Collaborative Research: Controls on Alkenone Temperature Estimates in Subtropical and Subpolar Waters

The subtropical front (STF) is the northern boundary of the Southern Ocean, separating oligotrophic, warm subtropical surface waters north of the STF from cooler, nutrient-rich, subpolar waters to the south. East of New Zealand, the STF is bathymetrically anchored to the Chatham Rise, a 1000 km long submerged continental plateau. The National Institute of Water and Atmospheric Research (NIWA), New Zealand, maintains two sediment trap arrays only 200 km apart on the Chatham Rise. The traps, although closely spaced, sit just out of the axis of the STF and thus allow comparison of subtropical and subpolar waters under similar environmental conditions such as weather and light levels over the annual cycle without the complication of frontal migrations.

In this project, researchers at Rutgers University and the University of Hawaii will examine at these sites the processes involved in the formation of the proxies on which paleo-sea surface temperatures (SST) records are based and resolve the issue of differential seasonality between the organisms which are arguably two of the most important paleotemperature estimators now in use (e.g. U37 K ' accuracy, foraminiferal ä18O values). The principle hypotheses to be tested are:

1. Episodic delivery of alkenones and foraminifera exported from the surface mixed layer are the underlying cause of differences between alkenone and foraminiferal temperature reconstructions.

2. Nutrient depletion in subtropical waters during summer months and subsurface production during prolonged winter darkness in subpolar waters are important environmental influences controlling the accuracy of U 37 K ' SST reconstructions.

Efforts in this work primarily and actively address the broader impact criteria of enhancing infrastructure for research. Collaborations among United States, New Zealand, and European scientists represent a significant investment in outreach with international colleagues by the US PI?s. The combined results will enhance the research of all members by disseminating shared data widely and serve to stimulate future partnerships. Additionally, training of students who will take central roles in this research addresses advancing training and learning. Better quantification of SST records will benefit paleoclimatic reconstructions and thus have societal benefits.