Lakes can provide important records of both natural and anthropogenic change for a variety of reasons. First, the lake, particularly if it has a deep central basin, can accumulate sediment, thereby yielding a continuous geologic record. Continuous geologic records are often difficult to obtain on continents because much of the land surface is undergoing erosion or only episodic deposition. Second, some lakes rapidly accumulate sediment that is rich in organic matter suitable for radiocarbon dating. Such lakes allow a well-dated, high-resolution record to be obtained. Third, the sediment particles that accumulate within a lake have both autochthonous (e.g., diatoms produced within the lake itself) and allochthonous (e.g., wind blown dust from outside the lake) origins. Therefore lake sediments can provide a record of both the lacustrine and watershed ecosystem responses to natural and anthropogenic change.

Faculty and students in the TREC program are studying both ancient and modern lakes from around the world because of the wealth of information contained within lacustrine sediment sequences. Several examples of lake research are shown below that illustrate the wide range of lake types and scientific questions that are being addressed. Lakes under study include:

• Lake Baikal, Russia


• Lake Bosumtwi, Ghana


• Lakes Dood, Telmen and Ugiy, Mongolia


• Lake Erie, Portage Lake, Silver Lake and Summit Lake, Ohio

A record of climatic change has been reconstructed for the past 7110 calibrated calendar (cal) years for Lake Telmen, Mongolia, based upon sedimentologic and geomorphic evidence from the lake-watershed system. Lake Telmen is a saline (presently 4 g L-1) closed-basin lake and is therefore sensitive to changes in effective moisture balance. Between 7110 and 6260 cal years ago, conditions in the Lake Telmen region were hyperarid and a small saline (approximately 20 g L-1) lake was present. Increased effective moisture balance but still arid conditions prevailed between 6260 and 4390 cal years ago. Since 4390 cal years ago, generally more humid conditions prevailed in the Lake Telmen region. As the lake deepened, a hypoxic hypolimnion became established below a well-developed summer thermocline resulting in varved sediment accumulation since 4390 cal years ago. Between about 2710 to 1260 cal years ago, a greater than present day effective moisture balance is recorded by a series of four lake highstand terraces. Sedimentologic profiles from lacustrine cores suggest an increase in effective moisture during the past approximately 680 cal years (Peck et al., 2002).

The sedimentary record from Silver Lake, a small kettle lake in west-central Ohio, preserves a continuous record of environmental change for the last 14 ka 14C. Rock and paleomagnetic measurements, loss-on-ignition (LOI) and smear slide analysis have been used to characterize a suite of 9.9 m long sediment cores. Correlation of the Silver Lake paleomagnetic secular variation (PSV) record to a radiocarbon dated PSV record from Minnesota was used to supplement existing Silver Lake radiocarbon dates and construct a robust age model.

Between 9.2 and 9.9 m (13 to 14 ka 14C BP) a compact sandy, quartz-rich mud has high magnetic concentration, coarse magnetic grain-size, increased amounts of high-coercivity minerals, high sediment density and low organic content. These characteristics suggest high mineral flux by fluvial and eolian processes shortly after deglaciation.

Above 9.2 m (< 13 ka 14C BP), the sediment is generally characterized by organic-rich mud with low concentrations of magnetically fine-grained, low-coercivity minerals. These sediment characteristics are interpreted to reflect generally warmer and wetter conditions. Within the upper 9.2 m, there are sandy-mud zones of high magnetic concentrations of magnetically coarse-grained, high-coercivity minerals with a low organic content and high sediment density. The most pronounced of these zones between 7.7-8.2 m depth (10,500 – 11,400 14C yr BP) also has an abrupt recurrence of spruce (Picea) pollen and this zone is interpreted as cold climatic conditions corresponding to the Younger Dryas event. Between 5.6-6.4 m (6,700-7,900 14C yr BP) and 1.7-4m (1,500-4,000 14C yr BP) magnetic characteristics and increases in ragweed (Ambrosia) pollen (Ogden, 1966) indicate drought and open vegetation conditions. During the late Holocene, 0.8-1.2 m (200-1000 14C yr BP), magnetic and sedimentologic properties of Silver Lake sediment suggest another cold climatic event. This time period encompasses the Little Ice Age.

At 76 cm (200 yr BP), there is a pronounced change in sediment from dark-brown organic-rich mud to light-gray laminated mud. Sediment accumulation rate increased 6-fold in the last 200 years. This change in sedimentation is interpreted as the result of deforestation of the region by European settlers which resulted in an increased flux of detrital material to the lake (Yifru, 20002).

Lake Bosumtwi is a hydrologically-closed crater lake located in the tropical forest lowlands of Ghana, Africa. The hydrologic closure and relatively small drainage basin make for a strong linkage between lake level and regional moisture balance. The goal of this study is to determine if variation in magnetic mineral concentration, grain-size and mineralogy may be related to changes in catchment landuse, reductive diagenesis, lake level, and Sahel dust flux due to rainfall variability since the last glacial maximum. Rock-magnetic measurements, made on an alternating gradient magnetometer, include hysteresis loops, isothermal remanent magnetization and coercivity of remanence. Magnetic mineral measurements of the concentration, grain-size and mineralogy of Lake Bosumtwi sediments show a potential linkage with regional climate variability. A pronounced shift in mineralogy occurred 12,000 calendar years BP. Magnetic mineral measurements show higher concentrations of high coercivity minerals prior to 12,000 BP which may relate to wind driven dust flux during the last glacial maximum. Lower concentrations of low coercivity minerals since 12,000 BP may relate to wetter climatic conditions, including the African Humid Period (Green et al., 2002)