Capturing Equatorial Pacific Variability with Multivariate Sr‐U Coral Thermometry

IF 3.2 2区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Paleoceanography and Paleoclimatology Pub Date : 2023-10-01 DOI:10.1029/2022pa004508

N. R. Mollica, A. L. Cohen, F. Horton, Delia W. Oppo, Andrew S. Solow, David McGee

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Abstract

Abstract Sr‐U, a coral‐based paleothermometer, corrects for the effects of Rayleigh Fractionation on Sr/Ca by regressing multiple, paired U/Ca and Sr/Ca values. Prior applications of Sr‐U captured mean annual sea surface temperatures (SSTs), inter‐annual variability, and long‐term trends. However, because many Sr/Ca‐U/Ca pairs are needed for a single Sr‐U value as originally formulated, the temporal resolution of the proxy is typically limited to 1 year. Here, we address this limitation by applying laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) to three Porites colonies from Jarvis and Nikumaroro Islands in the central equatorial Pacific (CEP), generating ∼25 Sr/Ca‐U/Ca pairs per month of skeletal growth. Both Sr/Ca and U/Ca vary significantly over small (sub‐mm) length scales and support the calculation of Sr‐U values using the original regression method. Over the represented temperature range of 24–31°C, the Sr/Ca‐U/Ca‐SST relationships are nonlinear, a finding consistent with predictions of the Rayleigh model. To reflect this non‐linearity, we developed a calibration using multivariate nonlinear regression. The multivariate, three‐coral calibration was applied to 20 years of monthly resolved Sr/Ca and U/Ca of a coral interval not included in the calibration, yielding RMSE = 0.73°C and r 2 = 0.85 ( p < 0.05; df = 256). The multivariate calibration performed significantly better than Sr/Ca alone ( r 2 = 0.28). Applying the new calibration to a subfossil Porites from Kiritimati Atoll, CEP (2200 Before Present) yields equivalent phase and amplitude of interannual variability, but water temperatures ∼1.6°C cooler than they are in this region today.

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用多变量Sr - U珊瑚测温法捕获赤道太平洋变率

Sr - U是一种基于珊瑚的古温度表，通过回归多个成对的U/Ca和Sr/Ca值来校正瑞利分选对Sr/Ca的影响。Sr - U的先前应用捕获了年平均海面温度(SSTs)、年际变率和长期趋势。然而，由于最初制定的单个Sr - U值需要许多Sr/Ca‐U/Ca对，因此代理的时间分辨率通常限制在1年。在这里，我们通过将激光烧蚀电感耦合等离子体质谱(LA‐ICPMS)应用于赤道太平洋中部(CEP) Jarvis和Nikumaroro群岛的三个Porites群落来解决这一限制，每月产生约25对Sr/Ca‐U/Ca对骨骼生长。Sr/Ca和U/Ca在小(亚毫米)长度尺度上变化显著，支持使用原始回归方法计算Sr - U值。在24-31°C的温度范围内，Sr/Ca‐U/Ca‐SST的关系是非线性的，这一发现与瑞利模式的预测一致。为了反映这种非线性，我们开发了一个使用多元非线性回归的校准。多变量三珊瑚校准应用于未包括在校准中的珊瑚区间的20年月度分解Sr/Ca和U/Ca，得到RMSE = 0.73°C和r2 = 0.85 (p <0.05;Df = 256)。多变量校准效果明显优于单独使用Sr/Ca (r 2 = 0.28)。将新的校准应用于基里蒂玛蒂环礁的亚化石Porites, CEP(2200年前)得到了等效的年际变率的相位和幅度，但水温比该地区今天的水温低1.6°C。

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来源期刊

Paleoceanography and Paleoclimatology Earth and Planetary Sciences-Atmospheric Science

CiteScore

6.20

自引率

11.40%

发文量

107

期刊介绍： Paleoceanography and Paleoclimatology (PALO) publishes papers dealing with records of past environments, biota and climate. Understanding of the Earth system as it was in the past requires the employment of a wide range of approaches including marine and lacustrine sedimentology and speleothems; ice sheet formation and flow; stable isotope, trace element, and organic geochemistry; paleontology and molecular paleontology; evolutionary processes; mineralization in organisms; understanding tree-ring formation; seismic stratigraphy; physical, chemical, and biological oceanography; geochemical, climate and earth system modeling, and many others. The scope of this journal is regional to global, rather than local, and includes studies of any geologic age (Precambrian to Quaternary, including modern analogs). Within this framework, papers on the following topics are to be included: chronology, stratigraphy (where relevant to correlation of paleoceanographic events), paleoreconstructions, paleoceanographic modeling, paleocirculation (deep, intermediate, and shallow), paleoclimatology (e.g., paleowinds and cryosphere history), global sediment and geochemical cycles, anoxia, sea level changes and effects, relations between biotic evolution and paleoceanography, biotic crises, paleobiology (e.g., ecology of “microfossils” used in paleoceanography), techniques and approaches in paleoceanographic inferences, and modern paleoceanographic analogs, and quantitative and integrative analysis of coupled ocean-atmosphere-biosphere processes. Paleoceanographic and Paleoclimate studies enable us to use the past in order to gain information on possible future climatic and biotic developments: the past is the key to the future, just as much and maybe more than the present is the key to the past.