Eleventh International Conference on Climate Change: Impacts & Responses

Abstract

Oxygen minimum zones (OMZ) are naturally occurring low-oxygen zones found at intermediate ocean depths. Changes in climate, ocean circulation, and marine productivity can change the size and location of OMZs through time. As the thickness of OMZs vary, their expansions can affect the marine ecosystem, economically important fisheries, and the global carbon cycle. In recent years, various parts of the world oceans are developing larger low-oxygen (hypoxic) regions linked to modern climate change and other anthropogenic effects. Understanding past instances of OMZ expansion is critical for forecasting future oceanic changes. The modern OMZ is the most extensive in the North Pacific. Our work uses sedimentary cores from Integrated Ocean Drilling Program Expedition 341 to reconstruct paleoenvironmental conditions at a continental slope site in the Gulf of Alaska (site U1419, 682 m water depth) over the past 60,000 years. Using multivariate quantitative analysis on benthic foraminiferal faunal assemblages and concentrations redox sensitive metals (Mo, Cd, Re, U), we reconstruct >10 hypoxic events during the study interval. The two most severe events occurred during the last deglacial (~17-13 ka) and between 30-50 ka (in MIS 3). We also use geochemical analyses (stable isotopes such as δ13C and δ18O of benthic and planktonic foraminifera) and the abundances of benthic foraminiferal taxa sensitive to changes in productivity to test hypotheses regarding the drivers of these events. Understanding the frequency, duration, and drivers of these past hypoxic events can inform policy makers of potential changes to future ocean environments.