L5: Natural Systems and Feedbacks
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are natural systems almost always open or closed?
open
what defines an open system?
flows of mass and energy across external boundaries of a system, and transfers of mass and energy internally (throughputs)
what are throughputs?
internal transfers of mass and energy within a system
what defines a closed system?
sealed boundaries and no transfers of matter across external boundaries
are there transfers of mass and energy internally within closed systems?
yes
what is an example of the cryosphere?
Borgen Bay, Anvers Island, West Antarctica
what are the inputs of glaciers?
precipitation (usually in snow form), rock detritus, gravity (input of all systems), insolation (incoming shortwave, solar radiation), geothermal heat
what are the outputs of glaciers?
water vapour, water, ice, rock detritus, heat
why is rock detritus considered a glacier input?
gradually becomes incorporated into the base of the ice sheet through erosion as the ice grinds across the avalanche surface. ingested material becomes incorporated into the system
where is water vapour, as an output in glaciers, at its highest level?
towards the margin
what can occur when insulation in a glacial system is particularly high?
direct transfer of solid ice converted into meltwater
how is rock detritus also an output of glacial systems?
discharged often underneath the ice and around margins of the ice sheets and into the ocean
why do ice sheets provide good timelines?
because they accumulate incrementally through time, providing an analogue
where have ice cores been extensively extracted from?
Greenland and Antarctica
how can we determine the age of ice in an ice core?
seasonally precipitation on the surface of ice is focussed during the autumn, winter and spring and then during the summer, there’s often a bit of melting. so you get a seasonal accumulation of precipitation, a little bit of melting back, and then more precipitation etc. gives an annual layering which can then be counted back
why are other methods of dating ice cores essential?
because you don’t always get preservation of annual layering
how can you use slivers of ice samples?
represent a particular time in the past. material contains ice, lithic material and dust incorporated into the ice sheet which can then be melted down into a mix of water, gas bubbles, and solid lithic material which represents a point in time.
how do bubbles form in ice cores?
fresh snowfall on the surface of the ice sheet is loosely packed and air is able to dominate around each crystal, creating an open system (atmospheric exchange). progressively, as snow falls, the deeper snow becomes denser as it gets compressed. at certain depth the air around the crystals become sealed and transitions into a closed system
is there a specific depth at which ice cores transition into a closed system?
no, the depth varies enormously
does the system transfer into a closed system much more rapidly in colder or warmer climates and why?
tend to transition faster in environments that are thermally a bit warmer as the snow accumulates faster e.g. compared to Antarctica where it may form 50 m in depth compared to just 5 m in a warmer system
is there an age difference between the age of the gas in the bubble and the crystal surrounding? and if so why>
yes because the gas bubble will be younger by some specified amount
what does the closed system gas bubble represent?
the atmosphere at that time by containing C02, CH4 and NOx as a sample from the historic atmosphere
what are feedbacks?
interactions between components within a system, or across the boundaries of one system with another system
what are the 2 types of feedbacks?
positive and negative