Measurements of the local energy balance over a coral reef flat, Heron Island, southern Great Barrier Reef, Australia (original) (raw)
Related papers
Journal of Climate, 2008
A regional-scale estimate of the surface heat budget of the Great Barrier Reef and Coral Sea (10°–26°S, 142°–155°E) has been developed for the period 1995–2005 in the hope of understanding the trends of sea surface temperatures and the surface heat balance. This report describes the methodology to acquire input parameters from satellite observations, the resultant individual components of the surface heat budget, and their validation with existing datasets and surface measurements. The accuracy of individual flux components of the heat budget were analyzed with an array of surface measurements. Derived monthly averaged latent and sensible heat flux estimates show RMS errors of approximately 25.2 and 3.4 W m−2, respectively. Monthly averaged longwave and shortwave radiation flux estimates show RMS errors of approximately 6.7 and 13.3 W m−2, respectively. These improved estimates allow a higher confidence in studies that examine recent sea surface temperature (SST) trends and observed...
We examined the seasonal and spatial variability in the temperatures of nearshore reef waters over 19 months across Coral Bay at Ningaloo Reef, Western Australia. Local deviations in the mean daily temperature of nearshore reef waters from offshore values (DT) were a linear function of the combined effect of net atmospheric heating (Q net ) and offshore wave height and period H s ffiffiffiffi ffi t p p . Whereas intra-annual variation in local heat exchange was driven mainly by seasonal changes in shortwave radiation, intra-annual variation in local cooling was driven mostly by changes in relative humidity (r 2 5 0.60) and wind speed (r 2 5 0.31) that exhibited no apparent seasonality. We demonstrate good agreement between nearshore reef temperatures modeled from offshore sea surface temperatures, offshore wave forcing, and local atmospheric heat fluxes with observed temperatures using a simple linear model (r 2 5 0.31-0.69, root-mean-square error 5 0.4-0.9uC). Using these modeled nearshore reef temperature records, we show that thermal stresses across the reef reached between 16uC weeks and 22uC weeks in the summer of 2011 when a mass coral bleaching event was reported, and between 12uC weeks and 13uC weeks in the following summer of 2012 when no mass bleaching was reported. After compensating for differences between observed and modeled thermal stresses, we found that maximum thermal stresses across the reef likely reached as high as 18-34uC weeks in the summer of 2011. The approach used here could thus improve our ability to predict spatial variation in thermal stress and bleaching across other wavedriven nearshore reef systems.
1] We investigate how local atmospheric conditions and hydrodynamic forcing contributed to local variations in water temperature within a fringing coral reef-lagoon system during the peak of a marine heat wave in 2010-2011 that caused mass coral bleaching across Western Australia. A three-dimensional circulation model Regional Ocean Modeling System (ROMS) with a built-in air-sea heat flux exchange module Coupled Ocean Atmosphere Experiment (COARE) was coupled with a spectral wave model Simulating Waves Nearshore (SWAN) to resolve the surface heat exchange and wave-driven reef circulation in Coral Bay, Ningaloo Reef. Using realistic oceanic and atmospheric forcing, the model predictions were in good agreement with measured time series of water temperature at various locations in the coral reef system during the bleaching event. Through a series of sensitivity analyses, we found that the difference in temperature between the reef and surrounding offshore waters (DT) was predominantly a function of both the daily mean net heat flux (Q net ) and residence time, whereas diurnal variations in reef water temperature were dependent on the diurnal fluctuation in the net heat flux. We found that reef temperatures were substantially higher than offshore in the inner lagoon under normal weather conditions and over the entire reef domain under more extreme weather conditions (0.7 C-1.5 C). Although these temperature elevations were still less than that caused by the regional ocean warming (2 C-3 C), the arrival of peak seasonal temperatures in the summer of 2010-2011 (when net atmospheric heat fluxes were positive and abnormally high) caused substantially higher thermal stresses than would have otherwise occurred if offshore temperatures had reached their normal seasonal maxima in autumn (when net atmospheric heat fluxes were negative or cooling). Therefore, the degree heating weeks calculated based on offshore temperature substantially underestimated the thermal stresses experienced by the reef in the period leading up to the observed bleaching event (3 versus 11 C-weeks).
