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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 !