Cook, T. (2019)
"Southern Hemisphere Sediments
Show Surprising Pliocene Cyclicity"
Eos, 100,
April 25, 2019
SUMMARY:
The team presents
the first high-resolution
paleoclimate reconstructions
derived from two deep-ocean
sediment cores,
Ocean Drilling Program
Site 1125 and
Deep Sea Drilling Project
Site 594,
using multiple proxies
to recreate variability
in Southern Hemisphere
climate and temperature
during the middle
to late Pliocene.
The team shows
100,000-year rhythms
when the planet
was warmer
than it is today.
All variables the authors measured,
including intermediate water stable
oxygen and carbon isotopic ratios,
as well as indicators of sea surface
temperature and surface productivity,
reveal a dominant 100,000-year rhythm
in climate fluctuations that overlays
the expected 41,000-year cycle.
Because this 100,000-year cycle
is detected from middle to surface water
depths at both sites, as well as
in other southwestern Pacific locales,
the researchers argue these middle
to late Pliocene climate excursions
likely extended across vast portions
of the Southern Hemisphere.
The authors’ evidence is consistent
with documented cycles in the angle
of the planet’s axial tilt and regular
variations in the shape of Earth’s orbit
around the Sun.
They attribute the rhythm observed
in their data to recurring wobbles
of the planet as it spins on its axis.
The study’s surprising conclusion
is that glaciations in the middle to late
Pliocene occurred at 100,000-year intervals.
The authors dispute the assumption
of 41,000-year cycles in previous studies.
DETAILS:
Phytoplankton bloom
over the study area
in the South Pacific Ocean
-- organic compounds produced
by ancient blooms, accumulated
in ocean floor sediment over time.
These sediments were used
to provide information about
past climate cycles at this location.
During the middle to late Pliocene
about 4.2 to 2.8 million years ago,
most of Earth’s continental ice
was in the Southern Hemisphere.
Fluctuations in temperature
and ice volume during this
relatively warm period
are attributed to cyclic changes
in the tilt of Earth’s axis
that recur every 41,000 years.
This 41,000 year theory is based
mainly on proxy data from
the Northern Hemisphere.
mainly on proxy data from
the Northern Hemisphere.