Quaternary GeoEcology
What is the 8.2 event?
- A sudden decrease in global temperatures that occurred ~ 8.2 ka or ~ 6.2 ka; - Will lasted for the next 2 - 4 centuries.
What are the limitations for paleoecological investigations?
- Selective dissolution (thin-walled species never make it to the sea floor); - Differential removal of easily-transported species; - Contamination by exotic species.
What are alkenones?
1. A few marine phytoplankton (especially coccolithophorid) respond to changes in water temperatures: - Alter molecular composition of cell membrane; - As water temp. decreases, increases production of alkenones (specialized organic compound) 2. Length of the carbon chains in alkenones is correlated with mean annual temp. - reflect conditions in euphotic zone (upper 10m) - subject to seasonality of phytoplankton blooms.
What is firn? ablation? The firn/equilibrium line?
1. Ablation: snow that is melted in summer month. 2. Firn: snow that survives (still existed) summer ablation. 3. The firn/equilibrium line: is the vertical boundary where net accumulation = net ablation.
What are the main ways that ice cores are dated?
1. Annual layers preserved in the ice cores analyzed with visual stratigraphy. As we go deeper, the layer is compacted. 2. Radio-isotopic methods (using stable isotopes of oxygen and hydrogen). 3. Tephrochronology (layers of ash - tephra) 4. Numerical ice-flow models 5. Geochemistry 6. Radioactive dating of gaseous inclusions: 7. Correlation with other markers (techniques) (www.talkorigins.org/faqs/icecores.html)
What are the carbonate and silicate organisms commonly used for paleo-ecological investigations?
1. Calcareous organisms: + Biogenic oozes: composed of calcareous or siliceous skeletons of marine organisms. - Plankton (floating, varied from 0 - 200m) - Benthic (bottom-dwelling) + Most important organisms for paleoclimate purposes: - Foraminifera (zooplankton) - Coccolithophores (algae) {sometimes grouped with other small calcareous organisms called nano-plankton}: a single-celled marine flagellate that secretes a calcareous shell, forming an important constituent of the phytoplankton. 2. Siliceous organisms: - Radiolarian (zooplankton) - Silicoflagellates (algae) - Diatoms (algae) * typically identified to special level: - plankton - provide ecological information about overlying water column environment: temperature / salinity. - Dinoflagellates: The cysts of organic-walled dinoflagellates (algae) are important paleoecological indicators of sea surface temperature and sea ice extent in high-latitudes.
What are the limitations (temporal / physical) of dating techniques in these records?
1. Counting annual layers: visual stratigraphy is a very time consuming process / the boundaries between layers are not as clear as we go down the core (compaction), hence, older years in the record seems to be blurred. 2. Radio-isotopic methods: 18O/16O ratio is used to compare long range climatic changes. - many factors cause changes in 18O are not stable (seasonal timing of precipitation / ice thickness gradually increased in glacial / more extensive sea ice = increased distance to moisture sources / isotopic composition of ocean water changed because of storage of water in large ice sheets). 3. Tephrochronology: After the eruption of volcanoes, the volcanic ash and chemicals are washed out of the atmosphere by precipitation. Eruptions have distinct markers within the snow which washed the atmosphere. --> record volcanic eruptions are used to calibrate the age of the ice-core --> volcanic ash is a common atmospheric constituent after eruptions. - required date of the eruption (usually not available); - alkaline precipitants of the ice ages limit this to < 8000 BC. 4. Ice-flow models: Need to measure the length of the ice core and calculate how many years it take for a glacier to reach that thickness --> most inaccurate method since we need to assume about the thickness of the annual layer changes with depth / original thickness of the annual layer). 5. Geochemistry (pH balances): Alkaline due to precipitation used as unique marker for glaciation: - can only interpret very approximate age ranges; - lag time between the glaciation and increased alkalinity is unknown. 6. Radioactive dating of gaseous inclusions: Glacial material from a given depth is molten --> gases trapped inside are collected with 14C and 36Cl dating --> required huge amount of ice to melt. 7. Correlation with other markers: strongly dependent on the accuracy of the previously defined markers. (www.talkorigins.org/faqs/icecores.html)
What are the four key features of thermohaline circulation and what drives thermohaline circulation (including which process dominates the process)?
