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Validity of and Dependency on Initial Conditions?

Posted by DocV on 29 Jul 2011 at 16:07 GMT

I haven't dug through all of the references cited in section 2.2 on Model Basin and Topography Modification, but it strikes me that the model results reported must necessarily be strongly dependent on initial land and basin topography. Two questions come to mind: 1) How confident can you be that the specific topographic modifications you made in your model in any way reflect the regional topography that was actually present at 1250 BC, and 2) Did you make any model runs without a barrier reef?

If you START with the premise that wind forced parting of a small, shallow water body is possible, then I have no doubt that you can choose your initial conditions and model parameters to get your computer model to 'make it happen' in a literal biblical sense. Does that mean it's a viable, natural mechanism? Or does that just mean you can choose model parameters to make a computer model do whatever you want it to do?

No competing interests declared.

RE: Validity of and Dependency on Initial Conditions?

drews replied to DocV on 02 Aug 2011 at 14:19 GMT

Chris Vyhnal -

I recommend consulting the references cited in section 2.2 Model Basin and Topography Modification, especially the publications by Stanley. The MEDIBA sediment cores provide important data for determining the coastal configuration of the eastern Nile delta in 1250 BC. Note that a simple calculation of eustatic sea-level rise is not valid for determining the ancient coastline of the Nile delta, as deposition of river sediment, subsidence, wave action, and tectonic uplift of the Sinai plate play a large role here.

1) I am confident enough in the topographical reconstruction to publish my hypothesis in a peer-reviewed scientific paper. Nevertheless, I recognize that good science is always willing to examine new evidence. Everything south of the Pelusium Line agrees well with other published scientific sources. The area of greatest uncertainty is the coastal sandbar forming the Lake of Tanis.

MEDIBA sediment core S19 from Pelusium shows re-worked sediments dated to the New Kingdom period. Consider citation #14: Stanley JD, Bernasconi MP, Jorstad TF (March 2008) Pelusium, an Ancient Port Fortress on Egypt's Nile Delta Coast: Its Evolving Environmental Setting from Foundation to Demise. Journal of Coastal Research 24(2): 451–462. On page 458 Jean-Daniel Stanley states: "Unit III - A mud-rich sand sample in this unit at a depth of 5.15 m from the top of core S-19 records a 14C date of 2610 +- 40 years BP. However, additional AMS dates at shallower depths (4.85, 4.03, and 3.8 m from S-19 core top) provide older ages in reworked sediment, (respectively, 3650 +- 40, 3160 +- 40, and 3070 +- 110 years BP)."

Where did those re-worked sediments come from? They cannot have come from the land to the south, because there are no surface watercourses running off the Sinai at that site. The re-worked sediments must have come from the west, driven from west to east by alongshore drift during the late Holocene. That alongshore drift is more likely to occur along a coastal barrier island stretching smoothly from the Damietta and Tanitic mouths of the Nile to Pelusium, than through a deeply indented Gulf of Tineh. Hence, MEDIBA sediment core S19 supports the existence of a coastal lagoon known as Lake Tanis during the New Kingdom period.

A series of sediment cores extending northward from T-78 through the Kedua Gap to the present shoreline would help to resolve this issue.

2) Cases T12 and T13 in Table 3 examine the case where there is no barrier reef and no Lake of Tanis, just a shallow shelf extending northward into the Mediterranean Sea. A dry crossing at the Kedua Gap without the coastal sandbar requires stronger winds.

Tulloch observed a viable, natural mechanism for wind setdown in 1882 (citation #5). He did not choose any initial conditions or model parameters. The next morning he observed a phenomenon that he took to be analogous to the biblical narrative. His observations are in accord with our model results.

A starting premise is a hypothesis, and that hypothesis is tested according to the scientific method. This paper described *two* premises: that a wind-forced parting could occur at an underwater reef, and that a wind-forced parting could occur in a curved body of water. The ROMS ocean model enforces the laws of physics. We failed to find any model configuration under which the first premise could succeed under realistic conditions, and consequently we consider that scenario to be unlikely. The second premise did succeed under model parameters that are within the range of published scientific literature, and we are pleased to report these findings in PLoS ONE.

Competing interests declared: I am the lead author.