Sea Surface Temperature Measurements Research Articles

A Microbolometer Airborne Calibrated Infrared Radiometer: The Ball Experimental Sea Surface Temperature (BESST) Radiometer

A calibrated radiometer has been developed to enable the collection of accurate infrared measurements of sea surface temperature (SST) from unmanned aerial vehicles (UAVs). A key feature of this instrument is that in situ calibration is achieved with two built-in blackbodies (BBs). The instrument is designed so that the 2-D microbolometer array produces infrared images incremented as the aircraft travels, resulting in a well-calibrated strip of SST. Designed to be carried by medium-class UAVs, the Ball Experimental SST (BESST) instrument has been also successfully flown on manned aircraft. A recent intercalibration of BESST was carried out at the University of Miami using their National Institute of Standards and Technology traceable water-bath BB and a Fourier transform interferometer, the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). The characterization of the BESST instrument with the Miami BB demonstrates the linearity and precision of the response of the microbolometer-based radiometer. Coincident measurements of SST from a nearby pier clearly demonstrated the excellent performance of the BESST instrument with a mean SST equal to that of the M-AERI and an RMS of 0.14 K very close to the microbolometer's advertised precision of 0.1 K. Cold calibration was not possible in Miami due to condensation, but a Ball BB was characterized relative to the Miami water-bath BB, and calibrations were made in Boulder at lower temperatures than were possible in Miami. The BESST instrument's performance remained linear, and the mean and RMS values did not change. UAV flights were conducted in summer/fall of 2013 over the Alaskan Arctic.

Movements, dispersion, and mixing of bigeye tuna (Thunnus obesus) tagged and released in the equatorial Central Pacific Ocean, with conventional and archival tags

A total of 31,242 bigeye tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140° W, 155° W, 170° W, and 180° meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701d (median=187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median=936M), with 71% eastward and 29% westward, and 95% within 3614M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from bigeye tuna at liberty for 30d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from bigeye tuna releases along the 140° W, 155° W, 170° W, and 180° meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude (σx) and latitude (σy) were 0.52° and 1.75°, for directed eastward and northward movements (u and v) were −2.01M/d and −1.41M/d, and for dispersive movement (D) was 496.7M2/d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of bigeye tuna between release longitudes. The amount of mixing of bigeye tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another.

Typhoon-enhanced upwelling and its influence on fishing activities in the southern East China Sea

Ocean–atmosphere interactions before and after the passage of Typhoons Haitang, Fung-wong, and Morakot across the southern region of the East China Sea (ECS) were examined by assessing satellite measurements of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration in conjunction with wind data. In terms of the satellite-derived data, the SST declined and chl-a concentration increased after the passage of the typhoons, and this could have resulted from the upwelling induced by typhoons via their long-duration, strong winds. According to fisheries data collected after the passing of Typhoon Morakot, the major fishing grounds of the torchlight fishery were found to have shifted northwards from the northern tip of Taiwan to the southern ECS. Moreover, the major target fish species changed from skipjack tuna (pre-typhoon) to squid (post-typhoon), signifying that the typhoon-enhanced upwelling might have caused the skipjack tuna, which typically prefer warm water, to have migrated elsewhere. In contrast, the nutrient-rich, upwelled water might have directly led to increases in chl-a concentrations and contributed the increase in local squid densities. This study suggests that typhoons can cause marked cooling of the sea surface as well as enhance upwelling that previously resulted in not only chl-a increases but also changes of local fish communities and, consequently, fishing activities.

Global observations of quasi‐zonal bands in microwave sea surface temperature

AbstractGlobal observations of quasi‐zonal jet‐like structures have recently been reported in estimates of upper ocean circulation. To date, these observations have come primarily from float‐derived and altimeter‐derived estimates of zonal velocity. Here, we explore the existence of similar structures in the ocean using satellite‐derived estimates of sea surface temperature (SST) from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR‐E). Applying an ocean front detection algorithm globally to microwave measurements of SST, we find that repeated ocean fronts occur along quasi‐zonal bands in a multiyear (2002–2011) average of detections. Such a pattern is also observed in SST gradient magnitude. Composite analyses of SST, sea surface height (SSH), and upper ocean temperatures from Argo profiling floats suggest repeated fronts in the subtropics occur as a result of neighboring anticyclonic and cyclonic eddies. Horizontal advection in the presence of a background temperature gradient likely plays a role as evidenced by the tilt of temperature anomalies with depth. High gradient events found within the bands are observed to propagate westward with speed comparable to mesoscale eddies and we estimate these events explain 20% of the observed variance in SST gradient magnitude (2002–2011). In a final analysis, we regress the decay of the bands with averaging period and observe mild‐to‐strong persistence throughout much of the World Ocean. These findings support the view that propagating eddies help give rise to the bands. Whether or not eddies follow preferred paths remain unanswered.

