Transcript Digging for Diatoms - Canadian Museum of Nature

Digging for Diatoms
Discovering Past Climates
What are diatoms?
• Diatoms are beautiful single-celled organisms that
live in glass homes made of silica. Their shells
consist of two valves that fit together like a shoebox
• Although thousands of species exist, diatoms are
usually divided in two groups: the pennates (penshaped) or the centric (rounded)
• They are abundant in both fresh and salt waters and
their remains are widely distributed in soils where
they form deposits.
Wim van Egmond
Pen-shaped or Rounded?
© Canadian Museum of Nature
Centric
Pennate
Cyclotella
Nitzschia
A Diatom by Any Other Name…
• There may be up to 100,000 different species of diatoms
(15,000 have been identified so far).
• Each species requires certain ecological conditions in
order to survive
Chemical
•Nutrients
•pH
•Salinity
Physical
•Temperature
•Light
• Genus Fragilaria thrives under colder and more nutrient
poor environments, while many centrics prefer warmer
and more nutrient-rich surrounding.
Who Touched the Thermostat?
• Because of their ecological eccentricities,
and the fact that their glass shells remain
long after they die, diatoms can provide
scientists with a stunning insight into the
environments and climates of the past!
• By dating a soil sample and studying its
diatom fossil content (number and type), we
can estimate the climate of a given period.
The Core of This Experiment…
• 485 cm sediment core
• Bottom of lake JR01
on Boothia Peninsula,
Nunavut Territory
• Base of core dated to
6700 years b.p. using
radiocarbon analysis
• Middle Holocene
• All of recorded human
history
© Canadian Museum of Nature
Where and How to Core?
Iqaluit
Boothia Peninsula
Lake JR01
Coring a Core…
© Canadian Museum of Nature
The Usual Suspects
• Fragilaria sp.
• Thrives in cold,
nutirent-poor
conditions
• Can assume a variety
of shapes but is always
symmetrical
• Usually no more than
15 microns in length
The Usual Suspects
• Nitzschia sp.
• Associated with
warmer and more
nutrient-rich
environments
• Completely
symmetrical and
smaller than other
pennates.
The Usual Suspects
• Cyclotella sp.
• Thrives in more
nutrient-rich
environments
• Good indicators of
shorter ice covers and
longer growing
seasons
• Perfectly round in
shape
The Usual Suspects
• Amphora sp.
• Prefers colder water
conditions and a less
productive (nutrientpoor) environment
• Partly symmetrical
and shaped like a halfmoon with both ends
pinched.
• Sometimes confused
with Cymbella which
has more striae.
Remember
More diverse and abundant =
Warmer
Less diverse and scarcer =
Colder
Early to Middle Holocene
(≈6700 years ago)
Neoglacial
(≈3300 years ago)
Medieval Warm Period
(≈855 years ago)
Little Ice Age
(≈380 years ago)
Recently…
(≈45 years ago)
Let’s Recap!