1. Deep water formation 2. Spreading of deep waters 3. Upwelling of deep waters 4. Near-surface current
What are some of the potential problems with using Delta(18O) tools?
1. Differential isotopic uptake of species: make oxygen isotopic fractionation in calcareous marine organism further complicated. Careful selection of specimen is required to avoid this problem. 2. Depth habitat of planktonic forams: Forams may not have lived at same water depth (glacial / interglacial); / water temp. in tropics decrease rapidly with depth --> small variations create substantial difference in temperature / water density (temp + salinity) is critical for many species. --> during glacial periods, water was more saline --> forams may have migrated upward in water column in response to density differences (vice versus in interglacial). 3. Oxygen isotopic composition is influenced by vertical migration and foraminifera seasonality. 4. Salinity has an influence over isotopic composition (large scale dilution effects / local changes in the effective moisture). 5. Differential preservation: - Dissolution afters the composition of the fossil assemblage (assemblages enriched in species resistant to dissolution). - ~ 25% of carbonate flux from upper waters reaches the ocean floor.
What are the general patterns of the water bodies named in terms below and their relationship to each other with respect to thermohaline curculations?
1. Gulf Stream - intense, warm ocean current in the western of North Atlantic Ocean. It moves north along the coast of Florida and then turns eastward off of North Carolina, flowing northeast across the Atlantic. 2. North Atlantic Deep Water (NADW) - deep water mass formed in the North Atlantic Ocean. Thermohaline circulation of the world's oceans involves the flow of warm surface waters from the southern hemisphere into the North Atlantic.
What are glacial termination(s) and why are they important components of ice core records?
1. Is the period of time during a glacial cycle when there is a relatively rapid transition from full glacial climates to full interglacial climates. - For the Quaternary period, terminations are numbered using Roman numerals from the most recent termination as "I" and with increasing value, e.g. "II", "III", and so forth, into the past. Termination I, also known as the Last Glacial Termination. - During the Quaternary, global climate experienced a recurring pattern of ice-sheet growth and decay. The length of Late Quaternary cycles varied between 80,000 and 120,000 years, with an average recurrence interval of about 100,000 years. 2. They are important because they are obvious in the data which can be used as markers to correlated and help calibrate with other data.
What are the 4 major categories that paleoclimatic (temperature) inference from fossil remains of marine organisms?
1. Oxygen isotope composition (foram, coccolith, diatom test): - If CaCO3 is inorganically crystallized, 18O is slightly concentrated in the CaCO3 relative to the amount in water. - Process is temperature dependent, diminishing as temperature increases. ` Drawbacks: isotopic fractionation varies locally with temperature / varies globally with ice volume / affected by salinity. 2. Quantitative interpretation of Species assemblage data (spatial variations) 3. Mg/Ca ratios in foram test (temperature) 4. Morphological variations in species related to environmental factors (ecophenotypic variations, coiling direction: (Lecture 10. P8-11)
What is TEX86?
86 carbon atoms of the lipid membrane in thaumarcheota (a group in the Archea), single-celled micro-organisms, which respond to water temperature changes. - Lipid include tetraethers with 86 carbon atoms; - As temp. increases, the organism incorporates more cyclopentane rings into their lipid membranes (which make them more rigid) --> paleothermometer based on the relative number of cyclopentane rings (0 - 4) in the lipid & effective for 0 - 30 degree C.
How do we track the sources of IRD in Heinrich cycles?
??In a belt in the Atlantic between 35-50 N, there is an increase in coarse lithic fragments from sediment cores in the North Atlantic. peaks in lithic fragments can be traced over wide areas.
What's the difference between D-O events and Heinrich events?
?D-O events involved the formation of extensive sea ice which forms and decays rapidly. Heinrich events involve calving of ice sheets into massive fleets of icebergs. Heinrich events occur during the coldest intervals of D-O events.
