When was the last time the Arctic was ice-free?

[NickB79]

I'd guess at least 2-3 million years ago, if not longer. I'd like to know if there's any more exact dates out there. Thanks.

[islandmkl]

1. couldn't have been all that long ago...

since according to the huckster and the flat-earth crowd, the earth is only what?...6 to 10 THOUSAND YEARS OLD!!!

[theoldman]

2. When the dinosaurs ruled the earth.

[muriel_volestrangler]

3. "at least a million years ago" from this paper

The Arctic system is moving toward a new
state that falls outside the envelope of glacialinterglacial
fl uctuations that prevailed during
recent Earth history. This future Arctic is likely
to have dramatically less permanent ice than
exists at present. At the present rate of change, a
summer ice-free Arctic Ocean within a century
is a real possibility, a state not witnessed for at
least a million years. The change appears to be
driven largely by feedback-enhanced global
climate warming, and there seem to be few, if
any, processes or feedbacks within the Arctic
system that are capable of altering the trajectory
toward this “super interglacial” state.
...
Despite 30 years of warming and ice loss, the
Arctic cryosphere is still within the envelope
of glacial-interglacial cycles that have characterized
the past 800,000 years. However, although
the Arctic is still not as warm as it was
during the Eemian interglacial 125,000 years
ago , the present
rate of sea ice loss will likely push the system
out of this natural envelope within a century.
Climate models corroborate this projection
with depictions of sea-ice-free summers within
the same time frame Assessment, 2005]. There is no paleoclimatic
evidence for a seasonally ice free Arctic during
the last 800 millennia.

http://atoc.colorado.edu/~dcn/reprints/Overpeck_etal_EOS2005.pdf

[jpak]

4. 55 milion years ago - Palaeocene-Eocene Thermal Maximum...

http://news.bbc.co.uk/2/hi/science/nature/5034026.stm

Fifty-five million years ago the North Pole was an ice-free zone with tropical temperatures, according to research.

A sediment core excavated from 400m (1,300ft) below the seabed of the Arctic Ocean has enabled scientists to delve far back into the region's past.

An international team has been able to pin-point the changes that occurred as the Arctic transformed from this hot environment to its present cold status.

<snip>

The core revealed that before 55 million years ago, the surface waters of the Arctic Ocean were ice-free and as warm as 18C (64F).

<more>

[OKIsItJustMe]

5. Then I'm guessing it was more recent than that

After all, it would take a while to cool down sufficiently from 18°C.

[happyslug]

6. The Arctic seems to have formed about 3 Million years ago:

The formation of an Arctic ice cap around 3 mya (Million years ago) is signalled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds...]

http://en.wikipedia.org/wiki/Pliocene

The East Antarctic Ice Sheet is older:
East Antarctica had some glaciers during the early Miocene (23-15 million years ago). Oceans cooled partly due the formation of

http://en.wikipedia.org/wiki/Miocene

[jpak]

7. The new sediment core data puts arctic ice back to P-E boundary...

from the link above...

<snip>

"Five hundred thousand years above where the Azolla was found, we found the first drop stones," explained Professor Brinkhuis, who is also a co-author on the third paper which details Arctic ice-formation.

"These are little stones that come from icebergs, icesheets or sea ice. So it must have been cold enough to have ice.

"Before we did this, it was thought that the ice field in the Northern Hemisphere only began about three million years ago; but now we have pushed that back to 45 million years ago."

Although the data tells us how the world changed from one with greenhouse conditions to one with ice house conditions millions of years ago, it may also help scientists to predict what will result from the present changes in climate.

<more>

[jpak]

8. One striking result was the massive poleward flux of water vapor under super greenhouse conditions

There was enough precipitation in and around around the Arctic Ocean to maintain low salinity surface waters (fresh water) conditions in the Arctic all year round.

Stream flow and discharge of Arctic rivers has increased dramatically since the 1930's, indicating similar processes at work today...