SST Products Research Articles

Research on Measurement Coverage and Uncertainty Analysis of GPM Microwave Imager SST Products

Research on Measurement Coverage and Uncertainty Analysis of GPM Microwave Imager SST Products

Testing marine data assimilation in the northeastern Baltic using satellite SST products from the Copernicus Marine Environment Monitoring Service

Testing marine data assimilation in the northeastern Baltic using satellite SST products from the Copernicus Marine Environment Monitoring Service

Comparación de los productos de TSM L3 generados a partir de los sensores AVHRR y MODIS frente al Golfo San Jorge, Argentina

<p>Since the early 1980s, the AVHRR sensor on board the NOAA satellites has provided SST estimates to the scientific community in general. Towards the end of the 1990s, a new generation of radiometers was added, combining a wider range of spectral measurements with improvements in technology, such as the MODIS sensor on board the Terra and Aqua satellites. The development of this last sensor was based on the years of NOAA/AVHRR series. Understanding the relationship between products derived from different sensors is critical to the continuous long-term monitoring of any variable and the construction of continuous time series. The objective of this work was to make a comparison of the monthly SST values for the 2003-2006 period calculated from data from the NOAA/ AVHRR series versus Aqua-MODIS on a sector of the middle Argentina Continental shelf off the San Jorge Gulf. For both sensors, the isotherms show a similar distribution pattern in all months. Pearson’s correlation coefficient was high, both in the seasonal (> 0.9) and monthly (> 0.8) analyzes. The comparative analysis of the temperature estimated by both sensors shows that SST products are similar and can be used to analyze large and continuous time series.</p>

Using a 1‐D model to reproduce the diurnal variability of SST

AbstractA wide range of applications, from air‐sea interaction studies to fisheries and biological modeling, need accurate, high resolution SST which requires that the diurnal signal is known; for many applications, diurnal estimates are necessary and should be included in blended SST products. A widely preferred approach to bridge the gap between in situ and remotely sensed measurements and obtain diurnal warming estimates at large spatial scales is modeling of the upper ocean temperature. This study uses the one‐dimensional General Ocean Turbulence Model (GOTM) to resolve diurnal signals identified from satellite SSTs and in situ measurements. Focus is given on testing and validation of different parameterizations of the basic physical processes known to influence the generation of a warm surface layer. GOTM is tested and validated using in situ measurements obtained at three locations, two in the Atlantic Ocean and one in the Baltic Sea, where different oceanographic and atmospheric conditions occur, in order to obtain an insight into its general performance. It is found that the model, with a 9 band solar absorption model rather than the standard 2 band scheme, performs well when using 3 hourly NWP forcing fields and is able to resolve daily SST variability seen both from satellite and in situ measurements. As such, and due to its low computational cost, it is proposed as a candidate model for diurnal variability estimates.

Assessing recent warming using instrumentally homogeneous sea surface temperature records.

Sea surface temperature (SST) records are subject to potential biases due to changing instrumentation and measurement practices. Significant differences exist between commonly used composite SST reconstructions from the National Oceanic and Atmospheric Administration's Extended Reconstruction Sea Surface Temperature (ERSST), the Hadley Centre SST data set (HadSST3), and the Japanese Meteorological Agency's Centennial Observation-Based Estimates of SSTs (COBE-SST) from 2003 to the present. The update from ERSST version 3b to version 4 resulted in an increase in the operational SST trend estimate during the last 19 years from 0.07° to 0.12°C per decade, indicating a higher rate of warming in recent years. We show that ERSST version 4 trends generally agree with largely independent, near-global, and instrumentally homogeneous SST measurements from floating buoys, Argo floats, and radiometer-based satellite measurements that have been developed and deployed during the past two decades. We find a large cooling bias in ERSST version 3b and smaller but significant cooling biases in HadSST3 and COBE-SST from 2003 to the present, with respect to most series examined. These results suggest that reported rates of SST warming in recent years have been underestimated in these three data sets.

