Reading Earth's Climate History
from Ocean Sediments (with an
example from Pleistocene Glacials
and Interglacials)
Larry Krissek
School of Earth Sciences
Ohio State University
Outline
¾
What is “climate” in the ocean?
¾
What does ocean “climate” affect?
¾
How are these effects recorded? An introduction
to proxies.
¾
An example of using a proxy – the input of icerafted debris (IRD) to the North Atlantic during
the last 1 million years
Geologic records of
climate change are
common.
What part of “climate”
does each represent?
And how complete is
the record?
More complete records in ocean basins
DSDP (Glomar Challenger); ODP & IODP (JOIDES
Resolution)
Long,
continuous, highquality sediment
cores
Shipboard “multi-sensor track”, measuring properties
of the core before splitting.
Example of split
cores (6 sections,
each 150 cm long +
the core catcher),
showing:
1) patterns of
layering,
2) color changes,
and
3) relatively
undisturbed
nature of the
cores.
Important measures or components
of “climate” – especially “climate” of the
surface ocean
¾
“Temperature” on land – sea surface temperature (SST) in
ocean
¾
Precipitation on land – sea surface salinity in ocean
¾
Winds (position & strength) on land – surface currents &
upwelling in ocean
¾
Glacial ice volume/extent on land – glacial input/calving &
sea ice in ocean
Trujillo and
Thurman,
2008.
Trujillo and
Thurman, 2008.
What do the components of ocean “climate” affect?
¾
Sea surface temperature
¾
¾
Sea surface salinity
¾
¾
Heat transport, distribution of nutrients, distribution and amount
of productivity
Glacial input/calving
¾
¾
Rates of evaporation, seawater density, distribution of planktonic
and pelagic species
Surface currents & upwelling in ocean
¾
¾
Heat transport, seawater density, distribution of planktonic and
pelagic species
Freshwater input, oxygen isotopic composition of seawater,
sediment input, nutrient input(?)
Sea ice
¾
Heat release, brine production, distribution and abundance of life
What records the characteristics and effects
of ocean climate? Paleoclimatic “proxies”
¾ Whole-core characteristics – sediment type,
sediment color
¾ Biological proxies -- indicator species or
assemblages; transfer functions
¾ Geochemical proxies -- stable isotopes;
elemental ratios
¾ Terrigenous proxies -- grain size; clay composition;
iceberg-rafted debris
Sediment type as a
paleoclimatic
proxy:
Diatomite -- open
water and high
productivity
vs.
Glacial sediments
(AND-1B core)
AND-001B, 000-500m
Yellow intervals
are diatomite,
deposited under
highly productive
open waters.
Green intervals
are glacial
sediments,
deposited on
seafloor below an
ice shelf (a
floating extension
of a large ice
sheet).
Sediments at ~100 m are ~1 million years old. Sediments at ~500 m
are ~5 million years old. Do these sediments carry a paleoclimatic
record? Minimum number of ice shelf advances and retreats during
this 4 million years?
Sediment color as a paleoclimatic proxy:
Site 1302, North Atlantic
The lighter color bands are enriched in carbonate.
The carbonate was eroded from limestones on land, and was transported to this
location by icebergs.
In other parts of the ocean, an enrichment in carbonate would indicate
increased productivity by calcareous plankton, and/or decreased dissolution in
the deep ocean.
Plankton (diatoms) as climatic indicators
Eucampia antarctica –
lives beneath sea ice
Thalassiosira spp. -lives in “normal” marine
conditions
Images from MIRACLE website, University College London
Plankton (foraminifers) as climatic
indicators
Neogloboquadrina pachyderma left-coiling or sinistral
(left photo) and right-coiling or dextral (right photo).
“N. pachy left” favors cold water; “N. pachy right” favors
warm water.
Images from Leonid Polyak, Byrd Polar Research Center, OSU
Variations in the
abundance of “N. pachy
left” in a North Atlantic
sediment core.
What do these changes
suggest about the SST at
this location through the
last 90,000 years?
From Ruddiman, 2001.
Sea surface temperatures of 18,000 years ago, estimated from plankton
assemblages (the CLIMAP project).
