Lecture Ice in the Ocean Ice Ages and Sea Level History

Outline for this week ESCI 1006 & 1106 Oceanography

-Sea ice

- Arctic and Antarctic sea ice Week 9: Lecture - Glaciers, ice streams, and icebergs - Ice cores as paleoclimatic archives

Ice in the ocean - Past climate

Ice ages and sea level history - Sea-level history

Parts of Chapters: 4 (p. 116-117), 5 (p. 147- 148), 6 (p. 176-177), 12 (p. 337-338; p. 352)

Types of Ice Sea ice formation

 Glacial ice - forms from the accumulation & compression When seawater begins to freeze at ~ –1.8o C, small needle-like ice of snow (land ice; source of icebergs) crystals (~3-4 mm in diameter) called frazil form. Frazil crystals consist of nearly pure fresh water.

https://www.cbc.ca/news/canada/newfoundland‐labrador

 Sea ice - forms from the freezing of sea water and is Don Perovich floating on the surface of the ocean. Sea ice covers ~7% In calm seas, the crystals form grease ice. Thin sheets of grease of the ocean but only 0.1% of Earth’s ice volume) ice, or nilas, have smooth and an oily or greasy appearance.

Sea ice formation Pressure ridge from colliding ice

In rough seas, ice crystals converge into slushy pancakes.

Don Perovich Pancake ice

Individual pieces pile up to form rafts and solidify. Any relatively flat piece of ice >20 m is called NOAA https://www.swisseduc.ch/glaciers/antarctic floe. Ice floes then freeze Sea ice that is not more than one winter old is known as first-year ice. together into ice fields. Sea ice that lasts one or more summers is known as multiyear ice.

1 Polynya is a semipermanent area of open When sea ice forms salt is expelled into the water (brine), raising the salinity of the near-surface water. water in sea ice

- Sensible-Heat (Open-Ocean) Polynyas - Latent-Heat (Coastal) Polynyas

https://www.express.co.uk NASA Thomas et al. 2008. Frozen oceans in polar regions. YouTube: Time-Lapse Camera : Underwater Icicle "Finger of Death"

Sea ice research: Ice breakers, submarines, satellites The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC)

RV Polarstern returns to the port city Bremerhaven, Oct 2020. BBC.

SCICEX: Youtube

Satellites measure sea ice concentration on a 25 km x Sea ice coverage 25 km grid. Sea ice concentration is the percentage of each pixel that is covered by ice.

NASA

Here no information about thickness

(Cryosphere Today)

2 Arctic sea ice seasonality

Winter Summer

2007 – NW passage

(Sverdrup, 2006)

Minimum Arctic sea ice and the NW Passage (NY Times The Big Melt videos x 2)

Antarctic sea ice seasonality Arctic vs. Antarctic sea ice seasonality Summer Winter ~1.3 million km2 ~21 million km2

3 Examples of possible impacts on mammals Projected changes in the polar bear habitat of sea ice disappearance

• Seals unlikely to survive (need sea ice to rest, give birth to and nurse their pups)

• Polar bears unlikely to survive (need sea ice to hunt seals and move from one area to another)

A polar bear near the coast of Spitsbergen. NY Times. Wikimedia Commons

Sea ice plays an important role in Sea ice and albedo Earth’s climate system

Albedo is the fraction of incoming solar energy that is reflected back to space by the Earth system. It ranges from 0 (darkest) to 1 (brightest).

The National Snow and Ice Data Center NASA

Meltwater ponds in Arctic summer

Outline for this week Types of Ice  Glacial ice - forms from the accumulation & compression of snow (land ice; source of icebergs) -Sea ice

- Arctic and Antarctic sea ice

- Glaciers, ice streams, and icebergs

- Ice cores as paleoclimatic archives

- Past climate

- Sea-level history https://www.cbc.ca/news/canada/newfoundland‐labrador

 Sea ice - forms from the freezing of sea water and is floating on the surface of the ocean. Sea ice covers ~7% of the ocean but only 0.1% of Earth’s ice volume)

4 The conversion of freshly fallen snow into Ice movement through a glacier

dense, crystalline glacial ice. zone of accumulation – lower limit is the equilibrium line zone of ablation – net loss by melting

Accumulation Equilibrium line Ablation

Ice flows under its own weight due to gravity.

