In this study, temperature data collected from the computers of divers has been shown to provide a novel data source. Data uploaded to the ‘diveintoscience’ portal were shown to have reasonable accuracy, demonstrated using comparisons with sea and lake surface temperature data, and through direct comparisons with CTDs and water baths. Most dive computers do not include dedicated temperature sensors but derive their temperature data from the thermal corrections being made to the pressure sensors used to inform the decompression algorithms. The temperature information stored by the computer may be limited by memory capacity which, in turn, influences the recording intervals which affects the quantity and quality of the data. However, simple algorithms can produce robust products that can be used by scientists to assess regional changes in physical oceanography, or to monitor climate change, assess the response of organisms to environmental change, or validate remote sensed data from satellites in coastal regions. Identification of the depth of the thermocline is likely to be possible in the future with a more structured collection of data, but will depend on the strength of the thermocline and the quality of the dive computer. For example, the minimum temperature recorded by dive computers can be compared to surface temperatures at the same location from modelled datasets (like the OSTIA database), providing an indication of coastal stratification. Though, importantly, we may predict a spatio-temporal bias in the regions and profiles sampled, with increased numbers of dives collected in regions with high visibility (stratified water-columns). Overall, our results show that divers can provide an accurate and useful source of aquatic temperature profiles that can augment existing monitoring programmes with global coverage. Though, the use of this data will depend on the scientific question in mind. For example, there may be scenarios where an error of 1 °C is un-acceptable, in which case improvements need to be made in the accuracy and consistency of dive computer temperature records.

The average difference between temperature recorded by the dive computer and by the CTD did not exceed 3 °C, and within model difference was on average less than 1 °C. This is in agreement with results from Azzopardi and Sayer (2012), which tested 47 different dive computer models by 14 manufacturers. The overall outcome indicated that in a range of test temperatures between 10 and 17 °C the median variance was 5.1 °C (with a range of −4.0 to 1.1 °C). In contrast, the temperature difference between surface temperatures recorded by the dive computer and the OSTIA SST database did not differ by more than 1.5 °C. The increased error in temperature readings from the dive computers, and the variability in the accuracy and precision of recorded data is an issue which needs to be resolved if temperature data are to be used to augment current climatologies. For example, the dive computers can have a consistent temperature error (as shown for model 3). By using a zero-offset calibration method, this error can be corrected, providing a simple means to validate temperatures recorded by dive computers. Thus, to improve the validity of uploaded dive computer data, websites focused on dive computer uploads could split uploads into two sections where calibrated and un-calibrated data can be stored separately. Further work is required to understand the effect that the water column structure has on the quality of the data extracted, including the level of variation that it is possible to detect. Additionally, information about the model and brand of the dive computer can be used to assign a level of quality to each upload.

Temperatures at depth are often only available offshore through the analysis of CTD data or modelling4,24. Many dive computer models store a single temperature value corresponding to the minimum temperature of the dive20. In the present study, CTD and dive computer minimum temperatures were relatively similar (within +/−1.5 °C, RMSE = 0.67 °C). When compared to global modelled temperature estimates at depth, RMSE values are higher than in this study (0.73 °C at between 5 and 100 m)24, suggesting that this minimum temperature value can be used to provide a reasonable estimate of water temperature with at least comparable accuracy to currently available modelled data. However, the depth that this temperature represents can be anywhere from the water surface to the bottom of the dive. The reason for the disparity between these depths, likely relates to the lag in the response of the temperature sensor of the dive computers, though the maximum depth of the dive can still be used as an indication of the depth of this temperature. Additionally, dive computer manufacturers do not have a standard method of reporting the minimum temperature or the location of this minimum temperature, potentially introducing an additional error. Validation against OSTIA and LST is likely to have removed large geolocation errors, as the temperature variance may exceed the data quality thresholds. An additional cross-validation could be developed to reduce the potential for geolocation errors using the database of dive site names and locations that will be compiled as the ‘diveintoscience’ data set grows. However, geolocation is unlikely to be a problem in the long-term as technology that is not widely available at present, including GPS on dive computes and navigation aids, become more common. Computer manufacturers could then provide a means to store temperature profile information from each dive with georeferenced start and end points, so that users are not reliant on memory to record temperature information or locations.

In situations where dive computers record depth and temperature continuously, more accurate estimates of temperatures at specific depths can be estimated, potentially providing temperatures at multiple depths. Some dive computer models require that divers remain at a constant depth for up to 12 minutes to obtain accurate temperature estimates. However, with further tests, it may also be possible to correct temperature estimates using continuously recorded depth and temperature information for each specific model of dive computer. Estimates of temperatures can be made from the temperature change within a minute at a set depth, rather than waiting for the temperatures to stabilise. Though this method requires further validation, the potential to assign temperatures to specific depths would be of great value.

This study has shown that a large set of depth-resolved temperature measurements can be collected quickly and easily from divers, and provide accurate readings of temperature after correction. It was also possible to get historic temperature information from the logbooks of individual divers meaning that a time series could be produced. As a result, we believe that dive computers are a useful and novel tool which can be used to augment temperature layers at sites all over the globe, but especially in under-sampled or highly changeable coastal environments. The compromise between portability and data quality is important when attempting to use dive computer data to augment existing temperature datasets, with further work required to calibrate and accurately geolocate dives to ensure data quality. Thus, at present, to ensure that dive computer data is accurate, the data needs to be quality assured prior to uploading, to minimise the incidence of errors. A potential method to check the quality of the data at the time of upload would be to record the model and manufacturer of the dive computer at upload, appropriate processing may then be carried out on the uploaded data using algorithms designed for each model type. Additionally, there is potential to work with dive computer manufacturers to improve the quality of the sensors in these devices, allowing divers to directly upload their data without cleaning. This accurate data may then be used firstly, by scientific diving organisations and socials networks to gain a greater understanding of dive sites and secondly, as a source of global sub-surface temperature data to augment or be complimentary to other ocean temperature climatologies (e.g. Argo11 or the Hadley Centre sea-Ice and Sea Surface Temperature (HadISST) data set25).

In the future, there is great potential to build on the diveintoscience portal to deliver a significant integrated aquatic monitoring interface for divers that goes beyond temperature data. The development of dive computers to include more sensors (e.g. salinity, oxygen) or the deployment of low cost in-situ sensors by dive schools and clubs (e.g. wave height) could further add to this potential. Divers generally are keen citizen scientists that are happy to collect information to help better understand the oceans26,27. Hence, a diver ocean monitoring programme that measures many environmental variables could be developed that delivers high resolution spatiotemporal data, even if only a small proportion of the 6–10 million dives and the many thousands of dive schools and clubs get involved. In addition to depth-temperature profiles uploaded by divers, other sources of temperature information can be collected and integrated into monitoring systems. For example, data collected by other ‘animals of opportunity’ including seals17, birds16 and fish28 may provide (potentially more accurate) in situ observations of temperature to fill data gaps in under sampled areas. Though, the quality and location of the temperature recorded will depend on the behaviour of the animal and the tag technology used. Species which frequently sample the entire water column will provide the most useful temperature information, such as, seals29 and sea bass30. Further exploration of the quality of this temperature and geolocation data are required, with the potential for an integrated monitoring of temperature data (and other variables) recorded using all ‘animals of opportunity’ in combination.