2010-09-23 22:38:53New way of transmitting heat to deep ocean: internal waves?!?!
John Cook

john@skepticalscience...
124.185.151.34

Here's another paper on deep ocean heat, Simulated Rapid Warming of Abyssal North Pacific Waters. They use modelling to simulate rapid warming of abyssal waters - the heat is transmitted via "internal waves". My initial reaction is skepticism borne of ignorance. Does anyone understand the phenomenon here? Abstract:

Recent observational surveys have shown significant oceanic bottom-water warming. However, the mechanisms causing such warming remain poorly understood, and their time scales are uncertain. Here, we report computer simulations that reveal a fast teleconnection between changes in the surface air-sea heat flux off the Adélie Coast of Antarctica and the bottom-water warming in the North Pacific. In contrast to conventional estimates of a multicentennial time scale, this link is established over only four decades through the action of internal waves. Changes in the heat content of the deep ocean are thus far more sensitive to the air-sea thermal interchanges than previously considered. Our findings require a reassessment of the role of the Southern Ocean in determining the impact of atmospheric warming on deep oceanic waters.

 

More details available in their press release including a cool pic of simulation results showing significant warming below 4000 metres:

 Figure 1

2010-09-23 22:57:49
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Wow, this would cause quite an upheaval in thinking, if true.

 

In the interest of promoting discussion I've taken the liberty of extracting the most tasty nuggets from the article:u

 

Recent observational surveys conducted during the World Ocean Circulation Experiment (WOCE) and the WOCE revisit (WOCE_rev) have revealed that the deepest waters of the major oceans have warmed during recent decades (35). This bottom-water warming ranges in magnitude from 0.003° to 0.01°C in the Pacific Ocean over the period 1985 to 1999 (3, 6). Such temporal changes are of particular interest as they can constrain estimates of the variability of abyssal circulation. The latter have implications for large-scale thermohaline transport and thus for the global three-dimensional heat budget that is presently of vital concern (7).

 

Despite its crucial importance, the physical mechanisms governing bottom-water warming are poorly understood because in situ observations are spatially and temporally sporadic. Recently, a highly accurate ocean data assimilation system has been constructed (8), based on a four-dimensional variational (4D-VAR) adjoint approach (9, 10) [supporting online material (SOM)], which can define the mechanism causing an oceanic climate fluctuation by an adjoint sensitivity analysis method that moves the ocean representation backward in time (11, 12) (SOM). We used the "Earth Simulator" supercomputer to perform the major numerical simulations required for this analysis (SOM).

The adjoint sensitivity analysis gives the temporal rate of change of a physical variable in a fixed time and space when model variables (e.g., water temperature, velocity, or surface air-sea fluxes) are arbitrarily changed in the 4D continuum of one temporal and three spatial coordinates. This is equivalent to specifying the "sensitivity" of a variable to small perturbations in the parameters governing the oceanic state (8, 1315). It has been applied to identify the possible causal dynamics, time scales, and pathways involved in the bottom-water warming.

Figure 2 shows the values of the temporal rate of change of bottom-water temperature taking place at 47°N-170°E (5200-m depth) in an allocated model time (defined as year zero) when water temperature changes by 1 K in an arbitrary grid point over a specific time period (in this case, from 0 to –45 years in reverse chronological order). Positive values (indicative of warming in the lowest layer) gradually fill the North Pacific Ocean floor over a 15-year period (Fig. 2, B and C) and then penetrate into the South Pacific through the narrow passage located to the northwest of New Zealand (Fig. 2D). This warming trend can be traced back to the deep Southern Ocean across the Antarctic Circumpolar Circulation region (Fig. 2E) where it then ascends the continental shelf slope around Antarctica. At the end of a 40-year period, the warm signature finally appears at the sea surface in a confined source region that lies off the Adélie Coast (Fig. 2F). The values of the temporal rate of the change, when the net surface air-sea heat flux is changed by 1 W m–2 in an arbitrary surface grid point (rather than through a change in water temperature), consistently suggest that the cause of the bottom-water warming in the North Pacific is the increase in the net surface air-sea heat flux into this localized source region (Fig. 2F). (The integrated effect in this region covers 73% of that over the whole Pacific basin, when the values of the temporal rate of the change are effectively assessed with the variance of the heat flux at each surface grid point.) This result implies that a reduction in the volume of AABW due to an increase in the net surface air-sea heat flux in this Southern Ocean region initiates the North Pacific abyssal warming...

 


Our simulation result reveals a subtle and prompt influence of the Southern Ocean source region on changes in deep-ocean temperature and thus ocean heat budgets. However, the 40-year time scale necessary for these thermal changes to manifest is much shorter than that required by the conventional mechanism, which relies on mass movement (16). In the case of an abyssal current flowing northward at a speed of 10–3 m s–1 (17), it would require more than 350 years to cover a distance of 12,000 km.

