Digging for Diatoms Discovering Past Climates

Wim van Egmond 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.

Pen-shaped or Rounded? NitzschiaCyclotella CentricPennate © 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. ChemicalPhysical Nutrients pH Salinity Temperature Light

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? Boothia Peninsula Lake JR01 Iqaluit

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

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!