Ice-Rafted Debris (IRD) And Global Climate Change (1)

Dr. Jens Bischof, Research Assistant Professor in the Department of Ocean, Earth, and Atmospheric Sciences at Old Dominion University (ODU) in Virginia, gave a presentation on his research on what is known as Ice-Rafted Debris (IRD) found at the ocean floor (his studies are conducted mostly in the Arctic Ocean).  The presentation was sponsored by Science and Reason in Hampton Roads (SRHR), and the Old Dominion University Department of Ocean, Earth, and Atmospheric Sciences.  Dr. Bischof has written a book about this subject, Ice Drift, Ocean Circulation, and Climate Change  (Praxis Publishing, 2000).
 
"As a geologist, Bischof's main interest is the reconstruction of ocean and atmospheric circulation patterns.  He notes that ice, wherever it forms in contact with land, encloses rock and mineral debris from its point of origin, which is eventually dropped as the ice drifts along in the ocean and melts.
 
The drifting, or rafting, ice leaves a trail of debris as deep-sea sediments.  Debris found in up to 1.5 million-year-old sediments from the Arctic Ocean, originally scraped from land masses by glaciers as they moved toward the sea, reveals complex circulation patterns of ocean surface currents, some of which are remarkably different from those of today." ⁽²⁾
 
Bischof's group take 1-meter long core samples from the ocean floor, which represents about 300,000 years of settled sediment.  The marine-life shells in the core sample are carbon-dated to establish the age at each point along the core. Fine mineral particles (less than 50 microns) in the core are assumed to have been transported by wind.  Particles larger than 50 microns are too heavy to be wind-dispersed, and are assumed to have been transported by icebergs and floes; these are the Ice-Rafted Debris (IRD).
 
The IRD is then characterized by mineral type (eg: quartz, carbonates, coal, and other types) and matched to known mineral outcroppings adjacent to the Arctic Ocean.  By linking these IRD rock and mineral grains, which were transported by drifting ice during times of continental glaciations, to their respective sources, Bischof and his colleagues were able to determine the directions of past ocean surface currents and to reconstruct an increasingly accurate picture of past climate changes.  The results of this work contributes to improving the accuracy of climate models used to predict future climate change.  The main findings are:

• very large variations in various IRD abundances with time, and
• typically, two main ocean circulation patterns that alternate with each other, frequently
  on time scales much less than the time resolution of the data (about 1000 - 3000 years).

Bischoff's group looked at the Norwegian Sea (between Norway and Greenland, north of Iceland), where there are not any icebergs today because the remnants of the warm Gulf Stream now go north through the area.
 
The Norwegian Sea cores showed almost no IRD in the Holocene Era (the last 10,000 years of earth history) when it was quite warm.  There was some IRD before then during the last Ice Age.  There was also an increase in IRD in very recent years.  This seems to indicate that the Gulf Stream (at least as it exits north thru the Norwegian Sea) can turn off and on, and is doing so now (ie., during the last several thousand years).
 
Bischof also finds that IRD is not well-correlated with average global temperature; the ¹⁸O abundance in marine shells correlates with global temperature much better (normal oxygen is ¹⁶O; ¹⁸O is the heavier isotope).  During the Holocene Era, global temperature was very steady.  However, the IRD record (in the same sediment cores) shows very sharp, very large spikes.  Perhaps these are caused by the collapse of ice sheets (such as just happened in Antartica).
 
Bischof also discussed larger climate issues:

• We know that global climate oscillates on its own with a period of decades.  We also know that the Arctic has been warming significantly since the 1970s.  We don't know if this is a trend or part of an oscillation.
   
  
• Temperature has correlated with atmospheric CO₂ levels over the last 100,000 years.  However, We don't know which is causal.  If CO₂ is causal, then it should lead the temperature behavior (ie., the CO₂ increase should precede the temperature increase, not happen at the same time).
   
  
• There is the possibility of swift, catastrophic change.  For example, warming underneath an ice sheet will significantly reduce friction and let the ice sheet slide rapidly into the ocean.  This would result in an equally rapid sea level rise that would, among other things, kill coral (since coral needs to be close to the surface and grows fairly slowly).  Evidence of massive coral die-offs in the Caribean between 100,000 and 600,000 years ago has been discovered.
   
  
• We also know from Greenland ice cores that temperature can change as much as 9 degrees C in 3 years.

In summation, we do not understand the direct cause of these climate changes.  Our climate models are very crude.  Therefore we cannot know that the changes we have observed in the last 100 years are anthropogenic (human-caused) or not.  We could be on the brink of a catastrophe.

Ice-Sheet Terminology:
 

 
Science and Reason in Hampton Roads (www.ScienceAndReason.org) is an organization devoted to the critical examination of dubious or extraordinary claims. It has organized haunted house investigations, Superstition Celebrations, and talks on topics from UFOs to alternative medicine.
 
For more information, contact Larry Weinstein, Professor of Physics and SRHR President, at 757-683-5803 or at weinstei@physics.odu.edu.

Related Link:
    Direct And Proxy Records Used For Understanding Climate Change

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(1) Adapted from a review of the presentation by Dr. Larry Weinstein,  President,
      Science And Reason In Hampton Roads (SRHR).
 
(2) "New Book's Findings From Arctic Ice Research Cast Doubt On Global Warming Trend",
      James L. Lidington,  The Courier,  Old Dominion University,  Vol. 30,  Issue 11,  May 18,
      2001.