Alkenone temperatures derived from suspended particulate organic material which was collected in austral summer 2001 from surface waters (5 m) south of the Brazil-Malvinas Confluence deviate from measured temperatures by-4° to-7deg;C when UK′37 ratios are converted to temperature using the Müller et al. (1998) calibration and up to-3°C when using the calibration of Conte et al. (2006). In contrast, alkenone temperatures determined from particulate material sampled north of the confluence reveal close correspondence to in situ temperatures or show slightly higher values. We suggest that the southern samples are biased by suspended organic detritus originating from the cold subpolar waters of the northward flowing Malvinas Current, whereas the northern samples carry an U K′37 signal of tropical/ subtropical origin, transported southward with the Brazil Current. On the basis of surface ocean transport pathways and velocities simulated with the large-scale geostrophic (LSG) ocean general circulation model, we identify areas of the world ocean where alkenone temperatures are potentially biased to higher or lower values due to long particle residence times and lateral advection by surface currents. © 2006 by the American Geophysical Union.