This study presents a high-resolution record of Cu and Zn isotopes in four Fe-Mn crusts from the North and South Pacific oceans. North Pacific crusts were collected on the Apuupuu seamount south of the Hawaiian archipelago and South Pacific crusts were recovered near Rurutu Island in the Tahiti archipelago. Major and trace element compositions suggest that Cu and Zn in these crusts is of hydrogenous origin, i.e., precipitated from seawater, and they may therefore mirror deep seawater metal isotope. We show that Cu and Zn display different isotopic patterns between the North and the South Pacific Oceans but show similar temporal evolution within each geographical area. Copper and Zn isotope composition of both North Pacific crusts vary between 0.57 ‰ to 0.73 ‰ for δ^65/63Cu_NIST976 and 0.97 ‰ to 1.25 ‰ for δ^66/64Zn_JMC-Lyon. In contrast, South Pacific crusts show resolvable temporal variations, with Cu and Zn isotopic ratios increasing sharply over the last ∼ 6 Ma from 0.16 ‰ to 0.51 ‰ and 0.67 ‰ to 1.09 ‰ respectively. Notably, we observed a positive correlation between δ^65/63Cu_NIST976 and δ^66/64Zn_JMC-Lyon values in Fe-Mn crusts from the South Pacific. The correlation suggests mixing between two components in Fe-Mn crusts, a hydrothermal component with δ^65/63Cu_NIST976 ∼ 0.2 ‰ and δ^66/64Zn_JMC-Lyon ∼ 0.7 ‰, and a Pacific deep seawater component with δ^65/63Cu_NIST976 ∼ 0.7 ‰ and δ^66/64Zn_JMC-Lyon ∼ 1.2 ‰. These values are fractionated from modern dissolved Cu and Zn by a factor of −0.3 ‰ and 0.5 ‰ respectively. We suggest that the deep Southern Pacific Ocean received sustained hydrothermal input during the last 6 Ma, which was recorded in the Cu and Zn isotope composition of Fe-Mn crusts precipitated thousands of kilometers away. Our study highlights that hydrothermal venting may be a significant source of Cu and Zn in the deep oceans despite their extensive precipitation within hydrothermal vent fields. We show that this source could be persistent through time, and thus, it could have a significant impact on the biogeochemical cycling of Cu and Zn in seawater which would ultimately be recorded by Fe-Mn crusts.

本研究提供了来自北太平洋和南太平洋的四种 Fe-Mn 结壳中 Cu 和 Zn 同位素的高分辨率记录。在夏威夷群岛以南的 Apuupuu 海山收集了北太平洋地壳，在大溪地群岛的鲁鲁图岛附近发现了南太平洋地壳。主要和微量元素组成表明，这些结壳中的铜和锌是氢来源的，即从海水中沉淀出来的，因此它们可能反映了深海水金属同位素。我们表明，Cu 和 Zn 在北太平洋和南太平洋之间显示出不同的同位素模式，但在每个地理区域内显示出相似的时间演化。对于δ ^65/63 Cu _NIST976，两个北太平洋地壳的铜和锌同位素组成在 0.57 ‰ 到 0.73 ‰ 之间变化δ ^66/64 Zn _JMC-Lyon为 0.97 ‰ 至 1.25 ‰ 。相比之下，南太平洋地壳呈现出可分辨的时间变化，Cu和Zn同位素比值在过去~6 Ma期间急剧增加，分别从0.16‰增加到0.51‰和0.67‰增加到1.09‰。值得注意的是，我们观察到南太平洋 Fe-Mn 结壳中的δ ^65/63 Cu _NIST976和δ ^66/64 Zn _JMC-Lyon值之间存在正相关关系。相关性表明 Fe-Mn 结壳中的两种成分之间存在混合，一种具有δ ^65/63 Cu _NIST976  ∼ 0.2 ‰ 和δ ^66/64 Zn _{JMC-Lyon的热液成分} ∼ 0.7 ‰, 和δ ^65/63 Cu _NIST976  ∼ 0.7 ‰ 和δ ^66/64 Zn _{JMC-Lyon的太平洋深海水成分} ～1.2‰。这些值分别以-0.3 ‰ 和 0.5 ‰ 的系数从现代溶解的 Cu 和 Zn 中分离出来。我们认为，在过去的 6 Ma 期间，南太平洋深海接受了持续的热液输入，这记录在数千公里外沉淀的 Fe-Mn 结壳的 Cu 和 Zn 同位素组成中。我们的研究强调，尽管热液喷口区域内有大量降水，但热液喷口可能是深海中铜和锌的重要来源。我们表明，这种来源可能会随着时间的推移而持续存在，因此，它可能对海水中铜和锌的生物地球化学循环产生重大影响，最终将被铁锰结壳记录下来。