Global ocean current reconstruction from altimetric and microwave SST measurements

AbstractOcean currents are a key component to understanding many oceanic and climatic phenomena and knowledge of them is crucial for both navigation and operational applications. Currently, they are derived from Sea Surface Height (SSH) measurements provided by altimeters. However, distances between tracks and the limited number of available altimeters lead to errors in the accurate location of oceanic currents. In this study, we investigate the capability of Sea Surface Temperature (SST) observations to reconstruct surface currents at a global scale. The methodology we use consists of estimating the stream function by taking the phase from SST and the spectrum of SSH and then comparing it with altimetric measurements. Results reveal that SST provided by microwave radiometers can be used to retrieve ocean currents during winter near the major extratropical current systems, which are characterized by an intense mesoscale activity and the presence of strong thermal gradients. We have also found that surface ocean current reconstruction based on Surface Quasi‐Geostrophic approach can be improved if the information about the energy spectrum provided by altimeters is used. This points to the development of a new method of reconstructing ocean currents based on the combination of the phase of SST images with the energy spectrum derived from along‐track altimetric measurements.

Spatio-temporal dynamics of biogeochemical processes and air–sea CO2 fluxes in the Western English Channel based on two years of FerryBox deployment

From January 2011 to January 2013, a FerryBox system was installed on a Voluntary Observing Ship (VOS), which crossed the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) up to 3 times a day. The FerryBox continuously measured sea surface temperature (SST), sea surface salinity (SSS), dissolved oxygen (DO), fluorescence and partial pressure of CO2 (from April 2012) along the ferry track. Sensors were calibrated based on 714 bimonthly surface samplings with precisions of 0.016 for SSS, 3.3μM for DO, 0.40μgL−1 for Chlorophyll-a (Chl-a) (based on fluorescence measurements) and 5.2μatm for pCO2. Over the 2years of deployment (900 crossings), we reported 9% of data lost due to technical issues and quality checked data was obtained to allow investigation of the dynamics of biogeochemical processes related to air–sea CO2 fluxes in the WEC. Based on this unprecedented high-frequency dataset, the physical structure of the WEC was assessed using SST anomalies and the presence of a thermal front was observed around the latitude 49.5°N, which divided the WEC in two main provinces: the seasonally stratified northern WEC (nWEC) and the all-year well-mixed southern WEC (sWEC). These hydrographical properties strongly influenced the spatial and inter-annual distributions of phytoplankton blooms, which were mainly limited by nutrients and light availability in the nWEC and the sWEC, respectively. Air–sea CO2 fluxes were also highly related to hydrographical properties of the WEC between late April and early September 2012, with the sWEC a weak source of CO2 to the atmosphere of 0.9mmolm−2d−1, whereas the nWEC acted as a sink for atmospheric CO2 of 6.9mmolm−2d−1. The study of short time-scale dynamics of air–sea CO2 fluxes revealed that an intense and short (less than 10days) summer bloom in the nWEC contributed to 29% of the CO2 sink during the productive period, highlighting the necessity for high frequency observations in coastal ecosystems. During the same period in the sWEC, the tidal cycle was the main driver of air–sea CO2 fluxes with a mean difference in pCO2 values between spring and neap tides of +50μatm. An extraction of day/night data at 49.90°N showed that the mean day–night differences accounted for 16% of the mean CO2 sink during the 5months of the study period implying that the diel biological cycle was also significant for air–sea CO2 flux computations. The 2years of deployment of our FerryBox allowed an excellent survey of the variability of biogeochemical parameters from inter-annual to diurnal time scales and provided new insights into the dynamics of air–sea CO2 fluxes in the contrasted ecosystems of the WEC.