Hurricane Irene Sensitivity to Stratified Coastal Ocean Cooling

Cold wakes left behind by tropical cyclones (TCs) have been documented since the 1940s. Many questions remain, however, regarding the details of the processes creating these cold wakes and their in-storm feedbacks onto tropical cyclone intensity. This largely reflects a paucity of measurements within the ocean, especially during storms. Moreover, the bulk of TC research efforts have investigated deep ocean processes—where tropical cyclones spend the vast majority of their lifetimes—and very little attention has been paid to coastal ocean processes despite their critical importance to shoreline populations. Using Hurricane Irene (2011) as a case study, the impact of the cooling of a stratified coastal ocean on storm intensity, size, and structure is quantified. Significant ahead-of-eye-center cooling (at least 6°C) of the Mid-Atlantic Bight occurred as a result of coastal baroclinic processes, and operational satellite SST products and existing coupled ocean–atmosphere hurricane models did not capture this cooling. Irene’s sensitivity to the cooling is tested, and its intensity is found to be most sensitive to the cooling over all other tested WRF parameters. Further, including the cooling in atmospheric modeling mitigated the high storm intensity bias in predictions. Finally, it is shown that this cooling—not track, wind shear, or dry air intrusion—was the key missing contribution in modeling Irene’s rapid decay prior to New Jersey landfall. Rapid and significant intensity changes just before landfall can have substantial implications on storm impacts—wind damage, storm surge, and inland flooding—and thus, coastal ocean processes must be resolved in future hurricane models.

How is the surface Atlantic water inflow through the Gibraltar Strait forecasted? A lagrangian validation of operational oceanographic services in the Alboran Sea and the Western Mediterranean

An exhaustive validation of some of the operational ocean forecast products available in the Gibraltar Strait and the Alboran Sea is here presented. The skill of two ocean model solutions (derived from the Eulerian ocean forecast systems, such as the regional CMEMS IBI and the high resolution PdE SAMPA) in reproducing the complex surface dynamics in the above areas is evaluated. To this aim, in-situ measurements from the MEDESS-GIB drifter buoy database (comprising the Lagrangian positions, derived velocities and SST values) are used as the observational reference and the temporal coverage for the validation is 3 months (September to December 2014). Two metrics, a Lagrangian separation distance and a skill score, have been applied to evaluate the performance of the modelling systems in reproducing the observed trajectories. Furthermore, the SST validation with in-situ data is carried out by means of validating the model solutions with L3 satellite SST products. The Copernicus regional IBI products are evaluated in an extended domain, beyond the Alboran Sea, and covering western Mediterranean waters. This analysis reveals some strengths of the presented regional solution (i.e. realistic values of the Atlantic Jet in the Strait of Gibraltar area, realistic simulation of the Algerian Current). However, some shortcomings are also identified, with the major one being related to the simulated geographical position and intensity of the Alboran Gyres, particularly the western one. This performance limitation affects the IBI-modelled surface circulation in the entire Alboran Sea. On the other hand, the SAMPA system shows a more accurate model performance and it realistically reproduces the observed surface circulation in the area. The results reflect the effectiveness of the dynamical downscaling performed through the SAMPA system with respect to the regional IBI solution (in which SAMPA is nested), providing an objective measure of the potential added values introduced by the SAMPA downscaling solution in the Alboran Sea.

Blending of satellite SST products using ensemble Bayesian model averaging (EBMA)

ABSTRACTSea surface temperature (SST) is an important parameter in understanding atmosphere–ocean circulation processes and monitoring global climate change. In addition to in situ observations of SST, a series of satellite-borne instruments provide global coverage of SST through infrared and microwave remote sensing. This study was the first application of the ensemble Bayesian model averaging (EBMA) method to the blending of satellite SST products to minimize inherent uncertainties and improve the validation statistics. Monthly SST products from moderate resolution imaging spectroadiometer, Advanced Very High Resolution Radiometer and Advanced Microwave Scanning Radiometer-EOS were used as ensemble members. The mean bias and root-mean-square error (RMSE) of the EBMA method were better than those of the individual members or generic methods such as ensemble mean and median. This is because the weighting scheme adjusted by the expectation–maximization algorithm was based on the suitability of each member derived from training procedures. The errors of EBMA in our experiment had almost no spatial and temporal autocorrelation with regard to the latitude and month, which implies that the EBMA method can serve as a viable option for blending of satellite SST, although more experiments are necessary to determine its feasibility in more detail.

