--> Abstract: The Influence of High Frequency Climate Variability on Paleoclimate Interpretation, by Martin Perimutter; #90101 (2010)

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The Influence of High Frequency Climate Variability on Paleoclimate Interpretation

Martin Perimutter
Chevron, Houston, Texas

Understanding past long-term climates states and their higher frequency variability can play an important role in helping to forecast future climate changes. The insolation cycles which drive high-frequency climate variability and their interference patterns have been mathematically resolved for the last 50 my.

Inferences can be drawn on these patterns back through at least the Paleozoic. However, different regions of the Earth have different climatic responses to the same insolation cycles and record the changes differently. In some locations the stratigraphic record offers up climate cycles easily to be recognized and measured. In other areas it’s more difficult because the climate does not change much or stratigraphers who interpret climate ignore changes to sedimentary delivery systems and environments of deposition caused by the specific climate response, don’t recognize preservation bias caused by climate cycles, and fail to include the phase relationship of sediment supply and sea or lake level cycles. These issues can cause the paleoclimatologist to misinterpret the actual temporal scales of climate change because they are looking for similar stratigraphic responses to the same climate cycle in areas that just don’t preserve them the same way.

Presently, most paleoclimate analyses and interpretations are resolved only for mean annual conditions for time intervals ranging from 0.1 to 1 my. However, the greatest insolation changes occur seasonally at the scale of precession (~20 kyrs) during periods of high eccentricity. Similar to the condition that causes summer in one hemisphere and winter in the other at the same time in the orbit, precession cycles cause Northern and Southern Hemisphere insolation to be about 10,000 years out of phase. Hot summers and cold winters in one hemisphere correspond to mild summers and mild winters in the other. The pattern reverses itself over a precession cycle so that similar climatic successions in opposite hemisphere, and their associated sediment yield cycles, will be 10,000 years out of phase, as well. These changes occur regardless of whether the earth is in a greenhouse or an icehouse state.

Until the Plio-Pleistocene glaciations were unipolar when they occurred. Under this condition precession-scale eustasy tended to track the insolation cycle of the glaciated hemisphere. Consequently, similar climatic successions in opposite hemispheres would have had sediment yield cycles with distinctly different phase relationships to glacioeustasy. Such differences would not exist in an ice-free world. The regional and temporal variations in the phase relationships between sediment and glacioeustatic cycles may not be consistent with basic assumptions about stratigraphy and can impact how we interpret the causes and frequencies of the stratigraphic cycles themselves.

This talk is a discussion of how these issues affect our understanding and interpretation of paleoclimate.

 

AAPG Search and Discovery Article #90101 © 2010 AAPG Foundation Distinguished Lecturer Series 2009-2010