The effect of inter-annual Atlantic water inflow variability on the planktonic protist community structure in the West Spitsbergen waters during the summer

We investigated the spatial and inter-annual variations in planktonic protist community taxonomic composition with respect to size and trophic structure in the West Spitsbergen waters during the 2007, 2009 and 2010 summers. The protist communities were studied along a longitudinal transect from Kongsfjorden through the shelf to open sea waters. Our investigation was conducted on the Atlantic water inflow, which varied between the years. We observed a weakening trend in the northward advection of warm, Atlantic water in the Eastern branch of the Fram Strait, which was confirmed by long-term satellite-derived sea surface temperature (SST) measurements. The changing hydrological regime affected the summer protist taxonomic composition, abundance and biomass. These communities were numerically dominated by nanoplanktonic phototrophs, primarily cryptophytes. The microplanktonic heterotrophs (ciliates and dinoflagellates) were the major contributors to biomass, especially during the warmest year, 2007. Compared with previous investigations conducted in colder years, we observed a lower relative contribution of diatoms to the total protist biomass. Our results indicate that differences in the strength of Atlantic water inflow may have consequences for the composition of the plankton community in Kongsfjorden and the adjacent Eastern Fram Strait.

DAILY BLENDED MICROWAVE AND INFRARED SEA SURFACE TEMPERATURE COMPOSITION

A simple system for daily cloud free sea surface temperature (SST) composition based on thermal AVHRR and microwave TMI data is presented in this paper. Barnes’ objective analysis (Barnes, 1964) is applied as an interpolator to merge these two data sources, which have different spatial and temporal resolutions in a daily SST composition and in a regular grid product. Three comparisons were carried out as follows. First, in situ SST (daily average) measurements from eleven PIRATA´s buoys were compared. The correlation coefficients results varied from 0.89 to 0.99, and RMSE, MAE and MBE values have not exceeded 0.57 for period from 2002 to 2010. Second, comparisons between daily SST composition and average daily in situ SST collected from twenty three drifting buoys for the period from May 2008 to October 2010. The statistics results are 0.94, 0.25, 0.19 and -0.002 for correlation, RMSE, MAE and MBE, respectively. Third, SST (daily average) time series generated by OSTIA project was compared. The temporal and spatial RMSE (considering the study area) values ranged from approximately 0.21oC to 1.50oC and its average was 0.47oC for the period from January 1st to May 31st, 2006. Besides, an investigation about the influence of the data homogenization in the SST interpolation is discussed. Validation results are quite consistent (with SST composition accuracy less than 1.0oC). Thus, aiming to fulfill the numerical oceanographic model assimilation purposes and other oceanographic features studies, the developed SST product may be recommended as a candidate.

Segmentation of Mesoscale Ocean Surface Dynamics Using Satellite SST and SSH Observations

Multisatellite measurements of altimeter-derived sea surface height (SSH) and sea surface temperature (SST) provide a wealth of information about ocean circulation, particularly mesoscale ocean dynamics which may involve strong spatiotemporal relationships between SSH and SST fields. Within an observation-driven framework, we investigate the extent to which mesoscale ocean dynamics may be decomposed into a mixture of dynamical modes, characterized by different local regressions between SSH and SST fields. Formally, we develop a novel latent class regression model to identify dynamical modes from joint SSH and SST observation series. Applied to the highly dynamical Agulhas region, we demonstrate and discuss the geophysical relevance of the proposed mixture model to achieve a spatiotemporal segmentation of the upper ocean dynamics.

A review of uncertainty in in situ measurements and data sets of sea surface temperature

Archives of in situ sea surface temperature (SST) measurements extend back more than 160 years. Quality of the measurements is variable, and the area of the oceans they sample is limited, especially early in the record and during the two world wars. Measurements of SST and the gridded data sets that are based on them are used in many applications so understanding and estimating the uncertainties are vital. The aim of this review is to give an overview of the various components that contribute to the overall uncertainty of SST measurements made in situ and of the data sets that are derived from them. In doing so, it also aims to identify current gaps in understanding. Uncertainties arise at the level of individual measurements with both systematic and random effects and, although these have been extensively studied, refinement of the error models continues. Recent improvements have been made in the understanding of the pervasive systematic errors that affect the assessment of long-term trends and variability. However, the adjustments applied to minimize these systematic errors are uncertain and these uncertainties are higher before the 1970s and particularly large in the period surrounding the Second World War owing to a lack of reliable metadata. The uncertainties associated with the choice of statistical methods used to create globally complete SST data sets have been explored using different analysis techniques, but they do not incorporate the latest understanding of measurement errors, and they want for a fair benchmark against which their skill can be objectively assessed. These problems can be addressed by the creation of new end-to-end SST analyses and by the recovery and digitization of data and metadata from ship log books and other contemporary literature.

