Proxy development and innovation: the baseline for progress in palaeoclimate research

We improve the understanding and readability of the geological and climate archives.

Objectives and Challenges

To reconstruct past climate variability and the interrelation of different processes for times prior to the instrumental era and anthropogenic influence, marine researchers have to rely on indirect evidence – on information provided by “proxies”, which stand as surrogates for particular climate and environmental variables. The analysis of particular marine sediment and ice core properties, water and air samples offers the potential to reconstruct an array of parameters (e.g. temperature, salinity, sea ice cover, global ice volume, nutrients, transport pathways, marine biological productivity, etc.), which allow to reconstruct regional and global changes in the climate system. Much of the success and progress in palaeoclimate research is based on proxy innovation, validation, and the application of multi-proxy approaches to reconstruct climate variability, processes and biogeochemical cycles. Hence, the development and calibration of proxies plays a critical role in climate research.

We therefore identify the following major challenges:

• Development of new analytical techniques and methods in order to discover new processes, pathways or mechanisms leading to the observed distributions in established proxies and Identification of possible new proxies (e.g., measurement of trace elements in aerosols stored in ice cores to provide information about transport pathways and source locations).
• Quantification of post-depositional signal modulation through transport and reaction processes in sediments (e.g., to quantify the lateral redistribution of sediments, its sources and timescales).
• Optimising the link between models and data by implementing proxy parameterizations into climate models in order to simulate proxy generation and burial in all available archives ("simulated marine-, lacustrine-, and ice cores"). This challenge will be tackled in close cooperation with T4-WP2.

Implementation

Most proxy calibrations are empirical relationships based on observations in recent systems that cover only part of the total variability through time. Ideally, proxy relationships should be based on an understanding of the mechanisms (biological, chemical, physical) by which proxies are linked to their environmental target parameters. With regard to microfossil shells and biomarkers, such a mechanistic understanding includes a detailed knowledge of the actual shell formation process (how are proxies incorporated?) and of the life cycle of the organism (when and where are proxies incorporated?). Because this primary signal is modulated we also need to investigate transport processes (water column/ sediment), bioturbation and preservation (degradation/dissolution and additional diagenetic processes). Similarly, it should be asked how the primary signals preserved in ice cores are modulated by transport, firnification (“lock-in”) and ice-flow. Within this WP we will work with different “proxy groups”, ranging from micro-fossils, over biomarkers and radionuclides to minerals and elements, which are preserved in ice and sediment records. Some of these can be combined to deconvolve additional environment parameters, others provide information on the same environmental target parameters and allow to cross-calibrate proxy records. In addition to proxies considering salinity and water temperature as well as nutrient cycling, particulate, dissolved and gaseous components of sediments and ice cores will be investigated with respect to their potential use as proxies for biogeochemical cycles. These materials include biomarkers, trace elements, mineral precipitation and dissolution, and natural radionuclides, which are related to the productivity of the surface ocean, the export to the seafloor, and the diagenetic “overprint” that occurs in the sediments.

The expertise and results generated in our WP will form the basis for several “numerical modules” needed in T4-WP2, notably a module on proxy incorporation, on bioturbation and on diagenesis. Vice versa, will the array of simulated proxies produced under T4-WP2 improve our understanding of the mechanisms behind the generation and modification of the primary signal (e.g., production, export, dissolution of different sedimentary/biological components). In addition, reservoir effects and kinetic constraints cause time lags between changes in environmental factors and their imprint in the (different) geological archives. Hence, we will learn about 1) leads and lags of different proxies in the same archive and 2) leads and lags of the same proxies in different archives. A process of iteration allows to better constraint proxy relationships.

This WP brings together a multidisciplinary consortium (geologists, biologists, chemists, physicists, mathematicians, mineralogists and paleoceanographers) that follows an integrated approach by combining laboratory experiments, field studies and numerical modelling. The ultimate goal of this WP is to develop new techniques and a process based understanding of relationships between different proxy groups and their respective target parameters in all available archives, in order to make past climate reconstructions and future climate predictions more reliable.

Milestones

• Multi-element characterisation by GC-TOF-ICP-MS (Gas Chromatography - Time of flight - Inductively coupled Plasma - Mass Spectrometer) and development of new analytical opportunities by using a femtosecond laser for sample ablation in combination with a multicollector ICP-MS-OES (Multicollector Inductively coupled Plasma - Mass Spectrometer and Optical Emission Spectrometer) (years 1-2).
• Development of conceptual models of proxy generation, transport and secondary modification, which will be translated into numerical modules to be implemented in Earth System Models that generate “simulated proxy records versus time” (close cooperation with T4WP2) (years 2-5).
• Better interpretation of leads and lags of proxies (e.g. δ¹⁸O) between different archives. Both real and “simulated” records will be used to match them internally in order to create a common time frame. This is a prerequisite to understand action and reaction in the climate system explaining leads and lags.

Deliverables

• Development of a process-based understanding of proxy generation (production, seasonality, incorporation) and transport (export, deposition), which includes:

         – Incorporation of (trace) elements into foraminiferal tests, coccolithophorids and other biogenic materials and development of compound specific δD as an independent proxy for seawater salinity.

         - Improve the opal-based isotopic proxies (δ³⁰Si, δ¹⁵N) of nutrient cycling and develop Selenium as a proxy for biological productivity (aerosols, ice cores).

         - Quantify particle fluxes, source and transport processes in marine sediment (Th, Pa, ²¹⁰Pb, etc.) and ice cores records (trace elements contained in aerosols).

         - Reconstruct regime shifts in pelagic and benthic systems during the past century, based on nutrients, radio nuclides, macroorganism bioarchives and biomarkers in the sediment (regime shifts as a consequence of climate change and human pressure).

• Assessment of postdepositional signal modulation (bioturbation, dissolution, lock-in depth, diagenetic overprint), e.g., development of improved indices describing organic matter preservation, carbonate-dissolution and opal-preservation and redox conditions in the bottom water and the sediment at the time of deposition.
• Development of numerical modules (considering proxy incorporation, bioturbation, diagenesis, etc.) to be implemented in the "simulated cores" experiment.