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This study fills an important gap in our understanding of past changes in the Southern Subtropical Front (S-STF) in the southwest Pacific Ocean. Paleo-sea surface temperatures (SST) were estimated from planktic foraminiferal census counts from cores straddling the modern S-STF in the Solander Trough, south of New Zealand. The estimated SST were compared for 6 time slices; glacial period (25-21 ka), Last Glacial Maximum (LGM; 21-18 ka), early deglaciation (18-16 ka), late deglacial/early Holocene period (14-8 ka), mid-Holocene period (8-4 ka), and late Holocene period (4-0 ka). The position of the S-STF was determined by two methods:(1) the location of the 10°C isotherm and (2) the location of the highest SST gradients. These new results suggest that the S-STF was not continuous between east and west of New Zealand during the glacial period. Steep SST gradients indicate that a strong S-STF rapidly shifted south during the LGM and early deglaciation. During the late deglacial and Holocene periods the position of the S-STF differs between the two methods with reduced SST gradients, suggesting a more diffuse S-STF in the Solander Trough at this time. The glacial SST data suggest that the S-STF shifted north to the west of New Zealand, while to the east there was a stronger SST gradient across the front. This was possibly the result of an increased wind stress curl, which could have been caused by stronger, or more northerly Southern Hemisphere westerly winds (SHWW), or a merging of the SHWW split jet in this region.

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[1] We present sea surface temperature (SST) estimates based on the relative abundances of long-chain C 37 alkenones (U 37 K 0 ) in four sediment cores from a transect spanning the subtropical to subantarctic waters across the subtropical front east of New Zealand. SST estimates from U 37 K 0 are compared to those derived from foraminiferal assemblages (using the modern analog technique) in two of these cores. Reconstructions of SST in core tops and Holocene sediments agree well with modern average summer temperatures of $18°C in subtropical waters and $14°C in subpolar waters, with a 4°-5°C gradient across the front. Down core U 37SST estimates indicate that the regional summer SST was 4°-5°C cooler during the last glaciation with an SST of $10°C in subpolar waters and an SST of $14°C in subtropical waters. Temperature reconstructions from foraminiferal assemblages agree with those derived from alkenones for the Holocene. In subtropical waters, reconstructions also agree with a glacial cooling of 4°to $14°C. In contrast, reconstructions for subantarctic preHolocene waters indicate a cooling of 8°C with glacial age warm season water temperatures of $6°C. Thus the alkenones suggest the glacial temperature gradient across the front was the same or reduced slightly to 3.5°-4°C, whereas foraminiferal reconstructions suggest it doubled to 8°C. Our results support previous work indicating that the STF remained fixed over the Chatham Rise during the Last Glacial Maximum. However, the differing results from the two techniques require additional explanation. A change in euphotic zone temperature profiles, seasonality of growth, or preferred growth depth must have affected the temperatures recorded by these biologically based proxies. Regardless of the specific reason, a differential response to the environmental changes between the two climate regimes by the organisms on which the estimates are based suggests increased upwelling associated with increased winds and/or a shallowing of the thermocline associated with increased stratification of the surface layer in the last glaciation.