marine sources of evidence

biogenous

oxygen isotope ratio

Biogenic sediment from ocean cores such as Calcaerous ooze formed above the Calcite Compensation Depth, from foraminifera marine snow or siliceous oozes from diatoms n radiolarians contain records of benthic and planktonic organisms. Biogenic sed reveals oxygen & carbon isotope ratios which r proxies for past climates.

oxygen isotope ratio:

Oxygen 16 & 18 r important here, with natural ratio of 1:500 w 16 dominating. In evaporation, 16 isotope preferentially evaporates bcs lighter, whereas condensation n precipitation favours 18 isotope. At low lats lighter 16 is evaporated preferentially and transported polewards, colder air holds less water vapour n promotes condensation/precipitation of O18. Thus as airmass reaches the poles it is depleted in O18 and rains lighter O16, enriching poles with lighter isotopes. Fractionation here is temp controlled, with higher temps incr energy n dropping degree of evaporation fractionation.

In glaciation O16-enriched rain forms vast ice sheets enriched in lighter isotope, with oceans enriched in heavier O18. As glaciation prefers lighter isotope. Whereas meltwater enriches oceans in O16 in interglacials.

Forams use unequal partition of isotopes between substances/phases (fractionation) in shell building, where they favour O18. Colder temperatures increase this preference, making shell more enriched relative to water. whilst warmer conditions do the opposite. Per 1 degree C temp rise foram delta O18 value drops 0.2 per mille relative to ocean water value.

Thus polar ice cores, extreme low delta O18 show cold/glacial conditions whereas marine sed cores show high delta O18 in cold/glacial conditions. As ice volume n temp effects the ocean oxygen isotopic ratio. (Lowe and Walker, 2014).

Proxy for ice n temp.

• Emiliani, 1955: 1.8 per mille delta O18 glacial vs interglacial, identified 4 quaternary glaciations via major delta O18 chnges in marine cores. but attributed to SST

• Shackleton, 1977 used 60 deep sed cores in combo w Emiliani data frm carribean n equitorial atlantic to show the 1.8 per mille delta O18 is from global ice-volume. As benthic (most common in deep sed) r less impacted by SST & the compiled records show similair global change in Late pleistocene thus showing glacial cycles control isotopic ratio.

• Lisiecki and Raymo, 2005: created LRO4 stack frm 57 benthic delta O18 records globally, using automating graphic correlation algorithim. Dates back 5.3Myr, first to exceed 850ka n 3 records. As orbital factors control ice volume, orbital tuning was used to create an age model helping date benthic records and align records with orbital forcings. This helped identify 24 new MIS in the early Pliocene, identified glacial cycles within quaternary, global land ice volume, sea level and deep-sea temp changes between 2.7-1.6ma from precession. This gave a master chronology of quaternary glacial cycles to compare against other records.

• Mix et al, 2001: 1/3 to ½ planktonic variability from local changes in ambient temp, salinity, evap/precip balance etc not just SST.

• Williams et al, 2000: delta O18 in marine cores across gulf mexico n greenland ice cores show consistent trends, but marine vs ice cores show reversed trends.

In some species (N. Pachyderma) physical changes like coiling direction affects them, with them coiling right if water temp above 9 degrees C but left if not. Also record isotope of oxygen, which ratio infers terrestrial ice volume or SST. (Lowe and Walker, 2014).

Via marine snow shelled organisms accumulate to create CaCO3 (calcaerous oozes) above the Calcite Compensation Depth if forams or SiO2 (siliceous oozes) if diatoms n radiolarians.

Forams extract oxygen from water for shell building with a preference for O18

• sed cores

A. de Vernal et al, 2006

niebler (1955)

ruddiman and mcintyre 1981

pachyderma lowe n walker

biogenous

carbon isotope ratio

foraminifera

(also use w3 fauna lecture)

terrigenous