Accumulation zone Ablation zone

Note the layers

Athabasca Glacier, Columbia Icefields, Alberta

Glacial mass balance determines Rate of movement advance vs. retreat – meters to 100s meters /year Zone of wastage (ablation) – area where there is a net loss to the glacier due to Melting Calving – breaking off of large pieces of ice into water (icebergs where the glacier has reached the sea)

Glacial budget (mass balance) - Balance, or lack of balance, between accumulation at the upper end of the glacier, and loss at the lower end

Ice advances if accumulation exceeds loss Ice front retreats if ablation increases and/or accumulation decreases Some glaciers may have rapid movements called surges.

5 Glacial retreat Erosional features and some depositional landforms

Glaciers are capable of great erosion (by plucking and abrasion) and sediment transport

During retreat, equilibrium line moves until a new balance achieved. Either way, ice within Glacial striation the glaciers continues to flow forward.

Rocks in ice acting like sandpaper to smooth and polish the Glacial deposits surface below. Produces rock flour & glacial striations. Ice lifting of loosened blocks of rocks and freezing to the base of the glacier. Transports. Deposits. Glacial drift refers to all sediments of glacial origin.

Till - material that is deposited directly by glacial ice. Till is a mixture of poorly sorted many different sediment sizes and striated rocks. The most common features created by glacial deposition are layers or ridges of till, called moraines. http://hugefloods.com/Lake-Missoula-Rock-Flour.html

Associated with valley glaciers are lateral moraines, formed along the sides of the valley, and medial moraines, formed between two valley glaciers that have joined.

Kaskawulsh Glacier, Yukon

Lateral

6 Terminal (or end) moraines mark the Glacial erratics

furthest (former) advance of the glacier. Ice-transported boulder, not derived from underlying bedrock.

Mt Lawson, BC

Erratic boulders

Okotok, AB 38

Erosional features and some depositional Glaciers landforms classified by size (& location) … valley glaciers vs. ice sheets

valley glacier at Mount Logan

Glacial erratic rock, Rice County, MN Valley (AKA: alpine) glaciers. Exist in mountainous areas https://mountainbikegeezer.com/woolly-bike-clubs-new-erratic-rock-trail/camerazoom-20141017151511634/ Each flows down a valley from an accumulation area near its head

Tributary & valley glaciers Continental ice sheets: Antarctica

Currently two major ice sheets - Greenland & Antarctica. Ice flows out in all directions from snow accumulation areas. Floating ice shelves extend from Antarctica. 42

7 Ice stream 2002 Breakup of Larson B Ice Shelf (fast flowing part [1 km/yr] of an ice sheet) (area about RI)

More complicated than just warming

(Ross Sea info)

Ice stream

Crevasse, fissure or crack in a glacier resulting from stress produced by movement. (Ross Sea info) alving (YouTube: Chasing Ice)

Edge of Tabular Iceberg (like this from Larson B) An iceberg is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open water.

Small pieces of crumbling icebergs are called "growlers" or "bergy bits".

https://www.jamstec.go.jp/e/about/press_release/20141027/

8 Sea ice vs. Icebergs Some differences

Sea ice: 1) Formed from seawater 2) Rejects salt but still contains some salt 3) Flat, thin; ice-breakers can break 4) Ice lasts seasonally up to a few years

Icebergs: 1) Formed on land from freshwater 2) No salt 3) Calved from outlet glaciers; bulky 4) Many (even hundreds of) years of accumulated ice Calving

Ice cores as paleoclimate archive Ice coring

An ice core station in Antarctica

(Sverdrup, 2006) (Sverdrup, 2006)

Ice core processing Polar ice cores

(Sverdrup, 2006) The Greenland Ice Sheet Project

YouTube: Ancient Ice Reveals Earth's Climate History

9 Summary • Sea ice - seasonal, multi-year ice formed from seawater - shrinking and thinning in the Arctic - Arctic vs. Antarctic • Glaciers and icebergs Know the difference between icebergs and sea ice

• Glaciers work as systems that respond to climate Mass balance controls advance & retreat; ice flows Erosional features & depositional landforms

• Ice streams - a region of an ice sheet that moves significantly faster than the surrounding ice • Ice cores - paleoclimate archive from poles and tropical mountains - past variations in CO2, ice age, and local temperature correlate well Petit e al., 1999 (redrawn Sigman & Boyle)