²³⁴Th-Based Carbon Export around Free-Drifting Icebergs in the Southern Ocean

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• 作者：T.J. Shaw¹ ; ^{shaw@chem.sc.edu"" rel=""nofollow} ; K.L. Smith Jr.² ; C.R. Hexel¹ ; Rebekkah Dudgeon¹ ; Alana D. Sherman² ; M. Vernet³ ; R.S. Kaufmann⁴
• 关键词：Iron fertilization ; Carbon sequestration ; Carbon export efficiency ; Atmospheric carbon drawdown
• 刊名：Deep Sea Research Part II: Topical Studies in Oceanography
• 出版年：2011
• 出版时间：June 2011
• 年：2011
• 卷：58
• 期：11-12
• 页码：1384-1391
• 全文大小：789 K

文摘

The impact of free-drifting icebergs on the efficiency of carbon export from the upper water column was measured using the disequilibrium of ²³⁴Th and its parent ²³⁸U. The study addressed the null hypothesis that free-drifting icebergs do not alter ²³⁴Th deficiency and carbon export compared to surrounding waters. Upper-water-column inventories of ²³⁴Th were measured at six stations in the Weddell Sea concurrently with four deployments of Lagrangian Sediment Traps (LSTs) during a cruise in March/April 2009. Four stations were sampled ranging from 0.3 km to <20 km of the edge of a large free-drifting iceberg (C-18a) and two were sampled at distances >60 km from C-18a. Temperature and salinity anomalies indicated enhanced upwelling and turbulent mixing extending downstream of the iceberg to a minimum of 20 km from the iceberg edge. Separate studies of the impact of C-18a on water column physical properties were used to define the extent of the iceberg's influence on surrounding waters.

The largest upper-water-column deficiencies in the inventories of ²³⁴Th were measured in close proximity and downstream of the iceberg and extending to below 100 m depth. A steady-state model was used to estimate the export of ²³⁴Th from the upper water column. Organic carbon export was calculated using C/Th from the concurrent LST collections. Comparison of stations within the iceberg's influence (close proximity and downstream to within 20 km of the iceberg) and far-field (greater than 60 km) measurements showed a factor of 3 increase in organic carbon export near the iceberg. The factor correlated well with the results from the near- and far-field LST measurements. Differences in the magnitude of carbon export at 100 and 600 m indicate that 90 percent of the exported material is regenerated by 600 m depth. This study confirms that the increased abundance of large free-drifting icebergs in the Southern Ocean can contribute to the drawdown of atmospheric CO₂ through increased organic carbon export.