Rare earth element and yttrium (REY) compositions of bioapatite (e.g., fish tooth and bone) can serve as potential paleoceanographic indicators. However, the REY enrichment of bioapatite and REY transfer from FeMn micronodule to bioapatite remain unclear owing to a lack of comparative study on these processes under variable redox conditions (oxic vs. suboxic), which hampers the utility of these indicators. To address these uncertainties, we conducted in situ geochemical analyses of fish teeth and FeMn micronodules from two REY-rich sediment cores (GC01 and GC02) collected from the Clarion–Clipperton fracture zone in the central equatorial Pacific. We found that the Ce/Ce* ratios of fish teeth from GC01 (sediments ΣREY = 723 ± 274 ppm) and GC02 (sediments ΣREY = 506 ± 65 ppm) gradually increased with depth under oxic conditions, with calculated oxic pore water-derived REY increasing from ∼0–3% on the surface to ∼11–24% at 200 cmbsf. In deep sediment columns (>200 cmbsf), the suboxic pore water contributed a small amount of REY (∼4% to ∼13%) to fish teeth, as evidenced by sharp increases in Ce/Ce* ratios of fish teeth and decreases in Ce/Ce* ratios and increases in Y/Ho ratios of micronodules. Therefore, the REY-patterns of fish teeth in core-deep samples were overprinted by oxic–suboxic pore waters may be unreliable archives of ancient bottom seawater.

中文翻译：

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深海富REY沉积物生物磷灰石稀土元素富集过程


生物磷灰石（例如鱼牙和鱼骨）的稀土元素和钇（REY）成分可以作为潜在的古海洋指标。然而，生物磷灰石的 REY 富集以及 REY 从 FeMn 微结到生物磷灰石的转移仍不清楚，因为缺乏对可变氧化还原条件（有氧与低氧）下这些过程的比较研究，这阻碍了这些指标的实用性。为了解决这些不确定性，我们对从赤道中部太平洋克拉里昂-克利珀顿断裂带收集的两个富含 REY 的沉积物岩心（GC01 和 GC02）中的鱼牙和 FeMn 微结核进行了原位地球化学分析。我们发现，在有氧条件下，GC01（沉积物ΣREY = 723 ± 274 ppm）和GC02（沉积物ΣREY = 506 ± 65 ppm）鱼牙的Ce/Ce*比率随着深度的增加而逐渐增加，并计算出含氧孔隙水的REY在 200 cmbsf 处，从表面的 ∼0–3% 增加到 ∼11–24%。在深层沉积物柱（> 200 cmbsf）中，低氧孔隙水向鱼齿贡献了少量 REY（∼4% 至∼13%），鱼齿的 Ce/Ce* 比率急剧增加和鱼齿的 REY 比率下降证明了这一点。微结节的 Ce/Ce* 比率和 Y/Ho 比率的增加。因此，深部样品中的鱼齿REY图案被含氧-缺氧孔隙水叠印，可能是古代海底海水的不可靠档案。