Proxies Flashcards
ESD
paleoenvironmental reconstructions
use proxies to recreate environmental shifts in the earth’s geological history (Raymond, 2015)
external causes of climate change: plate tectonics, orbital forcing, insolation
internal changes of climate change: land, ice, vegetation and atmosphere often exacerbated through amplification and dampening
sensor
“something that responds to shifts in the earth system”
proxy
“measurable physical characteristics of the sensor”
multiproxies are required and draw on multiple sources
to determine the cause of the sensored change -> improve equafinality
ice is multiproxy
isotopes, microparticles, aerosols, air bubbles (ghgs) (Raymond, 2015)
Vostok ice core -> 3,623m and 4 glacial cycles -> identified the correlation between ghgs and deglaciation (Petit et al., 1999)
Greenland ice core -> 250kyr -> benthic δ O-18 validated with pollen and C14 (Dansgaard et al., 1993)
LR04 Stack (Lisiecki and Raymo, 2005)
produced from 57 benthicδ O-18 records to infer ocean temp and ice volume -> SpecMAP orbitally tuned the data -> foundation for environmental reconstructions globally
proxies are limited by temporal resolution
e.g. tree rings from 10,000-present day while marine sediments 10,000,000-500yrs (Ruddiman, 2002).
marine cores calcareous oozes formed of foraminifera, right coil = warm and left coil = cold
Silliceous oozes formed of diatoms and radioloria
marine cores tend to be multiproxy e.g. aeolian dust (aridity), clay minerals (weathering), iceberg rafting (calving), fluvial sediment (rivers), foraminifera (ocean temperature), oxygen isotope ratios (sea ice volume and SST) (Anderson et al., 2007)
1947 piston corer has made them easier to acquire (Raymond, 2015)
marine cores have a low resolution
as they are limited by slow rates of sedimentation 1cm/1000 yrs
Terrestrial cores range in type e.g. glacio-marine sediments, aeolian sediment, fluvial sediment, tree rings, peat, pollen and speleothems
they respond rapidly to temporal changes and so have a higher resolution
terrestrial cores are often harder to interpret
diagenesis e.g. glacial advance reshaped terminal moraine (Raymond, 2015; Anderson et al., 2007).
types of dating
radiative -> determining age relative to other sources
absolute dating -> identifying an event and dating it to determine when it took place
correlation -> determining whether things coincide in occurrence
OSL -> time it takes to bleach and reverse the decay damage that radioactive elements did to sand grains as they became buried -> length of time for reversal = length of burial (Thomas and Wiggs, 2008)
cosmogenic nuclide dating -> cosmic rays (from space) lead to the production of cosmogenic nuclides within rock -> it is possible to estimate the age of boulders or glacial material as the concentration of nuclides results in the length of exposure (Anderson et al., 2007)
half life dating
cosmic-nuclide dating
carbon dating
potassium dating
uranium dating
oxygen fractionation -> O-16 (lighter) and O-18 (heavier) -> during glacial periods more O-16 locked in ice as it evaporates more readily and therefore enters the cryosphere as precipitation
CaCO3 in forams shells -> more O-18 in shells during glacial periods
Ca2+ and Mg2+ -> ratio in shells of organisms shift based on environmental changes (Saraswat et al., 2005) -> variable between species
C3 and C4 plants -> used to infer past climates as C4 plants have a higher rate of photosynthesis so tend to be more common in drier environments -> but variable
aeolian sediment -> Loess Plateau Chine 2.5Myr (Anderson et al., 2007)
geochemical elements -> leaf wax -> temperatures and precipitation rates (Tierney?)
