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The Fingerprint of Geologic Carbon on Glacial/Interglacial Atmospheric CO<sub>2</sub>

UTIG Seminars

The Fingerprint of Geologic Carbon on Glacial/Interglacial Atmospheric CO2

Lowell Stott
University of Southern California

When: Friday, April 6, 2012, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
Where: Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Deborah Khider, UTIG

Live Broadcast

image from Lowell's talk

The rise in atmospheric CO2 during the last glacial termination was accompanied by a 190% decrease in Δ14C of atmospheric CO2 from 17 to 10 kyB.P. Deep water Δ14C values reconstructed from marine carbonates do not track the atmospheric record but intermediate water Δ14C values throughout the Pacific do, except in the eastern equatorial Pacific (EEP) where there were large negative excursions in Δ14C at intermediate water depths (see figure). To explain the contrasting deep and upper ocean deglacial Δ14C history a new hypothesis calls upon release of CO2-rich hydrothermal fluids to intermediate waters during the deglaciation as the ocean warmed. The hypothesis posits that Hydrothermal systems in the oceans act as a CO2 capacitor, regulating storage and release of carbon, and in doing so, affect the radiative balance that determines Earth's climate on orbital time scales. Here we test this hypothesis with an Earth System model of intermediate complexity (cGENIE) and geochemical records from the Pacific. With an injection of ~1300Gt of 14C-dead DIC into intermediate waters in the EEP the model simulates ocean and atmospheric Δ14C changes through the glacial termination that agree with observations. An injection of DIC into intermediate waters causes a ~40μmol/kg drop in [CO3=] of tropical surface waters. Trace metal proxies of [CO3=]sat, together with foraminiferal abundance and carbonate preservation data from tropical Pacific sediment cores document lower [CO3=]sat in association with the Δ14C excursions. These data support the hypothesis that release of geologic carbon during deglaciation contributed as much as 60ppm to the rise in atmospheric CO2.


Figure. Upper panel, Epica Dome C ice core CO2 record. Lower panel Δ14C data across the Termination 1. Solid black line is IntCal (09). Open circles are benthic foraminiferal data from intermediate water depth cores from the Pacific [MV99-GC31/PC08, 23.5°N, 111.6°W, 705m; VM21-30, 1.2°S, 89.68°W, 617m; RR0503 JPC64, 37.42°S, 177°E, 651 m; SO161-SL22, 36.130°S, 73.400°W, 1000m; MD98-2177, 1.4°N, 119°E, 968m (this study]. The solid squares are data from Deep Water depths in the Pacific, [W8709A-13P, 42.1°N, 125.8°W, 2710m; ODP 877, 54.37°N, 148.45°W, 3647m; MD98-2181, 6°N, 126°E, 2100m]. Note how the deep water values do not track the atmosphere or intermediate water records between 18 and 10kyB.P.