Thermal waves on the Queensland shelf

Abstract

Thermocline waves are found on the continental slope and shelf of Queensland. Slope waves of period near 90 days accompany upwelling and downwelling. Shelf thermal waves are created by onshore surges of shelf- break water, which is 1-4.5�C cooler than lagoon water, depending on the season. The bottom surges are investigated by means of the cross-spectra of temperatures with longshore winds, with atmospheric pressure and with mean sea level. Longshore winds are found to be the driving mechanism and significant coherence is found near periods of 4 and 8 days (summer and winter, respectively) and in a band with periods of 10-70 days, perhaps peaking near 30 days. Correlation and cross-spectral analyses of temperature at sites 100 km apart suggest that the short period thermal waves popagate equatorward wheras the long period waves, which contain most of the thermal covariance, form a standing mode. Cross-spectral analysis of the root mean square amplitude of diurnal thermal variations with the longer-period thermal waves suggests that localized tidal upwelling brings bottom water over reefs.

Linear systems analysis of momentum on the continental shelf and slope of the central Great Barrier Reef

“…Such waves, trapped both in the GBR lagoon and at the shelf break, may propagate into the central GBR from generation regions in the southern GBR [Middleton and Cunningham, 1984] or from regions further south [Griffin and Middleton, 1986;Freeland et al, 1986]. Boundary current meanders [Andrews, 1983] and shelf break eddies [Wolanski, 1986a; D. M. Burrage et al, manuscript in review, 1991] are another possible source of significant shelf break current variability. We have thus established the feasibility of simply and economically hindcasting time-varying and mean currents in the central GBR using a suite of linear systems models forced by readily obtainable meteorological and oceanographic time series.…”

Strontium/calcium ratios in modern porites corals From the Great Barrier Reef as a proxy for sea surface temperature: Calibration of the thermometer and monitoring of ENSO

“…According to the previous authors, stratification results in no more than 0.3øC variation between surface and bottom temperatures. Andrews [1983b] showed the GBR Lagoon water and the Coral Sea surface water around 20øS have similar temperatures, but surges of cooler shelf-break water occur periodically and can be traced across the shelf on bottom water records. However, these incursions of cool water, characterized by short spikes of 1 øC on daily temperature records, have not been observed at Davies Reef, which is 40 km away from the shelf edge ( Figure 1).…”

Intrusive upwelling in the Central Great Barrier Reef

“…At the outer‐shelf, the near‐surface and near‐bottom T/S characteristics are significantly different during the peak of the intrusion (Figures b and d) reflecting different water masses. Cooler, saltier water near the seafloor corresponds with shelf‐break water which connects the onshore Lagoon Water with deeper Subtropical Lower Water (SLW) over the slope (see Figure in Andrews [] and Figure in Andrews []). SLW has been identified with a maximum salinity of 35.7 psu at a depth of 150 m [ Andrews , ].…”

“…Journal of Geophysical Research: Oceans 10.1002/2016JC012294 water masses. Cooler, saltier water near the seafloor corresponds with shelf-break water which connects the onshore Lagoon Water with deeper Subtropical Lower Water (SLW) over the slope (see Figure 3 in Andrews [1983a] and Figure 4 in Andrews [1983b]). SLW has been identified with a maximum salinity of 35.7 psu at a depth of 150 m [Andrews, 1983a].…”

“…The winds are characterized by southeasterly trade winds from April to October and are more variable, including poleward winds, during the summer monsoon [Wolanski, 1994]. Poleward flow can induce an onshore bottom Ekman transport advecting cooler water onshore [Andrews and Gentien, 1982;Andrews, 1983b]. Time series from 1980 to 1983 at Rib Reef, in Palm Passage, revealed large intrusion events associated with poleward wind bursts and onshore currents near the bottom [ Figure 5 in Andrews and Gentien, 1982; Figure 2 in Andrews and Furnas, 1986].…”