Paleocene Sea level cycles?

Andre

We have discussed sea level yoyo's from the Pleistocene ice age of which it is suggested that it balances with the ice volume paced on the poles. So all of a sudden a study pops up (courtesy of the author), Dr Madeleine Briskin:

Briskin, M, Fluegeman R, 1990, Paleocene Sea Level Movements with a 430,000 Year Quasi-Periodic Cyclicity, Palaios V-5 p 184-198

abstract

Sea level movements with quasi-periodicity of 430,000 years are identified in the marine sedimentary units of the Eastern Gulf Coastal Plain of Mississippi, Alabama and Georgia which represent a 5.8 million year record of strandline displacement during Paleocene time. Principal component analysis of the benthic foraminiferal fauna yielded six assemblages which when combined with two other qualitatively derived assemblages provided paleoecologic information which clearly reflects the influence of paleocirculation and paleoclimatic regime of the Eastern Gulf Coastal Plain.

The presence of the planktonic foraminiferal taxa Subbotina trinidadensis and Planorotalites pseudomenardii as well as paleolatitudes ranging from 15degrees N (for the Campeche Shelf) to 25degreesN (for the Coastal Plain) emphasizes a paleoclimatic regime which is dominantly tropical. A paleoceanographic model was derived which suggests that normal marine waters were brought into the Gulf of Mexico by two major currents:
1) the easterly flowing Pacific countercurrent which when deflected by the southernmost Gulf margin generated a minor cyclonic flow around the Campeche Shelf and
2) the west flowing equatorial Atlantic current generated by the southern margin of the North Atlantic anticyclonic gyre which fed the Central and Northern Gulf.

When integrated into the paleoceanographic model, the distribution of continental shelf benthic foraminiferal assemblages indicates a pattern which is dominantly controlled by:
1) the character of the circulation,
2) water mass properties,
3) latitudes and climate,
4) distance from the strandline.

Strandline displacements are related to transgressive and regressive sea level movements in an ice free Paleocene world. The well delineated 430,000 year quasi-periodic cycle observed in the sea level curve is identified as being astronomical in character. These results support the view that changes in the earth's orbit may trigger changes in the geometry of the Earth's surface in a way which causes sea level to oscillate with a quasi-periodicity of 430,000 years.

So you have cyclic sea level changes but supposedly no ice sheet to exchange the water volume with. The conclusion, barring an ice sheet yoyo, to tie the sea level changes to changes in the Earth's geometry caused by the Milankovitch eccentricity cycle is not supported by a mechanism. Anybody?

jim mcnamara

<snip>
the view that changes in the earth's orbit may trigger changes in the geometry of the Earth's surface in a way which causes sea level to oscillate with a quasi-periodicity of 430,000 years.

Um, what view - by that I mean what changes- specifically exactly measured or calculated geometric changes? Are there reviewed articles with supporting data for this notion? Notice the use of the word "notion", not hypothesis. I do not have JSTOR access, so I cannot see the bibliography.

Andre

As far as I can judge, an important part of the sea level cycle implies the changing ratio between coastal to deeper water single cell organism. The same technique I have seen being used here: see chapter 6 Eustatic sea level rise

Edit: futhermore it may be noted that we may have had an event, known as melt water pulse 1A, which also implied a quick sea level rise lacking evidence of a clear source. See this thread

Furthermore the speculation of earth geometry changes related to eccentricity, again, is for the account of the authors. The only thing that matters is how accurate the sea level fluctuation has been identified/calculated.

baywax

Quote by Andre

As far as I can judge, an important part of the sea level cycle implies the changing ratio between coastal to deeper water single cell organism. The same technique I have seen being used here: see chapter 6 Eustatic sea level rise

Edit: futhermore it may be noted that we may have had an event, known as melt water pulse 1A, which also implied a quick sea level rise lacking evidence of a clear source. See this thread

Furthermore the speculation of earth geometry changes related to eccentricity, again, is for the account of the authors. The only thing that matters is how accurate the sea level fluctuation has been identified/calculated.

Hi Andre. I feel the same way about using "continental rebound" as an explaination for sudden drops in sea level around the same time as the "melt waterpulses" are being claimed to have been taking place. The confusion is evident when you consider that I was surveying for 10,000 year old evidence of human habitation at 500 feet above sea level. This survey was based on the "continental rebound" theory. While at the same time there was underwater archaeology going on 120 feet below sea level in search of the same evidence of human habitation at 10,000 yBP.

One may be able to use "continental rebound" or "tectonic rebound", for that matter, as a model for what you are trying to explain. The continental rebound or continental depression would not have to be caused by ice fields but could be cause by varying pressures, currents and densities of the mantle being influenced by the effects of the Milankovitch eccentricity cycle (over time).

Andre

Well let's say that to climatologists and astronomers we might as well live on a solid rigid rock that undergo all kind of orbits and cycles. Geographist and geologist would probably tend to focus on the whereabouts of the inside and outside of the Earth respectively, seeing a complex set of shells, dynamically reacting tor all kind of thermodynamic processes. Who would focus out to see a complex set of shells, dynamically reacting to all kind of thermodynamic processes, behaving as multiple interacting gyroscopes undergoing all kind of orbits and cycles?

baywax

Quote by Andre

Who would focus out to see a complex set of shells, dynamically reacting to all kind of thermodynamic processes, behaving as multiple interacting gyroscopes undergoing all kind of orbits and cycles?

Yes you have to take every influence into account . Deciding that one factor contributes to the repeated changes in sea level is a risk and highly unlikely.

Andre

(Glaciation?) Cycles all around this time 200.000 years

Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse

André Bornemann et al

The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35°C. High-amplitude sea-level changes and positive d18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New d18O data from the tropical Atlantic show synchronous shifts 91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.

Of course the 200,000 years period is nowhere near any Milankovitch cycle. What's going on?

baywax

Quote by Andre

(Glaciation?) Cycles all around this time 200.000 years

Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse

Of course the 200,000 years period is nowhere near any Milankovitch cycle. What's going on?

Is there a proximity cycle where we get closer to the sun then further away? Or even closer to Jupiter then further? Also, are the larger planets contributing to our temperature by way of a changing proximity of the earth to them or a fluctuation of temp. on those planets?

Andre

That planetary interaction is one of the causes for the Milankovitch cycles, especially the eccentricity cycle, which appears pretty stable at around ~400,000 years, as it appeared visible as early as the Cambrian. In the least eccentric orbit there is little variation in climate but at the max eccentricity seasons may be more intens or a lot less, depending on the precession (~21ka) and obliquity cycle (~41). Anyway that's all way to slow for us to notice during a lifetime.

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