A more rapid teleconnection between the Southern Ocean surface heating and bottom-water warming in the North Pacific can nevertheless be effected through oceanic internal waves. A thinning of abyssal layers caused by a reduction in AABW formation in a Southern Ocean source region leads to a depression of isopycnal surfaces in the deep ocean (18). These isopycnal changes are transmitted as internal oceanic waves, which alter the pressure force locally and weaken the deep-water current through geostrophic adjustment (19, 20). Bottom-water warming could be then achieved by a reduction in the deep-water current that transports the cool waters of the AABW (3).

Internal topographic Kelvin waves are mainly responsible for the rapid transmission of the changes in the Southern Ocean to the equator (orange arrows in Fig. 2, D and E). The Kelvin waves travel along the deep-ocean trench east of New Zealand in a direction for which the lateral boundary is always on the left (in the Southern Hemisphere; SOM). They propagate along the density interfaces of the deep ocean at internal-wave speeds (21) of ~7.0 x 10–2 m s–1, corresponding to 2208 km per year (SOM). The signal travels in the opposite direction (with the lateral boundary on the right) in this sensitivity analysis because the calculation moves the ocean representation backward in time.

Internal and topographic Rossby waves are also responsible for the transmission over the undulating bottom topography in the west-central region of the Northern Hemisphere (Fig. 2B). Internal equatorial Kelvin waves, whose (reversed) propagation is identified by the westward equatorially trapped wave track in the deep layers (yellow arrows in Fig. 2C), drive the link between northern and southern hemispheres.

We have examined the proposed mechanism by using a new synthesized ocean data set from 4D-VAR data assimilation (22) (SOM). In this synthesized data set, the bottom-water warming is successfully reproduced as a positive temperature trend of ~0.003 K from 1985 to 1999 (between the WOCE and WOCE_rev observational periods) in the North Pacific (Fig. 3A). The term balance of the temperature equation in this abyssal region from the synthesized field (SOM) shows that an overall balance between the horizontal advective and diffusive cooling, and the vertical diffusive heating, is present throughout the period (blue bars in Fig. 3B). The geothermal heating effect is implicitly incorporated in the vertical diffusive heating. Local time change is a subtle positive value, representing the bottom-water warming, as a residual of these major terms. The standard deviation of each term shows that the temporal change in the horizontal advection mainly causes the variations of the local time change (red bars), implying that the changes in the abyssal circulation due to the wave propagations (SOM) constrain the bottom-water warming...


 

In this context, our derivation of a 40-year response time implies that the bottom-water warming from 1985 to 1999 in the subarctic North Pacific is linked to the decrease in the MSA value from 1945 to 1959, which corresponds to an increase in the net surface air-sea heat flux off the Adélie Coast. Quantitative diagnosis, based on values of the temporal rate of change of bottom-water temperature when net surface air-sea heat flux is steadily changed (Fig. 2F), shows that an observed bottom-water warming from 0.003 to 0.01 K is equivalent to an increase in the net heat flux from 1.0 x 10–1 to 3.2 x 10–1 W m–2 per year into the Southern Ocean off the Adélie Coast (SOM). This net heat flux enhancement is broadly consistent with the relevant decadal increase (3.8 x 10–1 W m–2 year–1) from 1945 to 1959, as estimated from the ratio of the MSA values (black curve in Fig. 4) to the net surface heat flux (green curve).

In summary, an increase in the heat input into the Southern Ocean off the Adélie Coast leads to bottom-water warming in the North Pacific on a relatively short time scale (within four decades). A reduction in bottom-water formation off the Adélie Coast due to enhanced heat input leads to a change in the configuration of the isopycnal surfaces through the action of oceanic internal waves and thus determines the pressure forcing over the whole abyssal region of the North Pacific. The consequent reduction in abyssal cooling by the deep-ocean current enables the substantial heating by the vertical diffusion inclusive of the geothermal effect to warm the bottom waters. The propagation speed of the internal waves determines the time scale of this teleconnection. The resulting increase in the integrated heat content can reach 1.2 x 1020 J year–1 below 4000-m depth in the Pacific basin.

These results suggest that the present global-change paradigm involving a warming surface regime over an abyssal ocean which, through its very slow response time, can be assumed to be a relatively stable regulator of Earth’s climate, must be revisited. Our finding of an invasive and rapid teleconnection between polar surface air-sea heat flux change and distant bottom-water warming indicates that the multicentennial-to-millennial developmental time scales currently envisaged in the predicted oceanic response to climate warming are probably too long. 

