scholarly journals Time, Probe Type, and Temperature Variable Bias Corrections to Historical Expendable Bathythermograph Observations

2014 ◽  
Vol 31 (8) ◽  
pp. 1793-1825 ◽  
Author(s):  
Lijing Cheng ◽  
Jiang Zhu ◽  
Rebecca Cowley ◽  
Tim Boyer ◽  
Susan Wijffels
Keyword(s):  
Water Temperature ◽  
World Ocean ◽  
Heat Content ◽  
Terminal Velocity ◽  
Global Scale ◽  
Global Ocean ◽  
Probe Type ◽  
Fall Rate ◽  
Dominant Term ◽  
Expendable Bathythermograph

Abstract Systematic biases in historical expendable bathythermograph (XBT) data are examined using two datasets: 4151 XBT–CTD side-by-side pairs from 1967 to 2011 and 218 653 global-scale XBT–CTD pairs (within one month and 1°) extracted from the World Ocean Database 2009 (WOD09) from 1966 to 2010. Using the side-by-side dataset, it was found that both the pure thermal bias and the XBT fall rate (from which the depth of observation is calculated) increase with water temperature. Correlations between the terminal velocity A and deceleration B terms of the fall-rate equation (FRE) and between A and the offset from the surface terms are obtained, with A as the dominant term in XBT fall-rate behavior. To quantify the time variation of the XBT fall-rate and pure temperature biases, global-scale XBT–CTD pairs are used. Based on the results from the two datasets, a new correction scheme for historical XBT data is proposed for nine independent probe-type groups. The scheme includes corrections for both temperature and depth records, which are all variable with calendar year, water temperature, and probe type. The results confirm those found in previous studies: a slowing in fall rate during the 1970s and 2000s and the large pure thermal biases during 1970–85. The performance of nine different correction schemes is compared. After the proposed corrections are applied to the XBT data in the WOD09 dataset, global ocean heat content from 1967 to 2010 is reestimated.

scholarly journals Using Neural Networks to Correct Historical Climate Observations

2018 ◽  
Vol 35 (10) ◽  
pp. 2053-2059 ◽  
Author(s):  
Thomas P. Leahy ◽  
Francesc Pons Llopis ◽  
Matthew D. Palmer ◽  
Niall H. Robinson
Keyword(s):  
Neural Network ◽  
World Ocean ◽  
Heat Content ◽  
Probe Type ◽  
Learning Approaches ◽  
Climate Data ◽  
Classification Problems ◽  
Content Change ◽  
Expendable Bathythermograph ◽  
The World

AbstractBiases in expendable bathythermograph (XBT) instruments have emerged as a leading uncertainty in reconstructions of historical ocean heat content change and therefore climate change. Corrections for these biases depend on the type of XBT used; however, this is unspecified for 52% of the historical XBT profiles in the World Ocean Database. Here, we use profiles of known XBT type to train a neural network that can classify probe type based on three covariates: profile date, maximum recorded depth, and country of origin. Whereas previous studies have shown an average classification skill of 77%, falling below 50% for some periods, our new algorithm maintains an average skill of 90%, with a minimum of 70%. Our study illustrates the potential for successfully applying machine learning approaches in a wide variety of instrument classification problems in order to promote more homogeneous climate data records.

scholarly journals An Algorithm for Classifying Unknown Expendable Bathythermograph (XBT) Instruments Based on Existing Metadata

2018 ◽  
Vol 35 (3) ◽  
pp. 429-440 ◽  
Author(s):  
Matthew D. Palmer ◽  
Tim Boyer ◽  
Rebecca Cowley ◽  
Shoichi Kizu ◽  
Franco Reseghetti ◽  
...  
Keyword(s):  
World Ocean ◽  
Heat Content ◽  
Deterministic Algorithm ◽  
Skill Assessment ◽  
Probe Type ◽  
Temperature Profiles ◽  
Time Varying ◽  
Basic Skill ◽  
Bulk Analysis ◽  
Expendable Bathythermograph

AbstractTime-varying biases in expendable bathythermograph (XBT) instruments have emerged as a key uncertainty in estimates of historical ocean heat content variability and change. One of the challenges in the development of XBT bias corrections is the lack of metadata in ocean profile databases. Approximately 50% of XBT profiles in the World Ocean database (WOD) have no information about manufacturer or probe type. Building on previous research efforts, this paper presents a deterministic algorithm for assigning missing XBT manufacturer and probe type for individual temperature profiles based on 1) the reporting country, 2) the maximum reported depth, and 3) the record date. The criteria used are based on bulk analysis of known XBT profiles in the WOD for the period 1966–2015. A basic skill assessment demonstrates a 77% success rate at correctly assigning manufacturer and probe type for profiles where this information is available. The skill rate is lowest during the early 1990s, which is also a period when metadata information is particularly poor. The results suggest that substantive improvements could be made through further data analysis and that future algorithms may benefit from including a larger number of predictor variables.

