Northeast Pacific Seawater Radiocarbon Recorded in Abalone Shells Obtained From Otsuchi Bay, Japan

Abstract

Reconstructing past ocean currents in the coastal regions is necessary to better understand the relationship between oceanographic changes and coastal ecosystems. It is known that variations have occurred with large-scale climate changes such as ENSO (El Niño Southern Oscillations) and PDO (Pacific Decadal Oscillations). Thus, reconstruction of past seawater conditions in coastal regions is needed to better understand the relationship between oceanographic changes and coastal ecosystems. Seawater radiocarbon is a unique proxy to understand the properties of water masses. Reef-building corals have been employed extensively and successfully in conducting this type of research into past ocean circulation histories. However, their distribution is limited to the low latitudes and hence alternative archives are required for studies in mid to high-latitude locations. Here, we use abalone shell samples obtained from Otsuchi Bay located in the Tohoku region on the Pacific coast of Northern Japan. Radiocarbon in abalone shells was compared with dissolved inorganic carbon in two-year-long records of river water as well as seawater. The data indicate that abalone shells can be used to reconstruct past seawater radiocarbon variations in northern Japan where coral skeletons are not available for ocean mixing studies.

Otolith radiocarbon signatures provide distinct migration history of walleye pollock around Hokkaido, Japan in the North‐Western Pacific

“…In contrast, the subarctic current (Oyashio current) delivers water with low Δ 14 C values of ca. −50‰ (Ishikawa et al., 2021 ; Ota et al., 2021 ; Satoh et al., 2019 ). Therefore, a large geographic gradient of Δ 14 C (−50 to 50‰) appears in oceanic regions influenced by these two current systems.…”

Salinity, oxygen isotope, hydrogen isotope, and radiocarbon of coastal seawater of North Japan

“…In addition, radiocarbon (Δ 14 C) is a powerful tracer in seawater. Δ 14 C is a widely used tracer in a broad range of fields, including oceanography and fishery science (Ota et al, 2019;Larsen et al, 2018;Hirabayashi et al, 2017;Mitsuguchi et al, 2016;Kumamoto et al, 2013;Tsunogai et al, 1995). In the modern ocean, anthropogenic radiocarbon invades the natural carbon cycles (Ostlund and Stuiver, 1980).…”

Lake water dissolved inorganic carbon dynamics revealed from monthly measurements of radiocarbon in the Fuji Five Lakes, Japan

“…Since radiocarbon reservoir ages reflect hydrosphere dynamics, there are many studies that consider changes in seawater radiocarbon in the ocean with time (e.g., Hirabayashi et al, 2017Hirabayashi et al, , 2019Ota et al, 2019;Servettaz et al, 2019). However, few systematic lake water reservoir age studies have been reported.…”