Diagnosis of high‐resolution upper ocean dynamics from noisy sea surface temperatures

The noise present in infrared satellite measurements of sea surface temperature (SST) hampers the use of surface quasi‐geostrophic (SQG) equations to diagnose ocean dynamics at high resolutions. Here we propose a methodology to reduce the contribution of noise when diagnosing surface vorticity, divergence, and vertical velocity from SST able to retain the dynamics at scales of a few kilometers. It is based on the use of denoising techniques with curvelets as basis functions and the application of a selective low‐pass filters to improve the reconstruction of surface upwelling/downwelling patterns. First, it is tested using direct numerical simulations of SQG turbulence and then applied to diagnose low‐frequency vertical velocity patterns from real MODIS (Moderate Resolution Imaging Spectroradiometer) images. The methodology here presented, which is not tied to the validity of SQG equations nor to the use of SST, is quite general and can be applied to a wide range of measurements and dynamical frameworks.

A Temporal Multiscale Analysis of the Waters off the East Coast of South Korea over the Past Four Decades

We address the trends in water temperature variability to understand the local global warming effects through different time scales using daily sea surface temperature (SST) measurements from 1966-2004. The abrupt SST changes off of the east coast of Korea are related to similar changes observed in the North Pacific. Seasonal water temperatures have increased by at least a factor of two or more in winter than in summer. While SSTs on annual timescales have increased significantly, SSTs on interannual timescales have decreased slightly at all stations. The anomalies in SST decadal time scales reveal maxima in temperature occurring in the mid-to-late 1970's, circa 1990 and circa 2000. These maxima coincide with major peaks in the North Pacific Gyre Oscillation (NPGO) with a lag of 4-7 months. The most significant warming appears in the long-term SST trends at each station where it approaches +0.05°C yr^(-1). Overall, the SST off the east coast of Korea has increased at rates that are far greater than what is reported in many other marginal seas.

Centennial-Scale Sea Surface Temperature Analysis and Its Uncertainty

Abstract A new sea surface temperature (SST) analysis on a centennial time scale is presented. In this analysis, a daily SST field is constructed as a sum of a trend, interannual variations, and daily changes, using in situ SST and sea ice concentration observations. All SST values are accompanied with theory-based analysis errors as a measure of reliability. An improved equation is introduced to represent the ice–SST relationship, which is used to produce SST data from observed sea ice concentrations. Prior to the analysis, biases of individual SST measurement types are estimated for a homogenized long-term time series of global mean SST. Because metadata necessary for the bias correction are unavailable for many historical observational reports, the biases are determined so as to ensure consistency among existing SST and nighttime air temperature observations. The global mean SSTs with bias-corrected observations are in agreement with those of a previously published study, which adopted a different approach. Satellite observations are newly introduced for the purpose of reconstruction of SST variability over data-sparse regions. Moreover, uncertainty in areal means of the present and previous SST analyses is investigated using the theoretical analysis errors and estimated sampling errors. The result confirms the advantages of the present analysis, and it is helpful in understanding the reliability of SST for a specific area and time period.

Resolved complex coastlines and land–sea contrasts in a high-resolution regional climate model: a comparative study using prescribed and modelled SSTs

