EAGER: The 17O-excess of dissolved O2 in the deep-sea: A possible tracer of Little Ice Age oceanography

从以前的工作中，我们知道，对海水中溶解氧（O2）的氧同位素测量可以区分两种类型的氧气，一种来自与空气中的氧气交换，另一种来自海洋中的光合作用。溶解氧（del 17O）中超过17O的含量使我们有可能估算出一片海水中每种氧的比例。重要的是，溶解O2的del 17O是一种独特的保守示踪剂，不受呼吸作用的影响，因此保留了在深水块的上游水源区域获得的特征。一般而言，del 17O在位于光区但不受与大气气体交换影响的上层水域中较高。这种水在整个海洋的季节性温跃层中都有。哥伦比亚大学拉蒙特·多尔蒂地球观测站的研究人员将利用“探索性研究早期概念基金”（EAGER）的资助，测量北太平洋深处和东北大西洋海水中的del 17O，以评估小冰期（LIA）期间北大西洋海冰覆盖的范围。他们假设，由于光的穿透和空气-水-气体交换的缺乏，海冰下海水的del 17O也会很高。这一假说可以解释新的观测结果，即来自海冰丰富地区的南极底水（AABW） del 17O高，而来自无海冰地表水的北大西洋深水（NADW） del 17O高。一个令人惊讶的观察结果是，南大西洋的NADW在17O年很高，这表明南部的高值是小冰期的残余，当时北大西洋有更广泛的海冰。如果这个假设是正确的，那么北太平洋深处将含有高del 17O值的溶解氧。同样，北大西洋东部盆地的老深水也会有很高的del 17O。这个项目将决定情况是否确实如此。更广泛的影响：如果上述假设得到证实，这项工作将为获得对近期气候历史的新见解开辟一条道路。因此，它将引入一种独特的方法来追踪水团的历史，从而使广大的海洋学界受益。同样，它将为研究古气候学的研究人员提供一种重建北大西洋小冰期条件的新方法

From previous work, it is known that oxygen isotope measurements of dissolved oxygen (O2) in seawater make it possible to distinguish between two types of oxygen, one derived from gas exchange with air O2 and the other produced by photosynthesis in the ocean. The excess of 17O in dissolved oxygen (del 17O) makes it possible to estimate the proportions of each type of oxygen in a parcel of seawater. And importantly, del 17O of dissolved O2 is a unique conservative tracer that is not affected by respiration and thus preserves the signature acquired at the upper water source regions of deep water masses. In general, del 17O is high in upper waters situated in the photic zone but that are not affected by gas exchange with the atmosphere. Such water is found in the seasonal thermocline all over the ocean. With funding from this Early Concept Grant for Exploratory Research (EAGER), researchers at the Lamont Dougherty Earth Observatory of Columbia University will measure del 17O in seawater of the deep North Pacific and NE Atlantic in order to evaluate the extent of sea-ice cover in the North Atlantic during the Little Ice Age (LIA). They hypothesize that the del 17O of seawater under sea ice will also be high due to light penetration and absence of air-water gas exchange. This hypothesis can explain new observations showing high del 17O in Antarctic Bottom Water (AABW) that originate from regions where sea ice is abundant, but not in North Atlantic Deep Water (NADW) originating from sea-ice free surface water. A surprising observation is that NADW in the South Atlantic is high in del 17O, and it is suggested that the high values in the south are a remnant from the Little Ice Age when the North Atlantic had more extensive sea ice. If the hypothesis is correct, then the deep North Pacific would contain dissolved O2 with high values of del 17O. Likewise, old deep water in the east basin of the North Atlantic would also have high del 17O. This project will determine whether or not that is indeed the case.Broader Impacts: If the hypothesis above is proven, this work will open a way to gaining new insights on climatic history of the recent past. As such, it will benefit the broad oceanographic community by introducing a unique way to trace the history of water masses. Likewise, it will benefit researchers dealing with paleo-climatology by providing a new way to reconstruct conditions of the North Atlantic during the Little Ice Age