Lake productivity: Closed systems, nutrient sinks CO 2 and O 2 from air and water Autochthonous vs. allochthonous inputs.

Lake productivity:• Closed systems, nutrient sinks

• CO2 and O2 from air and water• Autochthonous vs. allochthonous inputs

Lake factors:• Geography/topography• Nutrient sources• Size• Age

Lakes stratify and mix differently based on these factors

Lake mixing and productivity:

Monomictic: mix once per yearDimictic: mix twice per yearMeromictic: seldom mix

low productivity high productivity

Oligotrophic Eutrophic

Hypo > Epilimnion Hypo < Epilimnion

< allochthonous > allochthonous

< decay in benthic > decay in benthic

O2 > depth O2 < depth

Lake Nyos, West Africa

www.wired.com

Lakes are found in all ice-free areas of the Antarctic andnow many are known to be subglacial, some up to 4 km belowthe ice sheets

Lakes range from small ponds to large bodies of water, such as those found in the Dry Valleys

Initial research on lakes was in the Dry Valleys, which were discoveredduring the British Discovery Expedition in 1901-1903

Early focus on algae, algal mats, crustaceans and protozoans, and thephysical and chemical environment of the lakes

Antarctic Lakes

FreshwaterSalineEpishelfSupraglacialSubglacial

Freshwater lakes are most commonSome started as saline lakesSalinity varies up to 9 % salt concentration of seawater

Most are shallow (<50 m depth), deepest is Lake Radok at 350 mMost are monomictic and oligotrophic to ultra-oligotrophic

Ice cover limits productivity even further, less light penetrates

Lakes near penguin colonies have greaterproductivity, allocthonous inputs from guanoand greater chlorophyll a concentrations

Lake Boeckella, Hope Bay

Sediment cores provide history of alake, changes in productivity over time

Many stations use lakes as their freshwater supplyEsperanza Station, Hope Bay, and Lake Boeckella

Dry Valley Lakes

From Laybourn-Parry and Wadham. 2014. Antarctic Lakes. Oxford Univ. Press

http://www.lakescientist.com

Don Juan PondMost saline lake on earth

Lake Vanda

Transparent ice allows more solar radiation, warming below icePhosphorus deficient, ultra-oligotrophic and meromictic

http://www.georgesteinmetz.com

Bonney

Hoare

Fryxell

https://nemablog.wordpress.com/

Lake Bonney

www.ees.rochester.edu

Maximum summer temperatures of 3.5 ºC

Evolution of Dry Valley Lakes

From core from Lake Hoare and sediments from Fryxell

Biota in freshwater lakes include:

BacteriaVirusesProtozoaPhytoplankton including algae and

photosynthetic bacteriaZooplankton including cladocerans, rotifers, copepodsCyanobacterial mats in benthos

Antarctic freshwater zooplankton:

Rotifer (Phylum Rotifera)Cladoceran (Daphnia) and copepod

(Crustacea)

Ice cover on lakes reduces light penetration. At Lake Hoare, whichis permanently ice-covered, light penetration is reduced to only 1.7-3.3% of that striking the surface of the ice

Lake temperatures remain consistently low with little or no thermalstratification, especially if ice-covered. Thus, they remain amictic ormonomictic with temperature changes of a few degrees C.

http://blogs.agu.org

http://huey.colorado.edu/cyanobacteria/about/cyanobacteria.php

Cynobacteria are phototrophic bacteria that can fix nitrogen from the atmosphere.

The mats are comprised of cynobacteria,bacteria, and diatoms and form layers

These mats often occur in extreme andfluctuating environments

http://www.nhm.ac.uk/natureplus/blogs/Antarcticcyanobacteria/2010/12/23/cyanobacterial-mat-communities-in-lake-hoare

Saline Lakes

Defined as having salinity >9%

Usually are closed lakes, inflow but no outflow

Water loss by evaporation, which concentrates the salts over time

Productivity is generally higher in these lakes compared to freshwater lakes

Often meromictic, or seldom mix

From Laybourn-Parry and Wadham. 2014. Antarctic Lakes. Oxford Univ. Press

Meromictic lake with saline, anoxic monimolimnionbelow a colder, less saline and oxic mixolimnion

Pony Lake, Cape Royds, Ross IslandFreshwater in summer with ice meltSaline in winter as ice forms

https://sensibleheat.wordpress.com/

Epishelf Lakes

Freshwater systems overlying seawater or with direct connection to the sea

Usually rafted ice on edges

Almost entirely restricted to the Antarctic

Arctic examples are rapidly disappearing with collapse of ice shelves

Beaver Lake is about 7 miles longwith a permanent ice cover

Receives glacial melt water withmore dense marine water below

Biota includes strictly marine species of fish at the bottomwith freshwater diatoms in surface waters

Still little known on carbon cyclingand species diversity in these lakes

Beaver Lake

http://www.antarctica.gov.au/

Supraglacial Lakes

Range from small ponds to larger lakes several km2

Usually very shallow, short-livedVery low in biotaSome are deep, small holes that connect to the

sub-glacial hydrological systemAlso ice shelf lakes at ablation zone of ice shelves

https://en.wikipedia.org/wiki/Cryoconite

Cryoconite holes form from windblown dust, soot, microbes on glacial surface, dark color absorbsheat and melts ice below

http://www-es.s.chiba-u.ac.jp/~takeuchi/cryoconite.html

Subglacial Lakes

Hundreds now knownMost small, less than 10 km in lengthFirst discovered in 1960s using radio-echo soundingIsolated from the atmosphere for millions of years

https://en.wikipedia.org/wiki/Blood_Falls

Blood Falls, Taylor Valley

Lake Vostok

Largest and best known lake, 250 x 50 kmEstimated sediment record of 300-400 m on lake floorHas not been exposed to the atmosphere for 14 Ma

Radarsat image of lake below ice

Russians cored into lake in 2013, but rising water in borehole froze, samples contaminated

Thousands of microbes were in accreted ice just above lake, butcontamination is possible

Drilled a new bore hole and reached liquid water in January 2015

No word on results