L17: The Oxygen Isotope Record
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what are tidal oscillations encoded in?
sediments and biological archives e.g. shells
why are cockles good records of tidal increments?
lives in the intertidal zone, so mostly exposed, but twice a day it becomes submerged by high tide. each time it becomes covered, it lays a little bit of its shell and then stops when it becomes exposed, encoding the tidal increments within its shells
what expresses tidal increments the best?
intertidal species or intertidal sediments
what do the incremental layers represent in the shells of intertidal species?
spring-neap tidal cycles
how are the layers visible in sediments existing in intertidal settings?
through changes in grain size e.g. bring spring tides cause high velocity H2O to flow across the surface, depositing coarser grains and then finer grains during neap tides
do spring tides (high velocity) or neap tides (low velocity) deposit larger grain sediments?
spring tides
what do stromatolites help keep records of? and what does this enable?
daily increments and seasonal cycles. enables a number of days in the year to be deduced
what is the process of diel migration of plankton?
refers to the daily vertical migration of phytoplankton and zooplankton. plankton travel up to the ocean surface at night to feed, avoiding predation from seabirds, and then sink back down to considerable depths during the day time.
what are some examples of low frequency biotic and abiotic records?
annual/seasonal laminations in lake sediments (Varves) and annual layers in ice cores
how to lake sediments show annual/seasonal records?
during winter months, precipitation is higher, so more minerogenic material is washed from the catchment and into the lake basin. this deposits grey mineral grains during the winter. during the summer you have blooms of diatoms (phytoplankton) within the lake system, showing upas creamy yellow horizons
what name is given to laminations which are clearly annual in period?
Varves
what is an example of Varves in lake sediments?
lake van, Türkiye
where can we find annual layers in ice cores?
Greenland
what precipitation patterns are reflected in the crystal structure of ice cores?
during the winter, autumn and spring months you get more preservation of snow precipitation onto the surface of the ice sheet. during the summer, you have melting on the surface.
what information does annual layering provide us with? e.g. ice cores
enables us to extract environmental records e.g. temperature, dust, climate as well as timescale as we can count the layers
why are tree rings wider in the centre, compared to the outer edges?
the thicker tree rings represent the fast growth of the tree early on in life, which gradually slows
what is a very common signal in most biological records?
faster growth in early life
how long are dendrochronology records in Europe?
go back about 10,000 years as records have been spliced together stratigraphically/chronologically
how long can gold cockles live for? and what does this provide?
up to 200 years- providing 200 years of marine climate encoded within their shells
what does the dark growth check in tree rings represent?
the slowing of winter growth
what do the growth checks in shells represent?
late summer and very early autumn
what other things show growth increments?
coral, human teeth, gastropod statoliths (snails), fish otoliths etc.
why are corals important in terms of records?
help us understand tropical tropical climate change as they generally grow in subtropical tropical regions
what are coccoliths?
carbonate producing autotrophs