11:30 AM - 11:45 AM
[MIS15-28] 100-year climate reconstruction using Sr/Ca ratio and nitrogen isotope in modern Hawaiian coral skeletons
Keywords:Hawaii, coral skeletons, Sr/Ca ratio, Nitrogen Isotope
Hawaiian Islands are located at the central region of North Pacific Ocean where distinct interannual to interdecadal seawater temperature and nutrient variability exist. Despite the importance for observing climate change at the limited influence from the continental/terrestrial factors, there are scarce long-term records from in situ observations around Hawaiian Islands.
Reef coral skeletons provides high-resolution archives of changes of the past marine environment. Geochemical proxies such as Sr/Ca ratio, have been used in tracking seawater temperature for paleoclimate reconstructions in tropical regions. Also, nitrogen isotopes of organic matter in coral skeletons (δ15Ncoral) can be used to investigate seawater circulation as a nutrient tracer.
Modern Porites sp. coral cores sampled at eastern and western side of Oahu Island, were used in this study. X-ray photo of the coral slabs were used to determine maximum growth axis as measurement line. Coral powders were obtained at 0.2 ~0.4 mm intervals using a micro drill and Sr/Ca was analyzed using inductively coupled plasma optical emission spectrometer (ICP-OES). Age model for the Sr/Ca profile was made by anchoring the timing of maxima (minima) of Sr/Ca to the minima (maxima) of reference temperature records. Relationship between Sr/Ca and in situ temperature were used to reconstruct 100 years and 70 years of seawater temperature for west and east side of Oahu, respectively. The seawater temperature difference between east and west side during the overlapping period (1957 ~ 2015) showed interannual to interdecadal variability with an amplitude of approximately ±2℃, which was correlated to northeastern winds intensity (m/s). The windward eastern (leeward western) seawater temperature was higher when northeastern wind was stronger (weaker). Wind-driven dynamics such as the seawater upwelling at the leeward side, which brings nutrient rich seawater from mid-depth to the surface, could be a reason for the local temperature difference. For the δ15Ncoral analysis, the skeletal samples were cut out for one year according to the age model estimated from the Sr/Ca ratio (seawater temperature). After being demineralized with hydrochloric acid, the organic nitrogen in residual organic matter was oxidized to NO3-, and the NO3- was chemically converted to N2O and introduced into a continuous-flow mass spectrometry system. The δ15Ncoral of west side Oahu showed interannual variability, with average value of +4.2‰(±1.5‰, 1σ).
In this presentation, we discuss how local climate changes in the last 100 years were manifested among the interaction between atmosphere and ocean at the North Pacific, using records of coral Sr/Ca ratio and nitrogen isotope from both east and west sides.
Reef coral skeletons provides high-resolution archives of changes of the past marine environment. Geochemical proxies such as Sr/Ca ratio, have been used in tracking seawater temperature for paleoclimate reconstructions in tropical regions. Also, nitrogen isotopes of organic matter in coral skeletons (δ15Ncoral) can be used to investigate seawater circulation as a nutrient tracer.
Modern Porites sp. coral cores sampled at eastern and western side of Oahu Island, were used in this study. X-ray photo of the coral slabs were used to determine maximum growth axis as measurement line. Coral powders were obtained at 0.2 ~0.4 mm intervals using a micro drill and Sr/Ca was analyzed using inductively coupled plasma optical emission spectrometer (ICP-OES). Age model for the Sr/Ca profile was made by anchoring the timing of maxima (minima) of Sr/Ca to the minima (maxima) of reference temperature records. Relationship between Sr/Ca and in situ temperature were used to reconstruct 100 years and 70 years of seawater temperature for west and east side of Oahu, respectively. The seawater temperature difference between east and west side during the overlapping period (1957 ~ 2015) showed interannual to interdecadal variability with an amplitude of approximately ±2℃, which was correlated to northeastern winds intensity (m/s). The windward eastern (leeward western) seawater temperature was higher when northeastern wind was stronger (weaker). Wind-driven dynamics such as the seawater upwelling at the leeward side, which brings nutrient rich seawater from mid-depth to the surface, could be a reason for the local temperature difference. For the δ15Ncoral analysis, the skeletal samples were cut out for one year according to the age model estimated from the Sr/Ca ratio (seawater temperature). After being demineralized with hydrochloric acid, the organic nitrogen in residual organic matter was oxidized to NO3-, and the NO3- was chemically converted to N2O and introduced into a continuous-flow mass spectrometry system. The δ15Ncoral of west side Oahu showed interannual variability, with average value of +4.2‰(±1.5‰, 1σ).
In this presentation, we discuss how local climate changes in the last 100 years were manifested among the interaction between atmosphere and ocean at the North Pacific, using records of coral Sr/Ca ratio and nitrogen isotope from both east and west sides.