Global connections between aeolian dust, climate and ocean biogeochemistry at the

present day and at the last glacial maximumMaher et al., 2010, Earth-Science Reviews

Sept 20, 2013Monica Arienzo

REALLY COMPLEX: Global connections between aeolian dust, climate and ocean

biogeochemistry at thepresent day and at the last glacial maximum

Maher et al., 2010, Earth-Science Reviews

Sept 20, 2013Monica Arienzo

Positive Feedback

Negative Feedback

Iron and the Biological PumpWhy 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 with2. Iron must be bioavailable (depends on mineralogy)3. The source of the iron (size distribution)4. Duration of the iron source to ocean5. 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 with2. Iron must be bioavailable (depends on mineralogy)3. The source of the iron (size distribution)4. Duration of the iron source to ocean5. 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 nucleiAll 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 yOceanic residence time of ~ 20 y Th+4 is removed by scavenging

U+6 remains dissolved (UO22+)

U-Th disequilibrium – 230Th/232Th

Unsupported(excess) Th

Deposition of Th = to supply rate

U-Th disequilibrium – 230Th/232Th

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 ThAx at (h) and initial ThAx to calculate age

230

- λt

U-Th disequilibrium – 230Th/232Th: Example

x 130 = -0.335