PALEOCLIMATE AND OCEAN SEDIMENT TRANSPORT MECHANISMS THROUGHOUT A GLACIAL/INTERGLACIAL CYCLE: TERRIGENOUS MARS, GRAINSIZE, AND MAGNETIC FABRIC ANALYSIS OF ODP SITE 1233

Proxy records of past climate are key in thoroughly assessing the complex way Earth’s climate changes naturally over time, and the implications of human-induced climate change, in turn. ODP Site 1233 (41°0.005’S, 74°26.992’W, 838 mbsl) on the Chilean continental slope is particularly interesting because of its proximity to two different continental climate regimes and potential influence from different oceanic water masses. Site 1233 recovered a ~136m-long core of primarily hemipelagic (calcareous nannofossil) clay and silty clay with additional biogenic components present in varying amounts. Studies of this site tend to focus on the most recent 50 ky, where high sedimentation rates (~140 cm/ky) have allowed high resolution investigation of the last glacial period, although the full record includes a complete glacial/interglacial (G/I) cycle (Mix et al., 2003), but at lower sedimentation rates.

Terrigenous mass accumulation rates (t-MARs) can serve as a proxy for continental runoff, offering insights into erosion rates and sediment transport mechanisms, factors that may reflect the amount of precipitation, or glacial meltwater, a nearby continent experiences. Terrigenous grainsize (GS) can be a useful indicator of sediment source and transport mechanism to the site. Magnetic fabric analyses on unextracted samples can be combined with grainsize information to serve as a proxy for relative current speeds of the depositing ocean currents.

Preliminary results indicate initially high, but decreasing, continental input as the area goes through a G/I transition, as indicated by t-MARs and bulk magnetic susceptibility, suggesting wetter climates/greater glacial erosion from ~160 - ~145 ka and ~45 - ~10 ka. GS and magnetic fabrics, as current velocity indicators, reveal opposite effects from each other (coarser mean GS and a less developed fabric) both within the most recent G/I transition and when compared to the previous G/I transition. Within glacial periods, low t-MARs and low variability in magnetic fabrics and GS may indicate decreased erosion and dryer climates, with more stable but less vigorous ocean currents in this area. As we complete analyses on remaining samples, trends may become clearer.