What's the most likely cause of 8.2 event?
?Large ice sheets began melting, creating lake Agassiz which was dammed to the north by a remnant of the Laurentide ice sheet. When the dam failed it released the Lake Agassiz waters. The freshwater pulse slowed deepwater formation and the thermohaline circulation.
What is a biomarker?
A measurable substance in an organism whose presence is indicative of some phenomenon such as disease, infection, or environmental exposure.
What is vapor pressure?
A measure of the force exerted by a gas above a liquid
What is a coccolith?
A minute, rounded, calcareous platelet, numbers of which form the spherical shells of coccolithophores.
What is thermohaline circulation?
A part of the large-scale ocean circulation that is driven by global density gradients created surface heat and freshwater fluxes.
What is the Younger Dryas?
A return to glacial conditions which temporarily reserved the gradual climatic warming after the Last Glacial Maximum started receding around 20,000 BP.
What is a diatom?
A single-celled alga that has a cell wall of silica.
What is the Older Dryas?
A stadial period between the Bolling and Allerod interstadials; About 14 ka.
What is the lipid membrane?
A thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells.
What is the Gulf Stream?
A warm current of water that flows northward along the eastern seaboard of the U.S.
What is the Bolling-Allerod?
Abrupt warm and moist interstadial period that occurred during the final stages of the last glacial period. This warm period ran from 14.7 - 12.7 ka.
How do transfer functions work?
An operation on input to give output of a system. Transfer function (f) = output (f) / input (f) or take log and get difference. - Applied downcore to reconstruct past environmental conditions. Assumptions: + Former biological and environmental conditions are represented by modern analogs; + Relationships existed have not changed over time through species evolution + Core tops may represent periods of 100s or 1000s of years.
What is the ocean carbon pump (marine biological pump)?
Biological activity sequesters CO2 in ocean sediments and draws CO2 out of the atmosphere.
What are borehole temperatures?
Borehole temperatures are the 'remembered' ice temperature recorded after an ice core is extracted and left for a certain amount of time.
What is salt expulsion?
Brine rejection is a process that occurs when salty water freezes. The salt do not fit in the crystal structure of water ice, so the salt is expelled.
How does knowing paleoproductivity help us reconstruct past thermohaline circulation pattern?
CO2 changes in marine sediment records parallel Deta(18O) changes in ice core --> have roles in glacial-interglacial climatic changes. Ocean carbon content is 50-60x atm CO2 --> small changes in degassing rate --> large influence on atm CO2. Changes observed related to biological productivity. During photosynthesis, 12C is removed from water to produce organic material with low Deltal(13C). Low sea levels --> continental sources of phosphate eroded more quickly --> enhanced productivity in surface water (glacial periods) --> systematic reduction in Delta(13C).
What is CCD?
Carbonate Compensation Depth (CCD) - depth at which dissolution rate = rate of carbonate supply. Below CCD, sediments are composed mostly of clay and siliceous microfossils.
How is Delta(13C) used to reconstruct paleoproductivity?
Carbonate is derived from dissolved CO2. Organic matter falling through the water column causes Delta(13C) of dissolved inorganic carbon to decline. Low Delta(13C) indicates for a large input of organic carbon which means a more productive ocean.
Cd/Ca ratio?
Cd/Ca ratio is benthic forams is used as a proxy for ocean nutrient levels because Cd is incorporated in CaCO3.
What other chemical technique can be used in this fashion?
Cd/Ca ratios in benthic forams can be used as a proxy for ocean nutrient levels. Cd is correlated to phosphate (productivity). Cd is higher during glacial periods.
What do 'heavy water' and 'heavy oxygen' record in ice core records?
