Global connections between aeolian dust, climate and ocean biogeochemistry at the present day and at the last glacial maximum Maher et al., 2010, Earth-Science Reviews Sept 20, 2013 Monica Arienzo

REALLY COMPLEX: Global connections between aeolian dust, climate and ocean biogeochemistry at the present day and at the last glacial maximum Maher et al., 2010, Earth-Science Reviews Sept 20, 2013 Monica Arienzo

Positive Feedback Negative Feedback

Iron and the Biological Pump Why is this important? Increased iron leads to increased primary productivity in the surface waters Export of biogenic carbon to deep waters Decreased surface ocean pCO2 Drawdown of CO2 from the atmosphere to the ocean

Iron and the Biological Pump Hypothesis: Oceans are (for the most part) iron limited, therefore addition of iron leads to increased primary productivity Requirements: 1.Iron limited to begin with 2.Iron must be bioavailable (depends on mineralogy) 3.The source of the iron (size distribution) 4.Duration of the iron source to ocean 5.Threshold concentration of iron in the ocean

Iron and the Biological Pump Hypothesis: Oceans are (for the most part) iron limited, therefore addition of iron leads to increased primary productivity Requirements: 1.Iron limited to begin with 2.Iron must be bioavailable (depends on mineralogy) 3.The source of the iron (size distribution) 4.Duration of the iron source to ocean 5.Threshold concentration of iron in the ocean Iron solubility is highly variable and should be considered in models How do these requirements vary with changes to ocean chemistry (ie OA conditions)

Dust and climate Size: – Regional scale dust size invariance Radiative: scattering vs absorption – Impacts of where on the earth (desert) Cloud nuclei All are impacted by one or more: source, mineralogy, size, shape Scale up?

Present

LGM Scale is different

Equatorial Pacific: – Decreased dust W  E and South Lack of Modern S. Hemisphere data = hard to interpret paleo record – Antarctica: Dusty, Patagonia major source ? LGM Dust

Expansion of dust sources Equatorial Pacific: – Decreased dust W  E and South Lack of Modern S. Hemisphere data = hard to interpret paleo record – Antarctica: Dusty, Patagonia major source ? – South Atlantic: S. American dust source Paleoproductivity: increased during glacial with dust increase? Contradicting evidence? Is iron the only limiting nutrient? Feedback on climate? Millennial scale climate: dust peaks associate with H events and before D/O events, do these events feedback to the glacial climate? LGM Dust

U and Th chemically separate in aqueous solutions under oxidizing conditions: Oceanic residence time of ~ 400,000 y Oceanic residence time of ~ 20 yTh +4 is removed by scavenging U +6 remains dissolved (UO 2 2+ ) U-Th disequilibrium – 230 Th/ 232 Th Unsupported (excess) Th Deposition of Th = to supply rate

U-Th disequilibrium – 230 Th/ 232 Th Total Th = Unsupported (excess) Th + Supported Th (from U decay) 0 Step 1: Calculate the slope (m) Step 2: Calculate the accumulation rate (a) Step 3: Calculate deposition age at a given depth (h) Step 4: Use Th Ax at (h) and initial Th Ax to calculate age λt

U-Th disequilibrium – 230 Th/ 232 Th: Example x 130 =