Minor Heat: Hot winds arrive

January 10th, 2012
by Jo Law

This pentad has recorded the highest monthly maximum to-date of 26.3ºC on Tuesday January 10th at 11.46am at Bellambi AWS. The Illawarra also experienced some rainfall in the past five days, bringing the monthly total at Bellambi AWS to 10.6mm. We were examining the remanants left by the tide on Coledale beach when we were caught in the brief but heavy showers. At the time, the 15:06 low tide of 0.4m exposed rock formation normally underwater way out to sea, presenting us with an almost entirely different seascape.The fornightly alignment of the moon, the sun, and Earth produces spring tides, that is: above average high tides and below average low tides. The king tides experienced on the Australian east coast in the summer months are spring tides enhanced by Earth’s close proximity to the the sun during this time. (Incidentally in 2012, Earth was at perihelion, the closest point to the Sun in its elliptical orbit on January 5th ). The combined gravitational pull of our two celestial neighbours produces exceptionally high tides as well as exceptionally low ones. These dramatic semi-diurnal changes to coast line provide some opportunities to get a glimpse of intertidal marine life.

The Illawarra coast is classified as belonging to the Eastern Warm Temperate Zone which stretches from southern Queensland to northern Tasmania. This zone shares some common species and the recent low tides offer life at infralittoral fringe (low shore fringe) up for view. The rocky shore is home to the swift Red Bait Crabs (Plagusia chabrus), the abundant Common Ear Shell (Haliotis rubra), the ubiquitous Common Warrener (Turbo undulata), and many other whelks, shells, and snails. A moderate variety of algae species is also present. On visiting Wombarra beach today shortly after the 0.3m 16:21 low tide, Hollis was examining each type of seaweed at length. He was particularly attracted to the Green Sea Velvet (Codium fragile), compelled to give each one he encountered a good stroke.

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