2014
The U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) program has developed a daily global 5-km product suite based on satellite observations to monitor thermal stress on coral reefs. These products fulfill requests from coral reef managers and researchers for higher resolution products by taking advantage of new satellites, sensors and algorithms. Improvements of the 5-km products over CRW's heritage global 50-km products are derived from: (1) the higher resolution and greater data density of NOAA's next-generation operational daily global 5-km geo-polar blended sea surface temperature (SST) analysis; and (2) implementation of a new SST climatology derived from the Pathfinder SST climate data record. The new products increase near-shore coverage and now allow direct monitoring of 95% of coral reefs and significantly reduce data gaps caused by cloud cover. The 5-km product suite includes SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks and Bleaching Alert Area, matching existing CRW products. When compared with the 50-km products and in situ bleaching observations for 2013-2014, the 5-km products identified known thermal stress events and matched bleaching observations. These near reef-scale products significantly advance the ability of coral reef researchers and managers to monitor coral thermal stress in near-real-time.
The U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) program has developed a daily global 5-km product suite based on satellite observations to monitor thermal stress on coral reefs. These products fulfill requests from coral reef managers and researchers for higher resolution products by taking advantage of new satellites, sensors and algorithms. Improvements of the 5-km products over CRW’s heritage global 50-km products are derived from: (1) the higher resolution and greater data density of NOAA’s next-generation operational daily global 5-km geo-polar blended sea surface temperature (SST) analysis; and (2) implementation of a new SST climatology derived from the Pathfinder SST climate data record. The new products increase near-shore coverage and now allow direct monitoring of 95% of coral reefs and significantly reduce data gaps caused by cloud cover. The 5-km product suite includes SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks and Bleaching Alert Area, matching existing CRW products. When compared with the 50-km products and in situ bleaching observations for 2013–2014, the 5-km products identified known thermal stress events and matched bleaching observations. These near reef-scale products significantly advance the ability of coral reef researchers and managers to monitor coral thermal stress in near-real-time.
Small-Scale Spatial Analysis of In Situ Sea Temperature throughout a Single Coral Patch Reef
Journal of Marine Biology, 2011
Thermal stress can cause geographically widespread bleaching events, during which corals become decoupled from their symbiotic algae. Bleaching, however, also can occur on smaller, spatially patchy scales, with corals on the same reef exhibiting varying bleaching responses. Thus, to investigate fine spatial scale sea temperature variation, temperature loggers were deployed on a 4 m grid on a patch reef in Kāne'ohe Bay, Oahu, Hawai'i to monitor in situ, benthic temperature every 50 minutes at 85 locations for two years. Temperature variation on the reef was characterized using several summary indices related to coral thermal stress. Results show that stable, biologically significant temperature variation indeed exists at small scales and that depth, relative water flow, and substrate cover and type were not significant drivers of this variation. Instead, finer spatial and temporal scale advection processes at the benthic boundary layer are likely responsible. The implications for coral ecology and conservation are discussed.
Observations of the thermal environment on Red Sea platform reefs: a heat budget analysis
Coral Reefs, 2011
Hydrographic measurements were collected on nine offshore reef platforms in the eastern Red Sea shelf region, north of Jeddah, Saudi Arabia. The data were analyzed for spatial and temporal patterns of temperature variation, and a simple heat budget analysis was performed with the goal of advancing our understanding of the physical processes that control temperature variability on the reef. In 2009 and 2010, temperature variability on Red Sea reef platforms was dominated by diurnal variability. The daily temperature range on the reefs, at times, exceeded 5°C-as large as the annual range of water temperature on the shelf. Additionally, our observations reveal the proximity of distinct thermal microclimates within the bounds of one reef platform. Circulation on the reef flat is largely wave driven. The greatest diurnal variation in water temperature occurs in the center of larger reef flats and on reefs protected from direct wave forcing, while smaller knolls or sites on the edges of the reef flat tend to experience less diurnal temperature variability. We found that both the temporal and spatial variability in water temperature on the reef platforms is well predicted by a heat budget model that includes the transfer of heat at the air-water interface and the advection of heat by currents flowing over the reef. Using this simple model, we predicted the temperature across three different reefs to within 0.4°C on the outer shelf using only information about bathymetry, surface heat flux, and offshore wave conditions.
