FRESHWATER DIATOM TEMPERATURE-SIZE RELATIONSHIP; A PALEOTEMPERATURE TOOL?

Diatoms are sensitive indicators of environmental conditions in lacustrine settings. Furthermore, previous studies have documented that diatom valve size is inversely related to temperature. This relationship has been identified in the modern and cultured environments, but not yet in paleoenvironments. Here, we ask if this could be used to reconstruct paleotemperature. Toward that end, we have collected live diatoms from Mud Pond, Cold Stream Pond, and Mattaseunk Lake, of Central Maine, as well as Burnet Woods Lake of Western Ohio, to grow in culture. Together these cultures contained twenty different collective diatom species. In this experiment, diatoms were grown at 2°C intervals, from 4 to 14°C, for five generations. For each temperature, a sample was taken to represent each of the four lakes, and where possible, a count of up to 100 individual diatoms was taken. Diatom size, defined here as the maximum dimension of the valve, was measured.

This experiment confirmed that valve size is inversely related to temperature in most, but not all, species. For the majority of species, valve size decreased in relation to the increasing temperature at a range of 4.5 - 3.75% change per 1°C, a range consistent with previous studies. Some outliers existed, Pinnularia viridis; size increased with decreasing temperature, and Tabellaria flocculosa exhibiting no change. The next step is to take this thermometer tool and apply it to a known paleo temperature contrast, such as the Younger Dryas and Bølling-Allerød transition, as identified in Mattesunk Lake, to determine if there is a diatom response. If successful, the temperature-size relationship may serve as a summer temperature proxy.