Inferred temperature (indirect measurement) from the isotopic composition of the water molecules released by melting the ice core. Variations in isotopes reflect temperature effects from changing latitude, altitude, distance from moisture source, season, and long-term climatic fluctuations. 1. Water is made up of stable 1H (99.9%) and 2H (D) / 16O (99.7) and 18O. 2. Using mass spectrometers, ratio of the isotopes of oxygen and hydrogen (took from ice cores) and compare it with the isotopic ratio of an average ocean water standard (Standard Mean Ocean Water). 3. Water molecules in ice cores are depleted in the heavier isotopes (Rayleigh distillation). 4. Less 18O and D --> cold periods because it takes more energy to evaporate water molecules containing a heavy isotope from the ocean's surface. During process of transport polewards and cools, water molecules (with heavier isotopes) are lost in precipitation (fractionation) --> temperature dependent. (Lecture 7. P10-15 & www.scientificamerican.com/article/how-are-past-temperatures/)
Ventilation?
It is a critical factor in atm CO2 concentrations. Upwelling brings nutrient-rich water to the surface and increases biological activity.
What is important about Lake Agassiz?
It was a dammed lake that had a dam failure :) releasing freshwater into the ocean causing slowed deepwater formation and thermohaline circulation.
What is the modern analog technique?
It's the refined technique of calibration datasets and transfer functions: - Find the modern assemblages that most closely resembles each fossil assemblage from core tops; - Used statistical techniques - Modern SST of the top 10 modern assemblages then used in a weighted average to estimate the paleo-SST.
What kind of evidence exists to support the see-saw concept?
Large influxes of fresh water from glacial melting leads to a slowdown of the Atlantic meridional overturning circulation by disrupting the formation of North Atlantic Deep Water.
How do boreholes (potentially) record past temperature?
Ice is a poor heat conductor and 'remembers' its original temperature for a long time as it moves down through the ice sheet. - Ice deposited during the glacial period is still cold, and the coldest temperature in the ice sheet are found in the middle of the ice sheet; - The warmest temperatures are found at the bottom because the bedrock releases geothermal heat. (Lecture 7. P20)
What is fast ice?
Increased IRD produced by seasonal breakup of ice originally fastened to the shoreline.
What is PIP25?
Lipid biomarker produced by diatoms that inhibit sea ice which is an indirect measure of SST because the presence of sea is is related to SST.
Mediterranean Intermediate Water (MIW)?
MIW forms by evaporation of relatively-warm water in the semi-enclosed Mediterranean Sea. Increased salinity results and the water sinks to the bottom of the Sea. Less saline surficial water from the Atlantic Ocean flows into the Mediterranean Sea to replace the lost surface water while the deep warm and salty MIW flows over the sill at Gibraltar and sinks into the eastern North Atlantic Ocean. MIW then continues to flow westward at depths of 1-2 km reaching as far as the island of Bermuda in the western North Atlantic Ocean.
What produces IRD in marine sediment records?
Seasonal break-off of glacial ice that floats into warmer waters and melts dropping debris.
What are the main sources of marine sediments?
Sediments are mostly composed of a mix of biogenic and terrigenous material (originated from lithogenous, biogeneous, hydrogenous, cosmogeneous). + Lithogneous sources: are from the land which formed through weathering processed and composed of small particles from weathered rocks and volcanic activity. + Lithogenous sediments consist of: terrigenous and red clay. - Terrigenous sediments are produced when weathering processes occur above water. Wind and other natural sources then carry these particles to the ocean where they sink. - Red clay (abyssal clay) is mostly located in the ocean and formed from a combination of terrigenous material and volcanic ash.
What is foraminifera?
Single-celled consumers, rapid diversification during the Jurrasic and Cretaceous, used as guide fossils for the Cretaceous Period, diverse and abundant today.
Why do the stable isotopes record seasonal changes?
Stable isotopes record changes in temperature in the ice core. Using the annual layers (in the ice) and compare ratio of the isotopes of O/H from the ice cores versus the standard (Standard Mean Ocean Water), we can date back the atmospheric temperature in each layers (and sub-layers) represents for years and seasons. Hence, if we compare a series of layers and sub-layers, we can analyze the seasonal changes of past climate conditions.
What is SMOW?
Standard Mean Ocean Water: 1. Sea-water sample which comprises the international standard for D/H and 18O / 16O ratios. - Isotopic fractionation: Relative partitioning of the heavier / lighter isotopes between two coexisting phases in a natural system. - Equilibrium fractionation: Thermodynamic properties of molecules with different isotopes are different because the bonds between the atoms are just a bit different --> different masses. - Kinetic fractionation: Molecules with ligher isotopes move faster.