Further Exploring and Quantifying Uncertainties for Extended Reconstructed Sea Surface Temperature (ERSST) Version 4 (v4)

Abstract The uncertainty in Extended Reconstructed SST (ERSST) version 4 (v4) is reassessed based upon 1) reconstruction uncertainties and 2) an extended exploration of parametric uncertainties. The reconstruction uncertainty (Ur) results from using a truncated (130) set of empirical orthogonal teleconnection functions (EOTs), which yields an inevitable loss of information content, primarily at a local level. The Ur is assessed based upon 32 ensemble ERSST.v4 analyses with the spatially complete monthly Optimum Interpolation SST product. The parametric uncertainty (Up) results from using different parameter values in quality control, bias adjustments, and EOT definition etc. The Up is assessed using a 1000-member ensemble ERSST.v4 analysis with different combinations of plausible settings of 24 identified internal parameter values. At the scale of an individual grid box, the SST uncertainty varies between 0.3° and 0.7°C and arises from both Ur and Up. On the global scale, the SST uncertainty is substantially smaller (0.03°–0.14°C) and predominantly arises from Up. The SST uncertainties are greatest in periods and locales of data sparseness in the nineteenth century and relatively small after the 1950s. The global uncertainty estimates in ERSST.v4 are broadly consistent with independent estimates arising from the Hadley Centre SST dataset version 3 (HadSST3) and Centennial Observation-Based Estimates of SST version 2 (COBE-SST2). The uncertainty in the internal parameter values in quality control and bias adjustments can impact the SST trends in both the long-term (1901–2014) and “hiatus” (2000–14) periods.

Sensor-Specific Error Statistics for SST in the Advanced Clear-Sky Processor for Oceans

AbstractThe formulation of the sensor-specific error statistics (SSES) has been redesigned in the latest implementation of the NOAA Advanced Clear-Sky Processor for Oceans (ACSPO) to enable efficient use of SSES for assimilation of the ACSPO baseline regression SST (BSST) into level 4 (L4) analyses. The SSES algorithm employs segmentation of the SST domain in the space of regressors and derives the segmentation parameter from the statistics of regressors within the global dataset of matchups. For each segment, local regression coefficients and standard deviations (SDs) of BSST minus in situ SST are calculated from the corresponding subset of matchups. The local regression coefficients are used to generate an auxiliary product—piecewise regression (PWR) SST—and SSES biases are estimated as differences between BSST and PWR SST. Correction of SSES biases, which transforms BSST back into PWR SST, reduces the effects of residual cloud; variations in view zenith angle; and, during the daytime, diurnal surface warming. This results in significant reduction in the global SD of fitting in situ SST, making it comparable with SD for the Canadian Meteorological Centre (CMC) L4 SST. Unlike the foundation CMC SST (which is consistent with in situ SST at night but biased cold during the daytime), the PWR SST is consistent with in situ data during both day and night and thus may be viewed as an estimate of “depth” in situ SST. The PWR SST is expected to be a useful input into L4 SST analyses, especially for foundation SST products, such as the CMC L4.

A Multi-Channel Method for Retrieving Surface Temperature for High-Emissivity Surfaces from Hyperspectral Thermal Infrared Images.

The surface temperature (ST) of high-emissivity surfaces is an important parameter in climate systems. The empirical methods for retrieving ST for high-emissivity surfaces from hyperspectral thermal infrared (HypTIR) images require spectrally continuous channel data. This paper aims to develop a multi-channel method for retrieving ST for high-emissivity surfaces from space-borne HypTIR data. With an assumption of land surface emissivity (LSE) of 1, ST is proposed as a function of 10 brightness temperatures measured at the top of atmosphere by a radiometer having a spectral interval of 800–1200 cm−1 and a spectral sampling frequency of 0.25 cm−1. We have analyzed the sensitivity of the proposed method to spectral sampling frequency and instrumental noise, and evaluated the proposed method using satellite data. The results indicated that the parameters in the developed function are dependent on the spectral sampling frequency and that ST of high-emissivity surfaces can be accurately retrieved by the proposed method if appropriate values are used for each spectral sampling frequency. The results also showed that the accuracy of the retrieved ST is of the order of magnitude of the instrumental noise and that the root mean square error (RMSE) of the ST retrieved from satellite data is 0.43 K in comparison with the AVHRR SST product.

Diurnal cycling of sea surface temperature, salinity, and current in the CESM coupled climate model

AbstractA simple scheme is developed to represent Sea Surface Diurnal Cycling (SSDC) in Coupled General Circulation Models (CGCM). It follows Zeng and Beljaars [2005], but in addition to a night‐time deep well‐mixed ocean boundary layer and a deep day‐time stable layer, a shallow sub‐grid‐scale stable diurnal boundary layer is allowed to develop during the day, followed by a deepening convective layer. These four regimes have empirical property profiles and their governing parameters are determined by comparison of idealized experiments with published in situ and satellite observations. Mixing across the base of the shallow stable layer is governed by a gradient Richardson number, so prognostic equations are solved for salinity and current, as well as temperature. A conclusion is that the timing of peak warming depends on diurnal shear. The SSDC is implemented in the Community Earth System Model (CESM) for multiple purposes: the maximum diurnal amplitude of warming is found to exceed 5°C and to be more than 2°C over most of the ocean; the global distribution of average day‐time minus night‐time SST is used to validate the SSDC against a satellite SST product; and the mean seasonal surface heat flux and precipitation from an uncoupled CESM atmosphere are used to show the climate impacts that might be expected in a CGCM. Two major conclusions are that these impacts are not negligible and that much of the observed signals of diurnal cycling are captured by SSDC without the computational expense of resolving the relevant ocean processes.

