Ethology of the Zoophycos-producer:: Arguments against the gardening model from δ13Corg evidences of the Spreiten Material

Recently proposed ethological explanations for the trace fossil Zoophycos include gardening of microorganisms. Because microorganisms are known to fractionate strongly against C-13, especially under low oxic to anoxic conditions, it is argued that any gardening activity in the trace would result in a noticeable shift in delta(13)C(org) between spreiten and adjacent host sediment. In order to test this hypothesis, delta(13)C(org) of the Spreiten Material and directly adjacent host material was measured. Measured delta(13)C(org) in a glacial section of the core ranges from -22.6 to -22.9 parts per thousand for host sediment and between -22.8 and -23.2 parts per thousand for Zoophycos material. In an interglacial section the Zoophycos material measures -21.9 parts per thousand, whereas the host material ranges from -21.2 to -21.4 parts per thousand. The minimal difference between Zoophycos and host material suggests that gardening plays an insignificant role. The gardening hypothesis is therefore rejected in favor of a cache model, where food is squirreled away for poorer times.