DOI: 10.25921/r1mv-v061
title: NOAA/WDS Paleoclimatology - Northeast Pacific 100 Year Tree Ring/Geoduck SST Reconstructions

description: We demonstrate the potential for developing sea surface temperature (SST) reconstructions in the northeast Pacific from combinations of tree-ring and growth-increment chronologies of the long-lived marine bivalve, the Pacific geoduck. Six Pacific geoduck chronologies developed from site along the Washington-British Columbia coast are compared and combined with tree-ring chronologies from California to Alaska. All chronologies are annually resolved and strongly relate to local to regional-scale SST, though differences in the response season as well as the spectral properties of the two proxies are observed. Both proxy types closely track SST and when used in combination, yield a more robust SST reconstruction than tree-ring or geoduck chronologies could provide alone. In total, variance explained in SST is 63.9% at the regional-scale and 68.2% at a local scale, providing SST estimates for more than 60 years prior to the start of continuous instrumental records in this region. This study represents one of the few climate reconstructions where both proxies are annually resolved, and is the first to integrate regional networks of geoduck chronologies and tree-ring chronologies.
description: Sea surface temperature (SST) reconstructions for the northeast 
Pacific, based on tree-ring and annual growth-increment width 
chronologies of the Pacific geoduck marine bivalve (Panopea 
generosa, formerly P. abrupta).  Six Pacific geoduck chronologies 
were developed from sites along the British Columbia coast.  
Tree-ring chronologies from California to Alaska, archived 
in the International Tree Ring Data Bank (ITRDB)
(http://www.ncdc.noaa.gov/paleo/treering.html), 
were also used to produce the SST reconstructions.  
Geoduck growth-increment chronologies were developed 
with program ARSTAN: 
http://www.ldeo.columbia.edu/res/fac/trl/public/publicSoftware.html   
detrended using appropriate standardization for each data set 
(cubic splines, negative exponential, or linear regression 
with negative or 0 slope). The "standard" chronology from 
ARSTAN is reported.  All growth-increment widths are in mm. 

Geoduck samples were live-collected in 2003 and 2004 by the 
Canada Department of Fisheries and Oceans (DFO) Pacific Biological 
Station in Nanaimo, BC for analysis of population age structure.  
Oldest individuals with clearly visible growth increments 
were selected for chronology development and reconstruction 
of sea surface temperatures.  

To prepare growth increments for analysis, a single shell 
from each geoduck specimen was cut along the height axis 
of the valve through the center of the hinge plate region 
using a diamond-blade lapidary saw.  The cut surface was 
polished with 600-grit sandpaper and then etched with 
two-percent hydrochloric acid.  An impression (acetate peel) 
was made by pressing the etched surface of the hinge plate 
region against a piece of acetate film softened with a drop 
of acetone.  The resulting peel was placed between two glass 
slides and viewed through a dissecting microscope using 
transmitted light.  The hinge plate (inner shell layer) 
grows at a rate proportional to that of the outer shell layer, 
but is better protected from erosion and provides the most 
complete record possible.  All peel preparation was conducted 
by the DFO.  

Samples were visually crossdated to ensure that all annual 
growth increments were assigned the correct calendar year 
of formation.  Under the dissecting microscope at 60X 
magnification, two to eight overlapping digital photographs 
were taken with a Leica DC300 7.2 megapixel camera and tiled 
into a single panoramic image using Image Pro Plus 6.0 
(Media Cybernetics Inc., Silver Spring, MD).  In Image Pro 
Plus 6.0, growth increment widths were measured along continuous 
transects that followed the axis of growth.  Each growth 
increment was delineated at the end of the winter line 
(start of the new growing season), and each peel was measured,  
twice for some samples (noted by "a" and "b" labeling of 
measurement time series).  Crossdating at each site 
was verified using the International Tree-Ring Data Bank 
Dendrochronology Program Library (ITRDB DPL) program COFECHA. 
Measurement time series were standardized in COFECHA using 
cubic splines set at a 50% frequency response of 22 years. 
Measurement time series were detrended using negative 
exponential functions in the program ARSTAN. 

Images are stored at the Oregon State University Hatfield Marine 
Science Center, Newport, OR 97365. Geoduck peels are stored 
at the Pacific Biological Station, Nanaimo, BC.  

Pacific geoduck sampling locations. (All water depths 10 to 15 m):
Bartlett, BC, Canada: 49.12ºN -125.98ºW 
Brady’s Beach, BC, Canada: 48.76ºN -125.28ºW 
Cape Mark, BC, Canada: 52.13ºN -128.44ºW 
Goletas, BC, Canada: 50.78ºN -127.56ºW  
Tree Nob Islands, BC, Canada: 54.22ºN -130.79ºW 


Tree ring sites used in the SST reconstructions 
From the International Tree Ring Data Bank (ITRDB)
http://www.ncdc.noaa.gov/paleo/treering.html