Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective

Abstract

[1] A strong oxygen minimum zone (OMZ) currently exists at upper intermediate water depths on the northern Japanese margin, NW Pacific. The OMZ results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters. We investigated late Quaternary history (last 34 kyr) of ocean floor oxygenation and the OMZ using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off Shimokita Peninsula and Tokachi, northern Japan, at water depths between 975 and 1363 m. These cores are well located within the present-day OMZ, a region of high surface water productivity, and in close proximity to the source region of North Pacific Intermediate Water. Late Quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments. Foraminiferal assemblages are interpreted to represent three main groups representing oxic, suboxic, and dysoxic conditions. Assemblage changes in all three cores and hence in bottom water oxygenation coincided with late Quaternary climatic episodes, similar to that known for the southern California margin. These episodes, in turn, are correlated with orbital and millennial climate episodes in the Greenland ice core including the last glacial episode, Bølling-Å llerød (B/A), Younger Dryas, Preboreal (earliest Holocene), early Holocene, and late Holocene. The lowest oxygen conditions, marked by dysoxic taxa and laminated sediments in one core, occurred during the B/A and the Preboreal intervals. Suboxic taxa dominated mainly during the last glacial, the Younger Dryas, and most of the Holocene. Dysoxic conditions during the B/A and Preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern Pacific. Remarkable similarities are evident in the late Quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern Japan and southern California. The oscillations in OMZ strength, reflected by these faunal changes, were widespread and apparently synchronous over wide areas of the North Pacific, reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late Quaternary climate change on millennial and orbital timescales.Citation: Shibahara, A., K. Ohkushi, J. P. Kennett, and K. Ikehara (2007), Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: A benthic foraminiferal perspective, Paleoceanography, 22, PA3213,

The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

“…The increase in dissolved oxygen in O-LGM was considerable but agreed well with proxy reconstructions for the upper ocean. The oxygen-poor intermediate waters of the western North Pacific (Ishizaki et al, 2009;Shibahara et al, 2007), eastern North Pacific (Cannariato and Kennett, 1999;Cartapanis et al, 2011;Chang et al, 2014;Dean, 2007;Nameroff et al, 2004;Pride et al, 1999;Ohkushi et al, 2013;van Geen et al, 2003), eastern South Pacific (Martinez et al, 2006;Muratli et al, 2010;Salvatteci et al, 2016), equatorial Pacific (Leduc et al, 2010) and Indian Ocean (Reichart et al, 1998;Suthhof et al, 2001;van der Weijden et al, 2006) were better oxygenated at the LGM relative to the PI climate. An important consequence of oxygenating the upper ocean is a reduction in the strength of denitrification in these regions.…”

Millennial-scale paleoceanographic events and implication for the intermediate-water ventilation in the northern slope area of the Bering Sea during the last 71kyrs

“…4h). According to previous studies, these three species are regarded as a dysoxic species (Cannariato et al, 1999;Shibahara et al, 2007). The variation of total foraminifera specimens is in phase with that of CaCO 3 content, which indicates that the major component of CaCO 3 is foraminifera (Fig.…”

Late Pleistocene stratigraphy and palaeoceanographic implications in northern Bering Sea slope sediments: evidence from the radiolarian species Cycladophora davisiana

“…Similarly, the lamination deposits during the last deglaciation have been recognised in the western subarctic Pacific, and their depositional mechanism interpreted as a result of development of the oxygen minimum zone (OMZ) and/or reduced ventilation, according to benthic foraminiferal assemblage and geochemical analyses (e.g. Shibahara et al, 2007;Sagawa and Ikehara, 2008). It is likely that the well-ventilated upper intermediate water inferred from the high abundance of C. davisiana ($200-500 m considering a depth habitat of C. davisiana in the present Okhotsk Sea) was separated from the oxygen-poor lower intermediate water ($1000 m) indicated by the laminated sediments.…”