The Role of Seamounts in Ventilating the Oceanic Crust: Geochemical Fluxes and Their Impact on Global Geochemical Budgets Geoff Wheat Geoff Wheat UAF Southern Campus Photo by Polar World Seamount Biogeosciences Network March 2006

The Role of Seamounts in Ventilating the Oceanic Crust: Geochemical Fluxes and Their Impact on Global Geochemical Budgets Mike Mottl, Andy Fisher, Earl Davis Hans Jannasch, Miriam Kastner, Jim McManus

Ground Water Intrusion Mid-Ocean Ridges Ridge Flanks Subduction Ridges What are the geochemical fluxes associated with ridge flank hydrothermal systems?

More Water through Flanks Mid Ocean Ridges3.7 x kg/y Ridge Flanks2.1 x kg/y Three orders of Magnitude!!! Ridge Flanks ~65% of the River Flux Mg Anomaly of 0.2 mmol/kg (0.4% Seawater)  River Flux Mottl 2003; Wheat et al., 2004

Studies of Rock Alteration (Thompson, Alt, Bach, Gillis, Teagle) Modified from Alt et al., 1996 Pros: History of Rxn Type of Rxn Mg sw --> Clays Cons: ~8 Boreholes > 100 m Depth <1 trillionth of 1% of the area of the seafloor Poor Recovery (30% of 504B Flows) 1 seamount

Inferred flow direction FlankFlux 90, 92, 94, and 95 Need Formation Fluid Composition!! Modified from Fisher et al. (2003)

Spring Fluids and Cores from the Upper 5 m of Sediment Spring Fluids and Cores from the Upper 5 m of Sediment Modified from Wheat and Mottl 2000 Conservative Mixing Reaction

Direct Sampling of Springs Modified From Wheat et al., 2002

CORKs OsmoSamplers Concerns for Sediment and Metal Contamination Modified from Wheat et al., 2003

Reaction with Basalt and Old Buried Sediment Microbial Influence???

IODP Expedition 301 (Site 1301) IODP Exp 301 (2005) Microbial Affects!!!!

Ridge Flanks Spring Fluids - 64  C Source Seawater Source to Crust –Mg, F, Na, K, Li, Rb –S (sulfate) –C (alkalinity, TCO 2, DOC) –P (phosphate), U, V –Nitrate –Cu, Y, REE (except Ce) Crust Source to Seawater –Ca, Sr, Chlorinity (Hydration) –B, Si, Ge –Ammonium –Mn, Fe, Cu, Ni, Zn, Cd, Co –Mo, Ba –Ce, Cs Fluids have Lower 87 Sr/ 86 Sr, 98/95 Mo, and 13 C; Higher D/H; 18 O ??

Ridge Flanks Spring Fluids - 64  C Source Mg is at Steady State within the Ocean Riverine Mg Flux – High Temp Mg Flux = Ridge Flank Mg Flux (Result: Ridge Flank Flux is 65% of the River Flux) Ridge Flank Mg Flux / Mg Anomaly ==> Fluid Flux Fluid Flux x Ion anomaly = Ion Flux >10% of the Riverine Flux Mg, Na, K, Li, Ca, Sr, Sulfate, B, Mo, Ge 64  C Fluid ~7% of the Ridge Flank Convective Power Output Maximum Because Low Temp Fluids Also Affect Mg Fluxes (Note No PO 4 or Si)

Composition is Similar to Bottom Seawater modified from Hutnak et al. (2004) Sediment, Microbial, Redox Reactive ions 14 C age 300 y versus 4000 y Baby Bare BathymetrySeismic Heat Flow Coring

Fluxes Important to Sediment- Reactive Species

Modified from Wheat et al., 2003 Estimates From Global Data Sets

2.1 x kg/yr 65% of River Flux Flushing Time 70,000 yr 2.8 x mol P/yr 130% of DIP Flux Modified from Wheat and Mottl, 2004

Gaps in our Understanding Most Flow is Through Young, Cool Crust Reactions with Sediment Small Anomalies of Major Elements Ridge Flank “Amazon” 14 C age 300 y versus 4000 y Baby Bare (EPR Crust) Located on a recent Heat Flow, Seismic, Bathymetry, and Coring Cruise

Fluxes Are Better Constrained by Examining Ratios and/or Isotopes Modified from Wheat and McManus 2005

OLD CRUST 65 Ma Oceans 30.4 TW Conductive heat loss 20.4 TW Convective heat loss 9.9 TW Warm (Baby Bare) 64°C 0.6 TW (3% Conductive heat loss) Plenty of Potential Sites!! Mg, Na, K, Li, Ca, Sr, Sulfate, B, Mo, Ge Reactions with old Carbon Fisher and Von Herzen (2005)

Chemical Fluxes from Seamounts with Ridge Flank Hydrothermal Systems

Geochemist’s Paradise!! IODP? Modified from Wheat et al., 2002