9: Ice Rafted Debris Flashcards

1
Q

What can ice-rafted debris tell us about past climate?

A

Past ocean circulation patterns

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2
Q

What other sediment are we able to compare ice rafted debris to?

A

Forams

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3
Q

In the North Atlantic, what occurs when the global conveyor is “turned off”?

A

Very little deep-water formation -> gyre formation in N. Atlantic as the gulf stream takes a much more southerly route

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4
Q

What are Dansgaard-Oeschger cycles, Heinrich events and Bond cycles?

A

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.

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5
Q

What is the main proxy that accounts for the Dansgaard-Oeschger cycles and where was this proxy obtained?

A

Oxygen Isotopes, Greenland ice cores

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6
Q

What is the approximate length of a Dansgaard-Oeschger cycle?

A

~1500 year cycles (+/- 20%)

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7
Q

What occurs to ice rafted debris during a Heinrich event?

A

Sudden flood of ice rafted debris from ice sheets

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8
Q

What happens to the concentration of foram in Heinrich layers?

A

Drastically lowered

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9
Q

What is the approximate spread of coarse-grained detritus in the North Atlantic during a Heinrich event?

A

> 3000 km

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10
Q

What evidence do we have that a Heinrich event is a global event, not just a single ice sheet event?

A

Material deposited the same time from ice sheets from all different regions of the globe – Iceland, E/N Canada,

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11
Q

How is the source of sediment from Heinrich event determined to be primarily sourced from the Labrador Sea/Hudson Strait?

A

Isopachs of the Heinrich layer 1 (H-1) stretching out to N. Atlantic

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12
Q

What three things may control the magnetic signatures of sediment carried by ice?

A

Source rock type, amount of material, grain size dependency (?)

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13
Q

How can source rock type vary in ice-rafted debris?

A

Magnetic content (sediment > volcanic), magnetic mineral comp/size

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14
Q

Why might the amount of magnetic material vary in sediment deposits from ice rafted debris?

A

Mixed with other sediment components, dispersal and dilution processes

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15
Q

What does susceptibility look like for the Heinrich events, and why?

A

Peaks in susceptibility, as the material is basaltic (Icelandic) and sedimentary Canadian shield material

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16
Q

What name could you put to the lithology of the Laurentide ice sediment source?

A

Dolomite

17
Q

What magnetic parameters (and direction) were found for the Laurentide ice source?

A

High susceptibility, low Hcr, S-ratio

18
Q

What name could you put to the lithology of the European sediment source – i.e. non-Laurentide?

A

Chalk

19
Q

What is the primary reason for studying magnetic parameters of ice rafted debris?

A

To determine the primary source of the sediments and thus aid understanding of ice and climatic change

20
Q

What does the strong regional differences in magnetic parameters mean in terms of ice rafted debris?

A

Source characteristics, supply routes, ice catchments

21
Q

What secondary form of transportation is relevant to ice rafted debris studies?

A

Bottom transport of silt

22
Q

What is the relevance of ocean circulation models in terms of magnetic parameters?

A

Two models: northern sinking state and southern sinking state – magnetic parameters to determine which

23
Q

What are the four features of northern sinking water?

A

NADW formation vigorous, SWestward EGC, Labrador sea gyre + north extension of NAD, strong northeasterly NAD

24
Q

What are the four features of southern sinking water?

A

All deep water produced in southern ocean, SWestward EGC, no Labrador sea gyre, southward extension of EGC, weak easterly NAD