ABSTRACT:
Combining ocean and earth models, we show that there is a region in the central Pacific ocean where ocean bottom pressure is a direct measure of interannual changes in ocean
mass, with a noise level for annual means below 3 mm water equivalent, and a trend error below 1 mm/yr. We demonstrate this concept using existing ocean bottom pressure
measurements from the region, from which we extract the annual cycle of ocean mass (amplitude 8.5 mm, peaking in late September), which is in agreement with previous
determinations based on complex combinations of global data sets. This method sidesteps a number of limitations in satellite gravity-based calculations, but its direct implementation is currently limited by the precision of pressure sensors, which suffer from significant drift. Development of a low-drift method to measure ocean bottom pressure at a few sites could provide an important geodetic constraint on the earth system.
Citation: Hughes, C. W., M. E. Tamisiea, R. J. Bingham, and J. Williams (2012), Weighing the ocean: Using a single mooring to measure changes in the mass of the ocean, Geophys. Res. Lett., 39, L17602, doi:10.1029/2012GL052935.
Introduction:
The GRACE satellite gravity mission has revolutionized our ability to monitor regional mass redistribution in the earth system, and hence monitor changes in ocean mass and the source of those changes. However, GRACE does not monitor the degree 1 terms in mass movement, associated with geocenter motion, and is weak for the C2,0 harmonic [Chen et al., 2006; Swenson et al., 2008; Leuliette and Miller, 2009]. It also suffers from limited spatial resolution, making it hard to distinguish the much larger land signals from ocean signals near the ocean boundaries [Chambers et al., 2007], and secular trends include a contribution from glacial isostatic adjustment (GIA), the solid earth’s ongoing response to the change in load since the last glaciations [Tamisiea, 2011]. Together, these difficulties lead to an uncertainty approaching 1 mm/yr in the measured mass component of global sea level trend.
If sea level changes were spatially uniform, then variation of the volume of the ocean could be monitored using a single tide gauge. Similarly, spatially uniform changes in ocean bottom pressure (OBP) would mean ocean mass changes could be monitored with a single OBP Recorder. However, spatial variations mean that sea level measurements must be made over the entire ocean (by satellite altimetry), or statistical extrapolation must be used to mitigate the sampling problems of tide gauge data [Hughes and Williams, 2010; Church and White, 2006; Jevrejeva et al., 2006]. Fortunately, as we will show, OBP observations in one specific region do allow us to measure ocean mass changes with a single station.
h/t to Dr. Leif Svalgaard who has the full paper here
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I fail to see why satellites are needed after the design of a longer life bottom instrument is realized. Please consider reducing government waste!
Doesn’t sea water density change quite dramatically from place to place, varying from almost fresh to very dense?
Presumably these differences in density will affect pressure on the seabed.
Do these investigations allow for this?
Anthony:
The Abstract of the paper says
NO!
A model cannot measure anything except the opinions of those who constructed the model.
Opinions are NOT reality.
However, the output of a model can be used as an indication if the model can be shown to emulate reality with known accuracy, precision and reliability.
The paper says
However, it is not true that
“The dynamical signal is therefore small enough …”
because there is no determination – only a suggestion – that
“the statistical uncertainty estimate of 0.28 mm/yr is probably not far from the true dynamical OBP trend”.
How far is “not far”?
In conclusion, the paper may be right “that there is a region in the central Pacific ocean where ocean bottom pressure is a direct measure of interannual changes in ocean mass” but it only provides a “suggestion” of this being true and much more work is required to substantiate whether it is true or not.
Richard
Apologies for being off topic, but has anyone wondered where have all the tediously painful, pseudo-intellectual, trolls that used to post on WUWT, like R Gates, gone to?
Answer: They seem to have emerged at Judith Curry’s Climate etc where their verbal diarrhoea is in full flow.
As for this post, good luck with this measuring process, these guys are going to need it.
Pressure changes at the bottom of a static tank might reveal surface level changes, but this is a dynamic system. Sea water weighs 64.2 lb/cuft with a linear increase with depth. A minor temperature difference in this water column could result in a perceived silly millimeter change. Terra firma weighs average 125 lb/cu ft and is floating on liquid magma. Every day the Moon lifts and drops the Earth’s crust 18 inches, known as Earthtide. This lift/fall cycle allows adjustments of under crust mantle pressure spots, meaning there is NO fixed bottom reference point. To measure the top of the ocean, from pressure sensors on the bottom, is a preposterous grant gravy fiction, approved by green blinkered, logic-free bureaucrates.
What actually matters is what we see on our shorelines. There is no perceptible sea level rise where I live, my mothers home in Redcar is still above water. I see no need to worry.
DaveE.
Has anyone noticed that most of the new, interesting work on climate related items like sea level, ice ages, paleo climate, etc., are from mainly new blood. The prolific bunch that essentially ruined scientific journals with dross and activist plonk pre-climategate (how can anyone respect Nature, Sci American and their like again) have somewhat withdrawn and taken up defensive positions, sniping in shrill hyperbole and through law suits, the same old dead stuff about CO2. This and the somewhat sad and self denigrating global rants designed by Al Gore. Al, time to sell your positions in the carbon market and retire. Kevin, its over, let the young guys do the heavy lifting now. Don’t stand on the bridge like the Mann and watch your world fall apart.
