocean basins are less negative for 0-2000 meter depths than they are for 0-700 meter depths, indicating that the declines at depths of 0-700 meters are greater than the increases at the 700-2000 meter depths. Considering there is less than a decade of ARGO-era data with “full” coverage, there is no need to speculate about the cause. Note also that the trend for the North Pacific OHC anomalies is basically flat for the 0-2000 meter data, and that the same holds true for the 0-700 meter data.
Figure 8
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Figure 9
CLOSING COMMENTS
The undocumented (as of this writing) NODC 0-2000 meter Ocean Heat Content dataset appears as though it was prepared to show that Global Ocean Heat Content continues to rise during the ARGO era, and that it is intended to counter the argument that Global Ocean Heat Content has flattened during the ARGO era as shown in the NODC 0-700 meter dataset.
Due to the extremely limited number of observations at depths of 1000-5000 meters (shown in Figure 3 and in the animations), the 0-2000 meter Ocean Heat Content dataset should be used with great caution. It appears to me to be an ARGO-era 0-2000 meter Ocean Heat Content dataset spliced onto a long-term 0-700 meter dataset. For this reason, I, personally, would not expend the effort to analyze the long-term (pre-ARGO era) 0-2000 meter NODC OHC data beyond what has been presented in this post.
Each time I see the claim (based on many assumptions) by anthropogenic global warming proponent scientists that the rise in ocean heat content at depth “will come back to haunt us” I wonder why those same scientists have not bothered to attempt to document how much of the rise in OHC from the 1970s to the early 2000s (0-700 meters) was caused by the deep oceans upwelling warmer anomalies from past decades, other than the fact that there’s no data for them to do so. Could they believe that multidecadal variability is limited to Sea Surface Temperatures and does not impact temperatures at depth? Or is their intent to have the unsuspecting public believe it?
phlogiston says:
“Rather than a change in the temperature of upwelling water, I would think it more likely that the rate, timing and maybe locations of upwelling might change.”
Possibly both. Wouldn’t it be changing temperature differentials that would cause those other changes?
“How can something be warm on one side, warm on the other, cold in the middle, for billions of years?”
Because the net energy cost of evaporation (linked to surface pressure) is so high that after taking evaporation into account the rate of energy loss by the oceans is so large that the equilibrium temperature at the current level of geothermal input from below and solar input from above falls to 3.9C which is apparently the average global ocean temperature.
“IR heating at the top of the ocean will have a warming effect, but the primary mechanism is that a reduced temperature gradient will reduce evaporation.”
Actually the AGW contention (from only one scientists as far as I can tell) is that the warmed molecules at the top of the ocean skin change the temperature gradient from below and therefore inhibit upward energy flow from ocean bulk to ocean skin and thence to air which in theory alters the equilibrium temperature of the oceans via the operation of Fourier’s Law.
I have discussed that very point extensively elsewhere and come to the conclusion that that is not so because the increase in evaporation (a net cooling process) offsets the change in gradient that would otherwise occur.
Furthermore once the increased evaporation rate has used up the downward IR there is no energy left over to add to ocean heat content.
The net effect of downward IR on the background energy flow from ocean to air is therefore zero and GHGs cannot warm the ocean bulk.
Instead the extra energy remains in the air and gets converted to latent form and is then whisked away upward by convection for faster discharge to space.
All one sees is a miniscule change in the speed of the water cycle which pales into insignificance compared to solar and ocean induced changes in the water cycle.
Dave says:
October 25, 2011 at 5:47 pm
Thanks Dave, you are correct I was thinking about all the undersea activity. I know its not a constant but the amount of heat being sinked from all the lava flows, vents has to make some kind of impact. What was crossing my mind is that during increased levels of vulcanism that the up flow of heat generated would bring some of the cold deep water with it and provide some level of mixing. If it does it would seem to be on a small scale.
Being a diver I have personally experienced thermocline and have read the definitions of the effect but it still seems strange to me that the heat from the upper level traps and cannot to any large degree heat the lower layer. If I understand it right the increased density of the colder water makes it sink and the lighter warmer riders on top of it. So gravity is the mediating factor in the effect but still strange that heat will not easily cross this boundary. I know there is a tidal/gravity anomaly that is persistent to the NW of Australia does the thermocline behave the same there? This anomaly can also be seen in the sea level global height map.
John Eggert says:
October 25, 2011 at 4:24 pm
Damn. Have to prove myself a liar.
phlogiston says:
October 25, 2011 at 1:23 pm
“The concept of warm water “downwelling” to the ocean depths needs to be challenged . . .”
Have you fully accounted for salinity in that comment? Saltier water, such as one gets from a hot ocean, is denser than less salty water, such as occurs where ice is melting. Which density difference is greater? Hot / cold or sweat / salty? This is a question that can be answered to a very high degree of accuracy.
