Annual Laminae in Speleothems: Implications for Paleoclimate

By: Josephine Molé

What are speleothems and annual laminae?

Speleothems are depositional formations found in caves, the most common of which are stalactites and stalagmites. These structures are created by water that contains calcium carbonate percolating down from the surface and dripping through fissures in the cave.

They are made up of over 70 different minerals, and since the makeup is influenced by the climate, spleleothems are prime candidates for inferring information about paleo-environments.

The banding/laminae within the speleothem, much like tree rings, are used as a chronological tool and the analysis of the material that constitutes each annual lamina tells us about what type of climate created it on a year by year basis.

Laminae must be annualIn order to use laminae of a speleothem as a

paleoclimate proxy, it must be determined using other methods of dating (ex. uranium-thorium) for comparison that the banding is annual.

Also, (1) the laminae must be easily recognizable and distinguishable, (2) any intra-annual bands must be located and excluded from the study of annual bands, and (3) there should not be an abundance of missing laminae (hiatuses) in the speleothem.

If the surrounding climate is highly seasonal, it is a good indication that the speleothem laminae will be annual.

4 main types of laminae:Fluorescent: observed by using a mercury light source to produce

UV excitation - formed by the yearly fluxes of dissolved organic matter that generally contain humic or fulvic acids (humic substances).

Visible: alternates between Dark Compact Calcite (DCC) and White Porous Calcite (WPC) – formed due to seasonal differences in drip rate and seasonal changes in the relative humidity and carbon dioxide levels of the cave, or both.

Calcite-aragonite couplets: may be formed by several factors including temperature variations, drip rate, and concentrations of dissolved magnesium; however, the processes generating this type are not understood to a great degree

Trace element: located world-wide because they are, in essence, a collection of features and conditions that are responsible for the creation of fluorescent or visible laminae within speleothems

35 mm long stalagmite from NW Scotlandwith Fluorescent lamination

1087 bands were counted (900 AD to present) and comparison to Carbon-14 and Uranium series dating confirms their annual nature

Growth rate was compared to regional mean annual temperature and precipitation data and luminescence trends were examined…

The two analyses show the same thing: the growth rate of the banding is increased in warmer, drier conditions

This can be explained by the fact that the overlying peat produces carbon dioxide much more quickly in warm, dry periods than in wet, cold periods.

1 meter long aragonitic stalagmite with visible lamination from NE South AfricaComparison with

uranium series dating and dendochronology confirms laminae are annual.

Precipitation was found to correspond to band width (2 yr lag); while temperature correlates to intensity of the color of the bands (no lag).

40 cm long stalagmite with calcite-aragonite couplets from Drotsky’s Cave in NW Botswana

1500 yrs worth of annual deposition as confirmed by radiocarbon dating

Thickness of calcite bands correlate to annual rainfall; while thickness of aragonite bands correspond to average high summer temperatures

Since we know the ages of the layers, we can infer information about paleoclimate from analyzing the layer thickness and its correlation with the amount of rainfall or the average temperature.

1 meter long stalagmite from Cold Air Cave in South Africa (same sample as used for

previous visible laminae analysis)The trace element bands were determined to be annual in

nature and two chips 14 and 17 millimeters long were taken from the base of the speleothem for Secondary Ion Mass Spectrometry (SIMS) analysis.

SIMS is a method in which a beam of ions is accelerated and projected onto the sample surface and the emitted secondary ions are analyzed using mass spectrometry.

The first chip was found to have significant and regular variability of both Sr/Ca and Ba/Ca where the wavelengths and amplitude appear to coincide.

The second chip also possesses similar coincidence of elemental variation. These results suggest that there is a common, cyclical environmental factor that has caused the trace element variations.

What about comparison to other types of records that go much farther back in time than meteorological data?

In Mato Grosso do Sul State, Brazil, a 44 centimeter long stalagmite was extracted from João Arruda Cave. The bands were determined to be annual and have relatively uninterrupted growth for the past 3800 years using the usual procedure of Uranium series dating.

The stalagmite laminae were compared to different paleoclimate records for the region such as: sediments from Lake Titicaca, cores from the Sajama Ice Cap, samples from the Lago Taypi Chaka Khota, and sediments from the Siberia Peat.

Through comparison of speleothem analysis and the aforementioned records, it was found that the growth profile for the speleothem matches up with the known climate change of the area for hundreds to thousands of years.

This validates the method of analyzing stalagmite growth as an effective tool in making inferences about paleoclimate.

ConclusionThere is great potential for the analyses of

stalagmites to yield accurate information about paleo-environments.

It does not matter what type of lamination the speleothem contains as long as it can be confirmed as annual and is able to be compared with known climatic events and records.

Reconstructing paleoclimate opens doors to a plethora of new theories and investigations, anywhere from the production of thousand plus - year climate trends for furthering climate change research, to learning about extinct creatures through the type of paleoclimate in which they existed.

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