The models show that there is a region in the central Pacific ocean where ocean bottom pressure is a direct measure of interannual changes in ocean mass, with a noise level for annual means below 3 mm water equivalent, and a trend error below 1 mm/yr.
An hypothesis is declared (there is a region in the central Pacific ocean where ocean bottom pressure is a direct measure of interannual changes in ocean mass, with a noise level for annual means below 3 mm water equivalent, and a trend error below 1 mm/yr) based on their pet models. The hypothesis needs to be tested by direct measurements at this Pacific ocean location, to determine if it is valid or false, to assess if the conditions at the location is really as the models predict. Further, samples of the bottom ooze from this location need to be retrieved and evaluated to guide the design of the sensor.
As the hypothetical sensor will measure pressure as a proxy for ‘total ocean mass’ (Did I understand that correctly?), it must needs be incredibly accurate and stable over decades wrt to pressure and temperature while being impervious to direct penetration, permeation, corrosion, or diffusion from the ambient solution or elemental constitutients at the ocean bottom. What ambient pressures and temperature will this sensor be exposed to in service, at the bottom of the Pacific? What is the molecular and dissociated elemental make up of the primordial ooze at that depth?
The bottom of the ocean is necessarily exposed to a continual in-fall of organic and inorganic debris from the water column above. What is the in-fall rate at this location and how will this steadily accumulating in-fall of debris effect the sensor over time?
MtK
I’ve noticed that. Her site needs a team of moderators.
Peter Miller says:
November 9, 2012 at 3:26 pm
where have all the tediously painful, pseudo-intellectual, trolls that used to post on WUWT, like R Gates, gone to?
There are some left here…
e.g. the usual ones on http://wattsupwiththat.com/2012/11/06/solar-cycle-24-continues-weakly-perhaps-weakest-of-the-space-age
I have not read the paper because it is behind a paywall but when scientists write a paper about pressure than one has to doubt the conclusions. Pressure is an engineering unit. OBP is a combination of a) gravity b) density of the fluid d) height of the column of fluid and e) surface pressure (ie atmospheric pressure). All of these factors may vary around the globe and some can vary over time. A standard atmosphere is 101.3 kPa but atmospheric pressure can vary from about 96kPa to 104 KPa. Standard gravity is 9.807 m2/sec but can vary in the range 9.78 to 9.83 m2/sec . By definition the density of water at 4C is 1000kg/m3.. A 10m column of pure water at 4C in a standard atmosphere will give a pressure of 98.07kPa. Density of water will vary with temperature. Pure water at 20C has a density of 998kg/m3. Sea water contains salt which changes density – the approximate salt content is 35kg/m3. The average density of a deep water column near the equator maybe 1030 kg/m3.
I doubt if sea level can ever be measured to an accuracy of 1 mm particularly considering the variation in atmospheric pressure (work it out yourself).
Reports on “The South Pacific Sea Level & Climate Monitoring Project” have shown variations in sea level associated with SOI (calculated from the difference in atmospheric pressure between Darwin and Tahiti)
Dear Perfessers….
The water ain’t gittin’ no deeper in Charleston…..
Thank you,
Bubba
“There are some left here…
e.g. the usual ones on http://wattsupwiththat.com/2012/11/06/solar-cycle-24-continues-weakly-perhaps-weakest-of-the-space-age”
OK; So I go there and I wonder what it is I’m expected to do? Scroll through 212 responses and try to guess which ones are trolls? A little bit of specificity would go a long way here.
Mariss says:
November 9, 2012 at 6:36 pm
Scroll through 212 responses and try to guess which ones are trolls? A little bit of specificity would go a long way here.
Scroll from the bottom and make up your own mind
Somewhat off topic: a couple of years ago you featured a pie chart showing “What we know about climate”, “What we think we know about climate”, and “What we DON’T know about climate”.
I found it to be very enlightening (and humbling) when discussing various theories and observations, but have lost it.
Could you re-post it?
David A. Evans says: November 9, 2012 at 4:44 pm “…. no perceptible sea level rise where I live, my mothers home in Redcar is still above water. I see no need to worry….”
Larry Butler says: November 9, 2012 at 6:20 pm “…The water ain’t gittin’ no deeper in Charleston…..”
Mariss says: November 9, 2012 at 6:36 pm “…. I wonder what it is I’m expected to do? Scroll through 212 responses and try to guess which ones are trolls? A little bit of specificity would go a long way here…..”
I dunno, still seem to be plenty of trolls here, though they are the ‘drive by’ sort. Some people are even too lazy to do their own reading.
