OXYGEN ISOTOPE FRACTIONATION IN SHALLOW AND DEEP WATER STYLASTER SPP. HYDROCORALS

Six living colonies of Stylaster roseus (Cnidaria: Hydrozoa - commonly called rose lace coral) were collected from three locations off of the Cayman Islands at approximately 30m depth. Aragonite was sampled from the outer edge of each colony’s skeleton and analyzed for oxygen isotope content. Comparison of these data with local water oxygen isotope content and temperature suggest that unlike most other corals, S. roseus grows in oxygen isotope equilibrium with seawater.

While oxygen isotope analysis of S. roseus may be useful to assess growth rates and address ecological concerns about this species and its habitat, several characteristics may limit its potential use as a paleoclimate proxy. These include its small size, complex growth habit, lack of readily-apparent growth increments, and comparative scarcity in the fossil record. However other members of this genus, assuming they also grow in oxygen isotope equilibrium, may be useful as paleotemperature proxies.

Sequential oxygen isotope profiles were measured in two colonies of deep water Stylaster erubescens from the Charleston Bump (North Atlantic, Northwest Blake Plateau, ~500 m depth). Detailed time-series environmental data do not exist for these waters. However, the temperatures indicated by the coral’s oxygen isotope distributions agree with what was measured during the collection dives on the Johnson Sea Link. The profiles contain oscillations that may be interpreted as seasonal variation in temperature and/or water oxygen isotope content possibly related to changes in the Gulf Stream.

S. erubescens may therefore serve as a useful proxy of past deep marine conditions with sub-annual resolution. Estimated growth rates and measured colony size suggest sub-decadal life-spans, thus long continuous reconstructions may not be possible. However the abundance of fossil and sub-fossil samples in key locations may yield large numbers of brief floating records. Several important factors remain uncertain regarding this potential proxy, such as a better understanding of their growth patterns. Unlike S. roseus, S. erubescens often contain growth increments, but their periodicity and causes are uncertain.