Promoter hypermethylation-related reduced somatostatin production promotes uncontrolled cell proliferation in colorectal cancer.

BackgroundSomatostatin (SST) has anti-proliferative and pro-apoptotic effects. Our aims were to analyze and compare the SST expression during normal aging and colorectal carcinogenesis at mRNA and protein levels. Furthermore, we tested the methylation status of SST in biopsy samples, and the cell growth inhibitory effect of the SST analogue octreotide in human colorectal adenocarcinoma cell line.MethodsColonic samples were collected from healthy children (n1 = 6), healthy adults (n2 = 41) and colorectal cancer patients (CRCs) (n3 = 34) for SST mRNA expression analysis, using HGU133 Plus2.0 microarrays. Results were validated both on original (n1 = 6; n2 = 6; n3 = 6) and independent samples ((n1 = 6; n2 = 6; n3 = 6) by real-time PCR. SST expressing cells were detected by immunohistochemistry on colonic biopsy samples (n1 = 14; n2 = 20; n3 = 23). The effect of octreotide on cell growth was tested on Caco-2 cell line. SST methylation percentage in biopsy samples (n1 = 5; n2 = 5; n3 = 9) was defined using methylation-sensitive restriction enzyme digestion.ResultsIn case of normal aging SST mRNA expression did not alter, but decreased in cancer (p<0.05). The ratio of SST immunoreactive cells was significantly higher in children (0.70%±0.79%) compared to CRC (0%±0%) (p<0.05). Octreotide significantly increased the proportion of apoptotic Caco-2 cells. SST showed significantly higher methylation level in tumor samples (30.2%±11.6%) compared to healthy young individuals (3.5%±1.9%) (p<0.05).ConclusionsIn cancerous colonic mucosa the reduced SST production may contribute to the uncontrolled cell proliferation. Our observation that in colon cancer cells octreotide significantly enhanced cell death and attenuated cell proliferation suggests that SST may act as a regulator of epithelial cell kinetics. The inhibition of SST expression in CRC can be epigenetically regulated by promoter hypermethylation.

Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4): Part II. Parametric and Structural Uncertainty Estimations

Abstract Described herein is the parametric and structural uncertainty quantification for the monthly Extended Reconstructed Sea Surface Temperature (ERSST) version 4 (v4). A Monte Carlo ensemble approach was adopted to characterize parametric uncertainty, because initial experiments indicate the existence of significant nonlinear interactions. Globally, the resulting ensemble exhibits a wider uncertainty range before 1900, as well as an uncertainty maximum around World War II. Changes at smaller spatial scales in many regions, or for important features such as Niño-3.4 variability, are found to be dominated by particular parameter choices. Substantial differences in parametric uncertainty estimates are found between ERSST.v4 and the independently derived Hadley Centre SST version 3 (HadSST3) product. The largest uncertainties are over the mid and high latitudes in ERSST.v4 but in the tropics in HadSST3. Overall, in comparison with HadSST3, ERSST.v4 has larger parametric uncertainties at smaller spatial and shorter time scales and smaller parametric uncertainties at longer time scales, which likely reflects the different sources of uncertainty quantified in the respective parametric analyses. ERSST.v4 exhibits a stronger globally averaged warming trend than HadSST3 during the period of 1910–2012, but with a smaller parametric uncertainty. These global-mean trend estimates and their uncertainties marginally overlap. Several additional SST datasets are used to infer the structural uncertainty inherent in SST estimates. For the global mean, the structural uncertainty, estimated as the spread between available SST products, is more often than not larger than the parametric uncertainty in ERSST.v4. Neither parametric nor structural uncertainties call into question that on the global-mean level and centennial time scale, SSTs have warmed notably.