What is ocean current?
Steady flow of surface ocean water in a prevailing direction.
Why is Antarctica isolated from much of the climate in the rest of the Southern Hemisphere?
The Antarctic Circumpolar Current (ACC) flows west to east around Antarctica keeping warmer waters away. It is created by the lack of any landmass connecting Antarctica. It keeps warmer water away from Antarctica.
What is the North Atlantic Deep water ((NADW)?
Warm water from the Gulf Stream flows across the Atlantic Ocean; Water cools, becomes saltier, and sinks; create downwelling.
Deep Western Boundary Current (DWBC)?
warm, deep, narrow, and fast flowing currents that form on the west side of ocean basins due to western intensification. They carry warm water from the tropics poleward. Examples include the Gulf Stream, the Agulhas Current, and the Kuroshio.
Delta(13C)?
δ13C varies in time as a function of productivity, organic carbon burial and vegetation type. Biological processes preferentially take up the lower mass isotope through kinetic fractionation.
What are some models for how Heinrich events and other abrupt climate changes (like the YD) occur?
Hosing experiments that force freshwater into the Atlantic.
What are the four main ways that ice core records are used to reconstruct climate throughout the Pleistocene?
1. To reconstruct past air temperatures, the critical parameter is age preserved in ice cores as annual layers. Seasonal differences in the snow properties create annual rings (like tree-ring). These are reflected by physical characteristics of ice and firn. 2. Concentration of gases (as gas bubbles) in air spaces between crystals since the ice formed. 3. Dissolved and particulate matters in ice and firn. 4. Records for stable isotopes of heavy water (HDO) and atmospheric oxygen (H2O). * Other ways of dating include geochemisty, layers of ash (tephra), electrical conductivity, and using numerical flow models to understand age-depth relationships. * Ice cores provide records of snow accumulation, temperature, atmospheric composition, volcanic eruption, solar activity, and air chemistry. (Lecture 7. P9)
How do ice cores act as an archive for past atmospheric composition?
1. Water droplets in the atmosphere get condensed to form snow and fall on the ground. As they become bigger, they start forming ice crystal. 2. The increase of weight of the overlying material causes crystal to deform and recrystallize which causes: - increases in density; - air spaces between crystals become sealed into individual air bubbles. 3. Because of that, ice cores provide records of: - snow accumulation; - atmospheric temperature; - atmospheric composition; - volcanic eruption; - solar activity. (Lecture 7. P2 & 5)
How are the records from Greenland and Antarctica correlated (in time)?
Climatic variability in the Antarctic ice cores is very similar to Greenland. Ice core records are linked using atmospheric trace gases (CH4); changes in the atmospheric methane content are generally equilibriated globally quickly. Changes in atmospheric methane content should therefore register contemporaneously in both polar ice sheets. There is a good match in both ice sheets between 10 - 52 ka. Age uncertainties older than this are too large for accurate matching. Ice-core records can be linked using cosmogenic isotopes such as beryillium-10 and volcanic eruptions. During the 10 - 52 ka period (ice-age climate), the stable isotope record of the Antarctic and Greenland ice cores are anti-phased. Cooling episodes in Greenland coincide with warming episodes in Antarctica (and vice versa). - The consistent anti-phase behaviour has been called the 'bipolar seesaw'; this is a driving mechanism that transfers energy alternately between the poles. The bipolar seesaw is driven by ocean circulation changes, such as changes to the Gulf Stream. This bipolar seesaw could operate in warmer periods, with twentieth-century climate in the Arctic and Antarctic being shown to vary in an anti-phase seesaw pattern. Warming in the Arctic has been accompanied by Antarctic cooling, and vice versa. There are some problems with the bipolar seesaw hypothesis. For example, there are significant time lags in temperature shifts, but dating uncertainties make it difficult to ascertain which pole leads and lags. It is likely that there are other factors, in addition to ocean circulation changes, that drive anti-phased temperature patterns. (Lowe and Walker, 2015. Reconstructing Quaternary Environments)
Where are the places that deepwater form in the world's oceans and how does it form (there are multiple ways)?
