DOI: 10.25921/fnan-z180
title: NOAA/WDS Paleoclimatology - Eastern Equatorial Pacific 100KYr Alkenone SST Reconstructions

description: In this study, we use records of nitrogen isotope ratios (d15N), UK'37 temperature estimates, organic carbon and opal percentages from high-resolution sediment cores located in the eastern equatorial Pacific (EEP) to explore the mechanisms linking millennial-scale changes in low-latitude sea surface temperature, water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100,000 yr. Our results support a hypothesis that the Southern Hemisphere, and its connection to the low latitudes via shallow subsurface ocean circulation, has a primary influence on the biogeochemistry of the EEP. In addition, our results suggest that, during the last glacial stage, denitrification rates fluctuated on millennial timescales in response to water-column ventilation rather than upstream oxidant demand in intermediate-depth waters. However, due to the poor age constraints available for Marine Isotopic Stage (MIS) 3, the EEP sedimentary data presented here could support two conflicting mechanisms, one driven by enhanced intermediate overturning circulation in the Southern Ocean during Heinrich Events/Antarctic Warm Events, implying that subsurface flow rates control thermocline ventilation, and a second one consistent with more sluggish intermediate circulation during Antarctic Warm Events and giving a central role to the temperature control on oxygen solubility in Southern Ocean surface waters.
description: The data set contains alkenone-based SST estimates, bulk sediment 
d15N and Corg content from 4 cores from the eastern equatorial 
Pacific covering the late Quaternary, in addition to the opal 
record and the residual opal record (with variability >10 kyr removed) 
from ME0005A-24JC. The data from core ME0005A-24JC are presented 
against 2 age models: scenario 1 and scenario 2, as discussed 
in the original reference. 

Cores ME0005A-24JC, ME0005A-27JC and TR163-31P were analyzed 
for alkenone unsaturation at Dalhousie University following 
standard laboratory procedures detailed by Kienast et al. (2006). 
Sea-surface temperature estimates (UK'37 SST) were calculated from 
the ratio of the concentration of the di and triunsaturated alkenones, 
using the calibration of Prahl et al. (1988). The upper 500 cm 
of ME0005A-24JC were analyzed at WHOI following the same procedure 
and were previously published by Kienast et al. (2006). These data 
were shifted by +0.027 UK'37 units because of a laboratory offset 
determined from 10 replicate samples. Cores TR163-19P was analyzed 
at Brown University following similar laboratory procedures detailed 
in Herbert et al. (1998). Results from the last 25 kyr BP of cores 
ME0005A-27JC, TR163-19P and TR163-31P were previously published 
in Dubois et al. (2009). 

The sedimentary d15N composition of all cores was analyzed at UBC, 
Vancouver, following standard procedures. 

Total carbon was determined with an elemental analyzer. Inorganic 
(i.e., carbonate mineral) carbon was determined in a carbon dioxide 
coulometer. 

Organic carbon was estimated by subtracting inorganic from total 
carbon. Results for the last 35 kyr have been published by 
Kienast et al. (2006, 2007). 

Biogenic opal of core ME0005A-24JC (>510 cm) was determined 
colorimetrically following alkaline extraction of silica 
(Mortlock and Froelich, 1989). The upper 510 cm were analyzed 
at UBC following the same procedure and were previously 
published by Kienast et al. (2007). 

Age models for Marine Isotopic Stage 1 and 2 (MIS1 and MIS2, 
i.e. 0-25 kyr) in cores ME0005A-27JC, TR163-19P and TR163-31P 
were adopted as previously published (see Kienast et al., 2007). 
We present here an updated MIS1-2 age model of core ME0005A-24JC 
based on 4 radiocarbon dates on Neogloboquadrina dutertrei 
published by Kienast et al. (2007) and 2 additional dates 
on N. dutertrei published by Kusch et al. (2010). 
Radiocarbon ages were calibrated to calendar years 
using the software CALIB 6.0 (Stuiver and Reimer, 1993; 
deltaR = 167 ± 106 yr), and the MARINE09 calibration data set 
(Reimer et al., 2009). Note that the use of this new calibration 
data set (MARINE09) leads to small deviations (<600 yr) from 
the calendar ages published by Kienast et al. (2007) using 
the MARINE04 (Hughen et al., 2004) calibration data set. 

Because of the difficulty in dating sediments from the equatorial 
Pacific older than 50,000 yr, we created two different age models 
based on the hypotheses under investigation. 

Cores TR163-31P, TR163-19P and ME0005A-27JC were graphically 
correlated to ME0005A-24JC for the MIS3-4 interval using 
the software AnalySeries (Paillard et al., 1996). We based 
our correlation on a number of clear features in the d15N 
and opal records, making sure not to violate the MIS4 benthic 
d18O transitions. Finally, based on multiple geochemical proxies 
(not shown), we identify an ash layer at a depth of 9.8 m 
ME0005A-24JC, 4.31 m ME0005A-27JC, 3.10 m in TR163-19P 
and 6.61 m in TR163-31P, which we assume to be the Los Chocoyos 
Ash Layer. This Ash Layer was previously observed in the 
Gulf of Mexico and equatorial Pacific and has been dated 
to 84,000 yr BP on the basis of oxygen isotope stratigraphy, 
biostratigraphy and Pa-Th data (Drexler et al., 1980).