A COMPARATIVE STUDY ON UTILIZATION OF MULTI-SENSOR SATELLITE DATA TO DETECT POTENTIAL FISHING ZONE (PFZ)

Abstract. The satellite oceanography reveals the rolls on Potential Fishing Zone (PFZ) advisories in India is limited by the availability of the satellite data during the cloudy days and for the cloudy areas, because of the inability of the passive sensors to pass through the clouds. However, there is a huge demand from the fishermen community to provide PFZ advisories on cloudy days / monsoon period also as the period corresponds to the peak fishing season. Keeping in view of the demand and availability of the optimally interpolated merged product from Altimetry, it is proposed to utilize 4 km SST product obtained from the AVHRR. In view of this, a comparative analysis has been carried out on the feasibility of utilization of the Altimetry product for identification of PFZ Advisories. The analysis is carried out the synergize study on existing in AVHRR SST product are really matching with the high resolution EKE and SSHA products derived from Altimetry. From the analysis it was found that the Altimetry product is suitable for identifying cold core generation of waters for PFZ advisories with certain limitations. Also persistence of the ocean color environmental variables is cross-verified with catch weight observed from In-situ observation. The overall analysis derived from ocean color and altimetry products for delineating potential fishing zones enhance flawless information for future research.

Time-series measurements of settling particulate matter in Alfonso Basin, La Paz Bay, southwestern Gulf of California

More than 200 sediment trap samples were collected at 310 or 360m depth during 2002–2009 from the center of the 410m-deep Alfonso Basin in La Paz Bay, an arid, subtropical embayment of the southern Gulf of California. Sample splits were analyzed for total mass flux (TMF), particulate organic carbon (POC), inorganic carbon (CaCO3) and opal (biogenic silica BioSi). The lithogenic (Litho) and biogenic fluxes (Biogen), but especially the particulate organic matter (POM) and CaCO3, fluxes are relatively high compared with those recorded in a number of other coastal basins at depths less than ~500m. The average yearly Litho fluxes (mean of 133±158gm−2yr−1) are well correlated with the frequency of strong wind gusts and reflect the relative proximity of the mooring to shore and the importance of eolian transport. The sedimentation patterns are influenced by monsoonal shifts—cool temperatures and strong northerly winds in late fall and winter sustain a well-mixed deep surface layer and high lithogenic fluxes, whereas progressive heating and relatively weak southerlies in summer and fall lead to a shallower, more-stratified surface layer with lower nutrient levels, limited productivity and generally low particulate fluxes. There is considerable interannual variability in the size of the various fluxes. This is likely related to a number of regional and internal factors whose timing, intensity and interactions remain to be resolved.Although there is an inverse relationship between SST and satellite-derived net primary production (NPP) estimates, no correlation was found between NPP and the POC, CaCO3 and BioSi fluxes (r2<0.05 and p>0.05). Significant correlations (p<0.001) do exist, however, between the POC flux and the total mineral flux as well as with the CaCO3, Litho and BioSi fluxes (r=0.86, 0.82, 0.79 and 0.69, respectively). As suggested by the ballast ratio hypothesis, the strength of these correlations follows the relative density of the individual ballast components. Among the ballast minerals, the Litho fraction correlates strongly with CaCO3 (r=0.84), both fluxes being important during the windy cool season. The lithogenic fraction accounts for almost half of the total mass flux and is clearly a significant ballasting agent in this continental margin basin.

Somatostatin and diabetic retinopathy: current concepts and new therapeutic perspectives

Somatostatin (SST) is abundantly produced by the human retina, and the main source is the retinal pigment epithelium (RPE). SST exerts relevant functions in the retina (neuromodulation, angiostatic, and anti-permeability actions) by interacting with SST receptors (SSTR) that are also expressed in the retina. In the diabetic retina, a downregulation of SST production does exist. In this article, we give an overview of the mechanisms by which this deficit of SST participates in the main pathogenic mechanisms involved in diabetic retinopathy (DR): neurodegeneration, neovascularization, and vascular leakage. In view of the relevant SST functions in the retina and the reduction of SST production in the diabetic eye, SST replacement has been proposed as a new target for treatment of DR. This could be implemented by intravitreous injections of SST analogs or gene therapy, but this is an aggressive route for the early stages of DR. Since topical administration of SST has been effective in preventing retinal neurodegeneration in STZ-induced diabetic rats, it seems reasonable to test this new approach in humans. In this regard, the results of the ongoing clinical trial EUROCONDOR will provide useful information. In conclusion, SST is a natural neuroprotective and antiangiogenic factor synthesized by the retina which is downregulated in the diabetic eye and, therefore, its replacement seems a rational approach for treating DR. However, clinical trials will be needed to establish the exact position of targeting SST in the treatment of this disabling complication of diabetes.

