3:30 PM - 5:00 PM
[U03-P06] Comparison of radiocarbon in abalone shells and dissolved inorganic carbon in seawater collected from Otsuchi Bay, Northeast Japan
Keywords:Abalone, Seawater, Accelerator Mass Spectrometry (AMS), Otsuchi Bay, Water mass mixing
Off the Sanriku Coast in Northeast Japan, the Oyashio and Kuroshio currents mix in a complex manner. Global-scale climate variabilities such as El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are thought to influence the water mass around the Sanriku Coast, which may then impact the local marine ecosystems. However, how these global climate variabilities respond to 21st-century global warming and how they affect regional ocean circulation remains uncertain.
The nuclear bomb testing in the 1950s and 1960s caused radiocarbon concentration (Δ14C) in the Earth’s atmosphere to double. This artificial radiocarbon – the “bomb-14C” diffuses into the surface ocean layer through the air-sea gas exchange of carbon dioxide and acts as a useful tracer to study the water mass mixing such as upwelling and advection. Δ14C have been used to reconstruct water mass mixing using reef-building corals in low latitudes (e.g. Hirabayashi et al., 2017, 2019), but limited in high latitude waters where corals are absent (Kubota et al., 2018; Ota et al., 2019). Previous study (Ota et al., 2019) shows the capability of Ezo abalone shells for reconstruction of water mass variation for more than four years, as well as seasonal high-resolution Δ14C measurement. However, systematic comparison with water Δ14C has not been carried out.
In this study, we measured Δ14C values of shells of Ezo abalone (Haliotis discus hannai) and Δ14C values of seawater using a single-stage accelerator mass spectrometer (AMS) at the University of Tokyo, and then compared the Δ14C values and patterns of shells and seawater samples. Both the abalone shells and seawater were collected at the entrance part of Otsuchi Bay in 2022 May and June. Otsuchi Bay is located on the Sanriku Coast facing the Northwest Pacific Ocean where complex mixing of various water masses occurs. In the surface ocean layer, the Tsugaru current from the Japan Sea joins the cold, Δ14C-depleted Oyashio Current from the subarctic North Pacific and meets the warm, Δ14C-enriched Kuroshio current from the subtropical North Pacific. Understanding the horizontal and vertical mixing of ocean water masses is of great importance to local ecosystems and livelihood. This is the first comparison of Δ14C values of abalone shells and seawater from the same time and location. We will discuss the results and potential of the abalone shells as a paleoclimate archive during the presentation.
Reference:
At the end of the Japanese abstract.
The nuclear bomb testing in the 1950s and 1960s caused radiocarbon concentration (Δ14C) in the Earth’s atmosphere to double. This artificial radiocarbon – the “bomb-14C” diffuses into the surface ocean layer through the air-sea gas exchange of carbon dioxide and acts as a useful tracer to study the water mass mixing such as upwelling and advection. Δ14C have been used to reconstruct water mass mixing using reef-building corals in low latitudes (e.g. Hirabayashi et al., 2017, 2019), but limited in high latitude waters where corals are absent (Kubota et al., 2018; Ota et al., 2019). Previous study (Ota et al., 2019) shows the capability of Ezo abalone shells for reconstruction of water mass variation for more than four years, as well as seasonal high-resolution Δ14C measurement. However, systematic comparison with water Δ14C has not been carried out.
In this study, we measured Δ14C values of shells of Ezo abalone (Haliotis discus hannai) and Δ14C values of seawater using a single-stage accelerator mass spectrometer (AMS) at the University of Tokyo, and then compared the Δ14C values and patterns of shells and seawater samples. Both the abalone shells and seawater were collected at the entrance part of Otsuchi Bay in 2022 May and June. Otsuchi Bay is located on the Sanriku Coast facing the Northwest Pacific Ocean where complex mixing of various water masses occurs. In the surface ocean layer, the Tsugaru current from the Japan Sea joins the cold, Δ14C-depleted Oyashio Current from the subarctic North Pacific and meets the warm, Δ14C-enriched Kuroshio current from the subtropical North Pacific. Understanding the horizontal and vertical mixing of ocean water masses is of great importance to local ecosystems and livelihood. This is the first comparison of Δ14C values of abalone shells and seawater from the same time and location. We will discuss the results and potential of the abalone shells as a paleoclimate archive during the presentation.
Reference:
At the end of the Japanese abstract.