The Red Sea is one place where hot super-saline water does exist in packets at the sea bottom – hotter than the water above. So enough salinity can overcome temperature to determine water’s density. But this is the exception that proves the rule.
However, the atmosphere is not the only source of heat. The crust itself is a small, almost trivial source of heat. But it isn’t entirely trivial and it is constant. You cannot continually add energy to something without raising the temperature. That heat went somewhere. If it did heat the water, there would be upwelling of heat, resulting in convective heat transfer. So again, we are faced with the question. How can something be warm on one side, warm on the other, cold in the middle, for billions of years?
Yes there is geothermal input to the oceans. So indeed how can it be that, both in the tropics with surface water temperatures of 30+ C, and at the poles with surface water freezing, abyssal water is always 0-3C? How can near freezing water be sandwitched between warm surface and warmer bottom? The answer is when you have a 4000 m thick layer of a liquid with the extraordinary heat capacity of water, on a planet with gravity of 10 n.kg-1. (Most of the sea floor is cold despite volcanic activity in some places.)
Regarding the contribution of geothermal heating to the ocean heat balance I would recommend this paper as a starting point.
http://www.ocean-sci.net/5/203/2009/os-5-203-2009.pdf
Geothermal heating, diapycnal mixing and the abyssal circulation
J. Emile-Geay 1 and G. Madec 2,*
From the abstract
Geothermal heating and diapycnal mixing are found to interact non-linearly through the
density field, with geothermal heating eroding the deep stratification supporting a downward diffusive flux, while diapycnal mixing acts to map near-surface temperature gradients onto the bottom, thereby altering the density structure that supports a geothermal circulation. For strong vertical mixing rates, geothermal heating enhances the AABW cell by about 15% (2.5 Sv) and heats up the last 2000 m by ∼0.15◦C,reaching a maximum of by 0.3 ◦ C in the deep North Pacific.
Prescribing a realistic spatial distribution of the heat flux acts to enhance this temperature rise at mid-depth and reduce it at great depth, producing a more modest increase in overturning than in the uniform case. In all cases, however, poleward heat transport increases by ∼10% in the Southern Ocean. The three approaches converge to the conclusion that geothermal heating is an important actor of abyssal dynamics, and should no longer be neglected in oceanographic studies.
From the discussion section
The case is hereby made that geothermal heating is an important actor of abyssal dynamics. We recommend its inclusion in every model dealing with the long-term ocean circulation, for it substantially alters bottom water mass characteristics and generates a non-negligible circulation in the present-day climate. Further, recent results by Dutay et al. (2008) confirm its importance in correctly simulating tracer distributions in the deep ocean.
philip Bradley: Your reply excluded the requested papers. An RC link to, assumedly, a field study does not suffice.
wyn palmer
re:
http://pielkeclimatesci.wordpress.com/2011/10/21/my-recent-discussion-with-gavin-schmidt-on-real-climate/
The tenacity with which Gavin clings to the unscientific methodology used to determine the ‘global average temperature’ is quite remarkable.
I suspect that Gavin knows that the methodology is seriously flawed and further he knows that to concede the flaws and move to a more scientific basis will bring the AGW house of cards down.
philip Bradley: Your reply excluded the requested papers. An RC link to, assumedly, a field study does not suffice.
I thought a field study was what you wanted.
Otherwise, The global average SST is 2C to 3C higher than global average surface air temperature. Warm the atmosphere = reduce the temperature gradient and heat transfer is reduced.
This simple fact tends to get lost.
Correction to my above post. NE of Australia.
Philip Bradley says: “Otherwise, The global average SST is 2C to 3C higher than global average surface air temperature.”
Which Marine Air Temperature dataset are you using for your combined Land Plus Marine Air Temperature Data, COADS or MOHMAT? What land surface temperature dataset are you using for your LST data, since the big three land surface temperature datasets are provided in anomalies? Please graph them to show the 2 to 3 deg C difference and identify what datasets you’ve used.
You continued, “Warm the atmosphere = reduce the temperature gradient and heat transfer is reduced.”
Your original statement was that evaporation was reduced. Are you changing your hypothesis?
Also, please plot the Sea Surface and Marine Air Temperature datasets upon which you are basing this assumption and illustrate which temperature dataset, Sea Surface or Marine Air, rises faster–and explain why, based on your assumptions.