Adaptive Reduction of Striping for Improved Sea Surface Temperature Imagery from Suomi National Polar-Orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS)

Abstract The Suomi National Polar-Orbiting Partnership (S-NPP) satellite was successfully launched on 28 October 2011. It carries five new-generation instruments, including the Visible Infrared Imaging Radiometer Suite (VIIRS). The VIIRS is a whiskbroom radiometer that scans the surface of the earth using a rotating telescope assembly, a double-sided half-angle mirror, and 16 individual detectors. Substantial efforts are being made to accurately calibrate all detectors in orbit. As of this writing, VIIRS striping is reduced to levels below those seen in corresponding Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) bands and meets the program specifications and requirements. However, the level 2 SST products derived from level 1 sensor data records (SDRs) thermal emissive bands still show residual striping. These artifacts reduce the accuracy of SST measurements and adversely affect cloud masking and the output of downstream applications, such as thermal front detection. To improve the quality of SST imagery derived from the VIIRS sensor, an adaptive algorithm was developed for operational use within the National Environmental Satellite, Data, and Information Service (NESDIS)’s SST system. The methodology uses a unidirectional quadratic variational model to extract stripe noise from the observed image prior to nonlocal filtering. Evaluation of the algorithm performance over an extended dataset demonstrates a significant improvement in the Advanced Clear-Sky Processor for Oceans (ACSPO) VIIRS SST image quality, with normalized improvement factors (NIF) varying between 5% and 25%.

Relationship of Northeast Atlantic albacore juveniles with surface thermal and chlorophyll-a fronts

When the spring seasonal warming starts, North Atlantic albacore (Thunnus alalunga) juveniles and pre-adults perform a trophic migration to the northeastern Atlantic, to the Bay of Biscay, and to the southeast of Ireland. During this migration, albacore juveniles are mainly exploited by Spanish trolling and baitboat fleets. The present study analyzes the relationship between the albacore spatio-temporal distribution and the upper surface horizontal fronts in their migration paths and destinations. For this, albacore catches from personal fishing logbooks from Basque trolling and live-bait fleets and daily MODIS AQUA Chlorophyll-a and SST products covering the period 2003–2005 have being used. Gradients have been calculated with the front algorithm proposed by Belkin and O'Reilly (2009). The approach used to study the relationship of catches location with frontal areas is based in the comparison of distributions of gradient magnitude around catch locations versus gradient magnitudes in a Monthly Occupation Area. The results obtained show that there is a high spatio- temporal variability of SST and Chl-a fronts in the area. SST and Chl-a fronts are not coincident in time or in space. However, there is a clear seasonal pattern of SST and Chl-a frontal activity in the area with a peak in July for SST gradient magnitudes and a peak in April for Chl-a gradient magnitudes. The relationship of albacore juvenile catches with high gradient magnitude areas is different according to the months and fleets analysed. In general, there is no evidence of consistent adherence of albacore catches to areas with higher SST gradients. However, results suggest a potential association between both fleets catches and Chl-a high gradient magnitude areas in August and September.

A Coastal Seawater Temperature Dataset for Biogeographical Studies: Large Biases between In Situ and Remotely-Sensed Data Sets around the Coast of South Africa

Gridded SST products developed particularly for offshore regions are increasingly being applied close to the coast for biogeographical applications. The purpose of this paper is to demonstrate the dangers of doing so through a comparison of reprocessed MODIS Terra and Pathfinder v5.2 SSTs, both at 4 km resolution, with instrumental in situ temperatures taken within 400 m from the coast. We report large biases of up to +6°C in places between satellite-derived and in situ climatological temperatures for 87 sites spanning the entire ca. 2 700 km of the South African coastline. Although biases are predominantly warm (i.e. the satellite SSTs being higher), smaller or even cold biases also appear in places, especially along the southern and western coasts of the country. We also demonstrate the presence of gradients in temperature biases along shore-normal transects — generally SSTs extracted close to the shore demonstrate a smaller bias with respect to the in situ temperatures. Contributing towards the magnitude of the biases are factors such as SST data source, proximity to the shore, the presence/absence of upwelling cells or coastal embayments. Despite the generally large biases, from a biogeographical perspective, species distribution retains a correlative relationship with underlying spatial patterns in SST, but in order to arrive at a causal understanding of the determinants of biogeographical patterns we suggest that in shallow, inshore marine habitats, temperature is best measured directly.