Pulses of enhanced North Pacific Intermediate Water ventilation from the Okhotsk Sea and Bering Sea during the last deglaciation

L Max,A Mackensen,D Nürnberg,R Tiedemann,J.-R Riethdorf,H Kühn,L Lembke-Jene

doi:10.5194/cp-10-591-2014

Abstract

Abstract. Under modern conditions only North Pacific Intermediate Water is formed in the northwest Pacific Ocean. This situation might have changed in the past. Recent studies with general circulation models indicate a switch to deep-water formation in the northwest Pacific during Heinrich Stadial 1 (17.5–15.0 ka) of the last glacial termination. Reconstructions of past ventilation changes based on paleoceanographic proxy records are still insufficient to test whether a deglacial mode of deep-water formation in the North Pacific Ocean existed. Here we present deglacial ventilation records based on radiocarbon-derived ventilation ages in combination with epibenthic stable carbon isotopes from the northwest Pacific including the Okhotsk Sea and Bering Sea, the two potential source regions for past North Pacific ventilation changes. Evidence for most rigorous ventilation of the intermediate-depth North Pacific occurred during Heinrich Stadial 1 and the Younger Dryas, simultaneous to significant reductions in Atlantic Meridional Overturning Circulation. Concurrent changes in δ13C and ventilation ages point to the Okhotsk Sea as driver of millennial-scale changes in North Pacific Intermediate Water ventilation during the last deglaciation. Our records additionally indicate that changes in the δ13C intermediate-water (700–1750 m water depth) signature and radiocarbon-derived ventilation ages are in antiphase to those of the deep North Pacific Ocean (>2100 m water depth) during the last glacial termination. Thus, intermediate- and deep-water masses of the northwest Pacific have a differing ventilation history during the last deglaciation.

Highlights

Today, the renewal of North Pacific Intermediate Water (NPIW) is mainly coupled to physical processes in the Okhotsk Sea (Talley and Roemmich, 1991; Talley, 1993), where Dense Shelf Water is produced in coastal polynyas by brine rejection during wintertime sea-ice production (Shcherbina et al, 2003)
The δ13CDIC profile from the Okhotsk Sea shows a smooth decline of δ13CDIC values within the water column between 200–800 m water depth (Fig. 3). This marks the presence of fresh, newly formed Okhotsk Sea Intermediate Water (OSIW), which spreads across the Okhotsk Sea, subsequently exported through the Kurile Straits into the northwest Pacific
Changes in northwest Pacific intermediate water are simultaneous to variations in Atlantic Meridional Overturning Circulation and suggest a deglacial seesaw between strengthened intermediatedepth overturning of the subarctic Pacific and weakened meridional overturning of the North Atlantic

Summary

Introduction

The renewal of North Pacific Intermediate Water (NPIW) is mainly coupled to physical processes in the Okhotsk Sea (Talley and Roemmich, 1991; Talley, 1993), where Dense Shelf Water is produced in coastal polynyas by brine rejection during wintertime sea-ice production (Shcherbina et al, 2003). These water masses leave the Okhotsk Sea as Okhotsk Sea Intermediate Water (OSIW), mix with water masses in the northwest Pacific at intermediate depths and form NPIW (Yasuda, 1997). The deep North Pacific is only slowly replenished by Southern Ocean water masses due to the absence of deep-water formation in the North Pacific Ocean today (Warren, 1983; Emile-Geay et al, 2003)

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Conclusion