11:15 AM - 11:30 AM
[MIS15-27] Growth pattern analysis of Mercenaria stimpsoni shells and response to decadal-scale climate change in Abashiri Bay, Hokkaido
Keywords:sclerochronology, shell, periodicity analysis, AMO, PDO
Decadal-scale climate variability, such as the AMO and PDO, is known to cause periodic changes in sea surface temperature. Decadal-scale climate variability is directly linked to meteorological phenomena and is also influence climate changes such as the ENSO and monsoons. However, high temporal resolution and long-term periodic records are needed to understand the behavior of climate change on a multi-decadal scale. One promising paleoclimate archive is the shells of long-lived bivalves.
Recently, it was reported that shell growth line patterns of the long-lived bivalve Mercenaria stimpsoni, from the coast of Iwate correlate with AMO (Shirai et al., 2018). Although the record of growth pattern of a single shell is only about 100 years, by combining the shell growth patterns of multiple individuals, it is possible to reconstruct climate change longer than an individual longevity (Kubota et al., 2021). If the effects of AMO had reached the Pacific Ocean, these effects would have also been recorded on the other shells living in other coastal areas. In this study, we analyzed shell growth patterns of the Abashiri Bay, Hokkaido, to examine the relationship between the effects of climate and temperature fluctuations over several decades.
Abashiri Bay, Hokkaido, is a bay that opens to the Pacific Ocean (about 12m depth, with a sandy bottom). Sea surface temperature has been measured almost every day since 1982, and the average water temperature is 6.8°C, the average maximum temperature is 20.9°C, and the average minimum temperature is -1.8°C. Water temperature has varied from -5°C to 23°C from 1982 to 2021.
For the shell growth pattern analysis, we used shells from Abashiri Bay, Hokkaido, Japan. Shells were frozen, thawed, washed with soft-body parts removed, and dried at room temperature. Shell cut along the maximum growth axis, and the cross sections were polished. Thick sections were photographed with KEYENCE VHX-2000, and the number and width of growth lines were measured using imageJ. Growth increment widths were measured using both the Vertical and Interface methods. Next, we corrected the growth-derived trends from the growth patterns and extracted the environment-derived signals only. We then constructed a chronology SGI, which is the environment-derived signals extracted from shell growth patterns. The constructed chronological SGI was used for comparison with water temperature and multi-decadal-scale climate change.
The chronological SGI extracted from shells in Abashiri Bay, Hokkaido, was not correlated with PDO, but was correlated with water temperature variation and AMO. This correlation was independent of the method used to measure shell growth increment width. The chronological SGI of the Hokkaido, like the chronological SGI of the Iwate, was correlated with the AMO, suggesting that either (1) the Pacific Ocean was likely influenced by the AMO or (2) the controlling parameters other than water temperature may have had a similar periodicity to that of the AMO. This study could not clarify the physical mechanism of this phenomenon. Application of the methods developed in this study to fossil M. stimpsoni would allow us to reconstruct the cycle and intensity of climate change during past interglacial periods.
Recently, it was reported that shell growth line patterns of the long-lived bivalve Mercenaria stimpsoni, from the coast of Iwate correlate with AMO (Shirai et al., 2018). Although the record of growth pattern of a single shell is only about 100 years, by combining the shell growth patterns of multiple individuals, it is possible to reconstruct climate change longer than an individual longevity (Kubota et al., 2021). If the effects of AMO had reached the Pacific Ocean, these effects would have also been recorded on the other shells living in other coastal areas. In this study, we analyzed shell growth patterns of the Abashiri Bay, Hokkaido, to examine the relationship between the effects of climate and temperature fluctuations over several decades.
Abashiri Bay, Hokkaido, is a bay that opens to the Pacific Ocean (about 12m depth, with a sandy bottom). Sea surface temperature has been measured almost every day since 1982, and the average water temperature is 6.8°C, the average maximum temperature is 20.9°C, and the average minimum temperature is -1.8°C. Water temperature has varied from -5°C to 23°C from 1982 to 2021.
For the shell growth pattern analysis, we used shells from Abashiri Bay, Hokkaido, Japan. Shells were frozen, thawed, washed with soft-body parts removed, and dried at room temperature. Shell cut along the maximum growth axis, and the cross sections were polished. Thick sections were photographed with KEYENCE VHX-2000, and the number and width of growth lines were measured using imageJ. Growth increment widths were measured using both the Vertical and Interface methods. Next, we corrected the growth-derived trends from the growth patterns and extracted the environment-derived signals only. We then constructed a chronology SGI, which is the environment-derived signals extracted from shell growth patterns. The constructed chronological SGI was used for comparison with water temperature and multi-decadal-scale climate change.
The chronological SGI extracted from shells in Abashiri Bay, Hokkaido, was not correlated with PDO, but was correlated with water temperature variation and AMO. This correlation was independent of the method used to measure shell growth increment width. The chronological SGI of the Hokkaido, like the chronological SGI of the Iwate, was correlated with the AMO, suggesting that either (1) the Pacific Ocean was likely influenced by the AMO or (2) the controlling parameters other than water temperature may have had a similar periodicity to that of the AMO. This study could not clarify the physical mechanism of this phenomenon. Application of the methods developed in this study to fossil M. stimpsoni would allow us to reconstruct the cycle and intensity of climate change during past interglacial periods.