dendrochronology and dendroclimatology
use tree rings to infer environmental changes (Anderson et al., 2007)
noise -> harder to infer the climate signal
precision (values close to one another) v accuracy (true value)
Modelling types
multi-component -> non-lab based research
Empirical/statistical models -> look for relationships between variables
Conceptual models -> devise ideas based on understandings of the earth system
physically-based models -> empirically testing ideas
MSA concentrations were analysed in the Weddell Sea -> paper determined that the concentration increases during ablation due to increasephytoplankton activity near the edge of the ice
validated that the plankton were the source by analysing three different sites -> Berkner Island had the highest concentration of MSA and greatest plankton population (Abram et al., 2007) -> though previous papers and trend at Amudsen-Bellinghausen Seas did not correlate
Greenland Ice Core and Vostok Ice Core -> similar conclusions for climatic shifts
ice extent changes more dramatic across Greenland -> due to changes induced across the North Atlantic Ocean (Dansgaard et al., 1993)
Stalagmite in Southern Oman -> used to understand the Indian Ocean Monsoon -> analysed O isotope ratios -> drop in O-18 indicative of increased monsoon activity but also since precipitation and temperature control stalagmite formation
10.3-8ky B.P. -> glacial boundaries controlled the IO monsoon = behaviour correlated with the Greenland Ice core shifts
After 8ky B.P. -> NH solar insolation controlled the IO monsoon = no ice sheets and increased stability of the North Atlantic Ocean = weakening the land-sea thermal contrast (Fleitmann et al., 2003)
Mg/Ca ratios from G. ruber extracted from a core taken from the Comorin ridge in the Indian Ocean
Inferred temp changes to reveal that MIS2, 3 and 4 temperatures were lower than the West Pacific -> on the whole similar changes to the Pacific and therefore mechanism connecting them (Saraswat et al., 2005)
LGM (20,000 yrs ago) -> IO temperatures were 2.1°C cooler than present-day temperatures
Isotope Stage 5 (130,000-80,000 yrs ago – referred to as final interglacial prior to the Holocene) -> 1.4°C warmer than present-day temperatures (Saraswat et al., 2005)
Paper drew up a comparison between terrestrial pollen records and benthic δ O-18 records from marine cores to determine the correlation between the sources and therefore validate the earth’s climate history over the last 500,000yrs
concluded that the records did yield similar events, but that pollen tended to react more severely to climatic shifts, and often earlier than the marine cores. There was also more variability between the terrestrial pollen records and would need to be tuned to something separate to marine cores/orbital forcing (Tzedakis et al., 1997)
Marine and Ice cores -> often the backbone for geoproxies (Thomas and Burrough, 2012)
OSL -> used to determine rates of sedimentation and sand dune ages (Thomas and Wiggs, 2008)
Dongge Cave stalagamite -> South of China -> 9,000yr environmental history of the region by analysing O isotope ratios from 2124 measurements -> 2 seasons in the cave – dry and cool or wet and warm – controlled by shifts in the ITCZ as a northward displacement brings the Indian Ocean Monsoon into the region
IO Monsoon in the Holocene -> weakening due to NH solar radiation decreasing -> no northward displacement of the ITCZ and land-sea thermal contrast is weaker -> also some proposed links to ice rafting across the NH -> likely the weakening was triggered 8.2ka yrs due to a shift in North Atlantic Ocean circulation (Wang et al., 2005)
Vostok Ice core -> 4 glacial cycles -> emphasised the importance of
orbital forcing, greenhouse gases and the ice albedo effect on the global climate (Petit et al., 1999)
Analysis of an endorheic basin in Jubbah, Nefud Desert -> orbital cycles lead to the formation of lakes across the region
research on the basin used multiproxy analysis -> O isotopes, C isotopes, sediment size and mass spectroscopry -> revealed sediment layers two layers were 9m, another was 4m and the last was 2m -> determined that lakes formed during interglacial periods and evaporated during glacial periods over the last 360,000 years, i.e. Lake formation through MIS 11/9, 7, 5, 3 and parts of the early Holocene (Parton et al., 2018)
dating is complex
proxy data can often lead to inaccurate inferences (Parton et al., 2018)
