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| Fig. 1a Mean Average (CT) |
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| Fig. 1b Mean Average (SA) |
I. Some Background
Regular readers know that, as far as deep-ocean characteristics, in the past I typically used only two WOD Datasets (CTD and PFL) until recently (Databases Galore - 22, 23, and 24).
Today, I want to complete the narrative and the description of that change in Dredd Blog sources.
To do explain more about the specific characteristics of the data I will quote from the World Ocean Database Manual (PDF).
I am also using some long term (c. 1860 - 2018) graphs which present the data from those individual datasets in their collective (mean average) format as well as showing them along side each other in their individual format.
The technical format is TEOS-10 (in situ graphs were previously displayed here).
But before I get into the variations on the theme, let me mention Fig. 1a and Fig. 1b.
Those graphs show Conservative Temperature (CT) and Absolute Salinity (SA) during the span of time (1950 - 2018) when instruments used to measure seawater characteristics have been "improved versions."
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| Fig. 2a Mean Average (CT) |
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| Fig. 2b Mean Average (SA) |
II. Historical Variety
The complete span-of-time graphs of the same CT and SA, which include in situ measurements collected by scientists using less sophisticated instruments in times past.
The graphs depicting that, as well as data collected while using the most recent and most sophisticated instruments for collecting such measurements, are shown at Fig. 2a and Fig. 2b.
III. Data Collection Variety
The variation in results gathered over time is not difficult to discern, nor is it difficult to discern the variation in results caused by using a variety of instruments and a variety of collection techniques.
The graphs at Fig. 3a through Fig. 5b are paired CT & SA depictions of the datasets without the mean average values in graphs Fig. 2a and Fig. 2b.
Those graphs illustrate the significant differences in measurement varieties in the datasets.
IV. Dataset Descriptions in the WOD Manual
The following descriptions (between the two lines) are quoted from the manual (WORLD OCEAN DATABASE 2013 USER’S MANUAL, June 28, 2016, Version 2.2, pp. 5-7, pp. 15-17 PDF).
Note: the graphs are not in the manual.
D. DATASETS
The data in WOD13 are organized into eleven datasets that are briefly described in this section and listed in Table 2. A more detailed explanation of each dataset is provided in individual chapters of the World Ocean Database 2013 NOAA Atlas NESDIS 72 (Boyer et al., 2013).
1. Ocean Station Data (OSD)
Historically, Ocean Station Data (OSD) referred to measurements made from a stationary research ship using reversing thermometers to measure temperature and making measurements of other variables such as salinity, oxygen, nutrients, chlorophyll, etc. on seawater samples gathered using special bottles. The OSD dataset includes bottle data, low-resolution Conductivity-Temperature-Depth (CTD) data, Salinity- Temperature- Depth (STD), some surface-only data with specific characteristics, some low-resolution Expendable XCTDs, and plankton taxonomic and biomass measurements.
2. High-Resolution Conductivity-Temperature-Depth (CTD) Data
The CTD dataset contains data from Conductivity-Temperature-Depth instruments as well as STD data measured at high frequency vs. depth (pressure). CTD data are treated according to their resolution. All casts with a depth increment less than two meters are considered high-resolution CTD otherwise, the casts are considered as low-resolution CTD. The low-resolution CTD data reside within OSD dataset. High-resolution data collected by expendable Conductivity-Temperature-Depth (XCTD) instruments are also included in this dataset.
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| Fig. 3a CT (10m) |
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| Fig. 3b SA (10m) |
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| Fig. 4a CT (100m) |
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| Fig. 4b SA (100m) |
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| Fig. 5a CT (800m) |
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| Fig. 5b SA (800m) |
The MBT instrument was developed in its modern form around 1938 (Spilhaus, 1938). The instrument provides estimates of temperature as a function of depth in the upper water column. The MBT dataset contains data on water temperature profiles obtained from MBTs, Digital Bathythermograph (DBT) and Micro Bathythermograph (micro BT) instruments.
4. Expendable Bathythermograph (XBT) Data
The XBT was first deployed around 1966 and replaced the MBT in most measurement programs. This electronic instrument has a thermistor which measures temperature vs. depth. Depth is calculated using the elapsed time of its free descent through the water column and fall-rate equation. (See Section IV for information on XBT fall-rate error.)
5. Surface (SUR) Only Data
The SUR dataset contains data collected by any in-situ means from the surface of the ocean. The majority of the SUR observations were performed along ship routes in the Atlantic and Pacific oceans. In the SUR dataset each cruise is stored in the same form as a cast for other datasets. Each measurement has an associated latitude, longitude, and Julian year-day.
6. Autonomous Pinniped (APB) Data
The APB dataset contains in-situ temperature data from time-temperature-depth recorders (TTDR) and temperature and salinity data from CTD sensors manually attached to marine mammals such as northern elephant seals (Mirounga angustirostris).
7. Moored Buoy (MRB) Data
The MRB dataset contains temperature and salinity measurements collected from moored buoys located in the Tropical Pacific, tropical Atlantic, Baltic and North Seas, and area around Japan. These include the major ongoing Equatorial buoy arrays, TAO/TRITON, PIRATA, and RAMA.
8. Profiling Float (PFL) Data
The PFL dataset contains temperature and salinity data collected from drifting profiling floats such as Profiling Autonomous Lagrangian Circulation Explorer (P-ALACE), PROVOR (free-drifting hydrographic profiler), SOLO (Sounding Oceanographic Lagrangian Observer), and APEX (Autonomous Profiling Explorer). The main source of the PFL data in WOD13 is the Argo project.
9. Drifting Buoy (DRB) Data
The DRB dataset contains data collected from surface drifting buoys and drifting floats with subsurface thermister chains. The major sources of this data include the GTSPP project and Arctic buoy projects.
10. Undulating Oceanographic Recorder (UOR)
The UOR dataset contains data collected from a ConductivityTemperature-Depth probe mounted on a towed undulating vehicle. A description of the different types of UOR vehicles used for acquiring the data included in the WOD13 can be found in Appendix 2.21.
11. Glider (GLD) Data
The GLD dataset contains data collected from reusable autonomous underwater vehicles (AUV) designed to glide from the ocean surface to a programmed depth and back while measuring temperature, salinity, depth-averaged current, and other quantities along a sawtoothed trajectory through the water.
V. Conclusion
As the graphs in Section IV above show, the data variety is obvious.
What causes the variety is not so obvious.
Many things can play a part in the variety, that is why mean average in this context is less of a problem than it is in sea level change scenarios.
The previous post in this series is here.
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