Holocene Climate Change |
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Enlarge ImageAnne Cohen and colleagues at the Bermuda Biological Station for Research discover a massive brain coral (Diploria spp.) that lived and died during the Little Ice Age, almost 500 years ago. Although sponges and octocorals now inhabit the surface of the ancient mound, the skeleton inside preserves a record of ocean climate during this extended period of N Hemisphere cooling. (photo: Ross Jones, BBSR)
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Coral records of tropical Atlantic variability
Anne Cohen and WHOI grad student Casey Saenger work with the National Park Service at St Croix USVI to locate massive corals for paleoclimate work. This coral (Montastrea spp.) is estimated to be ~200 years old. First, subsamples are retrieved using a handheld drill driven by compressed air from a scuba tank. These are taken back to the lab at WHOI for preliminary analysis of growth rates and chemical composition. A temperature logger is strapped to the coral and a pink stain is introduced. The logger accurately records temperatures at the coral site every half hour. The stain will appear as a fine band in the skeleton and provide a time marker for our future work.
photographer: Ian Lungren (NPS)
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| Shifting perihelion from northern hemisphere summer in the early
Holocene to northern hemisphere winter in the late Holocene has
effected the seasonal cycle of incoming solar radiation. Since
the early Holocene, the amplitude of the seasonal cycle of incoming
radiation has decreased in the northern hemisphere and increased in the
southern hemisphere. The increasing tilt of the Earth’s axis
since the early Holocene caused a symmetrical change in the
distribution of the mean annual incoming solar radiation, with an
increase in the low latitudes and a decrease in the high
latitudes.
Why study the Holocene?
One goal of our research is to understand the response of the earth’s
climate to insolation forcing. The other goal of our research is
to understand the nature, significance and causes of recent, natural
climate variations that are too rapid and frequent to be driven by
insolation trends. Fluctuations in temperature, though smaller
than changes documented during the last ice age, had a clear affect on
people living at high latitudes. Changes in the hydrologic cycle
affected lower latitude civilizations. Much of our research on this
topic is driven by the need to assess what caused such changes and
whether such changes are likely to occur in the future.
Some of our specific research topics are:
• How did ocean temperatures, ocean circulation, climate dynamics, and the hydrologic cycle respond to insolation forcing?
• What was the origin of higher frequency Holocene climate variability?
• How widespread were Holocene centennial-millennial climate changes?
• Did the ocean circulation speed up or slow down during the Little Ice Age and earlier Holocene cold events?
• Are today’s ocean temperatures warmer today than they have been at any time during the last 10,000 years?
• How do
Holocene temperatures and climate variability compare to other recent
warm interglacials generally perceived as being “warm interglacials”
(Marine Isotope Stages 5 and 11)?
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