VARVES Annually laminated lake sediments Varve Formation Varve Preservation Varve Analysis Sample Preparation Analysis Techniques Paleoclimatic Information

Why Bother? Paleoclimate data provides a baseline record of climatic variability in which we can evaluate current climatic regimes and to understand how climate might change in the future. newsbusters.org

What Causes Varve formation? Annual cycles depositing variable sediments= couplets users.utu.fi

Seasonally Variable Components Mechanical Varves Variation in clastic sedimentation from seasonal runoff –In Northern environments runoff seasonality is associated with snow melt –In Tropical environments runoff seasonality controlled by Monsoonal circulation or other factors controlling the rainy season –In arid environments clastic layers might represent flood events rather than annual sedimentation because of a lack in rainfall

Biological Varves Variation in seasonal biological activity –Diatom varves

Carbonate varves –Carbonate layers precipitate out of the water column caused by decreased dissolved CO 2 –results from increased water temperature –or increased photosynthesis

Evaporites –Annual changes in lake level or lake chemistry causing precipitation of minerals

Varves from Eastern Finland, light layer = spring flood mineral layer, dark layer=organic summer-winter layer. Combinations of annual processes users.utu.fi

Varve Preservation Absence of Bioturbation –Reduce the impact of digging animals –Lack of or strong seasonality in benthic O2 Stratification of the water column –No mixing to stir sediments science.jpl.nasa.gov

Basin Dynamics Where do we find the above conditions? 1)Protected, Deep, Small surface area 2)Large and very deep with stratification of the water column 3)Small lakes that the sedimentation rate exceeds the rate of turbation Lake Malawi is one of the world's largest and deepest lakes

Shananon dissertation 2006

Varve Lake Analysis How do we extract paleoclimatic information from laminated sediments? 1)Get core 2)Split core 3)Generate age structure 4)Subsample core 5)Analysis users.utu.fi

Split core marine.rutgers.edu

Develop Age Structure Count layers Lead 210 Radiocarbon Others?

Preparation Slice out a slab from the core half Freeze dry frozen samples. Use acetone to remove water from wet Samples. Then use resin to remove the acetone and set sample into a resin puck.

Types of Analyses

Varve Thickness In clastic varves, varve thickness can be used to reconstruct past hydroclimatic regimes Caution: varve thickness can vary over decadal to century time scales--changing sediment discharge from rivers caused by channel migration or land use change In biogenic varves, varve thickness can be used as a proxy for biological productivity--inferences in temp etc. Evaporites:

Pollen Analysis Potential for high resolution analysis of vegetation change remf.dartmouth.edu

Digital image analysis 1)Take a digital image of the core 2) Graph the color density 3)Calibrate this to a climatic variable if you find a match en.gtk.fi

Scanning Electron Microscopy (SEM) Back-scatter electron imagery Useful for resolving physical and biological components of the annual cycle of sedimentation Potential for identifying inter- annual microlaminations Seasonal faunal successions in laminae less than 100µ thick

Scanning XRF Analysis XRF=X-ray Florescence Elements from Na-U XRF allows fro the identification of changes in elemental abundance on µ resolution Measurements can be made on clean wet surfaces or resin imbedded pucks Primary x-ray source the electrons in the elements. The sample then emits (florescence) x-rays with wave lengths characteristic of the elements in the sample. Shananon dissertation 2006

What can we learn from all this? Grain size can provide insight into past runoff intensity Organic matter can be used to determine strength and length of the primary production season Diatom species can be used to reconstruct past temperature regimes Pollen can be used to reconstruct past vegetation regimes

Calibrate varve record to instrumental record Shananon dissertation 2006

Questions?