John Solum

Send me a PM, I think I can help you.

I couldn't remember the change in volume from liquid water to ice, but according to this web site (http://www.secretsoftheice.org/icecore/sealevel.html)(which is pretty interesting in any case), the volume of liquid water is 90% the volume of ice. So that equates with ice volumes of 37X10^6 km^3 for an increase in salinity of 2.5% and 44X10^6 km^3 for an increase of 3%.

Bummer. I'd really be interested in hearing which part of the mantle he thinks can move that fast.

ps418

Anderson read some the literature I recommended, and came back with some half-baked arguments as to why larger ice sheets are not ruled out. Here is my response to his claims:
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Patrick;

I read over the journal articles you recommended. Have you read them yourself?

Indeed I have, and as I will now demonstrate, I read them much more carefully than yourself. Did you notice, BTW, that every single one of them agreed with me and disagreed with you about the LGM ice volume?

Also picked up a bunch of others and discovered some very interesting details. In picking a time for the flood in the geological record, I had a choice of two times, the H0 event at the end of the Younger Dryas or the much larger event after the LGM (H1). I have decided to use the earlier time period, dispite the larger gap this creates with the biblical date for the flood.

The date problem is acute enough, but what's 10+ thousand years between friends? A bigger question is How can H1 possibly correspond to the massive ice sheet reduction you envision when there are dozens of other ice-rafted layers preceding it? Wouldn't you expect the Heinrich layer marking your event to be conspicuously larger than the others, since vastly more ice was involved? This is another weak point ripe for attack.

We had been discussing oxygen isotopes 18/16 ratios, and the use of that ratio in determining the size of the Pleistocene ice sheets. Your argument was that the sheets could not have been above a certain size due to the ratio of O18/O16 found in ocean sediment bottom cores in foraminiferal from the ice age. Reference A, dealt with oxygen isotope ratios and pointed out that laboratory culturing of foraminiferal has only extended down to 15C with the result that the paleotemperature equations were all calibrated at significantly higher temperatures than would have occurred in much of the ice age ocean surface water. I have been checking, but so far have not found any later articles describing the results of the low temperature culturing needed for proper calibration, I have to assume they have not yet been done.

In fact, the evidence was right there in front of your face, but amazingly, you somehow missed it.

I noticed that you were careful to say that CULTURE calibration has been extended down to 15C. For the benefit of yourself and anyone else reading this thread, let me mention what you failed to mention. Although the CULTURE experiments cited by Mashiotta et al. only go down to 15C, their paper very clearly shows that the calibration extends down to 10C. Their experiments are at 16, 18, and 25C. But what Wmscott doesn't mention is that the authors have two other calibration points, at 12 and 10C, respectively, based upon core top samples. In fact, their figure 1 shows this very clearly:

"Fig 1: Mg-temperature calibration results from culturing experiments with live Globigerina bulloides and core-tope samples (indicated by the core name). For the culturing points each point is an analysis of between 8 and 12 laboratory-grown, amputated chambers . . .For the core tops, each point is an individual analysis of 10-20 shells. . . Core-top Mg/Ca values for G. bulloides from sub-Antarctic cores RC11-120 and V22-108 are plotted versus Levitus mean annual SST (11.5C at RC11-120 and 9.7C at V22-108) to extend the calibration back to 10C"

Notice how well that the core-top calibration points fit the experimental calibration points.

And Mashiotta et al. also note that although the the calibration data only extended down to 10C, which is a bit higher than the Subantarctic glacial SST temp, "One independent confirmation of our calibration is that other studies yield similar exponential slopes for the Mg/ca response in several species of planktonic foraminifera, including N. pachyderma, and benthics (table 1)" (p. 422).

Wmscott again:
Because of this problem, it is not possible to accurately remove the temperature component from oxygen isotope ratio evidence. Therefor, arguments in favor of larger ice sheets in the past, can not be excluded by O18/O16 ratios.

The only "problem" here is your somewhat inadequate attention to the data.

First, the lack of calibration below 10C may be a problem for estimating d18O seawater from a SUBANTARCTIC core, where glacial SST's may be slightly lower than 10C, but the Lea et al. curve is based on planktonic equatorial Pacific [2 degrees north latitude] forams for which the Mg/Ca and independent evidence indicates glacial SST's of 22-23C, well within the experimentally-calibrated range. As Lea et al. (2002, p. 291) note: "An extracted d18Owater record such as presented here has the advantage of no temperature component, but it still might contain local hydrological influence, although that does not appear to be the case for the Cocos Ridge record."