Beginning about 18,000 years ago as the glacial ended and rapid sea level rise followed, these types of high-tech activities seem most suitable — large changes in a short time hardly confused by other factors. Currently, with small changes, there are confounding issues, such as water mining, increased sedimentation, spreading ridges, crustal uplift and sinking, and perhaps a few others. While pressure measurements may be useful for some purpose, David A. Evans @ur momisugly 4:44 says “What actually matters is what we see on our shorelines.” And how does pressure tell us that?
Mariss says: November 9, 2012 at 6:36 pm
“……I wonder what it is I’m expected to do? Scroll through 212 responses and try to guess which ones are trolls? A little bit of specificity would go a long way here….”
Mariss, thinking further, and having just visited the site, I wonder what you really are wanting to discover? I find when I go there, I read through the comments in order to understand the discussion (and they are nicely threaded), and even follow the links and read discussed papers!!!!?
Can you enlighten me as to your methods of research, opinion forming, and entering into discussion?
It may save me an awful lot of time.
mods … sorry ….looks like an open HTML tag in my previous post…
Reply: No problem. Fixed. -ModE
markx said:
November 9, 2012 at 9:48 pm
[clipped examples]
I dunno, still seem to be plenty of trolls here…
——————————————————————
Those are trolls? Hah! He must not read many forums.
@markx:
Here near San Francisco, the old Alviso Harbor is now a reed bed and the docks have been removed. The channel is flanked by salt marshes, and the place where, during World War II, they built ships for the war effort is effectively land locked. The bay is significantly smaller than it was when ‘discovered’ a few hundred years ago. There isn’t any water rise, but the land does seem to be rising.
Then again, this IS California and we kind of expect our land to be moving around a lot 😉
That kind of observation isn’t ‘trolling’, it’s data.
The Trolls tend to toss out snark for the purpose of instigating a food fight.
IMHO, they have faded (as they typically do) due to the Election and will be back soon enough. They also fade about the time some government funded party is being held at the pork barrel ( i.e. such things as the Ipcc and related free rider events). But they come back when the new semester starts and they have to be back at “work”…
@Marris:
Who is a Troll is somewhat (highly?) subjective. It’s not really possible for me to tell you ‘who is a Troll’, only my opinion of who might be. So look for dogged repeating of “talking points”. Look for “talking past” the other person and not addressing points they make / raise. Look for emotional loaded language and ‘attack the messenger’ (and avoidance of an actual ‘searching for truth’ behavior). And look especially for tossing red meat insults, invective, and innuendo intended to start arguments / fights rather than reach answers. Then look for that same moniker doing those same things over and over and over…
IMHO, though, that particular thread / link doesn’t give a lot of good examples. Mostly it has examples of snark and sniping between the “Sun can’t do it” side represented by Leif, and the “Sun does it” crowd (such as Geoff) in their usual “does so – does not” pebble tossing (doesn’t really rise to mud tossing or rock throwing 😉
FWIW, in looking through a couple of postings / comments just now for a ‘good example’, I couldn’t find one… So now I’m wondering where the AGW True believers have all run off to as well…. Perhaps they were instructed to not rile the ‘skeptics’ before the election, lest they go vote… or they are still hungover from the party… 😉
Per the subject of the posting:
Again with the mythical precision via magical math…. fixing up that chaotic ocean surface and the thousand and one ‘moving targets’ that change the ocean… Heck, just the way the moon has a constantly changing tidal influence with various cycles from a month to 1200 years (and more?) means a larger error term for any one spot on the ocean floor (not to mention changes in circumpolar currents at the S. Pole and…
cementafriend
Please learn about the international measurement system SI and how the density of water varies with temperature. The density of water is NOT “By definition “1000kg/m3” “at 4C” “by definition”.
See ISPWA
Guideline on the Use of Fundamental Physical Constants and Basic Constants of Water, The International Association for the Properties of Water and Steam 2001
Even the bottom of the ocean is not tectonically stable hence the sensor cannot be considered a reliable reference point.
The sea floor is covered with debris, dead plankton and other micro animal skeleta, which rains down all the time. Since these new detectors are so sensitive this debris will affect readings. I do not expect sea floor movement due to plate tectonics to have much effect since this is a few cm per year.
We have great GPS based capacity to measure altitude with sub millimetric accuracy nowadays, this means that we can measure the rate of land rise or fall in harbours where we measure sea level, and as a result can correct for land fall and rise. From this and historical measures of sea level we can accurately determine the rate of sea level rise at about 2mm/year over most of the globe. As a result I am suspicious of results that don’t agree with this figure.
As far as sea level rise as a result of temperature change (stearic) goes; cooling can also cause sea level rise! Water is a very anomalous fluid in that it gets less dense below 4°C so water getting colder than 4°C can lead to sea level rise too – It also means that due to relative buoyancy effects the only place where cold water can penetrate below the point where temperature hits 4°C is at the poles where higher salinity water is created by salt formation.
So could higher rates of ice formation every winter (due to larger seasonal variation) actually be causing global cooling of the deep ocean due to the creation of greater volumes of higher salinity cold water, and thereby raising sea levels? Not the kind of question or hypothesis that is likely to be asked by the cult of AGW.