 

 

2010-09-23 23:40:26
Ari Jokimäki

arijmaki@yahoo...
91.154.102.68

Purkey and Johnson also mention this wave thing. Here is a quote from their paper:

However, a deep warming signal can propagate from the Southern Ocean to the North Pacific via planetary (Kelvin and Rossby) waves in less than 50 years (Nakano and Suginohara 2002), moving northward on western boundaries, eastward on the equator, then poleward at eastern boundaries, and westward into the interior (Kawase 1987). This remote warming signal could be driven by an increase and southward shift in Southern Ocean westerly winds (Klinger and Cruz 2009) or reductions in buoyancy fluxes near the AABW formation regions that decrease AABW formation rates (Masuda et al. 2010).

The Kawase (1987) was published in an AMS journal so the PDF is accessible for free in the abstract page:

http://journals.ametsoc.org/doi/abs/10.1175/1520-0485%281987%29017%3C2294%3AEODOCD%3E2.0.CO%3B2

2010-09-24 06:05:06
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.79.5
Given that Kelvin and Rossby waves play such an important role in ENSO, it shouldn't be too surprising that someone suggests they're a more common feature in ocean dynamics. Cool graph too, John, it would look good in a post. 
2010-09-24 08:39:00
Riccardo

riccardoreitano@tiscali...
93.147.82.100

Although the paper deals with just warming in the pacific, one should expect that similar behaviour may show up wherever you have downwelling of cold waters feeding distant deep waters in the same basin (topography matters). The mechanism looks plausible but it (obviously) needs to be confirmed.

Decoupling heat and masss transport by this mechanism is intriguing and may help explain (among other things) why temperature can vary much more rapidly the CO2 concentration.

2010-09-24 14:46:13Post?
nealjking

nealjking@gmail...
195.202.153.35

Dappeledwater,

This is an interesting new simulation result, but I am not sure why we would promote it, in the context of what SkS is trying to do. What would be the angle? 

2010-09-24 18:08:08
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.157.64

Neal, I know you won't believe it, but I expected you to say exactly that. Anyway, how does commenting on an interesting study equate to promoting it?. It's not like anyone's hitching their wagon to it. I can't see any problem with an explanatory, even handed post.

There's lot of uncertainty with OHC and people like Pielke Snr are using it as as opportunity to spread FUD, at least this study illustrates that some scientists are actually looking into mechanisms whereby the heat can get down to the deep ocean.   

2010-09-25 02:11:24
nealjking

nealjking@gmail...
195.202.153.35

Dappledwater,

I have nothing against interesting news. But I wonder if SkS would be in danger of harming its "brand", if we get into reporting every new idea in climate science? These are research concepts, and some of them will turn out to be flops: that's just how science works. Why should we give the deniers a spraycan to practice their graffiti?

2010-09-25 02:24:30
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Some things are good for the blog, others for more static rebuttal content. This would be a case of the former.

This is an intriguing paper because it offers one -possible- additional explanation for Trenberth's budget gap. Based on recent direct sampling of abyssal temperatures it's clear that "we've" seriously underestimated the role of deep water in sucking up heat via accepted circulation mechanisms; Trenberth's Travesty appears to be fully 20% smaller than at first glance now that we've got a slightly better handle on measurement. Imagine "we" follow this new avenue to its conclusion and find just another 10% of "missing heat" accounted for. Not so huge in the grand scheme of things but put all the omissions together and they begin to add up. 

As opposed to something more mundane, papers such as this serve as a reminder that skeptics leverage the conservative nature of science to wring "not there" from "we can't yet find it." 

2010-09-25 06:23:48
nealjking

nealjking@gmail...
195.202.153.35

doug_bostrom,

 My problem with posting this item is that, if someone pops a hole in it, denialist sites can claim, "SkepticalScience is grasping at straws to defend the mismatch between prediction and data. One of those straws has just snapped."

And since this is real science, there is a very reasonable probability that someone WILL pop a hole in it. Frontier results are NOT certain.

2010-09-25 11:55:59
doug_bostrom

dbostrom@clearwire...
184.77.83.151

True enough Neal. On the other hand skeptics can't distinguish what is a hole, whether a door is open or shut. They object to everything!

Purkey and Johnson cited this paper in their item about OHC and SLR, AABW. Going to the well once more, here's what came up:

"Those Rossby and Kelvin waves are about the only way I know for a signal originating in the Southern Ocean to make it to the northern Hemisphere in decades.  Kawase did a nice job elucidating the dynamics in his 1987 paper.  What Masuda et al. added was to diagnose the exact source of the changes with their data assimilation.  The uncertain part of that is that the result may be highly dependent on the physics of the model they use (which may not be optimal in terms of simulating how AABW is actually formed), and the statistics they build into the data assimilation cost functions (which I think one could argue are not very well constrained and are hard to get right)." 

