Transcript RadsEvol_Moore2 - Personal

Radiolarians and Climate
Evolution
through
Time
Ted Moore
Department of Geological Sciences
University of Michigan
Radiolarians
• The Nature of the Beast - (or, how little we know)
• What they are used for by Geologists
• How they have changed through time
– and the apparent association with climate
• How they have changed in the Cretaceous and Cenozoic
– and the apparent association with oceanographic change
• What they may be used for in the future
What are Radiolaria ?
Marine Protista (single cell)
Polycystine Radiolaria – One group (of several) that preserves well
Shell: Opaline (amorphous) SiO2 . nH2O
NO fresh water forms
NO benthic forms
ONLY marine (salinity > ~20 – 25‰)
Reproduction: cell division + sexual? (life span – weeks to months)
Cell Contains:
Central capsule (nucleus, respiratory, excretion organelles, vacuoles, lipids)
Outer cell (Calymma) alveoli (flotation), digestives vacuoles, symbiotic algae
Several types of “podia” for food capture, waste disposal
Illustrations
ALIVE ! !
Modern Radiolarians
Two Basic types preserved in sediments
Example: Spumellaria Evolution (Eocene to Recent)
Example: Nassellarian
Evolution (within Eocene)
Modern Radiolarians
Concentrated in upper 50 – 100m, but can be found at several 100 m water depth
Kling & Boltovskoy ‘02
About 200 extant species (more in tropics than in high latitudes)
Kling & Boltovskoy ‘02
How do Geologists use Radiolaria ?
• Dating ancient marine deposits on land
• Deciphering the structural complexity of
allochthonous terranes
How do Geologists use Radiolaria ?
High Species diversity make them Ideal for BIOSTRATIGRAPHY
Over 350 datums
spanning last 50 Ma
How do Geologists use Radiolaria ?
High Species diversity make them Ideal for Mapping Ocean Water Masses
Radiolaria are the longest ranging of of all the
shelled plankton
They first make their appearance in the Cambrian
How Did They Change with a Changing Climate ?
How Did Climate Change?
What shall we use for an index of climate change
through the Phanerozoic?
The interplay of CO2 and Solar Luminosity
Radiolarian Diversity
Add another Index of Climate
Major Extinctions: Three “Climate” Related
Two “Catastrophes”
The earliest Rads tended to have a
basic spherical shape
Big diversification
in Triassic
Apparent diminished size,
robustness of shells in Cenozoic
The apparent change in “robustness” of the shell is real !
Why this trend in silicification ?
Big, heavy Rads – Warm Oceans
Low Radiolarian Diversity in Warm Intervals
DIATOMS Arrive on the scene
Diatom – Radiolarian competition for silica in the low
latitudes only started near the end of the Eocene
Exp. 320 Scientific Party ‘09
Diatom – Radiolarian competition for Silica in the low
latitudes only started near the end of the Eocene
When the abundance of Diatoms
increased dramatically
What happened at the Eocene – Oligocene Boundary
The drop in deep water temperatures and
buildup of East Antarctic Ice Sheet
What happened at the Eocene – Oligocene Boundary
The drop in deep water temperatures and
buildup of East Antarctic Ice Sheet
What happened at the Eocene – Oligocene Boundary
The drop in deep water temperatures and
buildup of East Antarctic Ice Sheet
A fundamental change in vertical
ocean structure and stability
Radiolarian Diversity
What happened at the Eocene – Oligocene Boundary
The drop in deep water temperatures and
Radiolarian
Species Last
Occurrences
buildup
of East
Antarctic Ice Sheet
A fundamental
A dramatic
die-off of Eocene change in vertical
Radiolarianocean
Species structure and stability
What happened at the Eocene – Oligocene Boundary
As Diatoms Blossom in Abundance
The drop in deep water temperatures and
Radiolarian Species Last Occurrences
buildup of East Antarctic Ice Sheet
A dramatic die-off of Eocene
Radiolarian Species
The Modern Tropical Pacific
The Modern Tropical Pacific
The Modern Tropical Pacific
The Modern Tropical Pacific
Tropical W. Pacific
Radiolarian assemblage
13 Species dominate
2 Species
Common
to both
Tropical E. Pacific
Radiolarian assemblage
4 Species dominate
Seamounts
Spreading Ridges
Aseismic Ridges, Plateaus
Continental Slope, Rise
Zone of rapid
nutrient
regeneration
Modern density
structure
Seamounts
Seamounts
Ridges
Ridges
Spreading
Spreading
Plateaus
Plateaus
Ridges,
Ridges,
Aseismic
Aseismic
Rise
Rise
Slope,
Slope,
Continental
Continental
Zone of rapid
nutrient
regeneration
Eocene density
structure
(Weaker Density Gradient
Greater Vertical Mixing)
In what ways did low latitude Ocean Structure Change
from Warm Eocene to Cooler Oligocene – Miocene?
Warm Eocene
Temperature
Salinity
Warmer
Avg. Lower
Cool Paleogene-Neogene
Cooler
Avg. Higher
Pycnocline
Weak
Strong
Nutricline
Weak/Diffuse
Photic Zone
UNCHANGED
UNCHANGED
Mixing
energy
~UNCHANGED
~UNCHANGED
Topographic
roughness
~UNCHANGED
~UNCHANGED
Sharp/Shallow
What does the Warm Eocene structure mean in
terms of whole basin water masses ?
MODERN PACIFIC
MODERN PACIFIC
Temperature
MODERN PACIFIC
MODERN PACIFIC
Salinity
MODERN PACIFIC
MODERN PACIFIC
Salinity + Dissolved Silica
MODERN PACIFIC
What does the Warm Eocene structure mean in
terms of whole basin water masses ?
MIDDLE EOCENE
(a brazen guess !)
MIDDLE EOCENE
Salinity
(a brazen guess !)
N. Pacific deep water source
(depth 2.3 – 2.9 km)
65 – 40 Ma (Thomas, ’04)
Early diatom development in high southern latitudes
Later Appearance in N. Pacific, Equatorial Pacific
Cervato & Burkle, ‘03
What happened at the Eocene – Oligocene Boundary
The drop in deep water temperatures and
buildup of East Antarctic Ice Sheet
AND the Development of Antarctic Intermediate Water
The delivery of Dissolved Silica and other
Nutrients to the Equatorial Divergence Zone
MODERN PACIFIC
SPECULATIONS
The important interplay between Diatoms and Radiolaria is
associated with a profound change in Ocean Structure
and Circulation
Rads appear to develop more diverse assemblages under
relatively warm conditions (during overall cool climates)
Rads appear to develop more diverse assemblages under
relatively cool conditions (during overall warm climates)
[At least till the advent of DIATOMS – the more effective
competitors for DISSOLVED SILICA]
CONCLUSIONS
Radiolaria have been around for a LONG Time !
They are extremely well adapted to a pelagic environment
Multiple food sources
Vertical mobility
Very diverse assemblage
CONCLUSIONS
High diversity (for plankton), good preservation in sediments make
Radiolaria an important stratigraphic tool throughout the
Phanerozoic
These characteristics also make them useful in mapping
assemblages associated with different surface water masses
Geochemical paleoceanographic proxy development
remains a challenge
• Low abundance of individual species (rarely > 5 - 10%
of population)
• Complex ecology
• Hydrated, meta stable, non-xline, nature of tests
BUT . . . Challenges can represent Opportunities
• Trace elements, isotopes within the opaline shell
• Organic matrix of the shell
Beware the RAD ! !
Thank You !