Centennial changes in North Pacific anoxia linked to tropical trade Winds

Curtis Deutsch,* William Berelson, Robert Thunell, Tom Weber, Caitlin Tems, James McManus, John Crusius, Taka Ito, Timothy Baumgartner, Vicente Ferreira, Jacob Mey,

Alexander van Geen

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INTRODUCTION--OVERVIEW

1. OCEANOGRAPHIC CONTEXT OF THE EASTERN TROPICAL PACIFIC2. CLIMATE MODELS3. DATA FROM SEDIMENTS4. BIOGEOCHEMICAL MODEL5. ANOXIC VOLUME6. CLIMATE DATA

MODELING OF LONG TERM CHANGE OF NORTH PACIFIC ANOXIA LINKED TO TROPICAL TRADE WINDS

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HYPOTHESIS

The trends in the Pacific OMZ inferred from the δ15N originate from slowly varying strength of the zonal tropical(Walker) circulation and its effect on O2 demand, rather thanfrom changes in O2 supply due to gas solubility and thermocline ventilation associated with climate warming. We postulate a mechanistic link between equatorial wind stress and the extent of anoxia indicated by the decadal to centennial change in δ15N reconstructed from the sedimentrecord.

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1. OCEANOGRAPHIC CONTEXT

2. CLIMATE MODELS

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Climate ModelsTo extend the estimates of thermocline depth prior to the instrumental record, we use output from coupled climate model simulations conducted for the IPCC’s fourth assessment report (AR4). A total of 19 model simulations (Fig. S6), were run with 8 climate models (GFDL (2 versions), IPSL, GISS (2 versions), NCAR, MPI, Hadley), allunder the same radiative forcing, from a combination of greenhouse gases (CO2, N2O, CH4, and CFCs), and volcanic and anthropogenic aerosols. In each model, we calculate the mean depth of the 13o C isotherm in the ETNP, as done for the observations (see below). The models also confirm that the depth of the thermocline throughout most of the Eastern Tropical Pacific (including the anoxic zone region), are closely connected toequatorial wind stress (Fig. S8).

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3. DATA FROM SEDIMENTS

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4. BIOGEOCHEMICAL MODEL

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5. ANOXIC VOLUME

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6. CLIMATE DATA

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