Placing North Pacific paleo-oxygenation records on a common scale using multivariate analysis of benthic foraminiferal assemblages

Abstract

Dysoxic events are well-studied in Pleistocene and Holocene marine sediment records from the North Pacific using faunal, sedimentological, and geochemical paleo-oxygenation proxies. However, differences in proxy sensitivity and local conditions make it difficult to quantify the relative severity of dysoxia across the North Pacific. Here, we use multivariate analyses of taxonomically standardized benthic foraminiferal assemblages to quantitatively compare the severity and duration of dysoxic events at four intermediate depth sites within oxygen minimum zones in the Gulf of Alaska (GoA), Santa Barbara Basin, and Baja California Sur. Unlike previous faunal dissolved oxygen indices, the metric developed here incorporates the total faunal assemblage and is better correlated with co-registered geochemical proxies. We find that although the GoA site is usually better-oxygenated, it records dysoxic events of equal severity, but shorter duration, as the dysoxic events recorded at the lower latitude sites during the Holocene, Bølling–Allerød, and MIS3 interstadials. Decreases in oxygenation are contemporaneous across sites and the differences in the duration of severe dysoxia along latitude may be related to the stronger influence of well-oxygenated North Pacific Intermediate Water at high latitudes and variation in the northward extent of the California Undercurrent, which advects low-oxygen waters northward from the Eastern Tropical North Pacific. This suggests that future strengthening of the California Undercurrent may be capable of reducing dissolved oxygen in the subpolar North Pacific to levels more typical of the Equatorial Tropical North Pacific.