Estimating Global Ocean Heat Content Changes in the Upper 1800 m since 1950 and the Influence of Climatology Choice*

2014 ◽  
Vol 27 (5) ◽  
pp. 1945-1957 ◽  
Author(s):  
John M. Lyman ◽  
Gregory C. Johnson
Keyword(s):  
Heat Content ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Ocean Temperature ◽  
Vertical Separation ◽  
Ocean Heat Uptake ◽  
Expendable Bathythermograph ◽  
Heat Uptake ◽  
The Mean

Abstract Ocean heat content anomalies are analyzed from 1950 to 2011 in five distinct depth layers (0–100, 100–300, 300–700, 700–900, and 900–1800 m). These layers correspond to historic increases in common maximum sampling depths of ocean temperature measurements with time, as different instruments—mechanical bathythermograph (MBT), shallow expendable bathythermograph (XBT), deep XBT, early sometimes shallower Argo profiling floats, and recent Argo floats capable of worldwide sampling to 2000 m—have come into widespread use. This vertical separation of maps allows computation of annual ocean heat content anomalies and their sampling uncertainties back to 1950 while taking account of in situ sampling advances and changing sampling patterns. The 0–100-m layer is measured over 50% of the globe annually starting in 1956, the 100–300-m layer starting in 1967, the 300–700-m layer starting in 1983, and the deepest two layers considered here starting in 2003 and 2004, during the implementation of Argo. Furthermore, global ocean heat uptake estimates since 1950 depend strongly on assumptions made concerning changes in undersampled or unsampled ocean regions. If unsampled areas are assumed to have zero anomalies and are included in the global integrals, the choice of climatological reference from which anomalies are estimated can strongly influence the global integral values and their trend: the sparser the sampling and the bigger the mean difference between climatological and actual values, the larger the influence.

How Well Can We Correct Systematic Errors in Historical XBT Data?

2018 ◽  
Vol 35 (5) ◽  
pp. 1103-1125 ◽  
Author(s):  
Lijing Cheng ◽  
Hao Luo ◽  
Timothy Boyer ◽  
Rebecca Cowley ◽  
John Abraham ◽  
...  
Keyword(s):  
Reference Data ◽  
World Ocean ◽  
Heat Content ◽  
Systematic Errors ◽  
Global Scale ◽  
Systematic Difference ◽  
Quality Data ◽  
High Quality Data ◽  
Sources Of Uncertainty ◽  
Global Datasets

AbstractBiases have been identified in historical expendable bathythermograph (XBT) datasets, which are one of the major sources of uncertainty in the ocean subsurface database. More than 10 correction schemes were proposed; however, their performance has not been collectively evaluated and compared. This study quantifies how well 10 different available schemes can correct the historical XBT data by comparing the corrected XBT data with collocated reference data in both the World Ocean Database (WOD) 2013 and the EN4 dataset. Four different metrics are proposed to quantify their performances. The results indicate CH14 is the best among the currently available methods, and L09/G12/GR10 can be used with some caveats. To test the robustness of the schemes, we further train the CH14 and L09 by using 50% of the XBT–reference data and the schemes are tested by using the remaining data. The results indicate that the two schemes are robust. Moreover, the EN4 and WOD comparison datasets show a systematic difference of XBT error (~0.01°C on a global scale and 0–700 m on average). influences of quality control and data processing have been investigated. Additionally, the side-by-side XBT–CTD comparison experiment is used to examine the correction schemes and provides independent high-quality data for the assessment. The schemes that best correct the global datasets do not always perform as well at correcting the side-by-side dataset, and further examination of the discrepancy in performance is still required. Finally, CH14 and L09 result in very similar ocean heat content (OHC) change estimates in the upper 700 m since 1966, suggesting the potential of reducing XBT-induced error in OHC estimates.

scholarly journals Is the Upper Ocean Warming? Comparisons of 50-Year Trends from Different Analyses*

2008 ◽  
Vol 21 (10) ◽  
pp. 2259-2268 ◽  
Author(s):  
Mark Carson ◽  
D. E. Harrison
Keyword(s):  
World Ocean ◽  
Heat Content ◽  
Global Ocean ◽  
Upper Ocean ◽  
Ocean Temperature ◽  
Regional Trend ◽  
Upper Ocean Heat Content ◽  
Temperature Trends ◽  
Temporal And Spatial ◽  
Estimate Uncertainty

