Complementary constraints from carbon (13C) and nitrogen (15N) isotopes on the glacial ocean's soft‐tissue biological pump
Complementary constraints from carbon (13C) and nitrogen (15N) isotopes on the glacial ocean's soft‐tissue biological pump
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DOI：
10.1002/2015pa002905
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
A. Schmittner;C. Somes
中科院分区：
文献类型：
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作者：
A. Schmittner;C. Somes
海洋的碳和氮循环，包括13 C和15 N同位素的三维，基于过程的模型，用于探索软组织生物泵的理想化变化的影响。结果来自一个工业化前的控制运行（piCtrl）和六个模拟末次冰期最大值（LGM）的增加值的空间恒定的最大浮游植物生长速率μmax，加速生物养分利用模仿铁施肥。默认的LGM模拟，没有增加μmax，大西洋经向翻转环流较浅，较弱，海冰覆盖增加，导致280 Pg更多的呼吸有机碳（Corg）存储在深海中相对于piCtrl。在较冷的冰川温跃层中溶解氧浓度增加，这减少了水柱的反硝化作用，并延迟了固氮作用，从而增加了海洋的固定氮存量，并几乎在所有地方降低了δ 15 NNO 3。该模拟已经相对较好地拟合了碳和氮同位素的沉积物重建，但它高估了深海δ 13 CDIC，低估了高纬度地区的δ 15 NNO 3。增加μmax可提高Corg值，降低深海δ 13 CDIC，从而提高与沉积物数据的一致性。在模型的南极和北太平洋，由于当地营养盐利用的增强，μmax的适度增加导致δ 15 NNO 3的升高，从而提高了与重建的一致性。μmax适度增加的模型最适合两种同位素数据，而养分利用的大幅增加与氮同位素不一致，尽管它们仍然相当好地拟合碳同位素。最佳拟合模型再现了冰川δ 13 CDIC、δ 15 N和氧重建的主要特征，同时模拟了与工业化前海洋相比Corg增加了510-670 Pg。这些结果与软组织泵在LGM期间更有效的想法一致。循环和生物养分利用都可能起作用。然而，这些结论是初步的，我们的理想化的实验，不考虑底栖反硝化作用的变化和空间不均匀的风成铁通量的变化。该分析说明了碳和氮循环之间的相互作用以及它们的同位素提供的互补约束。碳同位素对环流变化敏感，能较好地反映Corg的三维分布，而氮同位素对生物养分利用更为敏感。
A three-dimensional, process-based model of the ocean's carbon and nitrogen cycles, including 13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results are presented from one preindustrial control run (piCtrl) and six simulations of the Last Glacial Maximum (LGM) with increasing values of the spatially constant maximum phytoplankton growth rate μmax, which accelerates biological nutrient utilization mimicking iron fertilization. The default LGM simulation, without increasing μmax and with a shallower and weaker Atlantic Meridional Overturning Circulation and increased sea ice cover, leads to 280 Pg more respired organic carbon (Corg) storage in the deep ocean with respect to piCtrl. Dissolved oxygen concentrations in the colder glacial thermocline increase, which reduces water column denitrification and, with delay, nitrogen fixation, thus increasing the ocean's fixed nitrogen inventory and decreasing δ15NNO3 almost everywhere. This simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well, but it overestimates deep ocean δ13CDIC and underestimates δ15NNO3 at high latitudes. Increasing μmax enhances Corg and lowers deep ocean δ13CDIC, improving the agreement with sediment data. In the model's Antarctic and North Pacific Oceans modest increases in μmax result in higher δ15NNO3 due to enhanced local nutrient utilization, improving the agreement with reconstructions there. Models with moderately increased μmax fit both isotope data best, whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well. The best fitting models reproduce major features of the glacial δ13CDIC, δ15N, and oxygen reconstructions while simulating increased Corg by 510–670 Pg compared with the preindustrial ocean. These results are consistent with the idea that the soft-tissue pump was more efficient during the LGM. Both circulation and biological nutrient utilization could contribute. However, these conclusions are preliminary given our idealized experiments, which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes. The analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes. Whereas carbon isotopes are sensitive to circulation changes and indicate well the three-dimensional Corg distribution, nitrogen isotopes are more sensitive to biological nutrient utilization.