Late Pliocene/early Pleistocene glacial meltwater discharge to the Gulf of Mexico: evidence from ODP Site 625

• Main Author: Costanza, Benjamin Matthew
• Format: Thesis
• Language: English
• Published: Boston University 2007
• Subjects: Earth Sciences; Ice Sheet
• Online Access: https://hdl.handle.net/2144/45371

Global ????^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 ????^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 ????^18O stratigraphy left the Site 625 time-scale highly uncertain. Here, we present a Site 625 benthic ????^18O stratigraphy for the LP/EP, which improves the Site 625 time-scale through correlation to the global ????^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 ????^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 ????^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 ????^18O anomalies.