We configured a coupled model system, comprising a regional climate model (RCM) and a regional ocean model, for the North Sea and Baltic Sea region at 6 nm resolution. A two-way nested fine-grid (1 nm) ocean domain is for the first time included for the Danish coastal waters in coupled RCMs to resolve the water exchange between the two regional seas. Here, we (1) assess the sensitivity of the near-surface atmosphere to prescribed sea surface temperatures (SSTs) from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim (ERAI) reanalysis and those modelled by the coupled system, and (2) examine different ocean responses in coarse and fine grids to atmospheric forcing. The experiments were performed covering the years 1990–2010, both using ERAI lateral boundary conditions. ERAI SSTs generally agree well with satellite SSTs in summer with differences within 1°C, but the ERAI overestimates the ice extent by 72% in winter due to the coarse resolution in the Baltic Sea. The atmosphere in the Baltic land–sea transition was more sensitive to high-resolution modelled SSTs with a significant improvement in winter, but it also provided a cold bias in summer as a combination of errors from both atmospheric and ocean models. Overall, the coupled simulation without observational constraints showed only minor deviations in the air–sea interface in the Baltic coastal region compared to the prescribed simulation, with seasonal mean differences within 2°C in 2 m air temperatures and 1°C in SSTs. An exception was in the Danish water, where the fine-grid ocean model yielded a better agreement with SST measurements and showed a smaller difference between the two simulations than the coarse-grid ocean model did. In turn, the modification on the atmosphere induced by modelled SSTs was negligible. The atmospheric–ocean–ice model in this configuration was found capable of reproducing the observed interannual variability of SST and ice extent in the Baltic Sea as well as the monthly extreme wind speeds and sea levels on a local scale for Denmark during the period 1990–2010. This article provides the first results in an attempt to resolve the Danish coasts with this accuracy in an RCM as a first step towards a fully coupled system for the region of interest.

SST spatial anisotropic covariances from METOP-AVHRR data

The Advanced Very High Resolution Radiometer (AVHRR) instrument on-board the METOP satellite is designed to provide very accurate measurements of Sea Surface Temperature (SST). In this work, using one year of METOP-AVHRR data and a geostatistical approach, we characterize the spatial anisotropy and non-stationarity of the SST variability using oriented ellipsoids. The method is also able to separate the true SST variability from the artificial error introduced by the METOP-AVHRR sensor. These spatial parameters are then used for producing variability atlases (available on-line) over the whole ocean.

Comparison of [formula omitted], [formula omitted] and LDI temperature proxies for reconstruction of south-east Australian ocean temperatures

Multiple organic proxies are used to reconstruct sea surface temperature (SST) but are rarely applied in concert. Furthermore, they have not been extensively calibrated for the Southern Hemisphere, particularly Australian waters. In an attempt to remedy this gap, we have used three organic temperature proxies: the alkenone unsaturation index (U37K′), the tetraether index from tetraethers consisting of 86 carbons (TEX86) and the novel long chain diol index (LDI) to reconstruct SST using seafloor sediments from the sediment/water interface from near the Australian southern and eastern coasts. The proxies revealed temperature offsets compared with World Ocean Atlas 2009 temperature values that are attributed to differences in seasonal biomarker flux and depth habitat of the source organisms. In the southeast Australian region, U37K′ and LDI provided better estimates of winter temperature at the surface than of any other season but overall were a robust measure of mean annual SST. TEX86H was consistent with previous data from other oceans; it estimated annual temperature best within the 75–100m water column. Comparison of the Australian results with the published global data sets confirm that TEX86H closely matched the correlation for annual temperature in the integrated 0–200m water depth profiles, whereas the other 2 proxies U37K′ and LDI showed different correlations. The results indicate that the combined application of the three independent biomarker proxies may provide useful surface and subsurface temperature information in the Australian region.

Corroboration and refinement of a method for differentiating landings from two stocks of Pacific sardine (Sardinops sagax) in the California Current

Abstract Demer, D. A., and Zwolinski, J. P. 2014. Corroboration and refinement of a method for differentiating landings from two stocks of Pacific sardine (Sardinops sagax) in the California Current. – ICES Journal of Marine Science, 71: 328–335. Efforts to survey, assess and manage Pacific sardine (Sardinops sagax) in the California Current may depend on accurate differentiation of the purported two migrating stocks. The southern stock spans seasonally from southern Baja California, México to Point Conception, California; the northern stock spans seasonally from Punta Eugenia, México northwards to southern Alaska. Their seasonal north–south migrations are approximately synchronous within their respective domains, resulting in segregated spawning and different identities. A decade ago, a practical method was proposed for differentiating landings from the two stocks using concomitant measurements of sea-surface temperature (SST). Here, we corroborate and refine the method using regional indices of optimal and good potential habitat for the northern stock, and SST-based indices associated with the 99.9 and 100% confidence intervals of the potential habitat. For months when the index is <0.5, (i.e. when the minority of a fishing region probably includes potential northern stock habitat), the landings are attributed to the southern stock, and vice versa. We applied this method to regional monthly landings data from 2006–2011 and the results indicated that an average of 63–72 and 32–36% of the summertime landings at Ensenada, México and San Pedro, southern California were probably from the southern stock, respectively, depending on the index used. Allocation error could be reduced if the landings were evaluated on finer spatio-temporal scales, particularly during habitat-transition periods. Our method may be used to improve estimates of northern stock biomass, spatial and length distributions, recruitment, and mortality.