2010-09-25 15:59:32
nealjking

nealjking@gmail...
195.202.153.35

doug,

Yes, the skeptics won't be able to determine it themselves. What I'm worried about is the following scenario:

1) Paper comes out proposing a mechanism that will accelerate the warming effect, or improve the match between modeled results and today's measurements, etc.

2) SkS posts this as exciting news that further strengthens to case that AGW is happening and is serious.

3) Time passes.

4) Someone finds a problem with the analysis, writes up a peer-reviewed paper that points out the flaw. The original authors withdraw the claim, or go quiet.

5) Skeptics emerge: "Look, that paper that SkS was promoting in step 2) has been proven to be a mistake in step 4). That just goes to show that SkS will jump on ANYTHING to defend the AGW point of view. Now we see they promoted mistaken science there. What else are they promoting that is wrong, or that will be proven wrong over the next few years? SkS cannot be trusted!"

You see the problem? 

 

2010-09-25 16:55:22
Riccardo

riccardoreitano@tiscali...
93.147.82.96

There no need to jump to strong conclusions, or better, never draw strong conclusions from a single just published paper. In particular, this paper is not pro- or anti- agw. It's, i'd say, pro science, one more little bit of knowledge.

If a post is to be written it should be a sort of "oceanography news". I don't know if it will prove better or worse for agw theory. For sure is a mechnism to move heat "rapidly" accross the oceans and that's "good" for agw supporters. But then there's the problem of proving that there has been a reduction in AABW formation; and then there's the cause of this reduction to understand, maybe a shift or a weakening of the westerlies; and then understand this weakening; and then ... who knows.

In a few words, I think we could wirte a post on " possible mechanism of rapid heat trasnfer in the oceans" without claiming that it disproves Pielke theory or that it proves where the missing heat is. Not a rebuttal but a "science bit".

2010-09-25 17:53:16
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.143.191

Neal, 

Doesn't matter what SkS posts, the skeptics have some ridiculous arse about face spin on it - look at the comments by the resident skeptics for example - if that's not graffiti well then what is?.  

Your item No.2 seems to be overstating the case, hence my earlier comment. There is a veritable vacuum regarding the OHC data and I'm surprised the skeptics aren't out pushing this particular barrow real hard.

How's this scenario?.

- Rational uninformed person surfing the internet comes across skeptics arguing global warming has stopped & that OHC is a better "metric" (anything that implies global cooling is always a better metric for skeptics)

- Said rational person comes across SkS & finds - hey, the atmosphere is still warming, the sea level is still rising, the ARGO data has a few issues and, contrary to skeptic claims there may indeed be mechanisms on scales less than centuries that heat can penetrate the deep ocean. In this context skeptic claims appear totally bogus, which of course they are.

Isn't that a better consideration, rather than worrying about the next load of baloney the skeptics come up with?. 


 

  

 

2010-09-26 02:02:14
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Bear in mind, I'm not advocating writing up this article as blog post. Rather, let's consider it as a case of what sort of news deserves mention on the blog. 

OHC is a major, fundamental mystery, something many of us suspect is the culprit for Trenberth's missing heat and as well is a focus of skepticism, thus it's an interesting topic to follow closely here.

If it's true that "missing heat" is in the oceans (and where else would it be?), a previously unidentified mechanism for moving heat into the oceans and working on a time shorter scale than multicentennial or millennial will eventually be identified. Quoting what GC Johnson mentioned, "...Rossby and Kelvin waves are about the only way I know for a signal originating in the Southern Ocean to make it to the northern Hemisphere in decades." A paper by a seasoned research team positing such a mechanism, describing it and publishing it in a journal of the caliber of Science is actually notable news directly relevant to this site's mission. 

If a blog post were to be done on this, a matter of five words or so would suffice to establish SkS's lack of committal as to whether the paper is durably and deeply significant.  No risk of reputation need be entailed. So it seems possible to establish some metrics concerning how "bleeding edge" the blog ought to be, how to select material sufficiently noteworthy for mention, as well as mechanisms for avoiding credibility loss.

2010-09-26 02:11:22
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Anyway, leaving aside the legitimacy of this paper as a topic for a blog post, I'm willing to bet that we'll find the "missing heat" in the ocean, but we won't find it's arrived there as one lump of 0.5W/m2 via a single previously unidentified mechanism. It'll turn out to be a collection of functions, such as P&K's apparent 20% delivered via AABW, other things we don't know about. Perhaps Masuda's overturning waves will account for 5%, perhaps 20%. It'll be interesting to find out.