Changing Oceans

Heat balance

Heat absorbed by the Earth re-emitted as longwave radiation

What are other long-wave radiation absorbed by?

-Co2

-Water vapour

-Nitrous oxides

Insolation+

Radiation reaching surface

Albedo=

Some of insolation is reflected by the surface

Examples of high and low albedo?

High albedo=Snow

Low albedo=Soil

What type of radiation is reflected back off to the atmosphere?

Infrared & longer wavelengths

What 2 things strongly absorb infrared?

H2o vapour & CO2

What caused CO2 levels to increase?

Industrial revolution

What has accelerated CO2 levels recently?

-Greater industry activity (burning fossil fuels)

-Deforestation & land clearance

Recent atmospheric CO2 changes?

From 1959 to 2011 there was increase of 24% atmospheric CO2

-Mauna Loa Observatory, Hawaii

What is harder to measure CO” or global temperature?

Global temperature

What is the effect of CO2 on the climate?

Mean global surface temperature increased by 0.74^oC

Direct Observations of recent Climate Change

What is past climate characterised by?

High frequency and high amplitude cycles

Past Climate features?

-High-mid latitudes: Glacial & Interglacial

-Lower latitude:Interpluvials & Pluvials

-Major changes in sea level

-Many cycles between warm & cold periods

-Milankovitch (1920): 3 astronomical

Axial tilt

-Tilt of earths spin

-~21.5^o to ~24.5^o and back every 42k years

-More intense seasons in both hemispheres

Eccentricity of the Orbit

-Orbit circular, elliptical & back ~100k

-Weaker effects on seasonality than axial tilt

-Intensifies seasons in one hemisphere

-Moderates seasons in the other hemisphere

Precession of the Equinoxes

-Wobble of spin axis

-Interplay between the 1st two factors

What did the 3 factors that Milankovitch calculated control?

Sunshine reaching high North latitudes (20%)

What is the problem with Milankovitch 3 factors?

No independent record of ice age timing

What does the ratio of oxygen isotopes (¹⁸O/¹⁶O) in seawater indicate?

The ratio reflects ice volume changes on land

-During glacial periods, oceans become enriched in ¹⁸O as ice caps store snowfall depleted in ¹⁸O.

-Marine organisms, like foraminifera, incorporate this isotope ratio into their shells, which become sediment records of past climate.

What did the records of ¹⁸O/¹⁶O from forams in deeps-sea cores:

Ratio fell & rose in accordance with Milankovitch cycles

Ice volume every 100Ky:

Eccen of orbit

Other 2 cycles (23Ky &m41 Ky):

Wrinkles

What did analysed Co2 in ice core bubbles from Antarctica & Greenland?

-Very good correlation between CO2 & temperatures

What can oceans regulate?

Atmospheric CO2

-Ocean can act as large CO2 sink & hold 50-60 times more CO2 than the atmosphere

Thermohaline Conveyor features

-Begins in North Atlantic

-At latitude of Iceland water cools 10-2^oC

-Gives off huge amount of heat

-Mild winters:North West Europe

-NaDW floods deep Atlantic, distributes around other oceans

How much has CO2 has risen from the past 200 years?

150 ppm

When was the last glaciation comparable rise?

5000 years

Evidence atmospheric CO2 rising accelerates global warming

-Past 5 decades: increased freshening of Nordic seas

-Slowed NADW formation

-Overflowed decreased 20% since 1950

-Accelerated melting of Greenland ice sheet

What is the percentage that models predict will happen with the Atlantic Thermohaline Circulation?

45% will collapse by 2100

What are the amplifying factors in quaternary CO2 variations?

-Ocean Circulation

-Albedo feedback

-Atmospheric CO2

Evidence of the oceans effectively pumping CO2 more efficiently during glacial periods:

-Enhanced PP & export during glacials

-More nutrients in surface mixed layer during glacials

-Increased aeolian Fe inputs

-Fe fertilised HNLC regions

Does all anthropogenic CO2 remain in the atmosphere?

No

-past 100 years:~30% anthropogenic CO2 taken up by oceans

Why does not all anthropogenic CO2 get absorbed?

-Increased atmospheric pCo2

-Increased PP & organic sedimentation