So, the single substantive reason you give for dismissing oxygen isotope ice volume estimates is worthless.

Lea et al. (2002) also note (p. 291):

"Comparison of the modified Cocos Ridge d18Owater record with a number of other sea level proxies indicates substantial agreement. The Cocos Ridge record is in excellent agreement with the Laberyie et al. (1987) d18Owater reconstruction based on Norwegian Sea benthic records and in very good agreement with the Shackleton (2000) d18Owater reconstruction based on Pacific benthic and Vostok d18O records. The Cocos Ridge record is also in very good agreement with sea level estimates based on uplifted and submerged reefs"

Second, the pore water measurements I cited would not be affected by any of the temperature or fractionation-related uncertainties affecting the foraminiferal proxy records. And to make matters worse for you, the pore water measurements yield slightly smaller values for the change in d18O of seawater than the foraminiferal proxy records. Duplessy et al. (2002) explain:

"At the sediment water interface, there is exchange of both water molecules and dissolved compounds with the overlying ocean bottom water . . . changes in the 18O of seawater propoagate downward into the sediment, leaving a profile of d18O vs depth in the pore fluid that is a record of the d18O history of seawater" (p. 318).

This method has yielded estimates of ~0.8-1 per mil change in seawater oxygen isotope ratios since the LGM. See:

Adkins, J., and D. Schrag, 2001. Pore fluid constraints on deep ocean temperature and salinity during the last glacial maximum, Geophys. Res. Lett. 28, pp. 771-774.

Schrag, D.P., Hampt, G., Murray, D.W., 1996. Pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean. Science 272, pp. 1930-1932.

At let me also highly recommended:

Duplessy et al., 2002. Constraints on the ocean oxygen isotopic enrichment between the Last Glacial Maximum and the Holocen: Paleoceanographic implications. Quaternary Sciene Reviews 21, pp. 315-330.

. . . which reviews dozens of papers and several different methods which have been used to estimate change in d18O seawater since the LGM, all of which agree with an ice-volume reduction of 52x10^6 km3 or less from the LGM to today.

Third, I have found another method of estimating the volume of the ice sheets, which is totally indepent of temp calibration. This constraint on the LGM ice volume is provided by paleosalinity measurements of pore-fluid samples from ocean cores [Cl- concentration]. To review, I stated in a previous post:

Finally, although I dont know of such work, I think the absolute amount of water removed from the ocean could, in theory, be estimated by changes in the ion concentration in various minerals. Obviously the more water that is drawn off the ocean, the higher the concentration of ions remain in the ocean.

And you stated yourself:

It appears to me that the estimates on ocean volume from this method [oxygen isotopes -PS] are pretty subjective. A better indicator of sudden shifts in ocean volume would be things that don't evaporate, like salt and other trace minerals.

I have now found exactly this type of study. Adkins and Schrag (2001) estimate a salinity decrease of ~2.5% from the LGM to today based on pore-fluid evidence from the Bermuda Rise core 1063A. This is close to, but a bit less than, Adkins and Schrag's predicted global mean LGM to holocene salinity increase of 3.16%. It is quite possible, however, that the lower than expected LGM salinity is a result of local hydrological factors, and does not represent the global mean. It will be interesting to see salinity pore-fluid results from more cores.


We do have evidence more water was removed from the sea than currently believed at the GLM. Salinity levels in the Red Sea cores [REF K] indicate the removal of possibly an additional 20m from the oceans, and that is assuming a low level of exchange between the Red Sea and the ocean.

Again, you've totally misunderstood the argument presented in this paper. Their abstract states:

Existing techniques for estimating natural fluctuations of sea level and global ice-volume from the recent geological past exploit fossil coral-reef terraces or oxygen-isotope records from benthic foraminifera. Fossil reefs reveal the magnitude of sea-level peaks (highstands) of the past million years, but fail to produce significant values for minima (lowstands) before the Last Glacial Maximum (LGM) about 20,000 years ago, a time at which sea level was about 120 m lower than it is today. The isotope method provides a continuous sea-level record for the past 140,000 years (ref. 5) (calibrated with fossil-reef data), but the realistic uncertainty in the sea-level estimates is around 20 m.

Here we present improved lowstand estimates—extending the record back to 500,000 years before present—using an independent method based on combining evidence of extreme high-salinity conditions in the glacial Red Sea with a simple hydraulic control model of water flow through the Strait of Bab-el-Mandab, which links the Red Sea to the open ocean. We find that the world can glaciate more intensely than during the LGM by up to an additional 20-m lowering of global sea-level. . .


