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Marine Geology > Paleoclimate Proxies > Flashcards

Paleoclimate Proxies Flashcards

1
Q

What is the main location to look at for the Marine Archive of Global Change?

A

Deep Ocean

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2
Q

Why is the deep ocean the preferred record?

A
  1. Quiet Environment: Deep Ocean is away from waves, tides, rivers, and turbidity currents you’re in a generally quiet environment. Much of the seafloor is terrigenous mud (Illite) and in shallow areas calcareous ooze.
  2. Relatively continuous deposition
  3. Low bioturbation in deep sediments (not a lot of living organisms living in the deep ocean)
  4. Higher quality climate records than found on land. On land erosion and human impacts affect the climate records.
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3
Q

What are the three types of Paleoenvironmental Proxies?

A
  1. Geological
  2. Biotic
  3. Geochemical
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4
Q

What are the three types of Geological Proxies?

A
  1. Sequence Stratigraphy
  2. Sediment Type
  3. Sediment Composition
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5
Q

What is sequence stratigraphy a proxy for?

A
  1. Changes in sea level
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6
Q

What is Sediment Composition a proxy for?

A

Paleoceanoograpy (current, w

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7
Q

What is Sediment Composition a proxy for?

A

Paleoceanography (current, winds, etc). What the sediment is composed of and traced back to the source.

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8
Q

Paleoceanography

A

Sientific study of Earth’s oceanographic history involving the analysis of the ocean’s sedimentary record, the history of tectonic plate motions, glacial changes, and established relationships between present sedimentation patterns and environmental factors.

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9
Q

What are the main types of terrigenous clays that are looked at for proxies?

A
  1. Chlorite
  2. Illite
  3. Kaolinite
  4. Montmorillonite
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10
Q

Chlorite

A
  1. Physical Weathering
  2. High latitudes
  3. Delivered by ice, wind, and cold water.
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11
Q

Illite

A
  1. Physical weather
  2. Temperate climates
  3. delivered by rivers & wind
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12
Q

Kaolinite

A
  1. Chemical Weather
  2. Low latitude (high concentration off equatorial West Africa)
  3. delivered by wind
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13
Q

Montmorillonite

A
  1. Chemical weather
  2. Commonly found in proximity to volcanos.
  3. Windblown ash
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14
Q

What are the four main types of Biotic Proxies?

A
  1. Foram distributions
  2. Biomarker Distributions
  3. Coral Distributions
  4. Living Organisms
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15
Q

What is Foram Distributions a proxy for?

A

Climate (temperature) and depth (sea level)

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16
Q

How does Walters Law apply to biotic proxies?

A

As sea level rises not only do sediments change but the foram changes because they like different environments.

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17
Q

Benthic forams

A

specific taxa & assemblages have distinctive distributions relative to temperature, proximity to shore, water depth, productivity, and dissolved oxygen.

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18
Q

Forams Zonal Distribution

A

approximates zonal climate belts

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19
Q

Biomarkers

A

organic molecules that are produced by living organisms.

20
Q

What are Biomarkers a proxy for?

A

Temperature (climate)

21
Q

What are the main types of Biomarkers?

A
  1. Alkenones UK’37
  2. BIT
  3. TEX86
22
Q

How can you use UK’37 as a biomarker?

A
  • Have found that there is a relationship between the type of Alkenone that is found and sea surface temperature (the temperature at which that organism lived)
  • The ratio of polyunsaturated to monounsaturated alkenones correlated with sea surface temperature.
23
Q

What is the problem with using UK’37 as a proxy?

A

alkenone production at different depths; seasonal variability

24
Q

What is the most common Biomarker proxy?

A

BIT & TEX86

25
Q

What is BIT & TEX86 a proxy for?

A

Temperature (Types of GDGT’s that form based off of temperature)

26
Q

What is the problem with using BIT & TEX86 as a proxy?

A

production in different parts of water column (different depths will have different temperatures)

27
Q

What is fossil coral a proxy for?

A

Long term sea level

28
Q

Describe how we used coral as a proxy?

A
  • Coral grows at or near mean sea level (MSL) (species variability) & keeps up with sea-level change.
  • Date coral reefs above and below sea level (14C, U-series)
  • Know when sea level was at an elevation of coral.
    • If you find coral above sea level – sea level fell
    • If you find coral above sea level – sea level rose
29
Q

What are living organisms a proxy for?

