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，人们知道，海水中溶解氧（O2）的氧同位素测量可以区分两种类型的氧，一种来自与空气O2的气体交换，另一种来自海洋中的光合作用。 溶解氧中过量的17 O（del 17 O）使得有可能估计海水中每种类型的氧的比例。重要的是，溶解O2的del 17 O是一种独特的保守示踪剂，不受呼吸作用的影响，从而保留了在深水区的上层水源区获得的签名。一般来说，del 17 O在透光层的上层沃茨含量较高，但不受与大气进行气体交换的影响。这样的水存在于整个海洋的季节性温跃层中。在探索性研究早期概念补助金（EAGER）的资助下，哥伦比亚大学拉蒙道格拉斯地球观测站的研究人员将测量北太平洋和东北大西洋深层海水中的del 17 O，以评估小冰期（LIA）期间北大西洋海冰覆盖的范围。他们假设海冰下海水的del 17 O也会很高，这是由于光的穿透和空气-水气体交换的缺乏。 这一假设可以解释新的观测结果，即南极底层水（AABW）中的高del 17 O来自海冰丰富的地区，但北大西洋深层水（NADW）中的高del 17 O来自无海冰的表层水。一个令人惊讶的观察是，南大西洋的NADW在del 17 O中很高，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。如果这一假设是正确的，那么北太平洋深处将含有高del 17 O值的溶解O2。同样，北大西洋东部盆地的旧深水也将具有高del 17 O。 更广泛的影响：如果上述假设得到证实，这项工作将为获得最近过去气候历史的新见解开辟一条道路。因此，它将通过引入一种独特的方式来追踪水团的历史，从而使广大的海洋学界受益。同样，它将通过提供一种新的方法来重建小冰河时期北大西洋的条件，使研究古气候学的研究人员受益

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