Alkenone surface hydrographic changes of the subarctic Northwestern Pacific since the last glacial: proxy limitations and implications of non-thermal environmental influences

Pai-Sen Yu,Xuefa Shi,Chia-Ju Liao,Yusuke Yokoyama,Min-Te Chen,A A Bosin,Jian-Jun Zou,Sergey A Gorbarenko

doi:10.1186/s40645-020-00339-x

Abstract

We investigated an alkenone-based sea surface temperature (SST) and the hydrographic change records of the subarctic Northwestern (NW) Pacific from the last glacial to interglacial. The core we investigated is a piston core (LV 63-41-2, 52.56° N, 160.00° E; water depth 1924 m) retrieved from the southern offshore east coast of the Kamchatka Peninsula, which is a location of high sedimentation rate, with highly dynamic interactions with the cold/warm water masses of the Bering Sea/the NW Pacific. Based on our alkenone analysis with a previously well-established chronology of the core, we found high glacial C37:4 contents suggesting larger freshwater influences prior to the last deglacial in approximately 27–16 ka BP. The most significant features of what we found are alkenone indicative of “warming” intervals with minimum alkenone productions that occurred prior to the stadial Heinrich event 1 and the Younger Dryas. In contrast, for the interval corresponding to the Bølling–Allerød period, our alkenone analysis shows relatively “colder” but maximum alkenone productions. We conclude that this particular subarctic alkenone SST proxy record is mainly masked by non-thermal environmental influences, such as strong shifts of timing and duration of the sea ice retreat and/or salinity changes in surface water at this site, which could cause changes in water stratification that affect nutrient supplies of the upper ocean that modulate growth durations of phytoplankton/coccolithophore productions. Our studies suggest that this subarctic alkenone “SST” proxy record is indicative of the changes of seasonality that control the timing and duration of the blooming seasons of coccolithophores. The alkenone “SST” proxy is also dominantly driven by water stratification effects that, instead of SSTs, reflect most likely a combination of the following local to regional climate and ocean current patterns: (1) the amount of meltwater inputs from high mountain glaciers at Kamchatka; (2) less saline, nutrient-rich Alaskan Stream waters from the Cordilleran Ice Sheet in the Gulf of Alaska; (3) downwelling waters associated with the interactions between the southward Eastern Kamchatka Current and the spinning-up of the North Pacific Subarctic Gyre; and (4) the strength of the Kuroshio Current since the last glacial.

Highlights

The Bering Sea, one of the marginal seas in the Northwestern (NW) Pacific, is a dynamic area to global climate changes
Apart from what we have from core LV 63-41-2 (Gorbarenko et al 2017, 2019), which was located in the Bering Sea and the subarctic NW Pacific (Fig. 1), here we present new results of the alkenone sea surface temperature (SST) analysis of LV 63-41-2
Though many proxies measured from the core have been well-presented, this study focuses on (1) presenting alkenone SSTs, C37 alkenone concentration, and C37:4 records based on a well-established age model of the core (Gorbarenko et al 2017, 2019); (2) investigating the magnitude and patterns of surface ocean conditions and upper ocean stratification off Kamchatka since the last glacial by interpreting the alkenone proxies and, more importantly, their limitations; and (3) advancing our understanding on any plausible mechanisms of climate, sea ice, SST variations, and surface circulations among the subarctic NW Pacific from the last glacial by integrating published alkenone records of a more regional scale

Summary

Introduction

The Bering Sea, one of the marginal seas in the Northwestern (NW) Pacific, is a dynamic area to global climate changes. The hydrographic system in the Bering Sea is dominated by the cool water mass from the Arctic Ocean and warm water mass from the northeast Pacific. The Eastern Kamchatka Current (EKC), the major surface current in the west blank of the Bering Sea, tightly links with the Bering Sea and the northeastern Pacific circulations (Woodgate et al 2005; Stabeno et al 2005; Panteleev et al 2006) (Fig. 1). The strong Aleutian Low and accompanying southwesterly winds drive the EKC, greater extension of sea ice formation and cooling of surface waters from the Bering Sea along the offshore of eastern Kamchatka Peninsula. The modern winter surface circulation pattern in the subarctic NW Pacific could be regarded as an analog in the changes of the glacial oceanic circulation

Results

Discussion

Conclusion