DOI: 10.25921/8hqw-cn84
title: NOAA/WDS Paleoclimatology - Equatorial Pacific Late Pleistocene Sediment Accumulation Rate Data

description: A possible imprint on equatorial Pacific sediments of a deglacial reinvigoration of the Southern Ocean overturning is increased opal accumulation rate. This would arise from the transmission of silica-rich deep water to the equatorial thermocline via Subantarctic Mode Water and an associated increase in diatom productivity. In search of this imprint, sediment cores from the central (TT013-PC72) and eastern (V19-30) equatorial Pacific have been analyzed for 230Th-normalized opal accumulation rates over the past five and three glacial terminations, respectively. Equatorial opal accumulation rates sustained relatively low values over much of the records and were punctuated by large increases centered on some terminations, but not all.  Furthermore, two periods of increased opal flux were observed that do not coincide with terminations.  Sources other than the Southern Ocean may need to be considered in the silica budget of the equatorial Pacific, but the d13C of Neogloboquadrina dutertrei can be used to support the presence of a deepwater nutrient signal in each case. Although a common deglacial mechanism, or a common imprint thereof, for each of the late Pleistocene glaciations remains elusive, the combination of opal flux and d13C of N. dutertrei provides a diagnostic for past injection of deepwater nutrients into the Equatorial Undercurrent.
description: NOTES:    
Data from TT013-PC72 reported here combine previously reported results 
with new data for the convenience of comparison. This compilation was done 
with data reports from Bradtmiller et al. (2006) and Anderson et al. (2008). 
    
Data from V19-30 also combines new data with those reported by 
Bradtmiller et al. (2006). 
    
Data from both Bradtmiller et al. (2006) and Anderson et al. (2008) 
have been updated to incorporate a more accurate half life of Th-230 
from 75,200 yrs to 75,690 years (Cheng et al. 2000). 
    
Age Models:    
In the case of PC72, we used the age model of Murray et al. (2000) 
as modified in the upper meter based on C-14 data of Anderson et al. (2008). 
For V19-30, we used the age model from Shackelton et al. (1983). 


EXPLANATION OF DERIVED PARAMETERS:    
xs230Th o and xs231Pa o    
xs230Th o and xs231Pa o refer to the measured value as corrected for     
ingrowth of 230Th (or 231Pa) from sedimentary and detrital uranium.      
These values are calculated using measured concentrations of 230Th     
(and 231Pa), 232Th and 238U, and assuming that all 232Th is detrital     
in nature.  It also assumes a detrital U/Th ratio, which varies by region.    
Concentrations are finally corrected for decay since deposition.    
xs(Pa/Th)o    
The initial xs231Pa/xs230Th ratio refers to the ratio of xs230Th     
and xs231Pa after both have been decay corrected using their     
respective half-lives.     
    
230Th-norm flux (g/cm^2/kyr) --230Th-normalized mass accumulation rate (or flux)    
For a discussion of this proxy and the relevant corrections and parameters, 
please see Francois et al. (2004)
    
F(opal) (g/cm^2/kyr) ---230Th-normalized opal accumulation rate (or flux) 
= opal(%)*230Th-norm flux