The role of ocean crust low temperature alteration carbonates in the global calcium cycle

大洋地壳玄武岩低温蚀变过程中形成的碳酸钙沉淀（LTA碳酸盐）是全球钙循环中重要的钙汇。据估计，总钙通量约占海洋总钙输出通量的10%。第一次测量的钙同位素组成的LTA碳酸盐指向一个显着的分馏。这表明钙通量对全球海洋钙同位素收支的影响是可测量的。LTA碳酸盐代表了我们对全球钙同位素通量的认识中的一个空白，这可能解释了新近纪同位素收支的差异。因此，我们计划从不同的地点、不同的地壳深度和不同的地壳年龄对LTA碳酸盐进行取样。我们将用氧同位素、微量元素和锶同位素来限制这些沉淀物中钙的来源。然后，我们将测量LTA碳酸盐的钙同位素组成，以估计从海洋到这个重要汇的全球平均同位素通量。该项目将有助于更好地限制钙同位素通量，并为当前钙同位素预算的差异找到解释。这些数据将进一步为不同地壳深度LTA碳酸盐的形成条件提供新的见解。他们将最终显示这些形成条件是否随时间而变化，以及LTA碳酸盐是否可以用作海水钙同位素组成的记录器。有价值的补充信息解释我们的数据预计从一个补充项目（A。克吕格尔湾巴赫;不莱梅大学），其目的是将IODP/ODP岩心中LTA碳酸盐分布的清单与这些碳酸盐脉的微量元素组成和年龄结构的精细调查联合收割机结合起来。因此，我们计划联合采样会议，并调查共同的样本，以保证两个项目的协同作用和数据的可比性。

Calcium carbonate precipitate that form during the low temperature alteration of ocean crust basalts (LTA carbonates) are an important calcium sink in the global calcium cycle. The total calcium flux has been estimated as representing about 10 % of the total Ca output flux of the ocean. First measurements of the calcium isotopic composition of LTA carbonates point to a significant fractionation. This indicates a measureable influence of this calcium flux on the global calcium isotope budget of the oceans. LTA carbonates represent a gap in our knowledge of the global calcium isotope fluxes that may explain discrepancies in the Neogene isotope budget. We therefore plan to sample LTA carbonates from different sites, different crustal depths and different crustal ages. We wil) use oxygen isotopes, trace elements and strontium isotopes to constrain the sources of calcium for these precipitates. We will then measure the calcium isotopic composition of the LTA carbonates to estimate the globally averaged isotope flux from the ocean to this important sink. With that the project will help to better constrain calcium isotope fluxes and to find an explanation for the discrepancies in current calcium isotope budgets. The data will further give new insights in the formation conditions of LTA carbonates at different crustal depths. They will finally show whether these formation conditions varied with time and whether LTA carbonates may be used as recorders of the ocean water calcium isotope composition through time. Valuable supplemental information for the interpretation of our data is expected from a complementary project (A. Klügel, W. Bach; Univ. Bremen) which aims to combine an inventory of the distribution of LTA carbonates in IODP/ODP cores with a fine-scale investigation of the trace elemental composition and age structure of these carbonate veins. Therefore we plan joint sampling sessions and to investigate common samples to guarantee the synergy of the two projects and the comparability of the data.