Theme 2
Theme 2: Biological proxies to better achieve paleoenvironmental reconstructions


The Earth is a continuously changing system of interacting components: plates, oceans, icecaps, atmosphere and biota. Plate collision leads to mountain building during which oceans are created or obliterated. This has a direct bearing on ocean and atmospheric circulation and hence on climate as one of the major driving forces of the evolution of life. The history of environmental change is archived in sedimentary sequences. The challenge is to open and read those archives, because they reflect System Earth's responses to its own inherent changes. They also contain the response to catastrophic events such as volcanic eruptions, sudden and massive release of gas hydrates or meteorite impacts. Many of the predicted scenarios for the Earth’s future (e.g. climate change, sea level rise, CO2 increase) are not unique in its history. By studying the geologic record we are able to answer questions on boundary conditions, dynamics and rates of change as well as resilience and response of biotic and abiotic systems. Such studies also allow clarifying the role of man in the present climate debate: are there significant differences between perturbations of the system due to natural causes versus perturbations caused by man?



Our ability to accurately reconstruct palaeo-environments and their dynamics is still relatively limited. In part this is due to the so-called no-analogue problem, e.g. the discrepancy between modern and past environmental conditions and biota. The biota of a Cretaceous ice-free world have no recent analogue. However, many physical and chemical variables (temperature, salinity, precipitation, wind strength) are similar and can directly be compared. In view of the threats the world is facing in the 21st century and beyond, the major challenge of palaeo-environmental reconstruction is to gain a better understanding of the System Earth by learning from the past. In that respect essential periods are those that exhibit abrupt changes from ice-house to greenhouse or fast warming steps in an icehouse world comparable to those that we experience now. In that context the development of new proxies, in particular those that allow quantitative reconstructions, is essential.


It must be stressed that palaeo-environmental studies and related development of proxies are multidisciplinary by nature; the greatest advances are expected by combining observational, experimental and modeling research. Key proxies for marine, freshwater and terrestrial research are those that are related to the major biogeochemical cycles (C, P, N, S, O2, Si, and Fe). Important are proxies that describe the state of the system, as reflected in physical parameters such as the vigor of ocean circulation and transport of heat. Outstanding among them are the physical reconstruction of climate and climate related parameters. Finally, proxies that describe bioproduction and the state of ecosystems (biodiversity, ecosystem stability, complexity of the web) are important as well.


Biotic proxies are traditionally based on remains of organisms, and isotopic and elemental patterns, but recently the application of molecular markers (lipids, DNA) has shown its potential.  Molecular biomarkers bridge between the life and earth sciences and can therefore play a prominent role in the biogeological research of the . However, for a wider application of molecular markers in biogeosciences further insight is needed on the lipid composition of archaea, bacteria and eukaryotes, their specificity and the relationship with the molecular phylogeny of these organisms and their preservation potential. Moreover, this research should be combined and confronted with classical paleontological and geochemical approaches. This will not only provide a cross validation of existing and novel proxies, but also detailed, accurate reconstruction of ecosystem dynamics in the geological past.