Marine sediment archives Flashcards by Lee Taylor

Why are marine sediment climate archives important?

Deposition
Annual to 1000’s years
100 to millions of years

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What are the biggest climate archive?

Marine
Accumulate in oceans, lakes, bogs, marches and land

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What method is used to collect marine sediments for studying past climates?

Marine sediment coring during oceanographic expeditions

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What do sediment layers in cores represent?

Different time periods, like tree rings, allowing reconstruction of past climates

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Why are deep-sea sediments valuable for climate research?

They build up over time and preserve detailed records of past environmental conditions

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What do micro fossils in sediments tell scientists?

They reveal past ocean temperatures, salinity, and ecosystems

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What information do oxygen isotope ratios provide?

Clues about past global temperatures and ice volume

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What is the dissolution of carbon?

Refers to the process where carbon, in a gaseous, liquid, or solid state, dissolves into a solvent, like water, to form a solution

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How does carbonate dissolution reflect climate change?

It increases during glacial periods due to higher deep-sea Co2 and acidity, and decreases during interglacial periods

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What are the types of common micro fossils found in marine sediments?

Calcareous:
Coccolithophores
Foraminifera
Pteropods
Ostracods

Silicious:
Diatoms
Radiolaria

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What are the foraminifera?

Single celled micro-organisms with reticulating (web like) pseudopodia

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How are the foraminifera structured?

Has either organic or shell like, agglutinated or secreted test
Cytoplasm extrudes through aperture and pores in the test
With a complex cell (Eukaryotes) and genetic material within the cell nucleus

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Where are foraminifera found?

Abundant in marine environments
Those with carbonate shells record information from the environment they calcified in

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How can foraminifera be used as climate detectives?

Foraminifera record past ocean conditions in their calcium carbonate shells through oxygen and carbon isotope ratios and species composition. These clues reveal changes in temperature, ice volume, ocean circulation, and carbon cycling, making them valuable indicators in climate reconstructions

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How are foraminifera extracted from deep-sea sediment (mud)?

The sediment is dried, washed through a fine sieve to remove clay, and the residue is dried again. Foraminifera are then picked out under a microscope for analysis

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Where are planktonic and benthic foraminifera found?

Planktonic foraminifera float in surface waters, and record conditions from the surface waters

Benthic foraminifera live on top of and in the sediments and in the sediments at the bottom of the ocean, and record bottom water conditions

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What does delta 18^O in foraminifera calcite reflect?

It reflects both the delta 18^O of seawater (related to global ice volume) and the seawater temperature during shell formation

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How does temperature affect delta 18^O in foraminiferal calcite?

Delta 18^O increases by 1% per thousand for every 4.2 degrees Celcius decrease in seawater in temperature, reflecting colder, saltier conditions, especially during glacial periods

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How do delta 18^O values differ between ice sheets and foraminiferal calcite?

In ice, delta 18^O reflects air temperature (colder = depleted); in foraminifera, delta 18^O reflects seawater temperature and delta 18^O (colder and saltier = enriched)

What are the causes for lower glacial atmospheric Co2?

Cooler seawater temperatures: increased Co2 solubility: likely glacial Co2 sink

Ocean inorganic carbon: likely glacial Co2 sink

Ocean biological carbon: likelyn glacial Co2 sink

Why is organic carbon better preserved in low-oxygen deep ocean waters?

Lower dissolved oxygen reduces the breakdown of organic material by microbes, allowing more carbon to be preserved as it sinks and accumulates in deep-sea sediments

How do proxy data like delta 13^C and phosphate indicate a reduction in deep Atlantic Ocean ventilation during glacial periods?

During glacial periods, delta 13^C DIC values decrease and phosphate concentrations increase, reflecting reduced deep ocean ventilation and less exchange between surface and deep waters

What is the basic process of photosynthesis in plants (marine and terrestrial)?

Photosynthesis involves the conversion of Co2 and H2O into organic matter using sunlight and nutrients, with Co2 as a by-product

Why do plants preferentially take up the 12C isotope during photosynthesis?

Plants preferentially take up the lighter 12C isotope because it is easier to incorporate into organic molecules compared to the heavier 13C isotope

What does the preferential uptake of 12C by plants lead to in terms of delta 13^C?

The preferential uptake of 12C leaves organic material depleted in the heavier 13C isotope, resulting in more negative delta 13^C value in the plant material compared to surrounding seawater or air

What role do nutrients play in photosynthesis?

Nutrients such as nitrogen and phosphorus, are required for photosynthesis to produce organic matter, supporting the growth of plants and marine phytoplankton

What does a lower delta 13^C value in deep atlantic water during glacial periods indicate?

It indicates reduced ventilation and accumulation of older, carbon-rich waters

How do benthic foraminifera reflect delta 13^C DIC of past seawater?

Their shell delta 13^C has a 1:1 relationship with surrounding seawater DIC, making them accurate climate proxies

What is the relationship between delta 13^C and phosphate in deep Atlantic waters?

They are inversely related- low delta 13^C values coincide with high phosphate concentrations during glacial periods

Why are interglacial deep atlantic water better ventilated?

Stronger thermohaline circulation brings oxygen-rich surface waters to the deep ocean, increasing delta 13^C and reducing nutrients like phosphate

how is 231^Pa/230^Th used as a kinematic proxy for ocean circulation?

It reflects the rate of particle scavenging and water mass transport- higher ratios indicate weaker circulation

What does a 231^Pa/230^Th ratio above 0.093 suggest?

Slower deep water transport or reduced AMOC during glacial periods

What is the North Greenland Ice CoreNGRIP core used for?

To reconstruct past climate changes in the North Atlantic, including interglacials and abrupt cooling events

What was the Younger Dryas and when did it occur?

A cold event from 12.68-11.60 ka BP; marked the last major climatic shift before the Holocene, ended by rapid warming over 10 years

What are Heinrich events?

Periods of large iceberg discharges that caused abrupt cooling in the North Atlantic

What is the source of the dust seen in NGRIP during cold events?

Northern Asia

What Italian lake record supports abrupt climate change evidence seen in NGRIP?

Monticchio lake, Italy

How do scientists synchronize ice cores from Greenland and Antarctica, and why is it neccessary?

They use methane synchronization because CH4 spreads rapidly and evenly in the atmosphere, allowing matching of events in both cores despite different accumulation rates and dating challenges

What might trigger millennial-scale climate oscillations?

Ice sheet instability, internal ocean variability (e.g. AMOC), or possibly solar forcing

How do millennial-scale oscillations spread through the climate system?

Via changes in ocean circulation (e.g. AMOC) and atmospheric teleconnections like shifts in the ITCZ

Why are these oscillations more prominent during glacials?

Glacial conditions are more unstable, with larger ice sheets and weaker, more sensitive ocean ocean circulation (AMOC)

What are the causes for millennial scale oscillations?

Ocean thermohaline circulation Sea-ice feedbacks Tropical processes

What is the most common trigger for abrupt climate events and millennial-scale oscillations?

These climate shifts are often linked to disruptions in thermohaline circulation- the deep ocean conveyor belt that redistributes heat globally

How does freshwater input into the North Atlantic affect climate?

It lowers seawater density, weakens AMOC, and can trigger abrupt cooling (e.g. Heinrich events)

What did MacAyeal propose about Heinrich events?

They result from internal instabilities in the Laurentide ice sheet, occurring every 7000 years

What is the bipolar seesaw?

A climate pattern where warming in one hemisphere causes cooling in the other, due to changes in ocean heat transport

How do scientists link ice cores with marine sediment records?

By aligning delta 18^O signals from foraminifera and ice cores using known climate events from greenland