New northwest Pacific radiolarian data as a tool to estimate past sea surface and intermediate water temperatures

Abstract

A new radiolarian data set for transfer function estimates of past sea surface temperature (SST) and intermediate water temperature was developed in this study for the northwestern Pacific Ocean covering a region from 1° to 50°N and 120° to 167°E. We analyzed 87 sediments surface samples, selected 30 species and/or species group found in shallow water for estimating past summer SST and 17 species and/or species group found in the intermediate water for estimating past intermediate water temperature. Since the intermediate water temperature changes greatly between 200 and 500 m, our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m. In this context, we estimated past summer SST and intermediate water (at ~500 m) temperature within an error margin of 0.9 and 1.2°C, respectively. A test of the accuracy of our transfer functions, conducted on core samples provided by IODP Expedition 346 Site U1429 in the northern East China Sea, showed that the reconstructed summer SSTs fluctuated between 17.2 and 26.5°C in selected late Pleistocene sequences. These temperatures corresponded to modern winter and summer SST, respectively, which highlights the ability of our new database to accurately reconstruct summer SST. The reconstructed intermediate water temperature fluctuates between 3 and 8°C, which corresponds to the observed temperature range at depths of ~500 m at high and midlatitudes, respectively.

Paleoceanographic history of the Japan Sea over the last 9.5 million years inferred from radiolarian assemblages (IODP Expedition 346 Sites U1425 and U1430)

“…Young forms of Spongodiscidae, whose taxonomy is still unsettled, are often named as Spongodiscus resurgens Ehrenberg group (e.g., Itaki 2009;Matsuzaki et al 2015a). However, whichever name is used, this form is likely related to the shallow subsurface waters of transitional subarctic areas in the Northwest Pacific (e.g., Kamikuri et al 2008;Matsuzaki and Itaki 2017;Okazaki et al 2004). In our study, both the species and species group were found at Site U1425 throughout the period since 9.5 Ma.…”

“…Species such as L. setosa, Spongodiscidae juvenile, and P. gracilipes are well-known extant species related to subarctic areas. Based on previous studies, we know that L. setosa is related to the shallow water of subarctic to arctic areas of the Northern Hemisphere (Atlantic and Pacific oceans) (Boltovskoy and Correa 2016;Matsuzaki and Itaki 2017;Okazaki et al 2004). At Site U1425, this species was recorded between 3.69 and 0 Ma, and its mean relative abundance is 1.7% (SD = 3.3; N = 44) ( Fig.…”

“…and Tetrapyle spp. are extant species groups, both known as a marker of warm shallow water in the North Pacific (e.g., Lombari and Boden 1985;Itaki et al 2010;Kamikuri et al 2008;Matsuzaki et al 2014b;Matsuzaki et al 2015b;Matsuzaki and Itaki 2017). However, the main difference between the two species groups is that while Tetrapyle spp.…”

“…The species S. osculosa is a transitional-subarctic to subarctic species inhabiting intermediate water depths in the North Pacific (Kling and Boltovskoy 1995;Kamikuri et al 2008;Matsuzaki and Itaki 2017). This species has a sporadic occurrence at Site U1425 and its mean relative abundance is 1% (SD = 1.4; N = 154).…”

“…The species L. weddellium is known as a subarctic-arctic species in the North Pacific (Tanaka and Takahashi 2008;Kamikuri et al 2008;Matsuzaki and Itaki 2017). At the middle to low latitudes of the North Pacific, this species is less abundant and inhabits intermediate water depths only .…”