The frigid underwater world of the Canadian Arctic is among the most poorly known regions on the planet; yet environmentally it is under assault. Drastic change could come upon us explosively, within decades, if we do not understand and deal with it now. Walter Adey has spent many years exploring the Labrador Sea with a team of graduate students using SCUBA to retrieve samples of rock-hard coralline algae. The data bank they’ve collected now numbers more than 3,000 specimens – every one of which can be dated by reading their yearly growth rings, similar to tree rings. However, as Scanning Electron Microscope images show, the layers here are arrays of calcite crystals intricately arrayed around cells, and dependent on temperature and salinity. Jochen Halfar, Adey’s geochemist associate, with sophisticated instrumentation, can determine rather precisely what critical seawater parameters were for every month of the lifetime of each plant – even whether the overlying sea was frozen or not! Both scientists are working on samples from the Labrador and Bering Seas. Some of the calcified algae samples are more 800 years old. This priceless record may well prove to be the ”missing link” needed to convince skeptics that global warming is not just a cyclical phase, but a very real and dangerous change that will irrevocably alter our planet – probably sooner than most scientists have expected.

Fig. A
Fig. A
Diver chipping-off a 450 year-old mound of Clathromorphum compactum from a 15 meter deep boulder in Labrador. The surrounding coralline carbonate pavement (cor-strome) harbors a rich infauna of boring invertebrates (bivalves and worms), numerous grazers (limpets, chitons and small sea urchins) and filter feeders (brittle stars, bryozoans and worms).
  Fig. B
Fig. B
Diamond-sawed section, and polished surface, of a Clathromorphum compactum mound like that shown in Fig. A. This specimen, with many, clear yearly rings, is about 250 years old. The holes are reproductive structures (conceptacles) which form abundantly in some years.
 
Fig. C
Fig. C  (click to enlarge)
Scanning Electron Microscope view, at 50X, of a different species of Clathromorphum, from the Aleutian Islands. The yearly layers of tissue, with cells impregnated with calcium carbonate and with abundant conceptacles, formed each winter, are clearly visible.
  Fig. D
Fig. D  (click to enlarge)
Index showing the extent of Clathromorphum compactum carbonate buildup as a function of depth and wave exposure, on a background diagram showing the dominant seaweeds and invertebrates. Labrador coast in the northwest Atlantic Subarctic.
Fig. D
Fig. E   (click to enlarge)
Yearly growth rates of Clathromorphum compactum from south to north (Gulf of Maine to Northern Baffinland) in the northwestern North Atlantic. These crusts grow continuously, slower in winter than summer. The amount of magnesium in the calcite laid down in cell walls, weekly to monthly, shows the change of water temperature with time over many hundreds of years in the past. Along with other changing measures of elements and isotopes, these corallines can provide an extensive archive of past water and atmospheric climate.
  Fig. D
Fig. F (click to enlarge)
All growth and calcite deposition in Clathromorphum species occurs in a meristem (cambium) below a thick layer of photosynthetic (epithallial) cells. As this 5000X SEM image shows, the growth and calcite deposition is complex (inner wall and inter-filament), but occurs in a well-defined plane of growth. This provides a precision match of chemical characteristics to water state that would be more diffuse with coralline species that spread their growth out with depth in the crust.
 


Copyright © 2008-2013, Walter H. Adey, PhD.