Details

Autor(en) / Beteiligte

• Kienast, S. S.
• Winckler, G.
• Lippold, J.
• Albani, S.
• Mahowald, N. M.

Titel

Tracing dust input to the global ocean using thorium isotopes in marine sediments: ThoroMap

Ist Teil von

• Global biogeochemical cycles, 2016-10, Vol.30 (10), p.1526-1541

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2016

Quelle

Electronic Journals Library

Beschreibungen/Notizen

• Continental dust input into the ocean‐atmosphere system has significant ramifications for biogeochemical cycles and global climate, yet direct observations of dust deposition in the ocean remain scarce. The long‐lived isotope thorium‐232 (232Th) is greatly enriched in upper continental crust compared to oceanic crust and mid‐ocean ridge basalt‐like volcanogenic material. In open ocean sediments, away from fluvial and ice‐rafted sources of continental material, 232Th is often assumed to be of predominantly eolian origin. In conjunction with flux normalization based on the particle reactive radioisotope thorium‐230 (230Th), 232Th measurements in marine sediments are a promising proxy for dust accumulation in the modern and past ocean. Here we present ThoroMap, a new global data compilation of 230Th‐normalized fluxes of 232Th. After careful screening, we derive dust deposition estimates in the global ocean averaged for the late Holocene (0–4 ka) and the Last Glacial Maximum (LGM, 19–23 ka). ThoroMap is compared with dust deposition estimates derived from the Community Climate System Model (CCSM3) and CCSM4, two coupled atmosphere, land, ocean, and sea ice models. Model‐data correlation factors are 0.63 (CCSM3) and 0.59 (CCSM4) in the late Holocene and 0.82 (CCSM3) and 0.83 (CCSM4) in the LGM. ThoroMap is the first compilation that is built on a single, specific proxy for dust and that exclusively uses flux‐normalization to derive dust deposition rates. Plain Language Summary Continental dust input into the ocean‐atmosphere system has significant ramifications for global climate and marine ecosystems. However, direct observations of dust deposition in the ocean remain scarce. Continental dust contains elevated concentrations of the trace element thorium, and dust input thus leaves a distinct geochemical signature in seawater and sea floor sediments. ThoroMap brings together thorium measurements from over 150 sediment core sites, unveiling a record of dust deposition to the global ocean in the recent geologic past. Key Points Continental dust input to the ocean is reconstructed using thorium isotopes A new global data base of dust fluxes is presented for the late Holocene and the Last Glacial Maximum Comparisons with recent coupled models identify regions of good model‐data agreement