Reworked Calcareous Nannofossils in the Gulf of Mexico: Readme file
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              World Data Center for Paleoclimatology, Boulder
                                and 
                   NOAA Paleoclimatology Program
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NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!!


NAME OF DATA SET: Reworked Calcareous Nannofossils in the Gulf of Mexico

LAST UPDATE: 1/2001 (Original Receipt by WDCA Paleo)  
CONTRIBUTORS: Marchitto, T.M., and Wei, K.-Y.

IGBP PAGES/WDCA CONTRIBUTION SERIES NUMBER: 2001-005

SUGGESTED DATA CITATION: Marchitto, T.M., and Wei, K.-Y., 2001, 
Reworked Calcareous Nannofossils in the Gulf of Mexico, 
IGBP PAGES/World Data Center for Paleoclimatology 
Data Contribution Series #2001-005. 
NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. 

ORIGINAL REFERENCE: Marchitto, T. M., and Wei, K.-Y., 1995. 
History of Laurentide meltwater flow to the Gulf of Mexico 
during the last deglaciation, as revealed by reworked 
calcareous nannofossils. Geology, 23: 779-782. 


FUNDING SOURCES: Yale University, 
Republic of China National Science Council

GEOGRAPHIC REGION: Gulf of Mexico
PERIOD OF RECORD: Last deglaciation

LIST OF FILES: Readme_Marchitto1995.txt (this file),
orca_reworked.txt (tab-delimited ASCII format).


DESCRIPTION: 
Counts of reworked (extinct) and indigenous (extant)
calcareous nannofossils in core EN32-PC4 from the Orca Basin, 
Gulf of Mexico (26.93N, 91.36W, 2260 m).  
Given versus core depth (cm) and radiocarbon age (kyr BP).  
Radiocarbon timescale based on AMS dates from Broecker et al. 
(Radiocarbon, 32: 119-133, 1990) as revised by Flower and Kennett 
(Paleoceanography, 5: 949-961, 1990).

Abstract:
The history of meltwater flow from the Laurentide Ice Sheet 
to the Gulf of Mexico during the last deglaciation, 
which holds possible implications for the cause of the 
Younger Dryas cold episode, is not well understood. 
We propose a new chronology based on using the percentage 
of reworked calcareous nannofossils in Orca Basin sediments 
as a proxy for erosion. The period of greatest meltwater flow 
to the gulf was between 12.7 and 12.1 ka (during the Bølling 
warm interval), and flow remained high until the beginning 
of the Younger Dryas cold episode at 11.3 ka; this corresponds 
to meltwater pulse IA. A sharp meltwater decrease at 12.2 ka 
may represent the Older Dryas glacial readvance. 
Little or no meltwater is inferred to have flowed to the gulf 
from ~10 to 9 ka, which is the time of the second major 
meltwater pulse, IB. Therefore, meltwater must have been 
permanently diverted away from the Gulf of Mexico 
at the beginning of the Younger Dryas.