DOI: 10.25921/s8m6-tv60
title: NOAA/WDS Paleoclimatology - Northwest Pacific RC10-196 Deglacial Biogenic Flux Data

description: The subarctic North Pacific Ocean holds a large CO2 reservoir that is currently isolated from the atmosphere by a low-salinity layer. It has recently been hypothesized that the reorganization of these high-CO2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation. This reorganization would leave some imprint on paleo-productivity records. Here we present 230Th-normalized biogenic fluxes from an intermediate depth sediment core in the Northwest Pacific (RC10-196, 54.7°N, 177.1°E, 1007 m) and place them within the context of a synthesis of previously-published biogenic flux data from 49 deep-sea cores north of 20°N, ranging from 420 to 3968 m water depth. The 230Th-normalized opal, carbonate, and organic carbon fluxes from RC10-196 peak approximately 13,000 calendar years BP during the Bølling/Allerød (B/A) period. Our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period, increased somewhat in the Northwest Pacific during Heinrich Event 1, and reached a maximum across the entire North Pacific during the B/A period. We evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the North Pacific, including changes in preservation, sediment focusing, sea ice extent, iron inputs, stratification, and circulation shifts initiated in the North Atlantic and North Pacific. Our analysis suggests that while micronutrient sources likely contributed to some of the observed changes, the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region-wide contemporaneous peaks in export production. We argue that paleo-observations are most consistent with ventilation increases in both the North Pacific (during H1) and North Atlantic (during B/A) being the primary drivers of increases in biogenic flux during the deglaciation, as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline.
description: We present 230Th-normalized biogenic fluxes from an intermediate 
depth sediment core in the Northwest Pacific (RC10-196) and place 
them within the context of a synthesis of previously-published 
biogenic flux data from 49 deep-sea cores north of 20ºN, 
ranging from 420 to 3968 m water depth. The 230Th normalized opal, 
carbonate, and organic carbon fluxes from RC10-196 peak 
approximately 13,000 calendar years BP during the Bølling/Allerød 
(B/A) period. This file includes: 
(a) radiocarbon data from N. pachyderma (s), 
(b) oxygen and carbon isotope data on N. pachyderma (s), 
(c) wt% and mass accumulation rates of opal, carbonate, 
    organic carbon, and authigenic Uranium, and 
(d) associated 230Th data. 

Note that MARtoc, MARcaco3, and MARopal (mg/cm2/y) are not 230Th fluxes, 
but are estimated as: MAR = f * LSR * DBD (where DBD = dry bulk density; 
LSR = linear sedimentation rate; f = measured fraction of TOC, CaCO3, 
and opal, respectively.) 

Methods:  
230Th-normalization was used to reconstruct particle flux to an 
intermediate depth sediment core, RC10-196.  An age model was 
determined using a combination of radiocarbon dates and oxygen 
isotope stratigraphy.  Oxygen isotope values were measured on 
N. pachyderma (sinistral coiling) from the 150-250 um size 
fraction at the Saskatchewan Isotope Laboratory at the University 
of Saskatchewan.  Radiocarbon analysis was conducted on three samples 
(two of N. pachyderma (sinistral coiling), one of mixed planktonic 
foraminifera), at Lawrence Livermore National Laboratory.  
These dates were converted to calendar age using the CALIB program 
(Stuiver and Reimer, 1993 (version 6.0)).  Prior to calibration, 
a reservoir correction of 450 years was applied, using estimates 
obtained by Sarnthein et al. (2007) on cores from the NW Pacific 
region.  Using this age model, sedimentation rates at RC10-196 
ranged from 4.2 to 5.9 cm/ka over the last 30,000 years. 
Samples for U-series measurement were spiked with yield tracers 
(229Th and 236U), digested in HCl, HF, HNO3 and perchloric acid 
(Fleisher and Anderson, 1991) and pre-concentration by anion 
exchange resin (Chase et al., 2003). Isotope spikes were 
calibrated against a natural U standard (CRM-145) and a natural 
Th standard (NIST 3159). Digests were analyzed by isotope dilution 
HR-ICP-MS (Axiom) at Oregon State University (Chase et al., 2003; 
Fleisher and Anderson, 2003). Mass bias was assessed by repeated 
analysis of CRM-145. Propagated uncertainties for individual 
analyses were ~ 4% for 230Th concentration while repeated 
digestion and analysis of an in-house sediment standard was 
reproducible to 6%. Excess 230Th and authigenic U were calculated 
from the sediment concentration data assuming a detrital U/Th ratio 
of 0.7 ± 0.1 (Henderson and Anderson, 2003). Thorium concentrations 
measured in the GEOTRACES intercalibration sediment sample were 
in agreement with the main distribution of the submitted data 
(Anderson et al., submitted manuscript).