Abstract There is great interest in World Ocean temperature trends, yet the historical global ocean database has very uneven coverage in space and time. Previous work on 50-yr upper ocean temperature trends from the NOAA ocean data archive is extended here. Trends at depths from 50 to 1000 m are examined, based on observations gridded over larger regions than in the earlier study. Despite the use of larger grid boxes, most of the ocean does not have significant 50-yr trends at the 90% confidence level (CL). In fact only 30% of the ocean at 50 m has 90% CL trends, and the percentage decreases significantly with increasing depth. As noted in the previous study, there is much spatial structure in 50-yr trends, with areas of strong warming and strong cooling. These trend results are compared with trends calculated from data interpolated to standard levels and from a highly horizontally interpolated version of the dataset that has been used in previous heat content trend studies. The regional trend results can differ substantially, even in the areas with statistically significant trends. Trends based on the more interpolated analyses show more warming. Together with major temporal and spatial sampling limitations, the previously described strong interdecadal and spatial variability of trends makes it very difficult to formally estimate uncertainty in World Ocean averages, but these results suggest that upper ocean heat content integrals and integral trends may be substantially more uncertain than has yet been acknowledged. Further exploration of uncertainties is needed.

scholarly journals Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise

2008 ◽  
Vol 21 (21) ◽  
pp. 5657-5672 ◽  
Author(s):  
Susan E. Wijffels ◽  
Josh Willis ◽  
Catia M. Domingues ◽  
Paul Barker ◽  
Neil J. White ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Decadal Variability ◽  
Heat Content ◽  
Time History ◽  
Global Ocean ◽  
Fall Rate ◽  
Rate Minimum ◽  
Fall Rates

Abstract A time-varying warm bias in the global XBT data archive is demonstrated to be largely due to changes in the fall rate of XBT probes likely associated with small manufacturing changes at the factory. Deep-reaching XBTs have a different fall rate history than shallow XBTs. Fall rates were fastest in the early 1970s, reached a minimum between 1975 and 1985, reached another maximum in the late 1980s and early 1990s, and have been declining since. Field XBT/CTD intercomparisons and a pseudoprofile technique based on satellite altimetry largely confirm this time history. A global correction is presented and applied to estimates of the thermosteric component of sea level rise. The XBT fall rate minimum from 1975 to 1985 appears as a 10-yr “warm period” in the global ocean in thermosteric sea level and heat content estimates using uncorrected data. Upon correction, the thermosteric sea level curve has reduced decadal variability and a larger, steadier long-term trend.

scholarly journals A Comparison of the Variability and Changes in Global Ocean Heat Content from Multiple Objective Analysis Products During the Argo Period

2021 ◽  
pp. 1-47
Author(s):  
Xinfeng Liang ◽  
Chao Liu ◽  
Rui M. Ponte ◽  
Don P. Chambers
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Heat Content ◽  
Global Scale ◽  
Ocean Heat Content ◽  
Objective Analysis ◽  
Global Ocean ◽  
Ocean Measurements

AbstractOcean heat content (OHC) is key to estimating the energy imbalance of the earth system. Over the past two decades, an increasing number of OHC studies were conducted using oceanic objective analysis (OA) products. Here we perform an intercomparison of OHC from eight OA products with a focus on their robust features and significant differences over the Argo period (2005-2019), when the most reliable global scale oceanic measurements are available. For the global ocean, robust warming in the upper 2000 m is confirmed. The 0-300 m layer shows the highest warming rate but is heavily modulated by interannual variability, particularly the El Niño–Southern Oscillation. The 300-700 m and 700-2000 m layers, on the other hand, show unabated warming. Regionally, the Southern Ocean and mid-latitude North Atlantic show a substantial OHC increase, and the subpolar North Atlantic displays an OHC decrease. A few apparent differences in OHC among the examined OA products were identified. In particular, temporal means of a few OA products that incorporated other ocean measurements besides Argo show a global-scale cooling difference, which is likely related to the baseline climatology fields used to generate those products. Large differences also appear in the interannual variability in the Southern Ocean and in the long-term trends in the subpolar North Atlantic. These differences remind us of the possibility of product-dependent conclusions on OHC variations. Caution is therefore warranted when using merely one OA product to conduct OHC studies, particularly in regions and on timescales that display significant differences.

scholarly journals How well can we derive Global Ocean Indicators from Argo data?

