Climate Change Has Significant Influence on Growth of Cold-Water Corals

28-10-2011   Cold-water corals form coral hills mounds on the ocean floor. NIOZ scientist Cees van der Land demonstrated in his thesis that these coral mounds do not grow during ice ages, but rather become abraded. After the end of the most recent ice age, about 11,000 years ago, these mounds began to grow. Van der Land analyzed coral mounds off the west coast of Ireland and he will defend his thesis on these at the VU University Amsterdam on Monday 7 November 2011.

Deep in the ocean along the continental margin, where there is no sunlight, mound-like structures can be found that consist of cold-water corals. These mounds may be as high as 380 meters and extend for kilometers. For the past five years, Van der Land has studied the development of mounds at the southeast and southwest margin of the Rockall Trough off the west coast of Ireland in the Atlantic Ocean.

Van der Land established the influence of several different factors on the growth or abrasion of a mound by analyzing sediment cores from the tops of the mounds. The mounds turned out to become abraded rather than grow during periods of cold (ice ages). However, since the melting of the most recent ice caps about eleven thousand years ago, the mounds seem to have been growing continuously, so cold-water corals seem to grow best during periods of warmth.

Other factors of influence are the availability of food and the strength and intensity of ocean currents on and around the mounds. These currents may transport food and sediment.

In addition, coral branches turn out to ‘catch’ sediment particles in the skeleton structure of the coral, which makes the mounds grow faster. The amount and composition of these particles largely determine the growth rate of the mound.

Diagenesis beneath the surface of the mounds causes coral dissolution and lithification of sediment. This forms a solid layer on which new corals can grow. The solid layer also slows down the abrasion of the mound by ocean currents.  

Thesis title: Land, C. van der. Impact of Diagenesis on Carbonate Mound Formation, 192pp.
The thesis is available online.

Fig. 1. (A) Overview of the Rockall Trough area, west of Ireland (depth lines per 500 meter).
(B) Multibeam map showing part of the area to the southwest side of the Rockall Trough.

Fig. 2. (A) Sediment core drilling on board RV Pelagia.
(B and C) Cold-water corals found at the top of a coral hill.
(D) A sediment core is hoisted on board.

Fig.3. X-ray images (A and B) and electron microscope images (C and D) of a cold water coral hill. Close-up of layers in a sediment core dominated by coral and petrified layers.