Eisenhauer, Anton

Goepfert, Tyler

Kirsch, Florian

Krause, Stefan

Liebetrau, Volker

Rashid, Rashid

OceanRep

Geophysical Research AbstractsVol. 20, EGU2018-13697, 2018EGU General Assembly 2018© Author(s) 2018. CC Attribution 4.0 license.Evaluating combined coral and Tridacna spp. carbonate paleo-SSTapproaches on recent and last interglacial time scales: A case study fromChumbe Island, ZanzibarFlorian Kirsch (1), Stefan Krause (1), Volker Liebetrau (1), Anton Eisenhauer (1), Rashid Rashid (2), and TylerGoepfert (1)(1) GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, (2) Faculty of Science, Zanzibar University, Zanzibar,TanzaniaPaleo-environmental records represent the backbone of past climate variability reconstruction, which is apre-requisite for future climate projections. Marine carbonate-producing organisms as corals and bivalves recorda suite of environmental parameters in their skeletal parts, thus providing geochemical archives of differentresolution and robustness. The variability of sea surface temperatures (SSTs) is one of the parameters of increasingsocio-economic relevance. Biogenic carbonate minerals record ambient seawater temperatures prevailing duringtheir genesis by isotope (δ18O) and element ratios (e.g. Sr/Ca, U/Ca).Especially due to their porous structure the susceptibility of fossil corals for early diagenesis and the impactof secondary mineralization processes is often observed as limitation for their archive reliability. In contrast,Tridacna shells provide dense carbonate material, presumably more resistant against geochemical alteration. Inorder to evaluate their geochemical proxy potential corals and Tridacna shells were sampled at two different sitesof Unguja and Chumbe island (Zanzibar, Tanzania), a northern most exposed and a sheltered western lagoonallocation.The northern site only provides strongly recrystallized coral and Tridacna material yielding no reliable U-Thage information, excluding them from SST approaches. Although the coral samples from the western samplinglocation are also dominated by calcitic mineralogy. The average U/Th age of 112 ky (±5 ky) BP still correspondswith the last interglacial maximum (Marine Isotope Stage 5e), which is the determined time interval of reefformation. This result points at least for the U-Th systematic on the option of an almost “closed system” behaviorduring recrystallization for these samples.The corresponding Tridacna fossils are still preserved in aragonitic mineralogy, suggesting only low diageneticoverprinting and supporting the coral data with reasonable age information around 114 (±6) ky BP.In contrast to the highly altered adjacent coral samples, first promising Sr/Ca SST approaches on these Tridacnacover a range from 25 to 37◦C and support further efforts on proxy calibration.Furthermore, current results on a recent to subrecent coral micro atolls from the lagoonal setting will be presented.

Evaluating combined coral and Tridacna spp. carbonate paleo-SST approaches on recent and last interglacial time scales: A case study from Chumbe Island, Zanzibar

http://oceanrep.geomar.de/44924/1/EGU2018-13697.pdf

Evaluating combined coral and Tridacna spp. carbonate paleo-SST approaches on recent and last interglacial time scales: A case study from Chumbe Island, Zanzibar

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