Improving seawater chemistry reconstructions using the biogenic silica archive

Exp. 395的主要目标之一是研究北大西洋海洋环流的变化与岩浆脉冲引起的测深变化之间的联系。利用实验395C期间收集的额外沉积物，我将针对支持这一总体巡航目标的两个问题。第一个问题是，我们能否定量地了解生物成因二氧化硅氧同位素组成的沉积后变化？生物硅是沉积记录的重要组成部分。超过50%的全球初级生产是由于硅藻，而高纬度环境保存生物硅远比其他流行的古档案（碳酸盐）。然而，在硅藻中观察到的抵消很难量化，这使得人们很难理解海洋中有多少原始化学信号被保存在这个化石中。因此，在我们能够自信地使用这个档案之前，我们需要提高我们的理解。该目标的目的是准确识别沉积序列中特定深度影响生物成因二氧化硅的成岩作用量，使硅藻和海绵针状化石更有信心地应用于气候重建。我将使用先进分析（碳酸盐团块同位素分析和三氧同位素分析）的新颖组合，对来自相同岩心材料样品的碳酸盐和生物成因硅化石进行分析，以解决这个问题。第二个问题是，在Exp. 395C地点观察到的初始沉积模式与什么过程有关？如果有的话，这些过程与循环的变化有什么关系？Exp. 395（计划于2023年进行）和Exp. 395C都有一个首要的主要巡航目标，即了解冰岛羽流的岩浆脉冲是否引起了深海环流的变化。该地区环流与北大西洋深水形成直接相关，对全球气候有重大影响。最初沉积在该地区新洋板块上的沉积物，无论年龄如何，似乎都非常相似（从Exp. 395C的初始岩心照片中可以观察到）。这些最初的沉积物也与上覆的沉积物截然不同，上覆的沉积物更类似于北大西洋上通常发现的沉积物。破译导致观察到的不同模式的原因和机制将使我们了解在沉积开始时该地区发生了什么，并确定这些初始沉积物是否适合限制环流的变化。

One of the primary goals of Exp. 395 is to examine the connection between changes in oceanic circulation in the North Atlantic and changes in bathymetry due to magmatic pulsing. Using the additional sediment collected during Exp. 395C, I will target two questions which support this overarching cruise goal. The first question is, can we quantitatively understand post-depositional changes in the oxygen isotope composition of biogenic silica? Biogenic silica is an important component of the sedimentary record. Over 50% of global primary production is due to diatoms, while high latitude environments preserve biogenic silica far better than the other popular palaeo-archive (carbonate). However, difficult to quantify offsets have been observed in diatoms, making it difficult understanding how much of the original chemical signal of the ocean is preserved in this fossil. Consequently, we need to improve our understanding before we can use this archive with confidence. The aim of this objective is to accurately identify the amount of diagenesis affecting biogenic silica at specific depths in the sedimentary sequence, enabling more confident application of diatom and sponge spicule fossils for climate reconstructions. I will use a novel combination of advanced analyses (carbonate clumped isotope analysis and triple oxygen isotope analysis) on both carbonate and biogenic silica fossils from the same samples of core material to tackle this problem.The second question is, what processes are related to the patterns of initial sedimentation observed at the Exp. 395C sites? And how, if at all, are these processes related to changes in circulation? Exp. 395 (scheduled for 2023) and Exp. 395C both have the overarching major cruise objective of understanding whether magmatic pulsing of the Iceland plume has caused changes in deep oceanic circulation. Circulation in this region is directly related to deep water formation in the North Atlantic, which has a major influence on global climate. The sediments initially deposited on new oceanic plate in the region, regardless of age, seem to be incredibly similar (as observed from initial core photos from Exp. 395C). These initial sediments are also strikingly different from overlying sediments which are more similar to those normally found across the North Atlantic. Deciphering the causes and mechanisms leading to the different patterns observed will allow us to understand what was happening in the region during the onset of sedimentation and determine if these initial sediments are suitable for constraining changes in circulation.