UNDERSTANDING PALEOCLIMATE SHIFTS IN THE GULF OF ALASKA USING FORAMINIFERAL-BASED PALEOCEANOGRAPHIC METHODS

We have used rapidly accumulating sediment cores from the coastal region of the Gulf of Alaska (GOA) to study decadal to century-scale oceanic variability over the last two millennia, well beyond the time covered by regional instrumental records. Paleoceanographic data have been obtained from several cores taken throughout the GOA which have been dated by AMS radiocarbon techniques on terrestrial macrofossils. The main objective is to obtain past temperature, salinity, and productivity records by means of isotopic (δ¹⁸O and δ¹³C) and faunal analysis of foraminifers. Other indicators of paleoproductivity obtained from sediment analysis include δ¹³C and δ¹⁵N ratios and organic carbon and opal mass accumulation rates. Based on carbon and nitrogen sediment proxies, there is a noticeable increase in productivity during the Little Ice Age, around 1250 AD. On a decadal-scale, mass opal accumulation rates indicate productivity increases after 1976, which correlates with a regime change documented by instrumental and salmon catch records. Carbon and oxygen isotopic data from benthic foraminiferal tests show a cyclical oscillation over the past 400 years with an average frequency of almost 58 years. This varies from the instrumental record of approximately 20 years throughout the twentieth century, yet corresponds with tree-ring data from the same geographic area and time frame. This data, when coupled with current studies of North Pacific climate, will give us a long-term perspective on climate fluctuations in the GOA that have occurred in the past, as well as insight into what may occur in the future.