Improvement of an aquaculture site-selection model for Japanese kelp (Saccharinajaponica) in southern Hokkaido, Japan: an application for the impacts of climate events

Abstract Liu, Y., Saitoh, S-I., Radiarta, I. N., Isada, T., Hirawake, T., Mizuta, H., and Yasui, H. 2013. Improvement of an aquaculture site-selection model for Japanese kelp (Saccharinajaponica) in southern Hokkaido, Japan: an application for the impacts of climate events. – ICES Journal of Marine Science, 70: . Japanese kelp (Saccharinajaponica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite- and ship-measured data (r2 = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). We found that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Niño/La Niña–Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003–2010. During El Niño events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.

Comparing historical and modern methods of sea surface temperature measurement – Part 2: Field comparison in the central tropical Pacific

Abstract. Discrepancies between historical sea surface temperature (SST) datasets have been partly ascribed to use of different adjustments to account for variable measurement methods. Until recently, adjustments had only been applied to bucket temperatures from the late 19th and early 20th centuries, with the aim of correcting their supposed coolness relative to engine cooling water intake temperatures. In the UK Met Office Hadley Centre SST 3 dataset (HadSST3), adjustments have been applied over its full duration to observations from buckets, buoys and engine intakes. Here we investigate uncertainties in the accuracy of such adjustments by direct field comparison of historical and modern methods of shipboard SST measurement. We compare wood, canvas and rubber bucket temperatures to 3 m seawater intake temperature along a central tropical Pacific transect conducted in May and June 2008. We find no average difference between the temperatures obtained with the different bucket types in our short measurement period (∼1 min). Previous field, lab and model experiments have found sizeable temperature change of seawater samples in buckets of smaller volume under longer exposure times. We do, however, report the presence of strong near-surface temperature gradients day and night, indicating that intake and bucket measurements cannot be assumed equivalent in this region. We thus suggest bucket and buoy measurements be considered distinct from intake measurements due to differences in sampling depth. As such, we argue for exclusion of intake temperatures from historical SST datasets and suggest this would likely reduce the need for poorly field-tested bucket adjustments. We also call for improvement in the general quality of intake temperatures from Voluntary Observing Ships. Using a physical model we demonstrate that warming of intake seawater by hot engine room air is an unlikely cause of overly warm intake temperatures. We suggest that reliable correction for such warm errors is not possible since they are largely of unknown origin and can be offset by real near-surface temperature gradients.

Comparing historical and modern methods of sea surface temperature measurement – Part 1: Review of methods, field comparisons and dataset adjustments

Abstract. Sea surface temperature (SST) has been obtained from a variety of different platforms, instruments and depths over the past 150 yr. Modern-day platforms include ships, moored and drifting buoys and satellites. Shipboard methods include temperature measurement of seawater sampled by bucket and flowing through engine cooling water intakes. Here I review SST measurement methods, studies analysing shipboard methods by field or lab experiment and adjustments applied to historical SST datasets to account for variable methods. In general, bucket temperatures have been found to average a few tenths of a °C cooler than simultaneous engine intake temperatures. Field and lab experiments demonstrate that cooling of bucket samples prior to measurement provides a plausible explanation for negative average bucket-intake differences. These can also be credibly attributed to systematic errors in intake temperatures, which have been found to average overly-warm by >0.5 °C on some vessels. However, the precise origin of non-zero average bucket-intake differences reported in field studies is often unclear, given that additional temperatures to those from the buckets and intakes have rarely been obtained. Supplementary accurate in situ temperatures are required to reveal individual errors in bucket and intake temperatures, and the role of near-surface temperature gradients. There is a need for further field experiments of the type reported in Part 2 to address this and other limitations of previous studies.