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Interhemispheric leakage of isotopically heavy nitrate in the eastern tropical Pacific during the last glacial period

机译：上一个冰川期热带东部太平洋同位素重硝酸盐的半球间泄漏

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We present new high-resolution N isotope records from the Gulf of Tehuantepec and the Nicaragua Basin spanning the last 50-70 ka. The Tehuantepec site is situated within the core of the north subtropical denitrification zone while the Nicaragua site is at the southern boundary. The 6 15N record from Nicaragua shows an "Antarctic" timing similar to denitrification changes observed off Peru-Chile but is radically different from the northern records. We attribute this to the leakage of isotopically heavy nitrate from the South Pacific oxygen minimum zone (OMZ) into the Nicaragua Basin. The Nicaragua record leads the other eastern tropical North Pacific (ETNP) records by about 1000 years because denitrification peaks in the eastern tropical South Pacific (ETSP) before denitrification starts to increase in the Northern Hemisphere OMZ, i.e., during warming episodes in Antarctica. We find that the influence of the heavy nitrate leakage from the ETSP is still noticeable, although attenuated, in the Gulf of Tehuantepec record, particularly at the end of the Heinrich events, and tends to alter the recording of millennial timescale denitrification changes in the ETNP. This implies (1) that sedimentary 615N records from the southern parts of the ETNP cannot be used straightforwardly as a proxy for local denitrification and (2) that denitrification history in the ETNP, like in the Arabian Sea, is synchronous with Greenland temperature changes. These observations reinforce the conclusion that on millennial timescales during the last ice age, denitrification in the ETNP is strongly influenced by climatic variations that originated in the highlatitude North Atlantic region, while commensurate changes in Southern Ocean hydrography more directly, and slightly earlier, affected oxygen concentrations in the ETSP. Furthermore, the 6 15N records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50-70 ka.
机译：我们提供了最近50-70 ka的Tehuantepec海湾和尼加拉瓜盆地的高分辨率N同位素新记录。 Tehuantepec厂址位于北亚热带反硝化区的核心内，而Nicaragua厂址位于南部边界。尼加拉瓜的6 15N记录显示了一个“南极”时机，类似于在秘鲁-智利附近观察到的反硝化变化，但与北部记录完全不同。我们将其归因于同位素重硝酸盐从南太平洋氧气最小带（OMZ）泄漏到尼加拉瓜盆地。尼加拉瓜的记录领先其他东部热带北太平洋（ETNP）记录约1000年，因为北半球OMZ（即在南极洲变暖期间）反热带开始增加之前，东部热带南太平洋（ETSP）的反硝化峰值。我们发现，ETSP硝酸盐大量泄漏的影响在Tehuantepec海湾记录中，尽管减弱了，但仍然很明显，尤其是在海因里希事件结束时，并且倾向于改变ETNP中千年时间尺度反硝化变化的记录。 。这意味着（1）不能直接将ETNP南部的615N沉积记录用作局部反硝化的代理，（2）ETNP（如阿拉伯海）的反硝化历史与格陵兰的温度变化同步。这些观察结果进一步证实了这样一个结论，即在上一个冰河时代的千年尺度上，ETNP的反硝化作用受到高纬度北大西洋地区起源的气候变化的强烈影响，而南大洋水文学的相应变化则更直接，更早地影响了氧气ETSP中的浓度。此外，这6个15N记录表明，在过去的50-70 ka内，持续不断地穿越浅层地下赤道的物理通信。

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