More recent studies indicate greater cooling of the tropics than shown
here.
From Ruddiman, 2001.
¾“Gold standard” of marine paleoclimatic proxies is oxygen isotope composition of
foraminifers.
¾Moisture moved from ocean to land to build ice sheets is depleted in O-18-bearing-water, so
ocean becomes isotopically “heavier” as ice sheets grow.
¾Forams secrete carbonate with oxygen isotopic composition determined by the oxygen isotopic
composition of ocean water at that time.
¾Isotopic composition of foram carbonate interpreted as a global ice volume record.
From http://earthobservatory.nasa.gov/Features/Paleoclimatology_OxygenBalance/
¾Oxygen isotopic composition
of foraminifers during the time
of Northern Hemisphere “Ice
Ages”
¾Interpreted as a global ice
volume record.
¾Key data set for defining
“orbital” or “Milankovich”
cycles
¾Note “cycles”, and change in
length of “cycles” at ~0.7 - 0.9
Ma.
(Ruddiman, 2001)
Note:
Maximum
change in solar
forcing is
~20%,
suggesting
amplification
within the
“climate
system”.
Greenhouse
gases are
primary
suspects.
“Orbital” or Milankovitch cycles – changes at 20,000
to 100,000 years
http://www.eoearth.org/article/Milankovitch_cycles
Iceberg-rafted debris (IRD)
-- “Large” grains in fine-grained matrix
-- Mid- to high-latitude sites, preferably on bathymetric highs
-- Icebergs released when glaciers extend to sealevel.
Simple interpretation:
more IRD => more icebergs => large ice sheets
-- Other controls: glacial thermal regime and load; nature of
glacial terminus; dispersal patterns (currents); melt
patterns (SST distribution)
Ice-rafted debris (IRD) as a paleoclimatic proxy
Icebergs off Cape York, Greenland. Note “dirty ice”, especially
in bergs in lower right quarter of photo.
From Wikimedia, courtesy of Mila Zinkova.
Ice-rafted debris (IRD) – indicator of glacial activity that extends to
sealevel on adjacent land; composition suggests source area
Sand-sized IRD
Coarse sand fraction IRD –
More commonly analyzed than gravel-sized IRD
Using IRD to explore glacial/interglacial fluctuations
of the last 1 million years around the North Atlantic
918
Krissek & St. John, 2001.
Composition of all IRD at
Sites 918 and 919.
918
Ba
Quartz, basalt, coarse-grained acidics,
coarse-grained mafics and sedimentary
rock fragments – consistent with onshore
geology.
CGM
919 farther offshore; in dispersal path of
icebergs starting farther north.
Site 919 IRD and
planktonic oxygen
isotopes
?
(gray bands indicate
interglacials)
1) No unique link between IRD
abundance and global ice
volume
2) Importance of transitions –
many IRD peaks near
transitions
3) Dispersal & melting effects
a) Polar Front east of 919
during Stages 2, 10, 12,
and 16 means icebergs
reach 919 before melting
b) sea ice during MIS 6
may have restricted
iceberg movement
offshore
4) Other effects?
Evidence for Climate Change at Shorter (“suborbital”) Timescales
“Heinrich Events” of the North Atlantic
Heinrich events – short-lived “armadas of icebergs” released into the North
Atlantic for 100-1000 years
Why? “Binge – purge” behavior of Laurentide Ice Sheet growth and
collapse?
http://www.ncdc.noaa.gov/paleo/slides/slideset/19/19_380_slide.html
Climate Change
¾
We’ve seen evidence for past climate change at
“orbital” and “suborbital” timescales
¾
What about future climate changes?
¾
Scientifically based projections of future climate
change and its effects?
Abbott, 2009.
“Climate” based on average annual No. Hemisphere
temperatures. The Mann “hockey stick” curve.
“Recent” CO2 values exceed highest of Pleistocene
IPCC, 2007
IPCC, 2007
Abbott, 2009
Estimated increase in surface temperature
by 2100.
Abbott, 2009.
Now a fairly strong concensus that this underestimates
potential sealevel rise.
IPCC, 2007
IPCC, 2007
IPCC, 2007