A

Short term sea level

30
Q

Describe how to use living organisms as a proxy for sea level?

A
  • Species of saltmarsh, foraminifera, encrusting gastropods live in the known range of sea level
  • Produce organic biomass (peat) or carbonate shells – radiocarbon
    • Reconstruct Sea Level from a marsh – High Marsh gets flooded once a month and low marsh gets flooded every high tide. If you take a sediment core and you see remnants of high marsh species vs low marsh species the sea level rose (need to confirm this).
31
Q

Paleoenvironmental Proxies are based on what?

A

What is living where

Biomarkers - temperature

What is living at a certain sea level

32
Q

What are the main four main geochemical proxies?

A

a. Foram δ18O
b. Foram Mg/Ca & Sr/Ca
c. Foram/biomarker δ13C
d. Biomarker δD

33
Q

What is Foram δ18O a geochemical proxy for?

A

Temperature/ice mass/temperature structure

34
Q

What is most oxygen made of?

A

O’16

35
Q

Why is O’16 the first to evaporate out of the water column?

A

It is lighter than O’18 which means that it is hydrodynamically easier to evaporate.

36
Q

Draw the Hydrologic Cycle and describe the Foram δ18O process.

A

Easier to only evaporate 16 O and the ocean becomes a bit heavier because its 18 O. The 16 O then goes up into the atmosphere and moves towards the polar regions where it snows down and becomes part of the ice sheet. Ice sheets then become packed with 16 O and the oceans become heavier and heavier with 18 O. Forams also get heavier during glacial periods because they are absorbing the 18 O.

37
Q

How can we use Foram δ18O as a geochemical proxy?

A
  • The oxygen is then available in the water. This is what the CaCO3 forams shells are making their shells out of.
  • CaCO3 has more Foram δ18O during glacial periods.
38
Q

What is Mg/CA a proxy for?

A

Temperature

39
Q

Explain how Mg/Ca be used as a geochemical proxy?

A
  • Foram is CaCO3 but sometimes when they are building their shells, they miss calcium and end up with magnesium or SR instead. MgCO3 or SrCO3
  • Tend to pick up more Mg or Sr at a higher temperatures.
40
Q

What is δ13C a geochemical proxy for?

A

strength of thermohaline circulation

41
Q

What is thermohaline circulation?

A

plays an important role in supplying heat to the polar regions. Therefore, it influences the rate of sea ice formation near the poles, which in turn affects other aspects of the climate system (such as the albedo, and thus solar heating, at high latitudes).

42
Q

What are the main types of carbon?

A

Carbon 12, Carbon 13, and Carbon 14

43
Q

What is the most type of Carbon found in the ocean?

A

Carbon 12

44
Q

What is the main type of carbon used in building foram shells and why?

A

Carbon 13

Carbon 12 is lighter so it is used in photosynthesis and so Carbon 13 is what is left. There is also very little carbon 14.

45
Q

Draw and describe how we can use δ13C as a geochemical proxy?

A

More photosynthesis happening at the surface (a lot of dust coming in from glaciers high nutrient load)

  • More C 12 and gets absorbed by all the photosynthetic organisms.
  • These organisms then die and sink to the bottom making C 12 buildup.
  • This is common during glacial periods. Cold dry environments on land tend to move a lot more nutrients out in the ocean. End up with high productivity high carbon uptake by photosynthesis during glacial periods. During glacial periods, tend to move a lot more C 12 from the surface water into the deeper water. The surface water becomes more enriched with C 13 and deeper waters enriched with C 12.
  • The forams at the surface will have more C 13 and the forams at the bottom (benthics) will have more C12.
46
Q

What is Biomarker δD a geochemical proxy for?

A

Salinity

47
Q

How is Biomarker δD used as a geochemical proxy?

A
  • This idea is looking at the amount of heavy hydrogen to light hydrogen. Easier to evaporate light hydrogen then heavy hydrogen.
  • During an ice age when most of the fresh water is locked up in ice sheets, the ocean gets more saline and get colder. End up with more heavy hydrogen in the oceans.

Marine Geology (15 decks)

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