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 (pen-shaped) 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? Centric Pennate Cyclotella Nitzschia © Canadian Museum of Nature
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 • 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 (nutrient-poor) environment • Partly symmetrical and shaped like a half-moon with both ends pinched. • Sometimes confused with Cymbella which has more striae.
Remember More diverse and abundant = Warmer Less diverse and scarcer = Colder