Deep waters are formed where the air temperatures are cold and where the salinity of surface waters are relatively high (high density). The combination of salinity and cold temperature make water becomes denser and sink to the bottom.
What is Lisocline?
Depth of maximized calcite dissolution; Usually varied from 2500 - 400 m.
What is biotic fractionation (vital effect)?
Differential isotopic uptake of species, where some species prefer to uptake light oxygen which make isotopic analysis become a lot more complicated.
Divergence (Upwelling)?
Divergence can occur at the ocean surface when two ocean currents split. Upwelling will occur at that location.
What is a horizontal ice core?
Due to ice flow, snow and ice crystals formed flew downslope. After being pushed up by the land, order of formations of snow (and ice) layers are now compressed in horizontal direction. Which make horizontal drilling of ice core in opposite direction to ice flow become practical in capturing the order of formation.
Rayleigh distillation and different factors in the stable isotopic fractionation for ice core record?
Equilibrium fractionation affects vapor pressure differently between isotopes. 'Normal' water vapor pressure is higher than that of HDO and heavy-oxygen water (high vapor pressure = easier to convert from liquid to gas). - It is easier to evaporate 'normal' water and easier to condense heavy water and heavy-oxygen water. During cold conditions (winter, colder climate), air masses arriving in Greenland have cooled more on the way --> more precipitation --> lower Delta(18O) values. - There is a correlation between temperature and isotopic composition. Water vapor that reaches the highest latitudes usually has traveled farther = many steps of losing rain, which depletes heavy isotopes. Cold air holds less water vapor, and has been depleted of most of its water = lighter because heavier isotopes condense. Factors that affects Delta(18O) at a location are: 1. Slight differences in seasonal timing of precipitation --> significant shifts in fractionation; 2. Gradual increases of ice thicknesses --> increase in elevation during glacial periods; 3. More extensive sea ice = increased distance to moisture sources; 4. Isotopic composition of ocean water changed because of storage of water in large ice sheet. (Lecture 7. P13-15)
Antarctic Intermediate Water (AAIW)?
Formed further north in the Southern Ocean at mid-depth. Tongue of salinity and important THC component Warmer and fresher than AABW
What are hosing experiments (modeling)?
Freshwater is dumped into the Atlantic and transported through the thermohaline cycle.
What is the Mg/Ca ratio?
Mg and Ca are found together in seawater and substitution of Mg in biogenic carbonate is temperature dependent where there are greater substitutions in warmer water.
What are some ways other than stable isotopes that we can reconstruct past ocean water temperatures?
Mg/Ca ratios Alkenones TEX86 IP25 P
What is the calibration techniques in marine sediment?
Multivariate statistical approach using modern distribution of forams from core tops. Former environmental conditions are represented by modern analogs. - Correlate assemblages with environmental variables (sea surface temperature)
What are other tracers used to track potential movements of thermohaline circulation and how do they work?
Neodymium is a daughter product of samarium and broadly reflects the age of continental rock sources contributed to the ocean (functions as a tracer for water masses entering the ocean). Kinematic tracers (Pha/Th) are daughter products of U decay and accumulate in ocean sediment because they are insoluble. Variation of Pa/Th over time indicates the strength of the AMOC (Atlantic Meriodional Overturning Circulation).
143Nd (Neodymium)?
Neodymium is the daughter product of samarium and broadly reflects the age of continental rock sources contributed to the ocean from water masses
How does the bipolar see-saw work?
North Atlantic temperature changes are mirrored by equal amplitude South Atlantic changes of opposite sign.
What is the bipolar see-saw?
North Atlantic temperature changes are mirrored by equal amplitude South Atlantic changes of opposite sign.
What is deuterium?
One of the two stable isotopes of hydrogen; which has 1 proton and 1 neutron, 2H.
What is silicoflagellate?
Planktonic marine chromists that are both photosynthetic and heterotrophic.
