A mechanistic investigation of the coral Mn/Ca-based trade-wind proxy at Kiritimati
A mechanistic investigation of the coral Mn/Ca-based trade-wind proxy at Kiritimati
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Kiritimati 珊瑚锰/钙信风代理的机械研究
DOI：
10.1016/j.gca.2022.04.030
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发表时间：
2022
影响因子：
5
通讯作者：
Cobb, Kim M.
中科院分区：
文献类型：
--
作者：
Chapman, Alice U.;Thompson, Diane M.;Hlohowskyj, Stephan R.;Carilli, Jessica E.;Gordon, Gwyneth;Goepfert, Tyler J.;Sayani, Hussein R.;Marchitto, Thomas M.;Cobb, Kim M.
热带太平洋信风的行为与厄尔尼诺-南方涛动和太平洋年代际变率有关，它们调节着气候变化的速度。尽管高分辨率信风观测很重要，但其时间跨度仅为过去30-40年，而且太少，无法评估十年风变率和长期趋势。以前的工作表明，生长在热带太平洋塔拉瓦岛（2°N，165°E）的造礁珊瑚在应对信风逆转时（即，西风）。因此，长寿珊瑚的Mn/Ca记录很有希望作为过去信风变化的指标。然而，在其他邻近岛屿与西向泻湖，有西风和珊瑚锰/钙尖峰之间的滞后和珊瑚之间的尖峰幅度的显着差异。为了解决珊瑚Mn/Ca记录风的不确定性，我们评估了沉积物、沉积物孔隙空间（孔隙水）和Kiritimati泻湖和内陆湖泊（1.9°N，157.5°W）水柱中的Mn库。我们发现，不溶性粉尘锰，一旦埋在泻湖沉积物中，变得减少和更可溶，导致其在沉积物孔隙水的积累。这锰水库，然后释放到水柱时，强烈的西风事件导致足够的水柱混合，达到泻湖沉积物。虽然这一机制与先前在塔拉瓦提出的一致，但塔拉瓦的溶解孔隙水Mn浓度比Kiritimati高近20倍。我们将这种差异归因于孔隙水取样的沉积物芯的水深和最近的西风事件和芯取样之间所经过的时间，这两者都影响孔隙水Mn库的“补给时间”。因此，泻湖水深和形态调节泻湖水和沉积物孔隙水锰浓度，影响西风如何将其信号印到珊瑚锰/钙。通过对这种珊瑚Mn/Ca-信风关系背后机制的更好理解，我们可以更好地评估这种珊瑚代理在空间和时间上的可靠性，并确定基于Mn/Ca的风重建的最佳地点，为风在未来气候变化中的作用的关键新见解铺平道路。
Tropical Pacific trade-wind behavior is linked to the El Niño-Southern Oscillation and Pacific Decadal Variability, which modulate the rate of climate change. Despite their importance, high-resolution trade-wind observations span only the past 30–40 years and are too sparse to assess decadal wind variability and long-term trends. Previous work demonstrated that reef-building corals growing at the tropical Pacific island of Tarawa (2°N, 165°E) exhibit spikes in the manganese-to-calcium ratio (Mn/Ca) of their skeleton in response to a reversal of trade winds (i.e., westerly winds). Records of Mn/Ca from long-lived corals therefore hold great promise as indicators of past trade-wind variability. However, at other nearby islands with west-facing lagoons, there is a lag between westerly winds and coral Mn/Ca spikes and a significant difference in the magnitude of spikes between corals. To address uncertainties in how winds are recorded by coral Mn/Ca, we assess the reservoirs of Mn in the sediment, sediment pore spaces (porewater), and water column of Kiritimati’s lagoon and inland lakes (1.9°N, 157.5°W). We find that insoluble dustborne Mn, once buried in lagoon sediments, becomes reduced and more soluble, leading to its accumulation in the sediment porewater. This Mn reservoir is then released into the water column when strong westerly wind events cause sufficient water-column mixing to reach lagoonal sediments. While this mechanism is consistent with what was previously proposed at Tarawa, the concentration of dissolved porewater Mn at Tarawa is nearly 20 times greater than at Kiritimati. We attribute this difference to the water depth of the sediment core from which porewater was sampled and the time elapsed between the most recent westerly wind event and core sampling, which both influence the “recharge time” of the porewater Mn reservoir. As such, lagoon bathymetry and morphology modulate lagoon water and sediment porewater Mn concentrations, which impact how westerly winds imprint their signal onto coral Mn/Ca. Armed with an improved understanding of the mechanism behind this coral Mn/Ca-trade wind relationship, we can better assess the reliability of this coral proxy through space and time and identify optimal sites for Mn/Ca-based wind reconstructions, paving the way for critical new insights into the role of winds in future climate change.