At any given time the chemical composition of ocean water reflects the balance of material fluxes between earth´s lithosphere, hydrosphere and atmosphere triggered by the dynamics of geological and biological processes on land and in the sea. In particular, the ocean water setting (e.g. temperature, pH, salinity) determines how elements and substances are partitioned in the ocean and atmosphere, which is particularly important for greenhouse gases like CO2. Therefore, reconstructing the elemental and isotope evolution of seawater through geological time is one of the main research objectives of the earth system sciences, with implications for our better understanding of the present global biogeochemical cycles and their impact on the earth's climate as well as economically important aspects like the formation of submarine hydrocarbon oil and gas resources.
Although the chemical conditions in the ancient seawater cannot directly be measured anymore, they can be reconstructed from the measurement of certain trace element and isotope ratios that serve as chemical indicators (proxies) retained in suitable geological archives such as preserved marine carbonates (corals, foraminifera, brachiopods).
However, the existing proxy database for reconstructing ancient seawater conditions suffers from
(i) post-depositional alteration of primary chemical composition
(ii) low stratigraphic and age resolution, and
(iii) analytical limitations measuring certain trace element and isotope ratios.
These limitations are reflected in relatively high statistical data uncertainties in the interpretation of proxy time series and error margins reported by earlier studies, thus challenging the reliability of the records and the robustness of proxy information. To overcome these problems we propose a multi-disciplinary approach considering ecological, geological, mineralogical and physical studies to determine trace element and isotope time series (i.e., during the Phanerozoic) from brachiopod shells. Brachiopods are selected because they
(i) are highly abundant in the geological record
(ii) have shells composed of a relatively stable low-magnesium calcite (LMC), and
(iii) provide a high potential for the preservation of primary chemical signals.
BASE-LiNE Earth will gain knowledge
- On the link of Brachiopod shells (fossil and recent ones) with marine ecology and biomineralization processes
- On pathways and processes of diagenetic alteration
- On reliable time series on trace element ratios (Mg/Ca, Sr/Ca, Li/Ca, Ba/Ca, B/Ca, U/Ca) and their isotope systems (e.g. d26Mg, d44/40Ca, 87Sr/86Sr, d88/86Sr, d53/53Cr, d7Li, d11B ) for the Phanerozoic Ocean.
Specific scientific objectives of the project are to:
- collect information on a.) the reliability and sensitivity of carbonate archive to environmental and compositional change in the adjacent water body, b.) the influence of the brachiopod physiology (vital effect) on biomineralogy, trace element composition and isotope partitioning in their calcitic shells, c.) the diagenetic pathways and processes superimposing original signals due to post-depositional chemical.
- determine trace element and isotope ratios from fossil brachiopod shells for the quantitative reconstruction of the seawater composition throughout the Phanerozoic and main time events associated with biological mass extinctions.
- test new archives, proxies and analytical methods to characterize the chemical evolution of the oceans.