Paleo-productivity?
Production that occurred prior to times when direct measurements are available.
What is a Dansgaard/Oeschger event?
Rapid climate fluctuations that occurred (~ 25 times) about every 1-3 thousand years during the last glacial period.
What causes D-O cycles?
Rapid climate fluctuations that occurred 25 times during the last glacial period characterized as short-lived transitions between warm and cold phases.
What is Brunhes Dissolution cycle?
The Mid-Brunhes dissolution interval (MBDI) represents a period of global carbonate dissolution, lasting several hundred thousand years, centred around Marine Isotope Stage (MIS) 11.
What is ice divide?
The boundary on an ice sheet, ice cap or glacier that separates opposing flow directions of ice, analogous to a water divide. Which is the optimal place for taking an ice core.
What is a nanofossil?
The fossil of a minute planktonic organism, especially a calcareous unicellular alga.
Where is the best place on a continental ice sheet to take a successful, long ice core (and why)?
The ideal place to collect a successful ice core is in the accumulation zone of a glacier. In the large ice sheets, there are huge and high plateau where snow accumulates in an ordered fashion. At the center of the ice sheets is the place where ice flow is at slower rate --> the stratigraphy of the snow and ice is preserved more. (Lecture 7. P5 & www.antarcticglacier.org/glaciers-and-climate/ice-cores/ice-cores-basics/)
How do the mountain glacier records compare to those from the poles?
The mountain glacier records (Tibetan core) had much shorter cycles from peak to peak than ones in the poles. (review Tibetan paper for more)
What does Delta(18O) indicate in fossil planktic and benthic foram shell chemistry?
The process of concentration levels of Delta(18O) in calcium carbonate is temperature dependent with level diminishing as temperature increases. --> we can use the concentration in the shell to back out the temperature of the water where it grew.
What is a dinoflagellate?
The second most abundant phytoplankton that can move in water.
What is provenance?
The source rock of sedimentary material.
What is paleotemperature?
The temperature or mean temperature of a locality at a time in the geological past.
What is the dry snow zone?
The zone with NO surface melting occurs, even in summer. Snowmelt and sublimation are extremely low.
How does Delta(18O) in shell chemistry relate to sea level change?
There is a relationship between oxygen isotopes, continental ice volume, and sea level changes. - If ice sheets remain constant, ice lost from an ice sheet will be enriched by ice sheet growth resulting in systematic enrichment of heavy oxygen without any change in ice volume. - There is a non-linear relationship between ice volume and Delta(18O).
How do processes like D-O cycles and Heinrich events have an influence over the tropics?
They affect the tropics by displacing the Inter Tropical Convergence Zone and changing the strength of monsoonal air flow. During interstadials, strong monsoon and northern position of the ITCZ results in anoxic conditions at depth (dark laminated sediments).
What are some conditions that appear to be required to produce Heinrich events?
They typically occur at the end of prolonged cooling episodes and are followed by an abrupt shift to warmer Atlantic sea surface temperature.
What is termination?
Time during a glacial cycle when there is a relative rapid transition from full glacial climates to full interglacial climates.
What is Antarctic Bottom Water (ABW)?
Water mass in the southern Ocean surrounding Antarctica with temperature ranging from -0.8 to 2 (degree Celcius) (35F), salinities from 35.6 - 34.7 psu.
Why is the study of abrupt climate change considered important as an area of study?
We are disrupting climate enough to cause an abrupt change.
Why is ice core data somewhat problematic?
When snow consolidates into ice, air is trapped in bubbles, preserving past atmosphere. Dating the trapped air is problematic because: - The consolidation of ice takes place at depth (the 'trapping depth') from pressure of overlying snow. Air can diffuse from atmosphere through unconsolidated snow and firn. Trapped air can be younger than surrounding it. - Trapping depth varies with climatic conditions: Air-ice age difference varies from 2.5 - 6.0 ka. Air from atmosphere may not mix uniformly. Movement could be different for various gases (larger molecules move slower / age of gases at depths may be different). (Lecture 7. P18)