The reason I ask, as you may be aware, I’ve dissected the satellite-era Sea Surface Temperature data (the Reynolds OI.v2 SST dataset), and I cannot find any evidence of anthropogenic greenhouse gas warming in that dataset. Volcano-adjusted SST anomalies for 33% of the planet (the East Pacific Ocean [90S-90N, 180-80W] have not risen during that time. And all of the rise since 1982 (the start of that dataset) for the rest of the world can be explained as multiyear responses to ENSO, combined with the additional variability in the North Atlantic caused by the Atlantic Multidecadal Oscillation. It’s actually very easy to see, once you know how ENSO works. Refer to the posts:
http://bobtisdale.wordpress.com/2011/07/26/enso-indices-do-not-represent-the-process-of-enso-or-its-impact-on-global-temperature/
And:
http://bobtisdale.wordpress.com/2011/08/07/supplement-to-enso-indices-do-not-represent-the-process-of-enso-or-its-impact-on-global-temperature/
If the sea surface warming is not a result of AGG, one might conclude the warming of the oceans to depths of 700 meters also cannot be caused by AGG. I was grateful when KNMI added the NODC OHC data (0-700 meters) to its Climate Explorer website a few years ago. It allowed me to illustrate and discuss how the rise in OHC can be due to natural variables as well: ENSO, changes in Sea Level Pressure, and AMO/AMOC. Refer to:
http://bobtisdale.blogspot.com/2009/09/enso-dominates-nodc-ocean-heat-content.html
And:
http://bobtisdale.blogspot.com/2009/12/north-pacific-ocean-heat-content-shift.html
And:
http://bobtisdale.blogspot.com/2009/10/north-atlantic-ocean-heat-content-0-700.html
I had to think about the heating issue of water in a context that my simple mind could understand. Water is not near as good of a heat conductor as I was thinking. A home hot water heater is the simplest analogy that came to my mind. The temperature gradient falls off very fast as the pipe leaves tank.
Is there any known method that would allow a double inversion layer as in heat/cold/heat ? With the heated water being less dense it seems to me that it will always find a way to rise. Are there any studies that shows how the heat generated from the sea floor vents dissipate?
Bob,
If from 1,000 to 2,000 meter dataset is basically “data free” would it not be appropriate to note on your primary chart that prior to year 2000 the OHC 0-2000m curve is simulated. Possibly instead of a solid red curve prior to 2000, using a dashed curve? I think that would make it clearer to the average person that prior to year 2000 the data is questionable (i.e. flaky/flimsy).
Like many others before, great post.
Some amazingly silly nonsense in some of these posts. Tropical lake bottom temperatures give us some idea of what the minimum seasonal temperatures are. In the temperate zones they hang around the T of maximum density, a few degrees above freezing. They sure don’t tell us anything about average surface T.
Paolo and Illis are right. Springer and phlogiston are full of it. And Paleozoic ocean bottoms? Certainly much warmer than now–what does pressure have to do with anything? This thread has devolved into another disgrace to basic physics.
Even swimming pools instruct us–they tend to be colder than the average air temperature even when they’re covered. They tend toward the nightime temperature simply because cold water descends, and warm water–all water–insulates. Some of the skeptics around here give the rest of us a bad name.
–AGF
“Even swimming pools instruct us–they tend to be colder than the average air temperature even when they’re covered. They tend toward the nightime temperature simply because cold water descends”
That doesn’t sound right.
When a strong sun shines into a pool the water near the surface gets warmer than the air above.
At night the air cools faster than the water so the water becomes warmer than the air.
I think AGF is confused because water in a pool FEELS cold even on a sunny day but that is only a matter of percepton because the water in the pool is lower than body temperature and due to the high thermal capacity of water it pulls energy out of the skin faster than does air at an even lower temperature.
That is why one gets hypothermia faster in water than in air of the same (or even lower) temperature.
To put it more clearly: water can only be heated from the bottom up; it can only be cooled from the top down. Polar winters are many orders of magnitude more effective at cooling than earth heat is at warming.
Here is a thermocline by month for the Sea of Galilee (Lake Kinneret): http://www.ilec.or.jp/database/asi/asi-09.html
Notice that at 40 meters T strays little from the minimum surface T. –AGF
Steve, let us count the ways we warm ourselves when drying off with a towel:
1. The towel insulates, like a blanket.
2. The towel removes water, reducing evaporative cooling.
3. The exertion excercises our muscles, warming us.
4. The towel may block the wind, reducing both evaporation and wind chill.
5. The act of drying constitutes friction, warming the skin.
Have I left anything out?
“To put it more clearly: water can only be heated from the bottom up; it can only be cooled from the top down”
Don’t oceans warm at the top when the sun shines on them and cool from the top when the sun is not shining ?
The Sea of Galilee would not have a significant Thermohaline Circulation and so landlocked bodies of water are not a good comparator.
Sure, different frequencies penetrate different depths, and light penetrates deepest, but this radiation can’t heat water any deeper than it can penetrate, whereas conductive cooling can affect the entire ocean, just as bottom heating can. Of course fresh water lakes present a very simple case, but this basic model is obiously lost on some of the commenters. The point I’m trying to make is that average surface T has nothing to do with ocean T in general, as the Sea of Galilee shows nicely. Obviously the deep ocean is warmer than the minimum surface T at the poles, so other factors are at play, including bottom heating and layer mixing.
Bob has some great points, but some people take it a bit too far.
http://itsnotnova.wordpress.com/2011/12/03/the-nova-travesty-cherry-picker-ahoy/