PLoS ONE, 2013
Evidence of global climate change and rising sea surface temperatures (SSTs) is now well documented in the scientific literature. With corals already living close to their thermal maxima, increases in SSTs are of great concern for the survival of coral reefs. Cloud feedback processes may have the potential to constrain SSTs, serving to enforce an ''ocean thermostat'' and promoting the survival of coral reefs. In this study, it was hypothesized that cloud cover can affect summer SSTs in the tropics. Detailed direct and lagged relationships between cloud cover and SST across the central Great Barrier Reef (GBR) shelf were investigated using data from satellite imagery and in situ temperature and light loggers during two relatively hot summers (2005 and 2006) and two relatively cool summers (2007 and 2008). Across all study summers and shelf positions, SSTs exhibited distinct drops during periods of high cloud cover, and conversely, SST increases during periods of low cloud cover, with a three-day temporal lag between a change in cloud cover and a subsequent change in SST. Cloud cover alone was responsible for up to 32.1% of the variation in SSTs three days later. The relationship was strongest in both El Niñ o (2005) and La Niñ a (2008) study summers and at the inner-shelf position in those summers. SST effects on subsequent cloud cover were weaker and more variable among study summers, with rising SSTs explaining up to 21.6% of the increase in cloud cover three days later. This work quantifies the often observed cloud cooling effect on coral reefs. It highlights the importance of incorporating local-scale processes into bleaching forecasting models, and encourages the use of remote sensing imagery to value-add to coral bleaching field studies and to more accurately predict risks to coral reefs.
Thermally Driven Exchanges between a Coral Reef and the Adjoining Ocean
Journal of Physical Oceanography, 2006
In this paper hydrographic observations made over a fringing coral reef at the northern end of the Gulf of Aqaba near Eilat, Israel, are discussed. These data show exchange flows driven by the onshore-offshore temperature gradients that develop because shallow regions near shore experience larger temperature changes than do deeper regions offshore when subjected to the same rate of heating or cooling. Under heating conditions, the resulting vertically sheared exchange flow is offshore at the surface and onshore at depth, whereas when cooling dominates, the pattern is reversed. For summer conditions, heating and cooling are both important and a diurnally reversing exchange flow is observed. During winter conditions, heating occupies a relatively small fraction of the day, and only the cooling flow is observed. When scaled by ⌬V, the observed profiles of the cross-shore during cooling velocity collapse onto a single curve. The value of ⌬V depends on the convective velocity scale u f and the bottom slope  through the inertial scaling, ⌬V ϳ  Ϫ1/3 u f first proposed by Phillips in the 1960s as a model of buoyancy-driven flow in the Red Sea. However, it is found that turbulent stresses associated with the longshore tidal flows and unsteadiness due to the periodic nature of the buoyancy forcing can act to weaken the sheared exchange flow. Nonetheless, the measured exchange flow transport agrees well with previous field and laboratory work. The paper is concluded by noting that the "thermal siphon" observed on the Eilat reef may be a relatively generic feature of the nearshore physical oceanography of reefs and coastal oceans in general.
Continental Shelf Research, 2014
A good understanding of diurnal warming in the upper ocean is important for the validation of satellitederived sea surface temperature (SST) against in-situ buoy data and for merging satellite SSTs taken at different times of the same day. For shallow coastal regions, better understanding of diurnal heating could also help improve monitoring and prediction of ecosystem health, such as coral reef bleaching.