2011 ◽  
Vol 8 (3) ◽  
pp. 999-1024 ◽  
Author(s):  
K. von Schuckmann ◽  
P.-Y. Le Traon
Keyword(s):  
Heat Content ◽  
Global Scale ◽  
Global Ocean ◽  
Argo Data ◽  
Steric Sea Level ◽  
Content Change ◽  
Time Period ◽  
Handling Methods ◽  
Proper Estimation ◽  
Year 2000

Abstract. Argo deployments began in the year 2000 and by November 2007 the array was 100 % complete, covering the global ocean from the surface down to 2000 m depth. In this study, Argo temperature and salinity measurements during the period 2005 to 2010 are used to develop a revised estimation of Global Ocean Indicators (GOIs) such as heat content variability, freshwater content and steric height. These revised indices are based on a simple box averaging scheme using a weighted mean. They include a proper estimation of the errors due to data handling methods and climatology uncertainties. A global ocean heat content change (OHC) trend of 0.55 ± 0.1 W m−2 is estimated over the time period 2005–2010. Similarly, a global steric sea level (GSSL) rise of 0.69 ± 0.14 mm yr−1 is observed. The global ocean freshwater content (OFC) trend is barely significant. Results show that there is significant interannual variability at global scale, especially for global OFC. Annual mean GOIs from the today's Argo samling can be derived with an accuracy of ±0.10 cm for GSSL, ±0.21 × 108 J m−2 for global OHC, and ±700 km3 for global OFC. Long-term trends (15 yr) of GOIs based on the complete Argo sampling (10–1500 m depth) can be performed with an accuracy of about ±0.03 mm yr−1 for steric rise, ±0.02 W m−2 for ocean warming and ±20 km3 yr−1 for global OFC trends – under the assumption that no systematic errors remain in the observing system.

scholarly journals In Situ–Based Reanalysis of the Global Ocean Temperature and Salinity with ISAS: Variability of the Heat Content and Steric Height

2016 ◽  
Vol 29 (4) ◽  
pp. 1305-1323 ◽  
Author(s):  
Fabienne Gaillard ◽  
Thierry Reynaud ◽  
Virginie Thierry ◽  
Nicolas Kolodziejczyk ◽  
Karina von Schuckmann
Keyword(s):  
Southern Ocean ◽  
World Ocean ◽  
Heat Content ◽  
Absolute Error ◽  
Ocean Heat Content ◽  
Global Ocean ◽  
Analysis Tool ◽  
Steric Height ◽  
The Impact

Abstract The In Situ Analysis System (ISAS) was developed to produce gridded fields of temperature and salinity that preserve as much as possible the time and space sampling capabilities of the Argo network of profiling floats. Since the first global reanalysis performed in 2009, the system has evolved, and a careful delayed-mode processing of the 2002–12 dataset has been carried out using version 6 of ISAS and updating the statistics to produce the ISAS13 analysis. This last version is now implemented as the operational analysis tool at the Coriolis data center. The robustness of the results with respect to the system evolution is explored through global quantities of climatological interest: the ocean heat content and the steric height. Estimates of errors consistent with the methodology are computed. This study shows that building reliable statistics on the fields is fundamental to improve the monthly estimates and to determine the absolute error bars. The new mean fields and variances deduced from the ISAS13 reanalysis and dataset show significant changes relative to the previous ISAS estimates, in particular in the Southern Ocean, justifying the iterative procedure. During the decade covered by Argo, the intermediate waters appear warmer and saltier in the North Atlantic and fresher in the Southern Ocean than in World Ocean Atlas 2005 long-term mean. At interannual scale, the impact of ENSO on the ocean heat content and steric height is observed during the 2006/07 and 2009/10 events captured by the network.

scholarly journals Towards accounting for dissolved iron speciation in global ocean models

2011 ◽  
Vol 8 (2) ◽  
pp. 2775-2810 ◽  
Author(s):  
A. Tagliabue ◽  
C. Völker
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Environmental Variability ◽  
World Ocean ◽  
Global Scale ◽  
Global Ocean ◽  
Test Bed ◽  
Fe Species ◽  
Effective Manner ◽  
Fe Speciation

Abstract. The trace metal iron (Fe) is now routinely included in state-of-the-art ocean general circulation and biogeochemistry models (OGCBMs) because of its key role as a limiting nutrient in regions of the world ocean important for carbon cycling and air-sea CO2 exchange. However, the complexities of the seawater Fe cycle, which impact its speciation and bioavailability, are highly simplified in such OGCBMs to avoid high computational costs. In a similar fashion to inorganic carbon speciation, we outline a means by which the complex speciation of Fe can be included in global OGCBMs in a reasonably cost-effective manner. We use our Fe speciation to suggest the global distribution of different Fe species is tightly controlled by environmental variability (temperature, light, oxygen and pH) and the assumptions regarding Fe binding ligands. Impacts on bioavailable Fe are highly sensitive to assumptions regarding which Fe species are bioavailable. When forced by representations of future ocean circulation and climate we find large changes to the speciation of Fe governed by pH mediated changes to redox kinetics. We speculate that these changes may exert selective pressure on phytoplankton Fe uptake strategies in the future ocean. We hope our modeling approach can also be used as a ''test bed'' for exploring our understanding of Fe speciation at the global scale.

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