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MARS2001
Module 1
| Question | Answer |
|---|---|
| Relative sea level | regional sea level; compared to local data/sohoreline |
| Eustatic sea level | global mean sea level; changes are controlled by volume of water, shape of container |
| Ways to measure sea level | tidal gauges (with help of Global Navigation Satellite System); remote sensing |
| Tidal gauges | used in many different forms depending on wave action; Global Navigation Satellite System (GNSS) is used to correct for changes in land height (measures what's happening to the land surface to see whether sea is rising or land is erodin) |
| Remote sensing (sea level) | Surface Water and Ocean Topography (SWOT) measures surface of the ocean and highs and lows |
| Effect of gravity on the earth | earth would look like a reference ellipsoid in theory if all parts of the earth had the same gravitational pull; however earth is actually a geoid because of differences in gravitational pull; this influences the sea level and currents |
| Sea level with geoid | can plot the sea level predictions using the geoid then plot actual sea level observations; subtract these from each other and whatever is left is what is actually affecting the sea level without gravity (climate effect) |
| Main problems of eustatic sea level change | glaciers melting (when ice sheets melt, the shape of the earth changes and so does the gravity field in that area); water is heating (expansion) |
| How to determine previous changes in sea level | coastal geomorphological indicators; coastal biological indicators; stable isotopes from marine fossils |
| Coastal geomorphological indicators | sequences of sediments, tidal notches |
| Coastal biological indicators | fixed (corals, oysters), not fixed (diatoms) |
| Speleothems (stalactites and stalagmites) in predicting sea level | form in partial flooded coastal caves; growth patterns are different when submerged (can't grow when submerged); can easily date the tip of one as it continues to form |
| Oysters in predicting sea level | are found at many latitudes and are datable with 14C; however, can also survive above sea level so not very precise |
| Corals in predicting sea level | are photo-obligates (grow underwater but close to sea level); easily dated to ~0.5 Ma; growth form of coral related to environment it lives in; can also use corals that remain underwater due to differences in their shape |
| Microatolls in predicting sea level | grow up to meal low spring water (MLSW); can be accurately surveyed and radiometrically dated; grow up to surface and then out sideways; can measure the current height above sea level and then date the coral; most precise measurement of sea level |
| Oxygen isotopes as environmental indicators | about 500 times more O16 than O18; both incorporated into water and CaCO3; can use this information to measure sea level change in the past; drill into deep ocean, pull out old sediment cores and find small foraminifera that has limestone |
| O16 and O18 differences | O16 evaporates more easily than O18 so more O18 is in ocean; water vapour with O18 is easier to condense and ends up back in water more often; more O18 is left in ocean during glacial periods |
| Oxygen in ice sheets | Ice sheets have more O16 than O18; therefore levels of O18 are low when sea level is high (ice sheets melting); when sea level is low, we have high O18 because more O16 is in the ice sheets |
| Ice ages | caused by Milankovitch cycles where the earth's orbit changes in 3 different ways; affects the amounts of heat that the high latitudes get when ice sheets form |
| 3 things in Milankovitch cycles | eccentricity (the path the earth takes around the sun, sometimes more oval sometimes more circle); tilt of the earth; precession (wobble of axis when it rotates) |
| Mass balance of ice sheets | warm water holds less carbon dioxide which is then released more into the atmosphere which causes ice sheets to become warmer and warmer and then start to melt; when we drive towards warmer climates, this processA to happen faster than cooler climates |
| Accumulation dominant ice sheets | ice front advances; accumulation of snow turning into ice is larger than ablation (melting calving, sublimation, wind erosion) |
| Ablation dominant ice sheets | ice front recedes; accumulation is less than ablation and so ice sheet starts to melt away |
| Ice sheet stability | NH ice sheets less stable (further from pole, no thermal isolation, smaller); accumulation during winter, ablation in summer; warmer summers = smaller sheets; marine ice sheets can be affected by rise sea levels, warm currents, warming air, rain change |
| Dramatic, unprecedented changes in ice sheets can cause: | submergence of land; enhanced flooding, erosion of land and beaches; salinisation of soils, groundwater and surface waters; loss of and change in marine and coastal ecosuystems; impeded drainage; more frequent storm events |
| Uncertainties in future predictions of ice sheet change: | modelling based on ice physics with limited understanding of ice sheet dynamics especially on long time scale; several different emission scenarios are available however impossible to predict which one is more likely |
