9: Ice Rafted Debris Flashcards
What can ice-rafted debris tell us about past climate?
Past ocean circulation patterns
What other sediment are we able to compare ice rafted debris to?
Forams
In the North Atlantic, what occurs when the global conveyor is “turned off”?
Very little deep-water formation -> gyre formation in N. Atlantic as the gulf stream takes a much more southerly route
What are Dansgaard-Oeschger cycles, Heinrich events and Bond cycles?
Bond Cycles = growth and sudden depletion of ice sheets, the point at which the depletion begins is called a Heinrich event. Within the bond cycles there are numerous Dansgaard-Oeschger cycles that are rapid warming and cooling cycles.
What is the main proxy that accounts for the Dansgaard-Oeschger cycles and where was this proxy obtained?
Oxygen Isotopes, Greenland ice cores
What is the approximate length of a Dansgaard-Oeschger cycle?
~1500 year cycles (+/- 20%)
What occurs to ice rafted debris during a Heinrich event?
Sudden flood of ice rafted debris from ice sheets
What happens to the concentration of foram in Heinrich layers?
Drastically lowered
What is the approximate spread of coarse-grained detritus in the North Atlantic during a Heinrich event?
> 3000 km
What evidence do we have that a Heinrich event is a global event, not just a single ice sheet event?
Material deposited the same time from ice sheets from all different regions of the globe – Iceland, E/N Canada,
How is the source of sediment from Heinrich event determined to be primarily sourced from the Labrador Sea/Hudson Strait?
Isopachs of the Heinrich layer 1 (H-1) stretching out to N. Atlantic
What three things may control the magnetic signatures of sediment carried by ice?
Source rock type, amount of material, grain size dependency (?)
How can source rock type vary in ice-rafted debris?
Magnetic content (sediment > volcanic), magnetic mineral comp/size
Why might the amount of magnetic material vary in sediment deposits from ice rafted debris?
Mixed with other sediment components, dispersal and dilution processes
What does susceptibility look like for the Heinrich events, and why?
Peaks in susceptibility, as the material is basaltic (Icelandic) and sedimentary Canadian shield material
What name could you put to the lithology of the Laurentide ice sediment source?
Dolomite
What magnetic parameters (and direction) were found for the Laurentide ice source?
High susceptibility, low Hcr, S-ratio
What name could you put to the lithology of the European sediment source – i.e. non-Laurentide?
Chalk
What is the primary reason for studying magnetic parameters of ice rafted debris?
To determine the primary source of the sediments and thus aid understanding of ice and climatic change
What does the strong regional differences in magnetic parameters mean in terms of ice rafted debris?
Source characteristics, supply routes, ice catchments
What secondary form of transportation is relevant to ice rafted debris studies?
Bottom transport of silt
What is the relevance of ocean circulation models in terms of magnetic parameters?
Two models: northern sinking state and southern sinking state – magnetic parameters to determine which
What are the four features of northern sinking water?
NADW formation vigorous, SWestward EGC, Labrador sea gyre + north extension of NAD, strong northeasterly NAD
What are the four features of southern sinking water?
All deep water produced in southern ocean, SWestward EGC, no Labrador sea gyre, southward extension of EGC, weak easterly NAD