They are saying that sea-level can drop by 20m more THAN the LGM without inducing salinity changes sufficient to produce an aplanktonic layer. They are not saying that their data are consistent with LGM sea-level 20m lower than -120m below!

To the contrary, their paper actually states several times that they estimate eustatic sea-level rise since the LGM was ~120m, but that some earlier deglacial sea-level changes were of LARGER amplitude. They state that "continuation of benthic faunas, albeit in reduced numbers and different compositions, indicates that all glacial sea-level drops of the past 500kyr left sufficient communication between the Red Sea and the open ocean to prevent worse salinization and consequent sterilization" (p. 163). They estimate sea-level drops of 139m for stage 12 (450kyr), 122-134m for stage 8, 125 +/-6m for stage 6, and 120 +/-5m for the LGM (p. 164-165).


"We conclude that the last glacial-interglacial cycle showed ice-volume fluctuations that were more than 10% smaller than those that occurred in three out of four of the immediately preceding main cycles. The stage 12-11 sea-level rise implies that over 30% greater ice-volume changes were involved in Quaternary glacial-interglacial cycles than would be expected on the basis of the last cycle alone" (p. 165).

There is much more to be said, but it will have to wait until I get the time to give it the treatment it deserves.

Cheers,

Patrick

[ February 24, 2002: Message edited by: ps418 ]</p>

ps418

Another point. . .

Anderson cited the presence of ice-rafted debris (IRD) layers in the North Atlantic as evidence for his flood theory. These 'Heinrich layers' were deposited by melting icebergs discharged from the Hudson straits as they drifted eastward, forming a west to east IRD belt. Although IRD is deposited all the time, Heinrich events are periods in which the rate of IRD deposition is greatly increased. These events have a quasi-periodicity of about ~7k yrs.

As there are about a dozen such IRD-rich layers from the past ~100k yrs, I asked Anderson which one he associates with the flood. He decided that Heinrich event 1 (14.5 cal yr BP) is the one he wants to associate with the flood, despite the fact that H1 occurred 10k yrs before the biblical flood date, and about 7k yrs before the Black Sea flood (which Anderson also associates with the biblical flood).


Since the volume of IRD deposited by a given Heinrich event should be proportional to the volume of ice displaced during the event, it is instructive to compare the IRD-layer deposited by Heinrich 1 (14.5k cal yr BP) with the IRD-layer deposited by Heinrich 2 (~19k cal yr BP). If Anderson's hypothesis is correct, we would expect H1 to be much thicker and more widespread than H2.

Dowdeswell et al. (1995) give detailed information on the thickness and distribution of Heinrich layers 1 and 2, based upon 51 sediment cores from the North Atlantic. The distribution and thickness of both layers is essentially identical, concentrated in a band between 40-60N lat and 20-45W lon, thinning from 40-70cm at the Hudson Strait to about ~5cm at 30W lon. The only difference appears to be that H2 is slightly THICKER than H1. Provenance studies indicate that, as expected, the H1 and H2 IRD has a Canadian Shield source. Veiga-Pires and Hillaire-Marcel (1998) use U-Th method to estimate MINIMUM durations of 800 yrs for both H1 and H2 (only 800 time too long to be consistent with Anderson's model).

Dowdeswell et al. (1995) cite estimates of about 1.4x10^6 km3 worth of icebergs produced by each event, based upon the volume of IRD in each layer, the volume of carried in the base of icebergs, and the assumption that the bergs where on average 1km thick (they may have been much thinner). Averaged over 250 yrs of deposition (rather than 800), this is equal to an annual iceberg production of only 2800km3.

The take-home points are that, 1) even making all assumptions favorable to Anderson, the volume of IRD is far, far smaller than what we would expect from Anderson's model, which has virtually the entire Laurentide ice sheet being displaced to the ocean by the flood, that 2) the minimal duration of the event is much too long to fit Anderson's model, and 3) that H2 is larger than H1, so the association of H1, but not H2, with the flood is completely arbitrary.

Patrick

Dowdeswell, J.A., Maslin, M.A., Andrews, J.T. and McCave, I.N., 1995. Iceberg production, debris rafting, and the extent and thickness of Heinrich layers (H-1, H-2) in North Atlantic sediments. Geology, v. 23, p. 301-304.

Veiga-Pires, C. et Hillaire-Marcel, C., 1998. U-Th isotope constraints on the duration of Heinrich events H0 to H4 in Southeastern Labrador Sea. Paleoceanography, 14: 187-199.


[ February 27, 2002: Message edited by: ps418 ]

[ February 27, 2002: Message edited by: ps418 ]</p>