FOSSIL AQUATIC ORIBATID MITES DEFINE PALEOCLIMATE INTERVALS IN LACUSTRINE SEDIMENTS: AN EXAMPLE FROM GLOVERS POND, NJ

Careful studies of stratigraphic distributions of fossil oribatid mites have been made at Glovers Pond in northwestern New Jersey over the past 25 years (Erickson, 1986, 1987, 1988, 1997). Sediments in this marl lake record a complete record from LGM to the present. Oribatid mites, minute Acarina that feed on fungal hyphae and bacteria in detrital settings, are ubiquitous and become preserved in lacustrine fossil records by several means. Species of the aquatic genera Hydrozetes and Limnozetesare very numerous in Glovers Pond sediments and have been extracted from a 7-meter core sampled at centimeter intervals. Numerical occurrences of all genera determined for sediment samples of 7 to 10 grams are normalized to 10-grams for stratigraphic comparison.

Hydrozetes spp. are fully aquatic, dwelling on living and detrital plant material in the littoral zone. They are opportunists whose numbers are controlled by rates of primary productivity, and thus by temperature and nutrient levels, as well as by the precipitation rates that supply the lake. Numbers of Hydrozetes respond quickly to temperature changes of seasonal proportion as would be altered by climate change.

Limnozetes is a genus comprised of Sphagnum-dwelling species. These mites live in the wetted portion of moss hummocks and deep portions of Sphagnum bog surfaces. They, too, are responsive to temperature change, but their numbers in lacustrine samples are more likely controlled by lake level and therefore Limnozetes species provide rainfall data. Flooding events and lake-level rises spread them over the basin, but sustained high populations are reflective of warmer temperatures and high Sphagnumproductivity as well.

The interval between 559 and 613 cm depth in core I-4 at Glovers Pond contains four major intervals of increased oribatid productivity and five of decreased productivity. These record paleoclimate intervals that include the Allerød, G/K, YD, Preboreal, Preboreal oscillation and the beginning of the Holocene warming intervals. The precise correlation of oribatid numbers with paleoclimatic events demonstrates the utility of these organisms as climate proxies.