Paleoceanographic shifts in the Gulf of Alaska over the past 2000 years: A Multi-proxy perspective

Abstract

The Gulf of Alaska (GOA) is a dynamic region influenced by climate variability on time scales ranging from days to millennia. Recent regime shifts suggest interdecadal GOA primary productivity patterns, yet it is unclear whether such fluctuations extend beyond the instrumental record. This thesis examined the nature of prevalent climatic and oceanographic patterns before the twentieth century using several marine sediment core proxies for paleoproductivity and paleoceanography. Sediment cores were from two locations: Bay of Pillars, Kuiu Island, in southeast Alaska (56.63 ̊N, 134.35 ̊W), and a central midshelf location (GAK4) along the Global Ecosystem Dynamics (GLOBEC) Seward Line (59.25 ̊N, 148.82 ̊ W). Proxy data from these cores include: percentages of organic carbon, nitrogen and biogenic opal; organic carbon-to-nitrogen ratios; stable isotope ratios from sediment organic matter (δ13C and δ15N) and foraminifera tests (δ13C and δ18O); and foraminifera faunal analysis. Bay of Pillars proxy data suggest that the onset of the Little Ice Age (LIA) ca. 1200 AD coincides with pulses of decreased salinity and increased productivity. GAK4 proxy data indicate increased productivity and decreased terrestrial input over the past century; as well as fresher surface water was during the latter portion of the LIA (1716 – 1894) and positive Pacific Decadal Oscillation phases.