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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