Global 𝛿^18O indicates that the late Pliocene/early Pleistocene (LP/EP) was
characterized by quasi-cyclic variations of continental ice volume with a period at ∼ 41-
kyrs. However, it is well-known that high-latitude summer insolation intensity, the
mechanism conventionally believed to control ice sheet growth/decay, is paced by cycles
near 21-kyrs. This mismatch constitutes the "41-kyr World Problem."
Isolating Northern Hemisphere ice volume change during the LP/EP is a
promising approach for testing recent 41-kyr World hypotheses. A previous study of
planktic 𝛿^18O at ODP Site 625, located in the northern Gulf of Mexico, documented
negative isotopic excursions attributed to episodic discharge of ^16O-enriched meltwater to
the study site via the Mississippi River. However, the lack of a benthic 𝛿^18O stratigraphy left the Site 625 time-scale highly uncertain.
Here, we present a Site 625 benthic 𝛿^18O stratigraphy for the LP/EP, which
improves the Site 625 time-scale through correlation to the global 𝛿^18O signal of the
LRO4 Stack. The new Site 625 chronology suggests the previous age-model may have
artificially enhanced the 1/_41-kyr frequency, while reducing natural temporal variability.
Upon comparing the timing of twelve planktic 𝛿^18O anomalies at Site 625 to cycles of
obliquity and June 21, 65°N insolation, no clear relationship is observed. However,
comparison of Site 625 planktic 𝛿^18O to benthic records clearly indicates that northern
Gulf of Mexico surface waters were at times severely impacted by locally and/or
regionally manifested influences beyond the global norm, thus demonstrating the need for
further inquiry of planktic 𝛿^18O anomalies.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45371 |
| Date | January 2007 |
| Creators | Costanza, Benjamin Matthew |
| Publisher | Boston University |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | This work is being made available in OpenBU by permission of its author, and is available for research purposes only. All rights are reserved to the author. |
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