Department of Ecology and Evolution, University of Chicago, Chicago, Illinois, United States of America.
PLoS One. 2011;6(10):e25766. doi: 10.1371/journal.pone.0025766. Epub 2011 Oct 3.
The anthropogenic input of fossil fuel carbon into the atmosphere results in increased carbon dioxide (CO(2)) into the oceans, a process that lowers seawater pH, decreases alkalinity and can inhibit the production of shell material. Corrosive water has recently been documented in the northeast Pacific, along with a rapid decline in seawater pH over the past decade. A lack of instrumentation prior to the 1990s means that we have no indication whether these carbon cycle changes have precedence or are a response to recent anthropogenic CO(2) inputs. We analyzed stable carbon and oxygen isotopes (δ(13)C, δ(18)O) of decade-old California mussel shells (Mytilus californianus) in the context of an instrumental seawater record of the same length. We further compared modern shells to shells from 1000 to 1340 years BP and from the 1960s to the present and show declines in the δ(13)C of modern shells that have no historical precedent. Our finding of decline in another shelled mollusk (limpet) and our extensive environmental data show that these δ(13)C declines are unexplained by changes to the coastal food web, upwelling regime, or local circulation. Our observed decline in shell δ(13)C parallels other signs of rapid changes to the nearshore carbon cycle in the Pacific, including a decline in pH that is an order of magnitude greater than predicted by an equilibrium response to rising atmospheric CO(2), the presence of low pH water throughout the region, and a record of a similarly steep decline in δ(13)C in algae in the Gulf of Alaska. These unprecedented changes and the lack of a clear causal variable underscores the need for better quantifying carbon dynamics in nearshore environments.
人为将化石燃料碳输入大气会导致二氧化碳（CO2）大量进入海洋，这一过程会降低海水 pH 值、减少碱度，并可能抑制壳材的生成。最近在东北太平洋已经记录到腐蚀性水，而在过去十年中，海水 pH 值迅速下降。在 20 世纪 90 年代之前，由于仪器设备的缺乏，我们无法确定这些碳循环变化是先发生的，还是对最近人为 CO2 输入的响应。我们分析了具有相同长度仪器记录的海水中 decade-old California mussel 壳（Mytilus californianus）的稳定碳和氧同位素（δ13C，δ18O）。我们进一步将现代贝壳与来自 1000 到 1340 年 BP 和 20 世纪 60 年代至今的贝壳进行了比较，并发现现代贝壳的 δ13C 值下降，这在历史上是没有先例的。我们发现另一种有壳软体动物（帽贝）的 δ13C 值也在下降，并且我们广泛的环境数据表明，这些贝壳 δ13C 值的下降不能用沿海食物网、上升流制度或局部环流的变化来解释。我们观察到的贝壳 δ13C 值下降与太平洋近岸碳循环的其他快速变化迹象相吻合，包括 pH 值下降幅度比根据大气 CO2 上升的平衡响应预测的要大一个数量级，整个地区都存在低 pH 值水，以及阿拉斯加湾藻类中 δ13C 值同样急剧下降的记录。这些前所未有的变化以及缺乏明确的因果变量，突显了需要更好地量化近岸环境中的碳动态。