| uncertainties in future predictions of ice sheet change pt.2: | other parts of climate system may be poorly modelled (e.g. changing ocean currents); land use and building/subsidence/removal of coastal ecosystems; different adaptations that might occur |
| different adaptions to rising sea level | no response; advance (move towards sea); protection (build coastal walls); retreat (move away from sea); accommodation (create infrastructure around rising sea); ecosystem-based adaptation |
| example of ecosystem-based adaptation to sea level rise | reefs are estimated to protect more than 100 million people from wave induced flooding |
| Sea surface temperature across the globe | generally warmer near equator and cooler at poles; poles have larger surface area to 'spread out' the heat (due to rotation of the earth) |
| Trade winds | spread out heat across oceans; winds driven by air pressure which is driven by the temperature differential |
| ENSO stands for | El Nino Southern Oscillation |
| What is the thermocline? | The rise of cold water from deep ocean to the surface; a natural occurrence; changes during ENSO cycles |
| Describe normal conditions of thermocline and circulation | natural thermocline allows cool water to come up from deep ocean and create cooler areas; normal flow of water back to the west (warmer water in west) |
| Describe conditions during El Nino | thermocline is suppressed down; temperature differential diminishes so air pressure decreases along with wind so warm water is able to flow back to the east; changes where rainfall occurs |
| Describe conditions during La Nina | increases thermocline; cooler waters in the east and warm water flows to the west; increased rainfall; typically follows an El Nino |
| How to record ENSO events in the past? | use southern oscillation measuring air pressure from Darwin to Tahiti; average sea surface temp. in middle of Pacific ocean allows us to guess future patterns from past history; cooler water is when it's being pushed from East to West (La Nina) |
| How are ENSO events classified? | 0.5 degrees above or below the average sea level temperature; 0.5 above = El Nino; 0.5 below = La Nina |
| ENSO's effect on sea level | ENSO drives waves (power, height, direction); due to change in atmosphere causing change in sea level; on East Coast of Australia, this causes change in stability of beaches (depending on direction of waves, beach 'rotates') |
| ENSO's effect on fisheries | chlorophyll conc. dependent on upwelling circulations; if circulations affected then affects primary productivity in oceans |
| Pelagic ecosystem in Humboldt Current ecosystem during El Nino | offshore winds drop; thermocline lowers (affects food upwell so biomass lowers); nutrients are cut off; biomass drops; less room for successful fishery |
| Two ways to model ENSO events | statistical or dynamic models |
| Statistical ENSO models | use data and compare to past ENSO events to determine if one is evolving; fast to run; can't adapt to 'novel' situations |
| Dynamic ENSO models | build a model based on real physics; begins with current conditions and runs forward; slower to run, but can infer novel conditions; future modelling (past 3 months) is difficult |
| What do we measure to record past ENSO events? | tree rings (which catch changes in precipitation); corals (that build new shells out of limestone which includes oxygen isotopes); speleothem records of precipitation patterns; marine sediments (low resolution) foraminifera (SST) and diatoms (upwelling) |
| Foraminifera proxies as a long-term record of ENSO | take a small bit of magnesium into their shell; as water warms, more magnesium incorporated into shells (exponential trend) |
| ENSO existence patterns in the past | Prior to 1.8Ma, system was an 'El Nino-like state'; there was a smaller temperature differential (variation) but then increases to present day; prediction if planet continues to warm we will return to permanent 'El Nino-like state' |
| How to use coral to plot previous ENSO events? | produce calcium carbonate shells with annual growth bands; photo-obligates; drill into coral to get average density bands; bright band shows river input (from flood water); reconstruct flood histories; as more flood events occur - more variability in ENSO |
| How to use oxygen isotopes to plot previous ENSO events? | use isotopes in calcium carbonate of coral; El Nino drives changes in O18; the more variation in O18 levels, the more El Nino events in the past |
| Oxygen isotopes in rainfall and ocean | rain supplies more O16 to surface (if rainy year, more O16 will be in ocean); coral take these elements and incorporate into skeleton; as it gets hotter, coral take less O18; more rainfall + hotter = less O18 |
| Papa New Guinea isotopes ENSO | very sensitive to ENSO cycles; mean SST in west drops during El Nino with very low rainfall; opposite during La Nina; therefore large effect on isotopes in the nearby coral |
Created by:
tkeen40
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