Abstract:The excess radiocarbon produced by nuclear bomb testing in the atmosphere in the 1950s–1960s (bomb‐14C) is used as a tracer in the surface ocean, extending our understanding of geophysics and biogeochemical cycles. However, there is no bomb‐14C record for the high‐latitude western North Pacific Ocean because of the paucity of long‐lived marine calcifying organisms equivalent to reef‐building corals. The shells of Stimpson's hard clam, Mercenaria stimpsoni, potentially provide such a record because the clam's l… Show more
“… Figure 3 (a) Δ 14 C value of three abalones, H66, H104 and H105 (b) Depth profiles of the Δ 14 C values of DIC in seawater and CTD salinity in Funakoshi Bay (black), Otuchi Bay in 2016 (red) (Kubota et al 2018) and Otuchi Bay in 2017 (blue; Satoh et al 2019). (c) Habitant of adult abalone at 2–6 m, H66 located.…”
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.
“… Figure 3 (a) Δ 14 C value of three abalones, H66, H104 and H105 (b) Depth profiles of the Δ 14 C values of DIC in seawater and CTD salinity in Funakoshi Bay (black), Otuchi Bay in 2016 (red) (Kubota et al 2018) and Otuchi Bay in 2017 (blue; Satoh et al 2019). (c) Habitant of adult abalone at 2–6 m, H66 located.…”
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.
“…In this study, we used 5 live M. stimpsoni specimens collected from the seafloor of Funakoshi Bay (site F-1, 20 m water depth; Figure 1) and 1 from Otsuchi Bay (site O-3, 5 m water depth) during a dive or by using a Smith-McIntyre mud sampler (see Online Supplementary Material) (Kubota et al 2018a). These specimens were frozen after recovery and then transported to the laboratory for the removal of their soft tissues.…”
Section: Methodsmentioning
confidence: 99%
“…As a result, mollusk shells continuously record the ambient environment, making them excellent archives of past environments and environmental disturbances (e.g., Murakami-Sugihara et al 2019). The cold-water venerid bivalve Mercenaria stimpsoni (Stimpson's hard clam), which lives in Funakoshi Bay, is a long-lived mollusk with a shell that displays distinct annual growth increments (Kubota et al 2017(Kubota et al , 2018aShirai et al 2018). It is thus possible to test the response of this marine mollusk to environmental perturbation, despite its low population density in the bay (Seike et al 2013), because gaps in the shell record can be filled by using crossdating to combine the records of multiple individuals.…”
Section: Introductionmentioning
confidence: 99%
“…Mercenaria stimpsoni is the most long-lived among modern bivalves living near the Japanese coast (Shirai et al 2018), and its shell growth pattern and the paleoenvironmental implications of the pattern have been documented previously (Tanabe et al 2017;Kubota et al 2017Kubota et al , 2018aShirai et al 2018). This species inhabits fine sandy substrata in the shallow coastal zone (water depth 5-30 m) along mid-to high-latitude coasts of the northwest Pacific, the Sea of Japan, and the Sea of Okhotsk (Habe 1977).…”
Section: Introductionmentioning
confidence: 99%
“…At ontogenetically older stages (>15 years), shell growth occurs only in summer and the growth rate is very low (0.05-0.1 mm/yr). Growth cessation lines are visible in shell cross sections, and the calendar year of past growth increments of a live-caught clam can be obtained by counting the annual growth lines backward from the most recent (Kubota et al 2018a;Shirai et al 2018).…”
Tsunamis are huge disasters that can significantly damage benthic organisms and the sea-bottom environment in coastal areas. It is of great ecological importance to understand how benthic ecosystems respond to such destructive forces and how individual species are affected. Investigating the effect of such disasters on animals that are seldom caught alive is particularly difficult. Bivalve mollusks are especially suitable for investigating how a tsunami affects coastal benthic species because they preserve an environmental record in their shells that can be extended back in time by crossdating the records of multiple individuals. Here we studied dead shells of Mercenaria stimpsoni, a long-lived clam, and precisely determined the time of death by using nuclear bomb–induced radiocarbon (bomb-14C) and by counting annual growth increments. First, a quasi-continuous, regional bomb-14C record was created by analyzing the shells of 6 live-caught M. stimpsoni individuals. Then 27 dead shells collected from the seafloor of Funakoshi Bay were 14C-dated and analyzed. The results showed that the huge tsunami that struck northeastern Japan on 11 March 2011 caused mass mortality of this bivalve in Funakoshi Bay. Nine of the 27 clams died during the March 2011 tsunami, probably by starvation after burial by tsunami deposits or exposure above the seafloor as a result of sediment liquefaction during the earthquake. The dating method used in this study can help us understand how long-lived marine organisms with low population density are affected by huge natural disasters such as a tsunami.
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