Seth M. Bushinsky, Zachary Nachod, Andrea J. Fassbender, Veronica Tamsitt, Yuichiro Takeshita, Nancy Williams
{"title":"Offset Between Profiling Float and Shipboard Oxygen Observations at Depth Imparts Bias on Float pH and Derived pCO2","authors":"Seth M. Bushinsky, Zachary Nachod, Andrea J. Fassbender, Veronica Tamsitt, Yuichiro Takeshita, Nancy Williams","doi":"10.1029/2024GB008185","DOIUrl":null,"url":null,"abstract":"<p>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<sup>−1</sup> (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<sup>−1</sup> (−3.0 ± 3.4 (CI<sub>95%</sub>{−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 CO<sub>2</sub> (<i>p</i>CO<sub>2</sub>) 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 <i>p</i>CO<sub>2</sub> by −3.2 μatm (−3.2 ± 3.9). This adjustment to float <i>p</i>CO<sub>2</sub> represents half, or more, of the bias in float-derived <i>p</i>CO<sub>2</sub> reported in studies comparing float <i>p</i>CO<sub>2</sub> to shipboard <i>p</i>CO<sub>2</sub> measurements.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 5","pages":""},"PeriodicalIF":5.4000,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Global Biogeochemical Cycles","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1029/2024GB008185","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
引用次数: 0
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.
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.