DOI: 10.25921/6tka-8q78
title: NOAA/WDS Paleoclimatology - Master Shell Growth Chronology from the Gulf of Maine 1762-2013 AD

description: The Gulf of Maine is undergoing rapid environmental and ecological changes, yet our spatial and temporal understanding of the climatic and hydrographic variability in this region, including extreme events, is limited and biased to recent decades. In this study, we utilize a highly replicated, multi-century master shell growth chronology derived from the annual increments formed in the shells of the long-lived bivalve Arctica islandica collected in 38 m from the central coastal region in the Gulf of Maine. Our results indicate that shell growth is highly synchronous and inversely related to local seawater temperatures. Using composite analyses of extreme shell growth events from CE 1900 to 2013, we extend our understanding of the fac- tors driving oceanic variability and shell growth in the Northwestern Atlantic back to CE 1761. We suggest that extreme shell growth events are primarily controlled by Gulf of Maine sea surface temperature (SST) and stratification conditions, which in turn appear to be largely influenced by SST patterns in the Pacific Ocean through their influence on mid-latitude atmospheric circulation patterns and the location of the eddy-driven jet. The large-scale jet dynamics during these extreme years manifest as precipitation and moisture transport anomalies and regional SST conditions in the Gulf of Maine that either enhance or inhibit shell growth. Pacific climate variability is thus an important, yet understudied, influence on Gulf of Maine ocean conditions.
description: Live and dead Arctica islandica shells were collected in 2010, 2011, 2012 and 2014. All shell material is archived and stored at Iowa State University. A cross section of shell along the maximum growth axis was embedded in clear epoxy (Beulher Epoxicure resin and hardener) before sectioning the embedded shell along the maximum growth axis.  One of the two mirrored surface shell cross sectioned blocks was used for crossdating chronology work while the other was saved for later geochemical analysis.  To obtain the clearest view of the growth increments, the cross sectioned shell surface was polished with five silicon carbide grinding paper levels (120, 400, 600, 800, 1200). Photographs of acetate peels and measurements of shell increments were completed at Iowa State University using a uEye camera and Buelher’s OmniMet v9.5.  Prior to measuring the thickness of annual increments, individual shell increments were visually inspected and temporally aligned using several visual crossdating techniques (marker years, modified list method, and skeleton plots).  Visual crossdating was statistically verified using SHELLCORR and COFECHA.  If either program flagged a potential problem, the increments in question were visually inspected.  Measurement series were only changed if an error from measuring or visual crossdating was clearly visible upon reinspection.  Applying these techniques of crossdating sclerochronological archives resulted in precisely dated and a highly replicated master shell chronology (average expressed population signal = 0.94; series intercorrelation =0.76) from a site within the central Gulf of Maine (northwestern Atlantic Ocean).  Arctica islandica growth-increment chronologies were developed with program ARSTAN: http://www.ldeo.columbia.edu/res/fac/trl/public/publicSoftware.html and detrended using appropriate standardization for each data set Authors (Exactly as written in the publication citation) (cubic splines, negative exponential, or linear regression with negative or 0 slope). The "standard" chronology from ARSTAN is reported.