Maureen Helen Davies
Published: 2011
Total Pages: 164
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The deglacial behavior of the sub-Arctic North Pacific is poorly constrained, with many published records suffering from limited age control due to extensive post- depositional biogenic carbonate dissolution. Potential alternative dating methods could include the correlation of stable-isotopic and/or paleomagnetic secular variation records to an independently-dated regional template, however no such template currently exists. Cores EW0408-85JC (59°33.32'N, 144°9.21'W, 682 m water depth) and EW0408-79JC (59°33.32'N, 144°9.21'W, 682 m water depth) are located above the carbonate compensation depth on the Gulf of Alaska margin, affording an opportunity to inter- compare stable-isotopic and paleomagnetic variability from a single location, as well as to place observations of Northeast Pacific paleoclimate and paleomagnetic secular variation in a global context via an independent radiocarbon-based chronology. We evaluate three possible age models for core EW0408-85JC and their implications for North Pacific stable isotopic and paleoventilation behavior. These include calibrated planktonic and benthic foraminiferal radiocarbon dates, assuming constant reservoir ages, as well as a correlation of planktonic [delta]18O in foraminifera to [delta]18O in a layer-counted Greenland ice core (NGRIP). We conclude that the calibrated planktonic dates provide the most accurate chronology. Benthic foraminiferal radiocarbon dates evaluated on this age model indicate that intermediate-depth ventilation ages at the site increased to>2,670 ± 180 during Termination 1, implying reduced ventilation relative to the Holocene average of 1,740 ± 210 yr. The shift to lower ventilation ages occurs at ~10,500 cal ybp, coeval with the flooding of Beringia and the opening of the Bering Strait, suggesting that flooded shelves and net export of low- salinity surface waters enhanced ventilation of the North Pacific. Oxygen isotope data from planktonic and benthic foraminifera, interpreted on this age model, document surface freshening by 16,650 ± 170 cal ybp, likely due to freshwater input from retreating regional glaciers. A sharp transition to laminated hemipelagic sedimentation at 14,790 ± 380 cal ybp is coincident with abrupt warming and/or freshening of the surface ocean (i.e. additional [delta]18O reduction of 0.9 [per mil]), essentially coincident with the Bolling Interstade of Northern Europe and Greenland. Cooling and/or higher salinities returned during the Allerod interval, coeval with the Antarctic Cold Reversal and continuing until 11,740 ± 200 cal ybp, when the onset of warming coincides with the end of the Younger Dryas. This may indicate convolved Northern and Southern drivers of climate variability in the North Pacific. Two laminated opal-rich intervals record episodes of high productivity are observed from 14,790 ± 380 to 12,990 ± 190 cal ybp, and from 11,160 ± 130 to 10,750 ± 220 cal ybp. These events likely correlate to similar observations elsewhere on the margins of the North Pacific, and may be driven my remobilization of iron from newly inundated continental shelves during episodes of rapid sea-level rise. High-resolution paleomagnetic secular variation (PSV) records from the Gulf of Alaska constrain regional field behavior and provide information on larger scale geomagnetic dynamics. Both cores studied (EW0408-79JC and 85JC) preserve a generally strong and relatively stable (MAD