The Holocene

Retreat (melting) of the Ice Sheets Graph

• Climate warming started ~18ka

• Radiocarbon dated materials from moraines used to reconstruct glacier margin at different times

  • You can find out barriers of glaciers by mapping out moraine margins (in map)

• Melted completely by 6ka

• Vegetation follows glacial retreat, then animals, then people follow

Retreat of Ice Sheets - Proglacial Lakes

• As glaciers retreat they form proglacial lakes

• Eventually disappear with isostatic rebound

Retreat of the Ice Sheets - Deglacial Floods

• Pulses of flooding events

• Lake Missoula - blocked by ice like a dam when glacier retreats dam bursts releasing water

  • Water starts filling valley, ice dam gives way and water spreads more 

  • Massive lake drains rapidly, ice cap diverts massive flood south 

• Water goes back to the ocean 

• Form channeled scablands (the remains)

Retreat of the Ice Sheets - meltwater pulses, younger dryas

These deglacial flood events = meltwater pulses

Measured in δ18O in ocean forams and coral

• much lighter/lower δ18O comapred to ocean b/c of glacial water

Younger Dryas - where there’s no meltwater pulses! No melting because of a cold blip

Younger Dryas

Mid-deglacial pause in ice melting, a cold snap where glaciers re-expanded (12.8-11.7ka)

Lots of evidence for it - moraines, forams, pollen

What caused the Younger Dryas?

Slowdown of the thermohaline circulation

• Meltwater could go out to the Gulf of Mexico and out of the Hudson Bay where deep water forms and salty cold water sinks

• This could have messed up salinity concentrations (less b/c of freshwater)

  • Freshwater cut off deepwater formation

Recovered quickly and went back to warming in just 100 years

Holocene Thermal Maximum

Maximum solar insolation at 65°N by 10 ka

African Humid Period (9-10ka)

Precession-driven peak in insolation (caused stronger monsoons)

• Green Sahara

• Large lakes in Northern Africa

precession affects mid-latitudes

Following the Holocene Thermal Maximum, there’s been a neoglacial cooling trend over the past 6ka. Why?

Decrease jn summer insolation right after the Holocene Thermal Maximum

• Because of precession and obliquity past 6ka 

• Less seasonality and decreased summer insolation

Neoglacial Cooling - driven by decrease in NH summer insolation

Is the Holocene a “norma/” interglacial period?

Even though it is similar looking to past interglacials, never have we seen CO2 concentrations this high before and this time period can be a metric for future climate change

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