Background
When viewed under long-wave UV light, slices of coral cores may reveal bright yellow luminescent lines that are readily distinguished by the human eye.  These lines were first described by Isdale (1984), who observed them in an inshore Great Barrier Reef Porites colony.  Their relative locations within the cores, in the authors' words, were "closely related to the timing and intensity of runoff from Queensland's largest river, the Burdekin (Isdale, 1984; Isdale et al., 1998), and also Queensland summer monsoon rainfall (Lough, 1991)."  Originally, the lines were "attributed to terrestrial humic substances incorporated into the coral skeleton during river flood events (Boto and Isdale, 1985; Susic et al., 1991)."  More recently, however, Barnes and Taylor (2001) have concluded they are "the result of reduced calcification as the coral responds to low salinity conditions associated with coastal runoff."

What was done
Based on the relative locations of yellow luminescent lines seen in multi-century Porites cores obtained from eight different locations on the central Great Barrier Reef, the authors developed "a 373-year chronology by cross-dating techniques adapted from dendrochronology."  This master chronology, dating back to AD 1615, proved to be a good proxy for both Burdekin River runoff and Queensland summer rainfall.

What was learned
In the words of the authors, their data demonstrate that "low-salinity runoff regularly reached the main reef tract during the relatively wet decades of the late 1890s, 1910s, 1950s and 1970s."  They also found that "Burdekin River runoff was significantly inversely related to ENSO variability for much of the period from the AD 1650s to 1800."

What it means
The authors' observations provide additional support for the findings described in our Editorial of 26 March 2003, i.e., the huge (5- to 10-fold) increase in sediment transfer to the Great Barrier Reef that commenced shortly after European settlement of the Burdekin catchment that began in 1862, which well-entrenched phenomenon we believe to be responsible for predisposing today's corals to bleach more readily than they did in the past in response to periodic increases in water temperature.

The authors also suggest "that ENSO-related teleconnections were as dominant then [the 1650s to 1800] as in recent decades."  Indeed, they unequivocally state that "recent evidence for decadal variability in the strength of ENSO and its teleconnections is not confined to the period of the instrumental record and has occurred over the past several centuries," some of which periods, we note, were much colder than what climate alarmists typically refer to as the "unprecedented" warmth of the latter part of the 20th century.  The authors thus conclude that "such variability must, therefore, be a mode of 'natural' climate variability."  This finding clearly indicates that global warming does not enhance "the strength of ENSO and its teleconnections," which conclusion clearly refutes the contrary claims of the world's climate alarmists.

References
Barnes, D.J. and Taylor, R.B.  2001.  On the nature and causes of luminescent lines and bands in coral skeletons.  Coral Reefs 20: 221-230.

Boto, K. and Isdale, P.J.  1985.  Fluorescent bands in massive corals result from terrestrial fulvic acid inputs to nearshore zone.  Nature 315: 396-397.

Isdale, P.  1984.  Fluorescent bands in massive corals record centuries of coastal rainfall.  Nature 310: 578-579.

Isdale, P.J., Stewart, B.J., Tickle, K.S. and Lough, J.M.  1998.  Palaeohydrological variation in a tropical river catchment - a reconstruction using fluorescent bands in corals of the Great Barrier Reef, Australia.  The Holocene 8: 1-8.

Lough, J.M.  1991.  Rainfall variations in Queensland, Australia: 1891-1986.  International Journal of Climatology 11: 745-768.

Susic, M., Boto, K.G.B. and Isdale, P.J.  1991.  Fluorescent humic bands in coral skeletons originate from terrestrial runoff.  Marine Chemistry 33: 91-104.