13:45 〜 15:15
[SCG52-P20] 海洋-堆積物間のNd質量収支計算に基づくレアアース泥生成の支配因子の長期変動の検討
キーワード：レアアース泥、ネオジム、質量収支、モデリング、海底堆積物
Deep-sea sediments enriched in rare-earth elements (REE), termed REE-rich mud, is expected as a promising resource for the industrially critical metals [1]. Understanding factors controlling the long-term variations in the grade and distribution of REE-rich mud is important to narrow down promising ocean areas for the future development. Previous studies suggested that a sedimentation rate controls the REE content in deep-sea sediments [2] and that the depositional fluxes of biogenic calcium phosphate (BCP) and eolian dust have significant influence on the grade of REE-rich mud [3]. To quantify the influence of various environmental factors on the REE-rich mud formation and their temporal variation, a theoretical approach via numerical modeling is valuable.
In this study, we constructed a Nd mass balance model considering the interactions between the ocean and sediments, such as the discharge of dissolved elements from sediments to the ocean. Relationships between the eolian dust flux supplied to the ocean and the sedimentation rate are also included in the model. Using this model, we investigated the factors controlling the REE content in the REE-rich mud by a sensitivity analysis. The result showed that the discharge of REE-elements from continental margin to the ocean have a great influence on the REE-enrichment in deep-sea sediments. In addition, we calculated a long-term variation of the REE content in the REE-rich mud considering changes of carbonate compensation depth and eolian dust flux and compared the simulated result with REE concentration data of two sediment cores in the Pacific Ocean. Consequently, while the model reproduced a general long-term trend of REE contents in the REE-rich mud, the absolute value of the modeled REE content were significantly smaller than the observed highly REE-rich layers. An explicit incorporation of the effect of BCP flux would improve the simulated result.
[1] Kato et al. (2011) Nat. Geosci. 4, 535-539. [2] Yasukawa et al. (2016) Sci. Rep. 6, 29603. [3] Mimura (2021) The university of Tokyo, Ph. D. thesis.
In this study, we constructed a Nd mass balance model considering the interactions between the ocean and sediments, such as the discharge of dissolved elements from sediments to the ocean. Relationships between the eolian dust flux supplied to the ocean and the sedimentation rate are also included in the model. Using this model, we investigated the factors controlling the REE content in the REE-rich mud by a sensitivity analysis. The result showed that the discharge of REE-elements from continental margin to the ocean have a great influence on the REE-enrichment in deep-sea sediments. In addition, we calculated a long-term variation of the REE content in the REE-rich mud considering changes of carbonate compensation depth and eolian dust flux and compared the simulated result with REE concentration data of two sediment cores in the Pacific Ocean. Consequently, while the model reproduced a general long-term trend of REE contents in the REE-rich mud, the absolute value of the modeled REE content were significantly smaller than the observed highly REE-rich layers. An explicit incorporation of the effect of BCP flux would improve the simulated result.
[1] Kato et al. (2011) Nat. Geosci. 4, 535-539. [2] Yasukawa et al. (2016) Sci. Rep. 6, 29603. [3] Mimura (2021) The university of Tokyo, Ph. D. thesis.