Offset Between Profiling Float and Shipboard Oxygen Observations at Depth Imparts Bias on Float pH and Derived pCO2

IF 5.4 2区 地球科学 Q1 ENVIRONMENTAL SCIENCES
Seth M. Bushinsky, Zachary Nachod, Andrea J. Fassbender, Veronica Tamsitt, Yuichiro Takeshita, Nancy Williams
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Abstract

Profiles of oxygen measurements from Argo profiling floats now vastly outnumber shipboard profiles. To correct for drift, float oxygen data are often initially adjusted to deployment casts, ship-based climatologies, or, recently, measurements of atmospheric oxygen for in situ calibration. Air calibration enables accurate measurements in the upper ocean but may not provide similar accuracy at depth. Using a quality controlled shipboard data set, we find that the entire Argo oxygen data set is offset relative to shipboard measurements (float minus ship) at pressures of 1,450–2,000 db by a median of −1.9 μmol kg−1 (mean ± SD of −1.9 ± 3.9, 95% confidence interval around the mean of {−2.2, −1.6}) and air-calibrated floats are offset by −2.7 μmol kg−1 (−3.0 ± 3.4 (CI95%{−3.7, −2.4}). The difference between float and shipboard oxygen is likely due to offsets in the float oxygen data and not oxygen changes at depth or biases in the shipboard data set. In addition to complicating the calculation of long-term ocean oxygen changes, these float oxygen offsets impact the adjustment of float nitrate and pH measurements, therefore biasing important derived quantities such as the partial pressure of CO2 (pCO2) and dissolved inorganic carbon. Correcting floats with air-calibrated oxygen sensors for the float-ship oxygen offsets alters float pH by a median of 3.0 mpH (3.1 ± 3.7) and float-derived surface pCO2 by −3.2 μatm (−3.2 ± 3.9). This adjustment to float pCO2 represents half, or more, of the bias in float-derived pCO2 reported in studies comparing float pCO2 to shipboard pCO2 measurements.

剖面浮子和船载氧观测之间的偏移造成浮子pH值和所得二氧化碳分压的偏差
Argo分析浮标上的氧气测量数据现在远远超过了船上的数据。为了校正漂移,浮子上的氧气数据通常会首先调整到部署模型、船舶气候学,或者最近进行的原位校准的大气氧气测量。空气校准可以在海洋上层进行精确测量,但在海洋深处可能无法提供类似的精度。使用质量控制的船载数据集,我们发现在压力为1,450-2,000 db时,整个Argo氧数据集相对于船载测量值(浮子减去船)的中位数偏移为- 1.9 μmol kg - 1(平均值±SD为- 1.9±3.9,95%置信区间约为平均值{−2.2,−1.6}),空气校准浮子偏移为- 2.7 μmol kg - 1(−3.0±3.4 (CI95%{−3.7,−2.4})。浮子氧和船载氧之间的差异可能是由于浮子氧数据的偏移,而不是由于深度的氧变化或船载数据集的偏差。除了使长期海洋氧气变化的计算复杂化外,这些浮子的氧气抵消影响了浮子硝酸盐和pH值测量的调整,从而使CO2分压(pCO2)和溶解无机碳等重要的衍生量产生偏倚。用空气校准的氧气传感器校正浮子,使浮子的pH值中值改变3.0 mpH(3.1±3.7),浮子的表面二氧化碳分压改变−3.2 μatm(−3.2±3.9)。在比较浮子pCO2和船载pCO2测量结果的研究中,浮子pCO2的这种调整代表了浮子pCO2产生的偏差的一半或更多。
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来源期刊
Global Biogeochemical Cycles
Global Biogeochemical Cycles 环境科学-地球科学综合
CiteScore
8.90
自引率
7.70%
发文量
141
审稿时长
8-16 weeks
期刊介绍: Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.
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